M40 Timing Belt Change

BMW M40 Timing Belt Change, Water Pump & Major Service Guide

This how-to guide follows the process of our M40 timing belt change on a BMW E30 and completing a full major service DIY style in your garage.

Our E30 is a 1991 316i manual coupe with the four-cylinder M40B16 engine sporting 103k miles on the clock. I’ve got bigger plans for this car going forward, but for the time being, I wanted to perform the M40 timing belt change and keep the car as a going concern, or a “rolling restoration”.

It had nearly a year’s MOT when I picked it up which was an excellent starting point.

BMW E30 coupe in Rare Titian Red colour.

I drove the car home to Yorkshire on a wing and a prayer from about 200 miles away down south to get it home, and it was running alright. In fact, it was running much better when I got home than it did before we set off in it.

However, this M40 engine is definitely on borrowed time with the cambelt.

Looking at the history with the car and also the two timing belt service stickers in the engine bay, I can see that It’s not had the cam belt replaced in a whopping in 18 years. It’s done 20k miles on this old cam belt too which is the recommended replacement interval anyway.

This E30 had been sat for around 5 years prior to me purchasing having been started only occasionally to move it. Luckily it must have been undercover for much of this as the body shell appears to be solid, which is seldom the case with these cars.

As the car had been unused for so long, and judging by the fact the timing belt was potentially 18 years old, we decided to perform a major service including replacing the water pump, thermostat, coolant, v-belts, rocker cover gasket, oil and oil filter, fuel filter, air filter and spark plugs while we’re at it.

I also wanted to run some engine flush through it to clear out any nasty old oil deposits which might be lingering from ancient engine oil.

I sourced these BMW M40 engine service parts from a variety of places online in search of the best deal. As previously mentioned, I want to keep the car going for now ahead of bigger plans, so I intended to give the M40 engine what it needs as cheaply as possible.

I have kindly included links to each service item I purchased below which should save you from having to figure it out yourself.

BMW E30 M40 Timing Belt Change & Servicing Parts List

BMW E30 Service parts for M40 timing belt change

Removing a BMW E30 Bonnet

The first step is arguably an optional one. But I would strongly recommend removing the bonnet (or hood) completely as it will really get in the way. When you’re performing a major task like this then you need all the access you can get to do the job.

Luckily, the BMW E30’s bonnet is very easy to remove. But start with unhooking your battery, you’ll want it to be unhooked throughout this servicing process anyway.

Our E30 has definitely had the bonnet removed before as the two wires for the washer jets and the washer fluid pipe had previously be cut and reconnected which made our lives even easier.

Once the pipe and wiring has been disconnected I’d recommend slackening off (but not taking out completely) the 4 bolts on the car side rather than the bolts on the bonnet side, this way you will be likely to have fewer problems when it comes to putting the bonnet back and re-aligning it into its original position with even panel gaps.

Once you’ve got these 4 bolts ready to come out, you need to turn your attention to the bonnet stay which consists of a bracket arm with a gas strut, held in place by a larger nut and a retaining clip.

At this point, I would suggest calling in a helping hand to make sure you don’t have any disasters such as dropping your bonnet on the floor, or it falling shut on your head, which really hurts!

Removing an E30's bonnet or hood

Get your buddy to hold the bonnet in its upright position while you remove the bonnet strut assembly. Then move onto taking those 4 bolts that we mentioned earlier out completely, starting with the one that has an earth connection from the wiring.

After you remove these 4 bolts, if your friend has held it steady, the bonnet should still be resting in the same place on the car giving you time to put the bolts to one side and support one side of the bonnet ready to lift it away.

With a person on either end of the bonnet, lift it carefully away from the car and carry it out of the way.

To avoid damaging it, I’d recommend placing it nose down leaning against a wall, preferably on something soft like a mat to save marking the paintwork.

At this point, your bonnet is no longer an obstruction, and you’re ready to get stuck into the BMW M40 timing belt change.

Removing the Fan Shroud

You will want to start out by removing the front fan shroud connected to the backside of the radiator.

This is made easy by the plastic rivets, there are only two, one on either side at the top. Once these are out you can unhook the shroud from its bottom mounting points and negotiate it around the fan and out of the engine bay.

Removing the fan shroud from the radiator.

With this removed, you will have even more access to the front side of the M40 engine.

Removing an M40 Distributor Cap

The next task is to carefully remove the distributor cap via the three captive bolts through its plastic cover. You can leave the ignition leads attached, but you may need to remove the clip-on plastic cover from these to do so. I am not sure as my cover was already missing.

Once the distributor cap is disconnected, tuck it around the side of the engine near the exhaust manifold out of the way.

Removing the distributor cap.

At this point, you should also pull out the rubber breather hose connected to the rocker or valve cover, just below the front of the engine’s intake plenum.

Removing the Rocker Cover

You will then want to turn your attention to the 8 bolts which seal the M40 engine’s rocker cover on. Access to these is good and it’s an easy task to take them out with a socket on an extension bar.

Once the bolts are all removed, stand at the side of the car above the driver’s front wheel and give the valve cover a wiggle back and forth to release it from the rocker cover gasket. Carefully lift it away from the engine while moving it slightly to your right to clear the breather hose connection you removed the pipe from earlier.

Removing the M40's valve cover.

Under the rocker cover should be a plastic windage tray which sits over the valves and cams.

Inspecting the M40 Camshaft & Testing the Oil Feeder Pipe

At this point, I inspected the inside of the rocker cover which came off my M40 engine and noticed a fair amount of dried-on oil deposit which isn’t always the best sign.

Luckily however there did not appear to be any sign of coolant mixing with the oil which usually manifests itself as a mayonnaise-like substance if the head gasket has failed.

You can carefully remove the plastic windage tray and reveal your valve train beneath.

This is a great opportunity to inspect the cam lobes on your M40’s camshaft for signs of scoring or wear. The thin metal tube which sits above the camshaft and runs its entire length is an oil feeder pipe which directly squirts oil onto your cam lobes as they’re turning to keep them fully lubricated.

On the BMW M40 engine, this pipe can be a weak point, especially if the engine has not had regular oil changes throughout its life. In short, this oil pipe can get blocked up over time and will no longer provide sufficient lubrication to the cam lobes, leading to excessive wear.

As I was quite sure that my BMW E30 had not been serviced recently or regularly for many years, I was not entirely sure what condition my camshaft was going to be in. My findings were a mixture of wear and some scoring on the majority of the lobes, but nothing catastrophic or extreme.

I concluded that this little M40 engine, while not in peak condition, was likely to keep soldiering on for many, many miles to come, and it was worth continuing with the M40 timing belt change and major service as planned.

Pleased with my findings so far, I quickly reconnected the distributor cap and battery, laid down an oily shop rag below the open engine, and proceeded to fire it up to observe whether all of the oil feed ports were clear and flowing for the camshaft.

Checking M40 camshaft wear and oil feeder pipe is clear.

The engine sputtered into life with the camshaft rotating rapidly and the bobbing of each valve spring up and down in sequence.

After a second or two, oil started squirting out of the feeder pipe burst into life squirting black old oil onto the camshaft to be flicked all over the place by all 8 cam lobes. I was glad I laid down that rag. This M40 engine has noisy lifters that make quite a tick, I was worried this oil spray bar was blocked and I was going to find a very worn top end, but in actual fact, it looks okay considering.

That step is not necessary, and I wouldn’t advise it, but it was very entertaining, and I couldn’t resist the opportunity to see the valvetrain in action.

Once again, unhook the battery, and the distributor cap and took it to one side. The next step is to drain the coolant.

Draining the Coolant from a BMW E30

There are a few ways to drain the coolant from the E30, there’s a small plastic screw at the bottom of the radiator on the passenger side which you can undo to allow the coolant to drain directly down to floor level through a gap in the undertray.

However, we didn’t realise it could be this simple until it was too late and we’d pressed on with a quicker (but messier) method.

Feel free to undo the radiator screw and sip tea as the coolant pours steadily into your container.

But if you want to do it our way, start by undoing the jubilee clip from the large coolant pipe connected between the lower driver side of the radiator and the thermostat housing on the front of the engine, just below where the distributor cap lives.

Be aware, this is a very messy affair whichever way you do it, and it’s advised you have a large aperture container to drain the coolant into as well as a good few scruffy old towels on hand to mop up and uncaught fluid (and there will be plenty).

Removing a coolant pipe to drain off the coolant.

Wiggle off the end of the coolant pipe connected to the thermostat housing and quickly direct the flow down into your container below the engine as though you were wresting an angry Boa Constrictor.

Once the coolant appears to be drained, remove this large coolant pipe completely, and also remove the other large coolant pipe on the other side of the radiator. Expect more coolant to come out and surprise you.

Removing the Auxiliary Belts

After you’ve mopped up, you’ll be able to turn your attention to auxiliary v-belts. Start with the belt that turns the alternator pulley.

You will see a long bolt which both secures the alternator and tensions the belt. Loosen the nut on the cabin side of this bolt and you will be able to un-mesh the teeth that secure it in place on the head (on the opposite end of the bolt). Following this, you’ll be able to lever the alternator upwards enough to release the tension from the belt and slip it off the pulley.

Removing the aux belts from an E30.

You can then negotiate the unhooked v-belt around the clutch fan blades and remove it from the engine bay.

This will also free up more access to remove the power steering pump belt below. This one comes off a bit easier by turning the pulley while wedging the belt off with a screwdriver or similar. Negotiate this belt around the fan too.

Attempting to Remove the Clutch Fan

At this point, you’ve got all the access you’re going to get in order to remove that large clutch fan from the front of the engine. We’d made a little attempt to remove ours earlier on but without success.

Bear in mind that these clutch fans are notoriously awkward to remove and are attached to the water pump pulley allowing them to spin freely, limiting your ability to give it maximum turning force. It’s also well worth noting that the fan is reverse threaded.

How to remove an E30 clutch fan.

You can wedge a strong screwdriver in between the bolt heads on the water pump pulley to give yourself something to lever against and then use sharp bursts of force to remove the clutch fan with a large spanner. These fasteners usually respond well to sharp inputs or torque to get them moving rather than steady pressure.

If this fails, however, don’t fear, it failed for us too and we still managed to complete the job by simply removing the entire water pump with the fan still attached later.

Removing and Inspecting the M40 Rotor Arm

Rather than getting disheartened, move on to removing the rotor arm which lives under the distributor cap which you removed earlier. The rotor arm is held on by 3 small Allen head bolts which are usually nice and easy to remove.

This is a good opportunity to inspect both the rotor arm and the points or contacts in the distributor cap. If these are well worn it can often lead to rough running. If yours are knackered then you’d be wise to replace them, however with a good clean up you can often eek them out for a bit longer.

Taking off the distributors rotor arm.

Ours looks as though it’s on its last legs and the distributor cap rotor contacts are quite worn, interestingly, however, it was still doing its job, so I gave the parts a cleanup and decided I’d cross my fingers and reuse them later on.

With the rotor arm removed along with the black cup that sits beneath it, you will get your first glimpse of the old cambelt on the cam sprocket ahead of the M40 timing belt change.

Removing the M40 Engine’s Thermostat

Now that most things are out of the way (bar that pesky clutch fan), its time to move on to removing the thermostat from the M40 engine.

This is nice and easy to do at this point as the thermostat housing is the metal tube you disconnected the large coolant hose from earlier, just below where the rotor arm lives.

It’s a case of removing the three hex bolts that hold the housing in place to reveal the thermostat itself.

How to remove the E30's thermostat and housing.

The thermostat can sometimes just drop out once the housing is removed, but other times it can be firmly wedged in place. Ours was a bit stuck so we carefully levered it with a screwdriver and it popped out.

Old thermostats often look in good condition having spent their lives sealed away from the elements, however, looks can quite often be deceiving and over time they can weaken and fail to do their job properly. If you’re going this far, it’s well worth replacing the thermostat too.

With the thermostat and its housing removed, you can then remove the bolts from the top part of the M40 engine’s front cover to reveal more of the timing belt.

Removing the Water Pump from an M40 Engine

As we’d not had any luck in trying to get the clutch fan to budge, we decided to work around the issue and move straight on to extracting the water pump it’s attached to.

Annoyingly, this is another notoriously difficult part to remove from the M40 engine, and not having the clutch fan removed makes it even more awkward to battle with.

My first suggestion is that you remove the bolts that hold the pulley onto the water pump, you won’t be able to remove this with the clutch fan in the way, but you’ll be able to slide it over for extra access to the water pump, and you need all you can get here.

Then, remove the 4 bolts which secure the water pump in place and see if you can give it a wiggle, a few taps with a hammer and you might get lucky.

We didn’t, so it was onto the proper way to remove an M40 water pump.

When removing the 4 bolts from the water pump, you may have noticed that there are two additional holes which were not occupied by bolts. There’s one at the top and one at the bottom.

No, you’re not missing 2 bolts, these additional ears on the water pump with threaded holes in them are actually there to help you extract the water pump. BMW must’ve known that these were a real pain to remove and kindly provided these as a solution, and this is the proper way to remove your water pump if all goes to plan.

Carefully thread in two of the screws you removed into these additional ears on the pump and start gently tightening them up in sequence. Again, if you’re lucky the water pump will begin easing out and you’ll be well on your way.

We were not lucky this time either, despite taking lots of care to tighten up the bolts very slowly and in sequence, with a few light taps of the hammer to ease it along, both the ears on our water pump snapped clean off very quickly.

BMW water pump removal ears snapped off.

Using this method, our stubborn water pump hadn’t moved in the slightest and we were left frustrated and scratching our heads as to how we could remove it.

A brainwave later, we resorted to Neanderthal tactics and decided to bring in the bigger hammer.

The trick to removing a very stuck water pump from an M40 like this is to get it rotating first.

With a steel chisel or a very sturdy big screwdriver, hammer the supporting braces cast into the water pump left and then right until you manage to get the whole thing moving. Ours moved only very slightly at first despite giving it grief, but after a few knocks back and forth it slackened off considerably.

Enter the grips. With the water pump rotating more and more, we decided to have a go at twisting it further with a particularly large set of grips. To our surprise, from this point, the water pump came out of the block with ease, with another unexpected large gush of coolant to mop up.

Removing water pump from the M40 with coolant spillage.

With the connected water pump, pulley and the clutch fan removed, they should be much easier to split.

We found that by securing the water pumps impeller very tightly into a vice, we could get much better purchase on the clutch fan nut. After a few sprays of WD-40 as penetrating oil and a bit of heat to help things along, the reverse thread of the clutch fan broke free from the water pump allowing the three parts to be separated.

Removing the M40 Crank Shaft Pulley & Harmonic Damper

Move on to tackling the crank pulley. This is a bit of an awkward task as the 6 substantial bolts tend to be in very tight, tight enough that you will be turning the engine over instead of turning the bolt.

M40 engine crank pulley and harmonic damper.

The best way to take these out is with a socket on a short extension, coupled with a big spanner to hold the crankshaft bolt to prevent the engine turning over.

If you’re doing this from the top like we did, its particularly awkward as the bolts are well recessed into the pulley meaning you can’t see them at all, and can only work by feel.

With this method, however, you should be able to remove all 6 bolts and take both the crankshaft pulled and the harmonic damper off the front of the engine.

Now, these are out of the way, you can get on with removing the bottom timing belt cover from the front of the M40 engine and reveal the timing belts entire path.

Out of interest, we used the big spanner we used to stop the engine turning over earlier to turn the engine over by hand and observe the condition of the timing belt before getting to the removal process.

The belt, all the sprockets and the timing belt tensioner all looked to be in good condition, although looks can be deceiving with these parts.

Locking the Camshaft and Flywheel on an M40 Engine

The M40 camshaft locking tool consists of two parts. A strangely shaped metal plate with a square notch cut out of the middle which is to lock the camshaft itself from the top, and a metal pin which is to lock the flywheel.

Ideally, you must start by turning the engine over by hand, again with the big spanner on the crank nose. Observe the end of the camshaft closest to you and you’ll see that part of it is square, this as it happens, is what the notch on the tool slots over to hold it in place.

This square part of the camshaft has two small dimple holes in it on one of its 4 sides, the side with these two dimples must face up, and this is top dead centre. Turn the engine until these two dimples on the camshaft are facing upwards.

Instead of locking the camshaft there and then with the top timing tool, instead, turn your attention to the flywheel aspect of the locking.

The M40 engine has a small hole low down by the firewall which passes through to the flywheel from the back. The M40’s flywheel has a matching hole in it. The idea is that when these holes are lined up perfectly, you can put the pin through both to lock the flywheel solidly in place.

Finding this hole in the engine bay is much easier said than done. I’d done a fair amount of searching around online to find out exactly where this hole was, but there was a fair amount of confusing and misleading information on the topic. Even e30zone wiki and the Haynes manual didn’t lead me to the answer this time.

All I really knew, was there is a hole leading through to the flywheel which narrowed me down to the back of the engine low down at the bell housing. I also knew that there should be a small plastic plug filling this hole, but they can often fall out and go missing, so no guarantee it’s there.

After some fiddling around I located the hole which did indeed have the plastic plug still in place.

As your facing the car from the front, the hole you’re looking for is on the right-hand side (inlet side) of the engine where it bolts onto the gearbox bell housing.

It’s very dark down there, and awkwardly the hole is between two strengthening gussets in the casting making it impossible to see from directly above anyway.

If you get a torch down there to light the area up and view from near the airbox you can just about peer through and spot it.

I suspect this would be far easier to access from below if you knew what you were looking for.

The plug pulls out easily if yours is still in place, but from the top, getting the locking pin in is somewhat difficult because you will have to do it all by feel and won’t be able to see what you’re doing.

If the hole on your M40 engine is crusty, dirty and rusty like mine was then you will struggle further still as the pin provided is a very close fit (as you’d expect). To get around this, you can give the area a scrub with a wire brush and use a file to slightly chamfer the end of the pin.

Once in for the first time, our pin then freed up a bit and allowed us to move it in and out slightly and feel whether the second hole, the one in the flywheel, was lined up to receive.

Despite getting the camshaft in the right position, it’s highly unlikely that your pin will go straight in through the hole and into the flywheel’s hole first time.

It can be done without, but this is around the time where you will ideally need a mate to help you.

Get your friend to very slightly turn the engine back and forth using the big spanner while you put pressure on the back of the pin. If you’re lucky you will feel when they are lined up, it may even slot through into placer by hand.

Ours was a little stiff so you we gave the pin a couple of light taps with a hammer to get it securely in place into the flywheel.

M40 fly wheel locking tool in place.

You’ll know for sure that its in properly when you try to turn the engine again and find that it’s locked, although with a slight amount of play, as expected.

Now your flywheel is locked, you can put your camshaft locking tool in place around the square part on the cam. You’ll notice that the tool is not symmetrical, and the shorter end is the one which faces the plenum chamber.

M40 camshaft locking tool positioned to lock the timing.

Well done, your timing is locked into top dead centre position ready for you to perform the M40 timing belt change.

M40 Timing Belt Change for BMW E30

Now the timing is locked, its time for the main event. First things first, before you start tugging away at the timing belt to remove it, remove the timing belt tensioner which is the smaller splined pulley between and to the left of the cam sprocket and crank sprocket.

The tensioner comes off nice and easily with a socket and ratchet and you will see the belt relieved of tension as this sprocket pivots away slightly.

Now you can get back to pulling at the cam belt to remove it from the engine, it shouldn’t be too difficult to remove at all and should simply slip off.

E30 timing belt removed from the M40 engine.

We inspected our old cam belt a bit more closely now it was off and visually it looked absolutely fine. However, these belts can look brand new right up to the day they fail in our experience, so it’s definitely not advisable to judge a cambelt by its appearance.

With the belt out of the way, you can replace the two rollers which are the smaller two without teeth that press on the backside of the belt to guide it around within the timing cover. These also come out easily with a bolt in each.

Crack open your M40 timing belt change kit and get the new rollers out and fit them to the engine as your first new parts to go on. Remember, smaller one to the top right, larger to the bottom left. Take care not to overtighten these as it can damage their bearings.

Get the new tensioner out of the m40 timing belt change kit and put it onto its stud loose for now, put the washer and nut back on but not nipped up to allow the sprocket to move.

Now you’re ready to thread your new timing belt on. Start by hooking the belt around the crank sprocket at the bottom and get the rest of the belt into the right orientation and sitting roughly in the right path ready to feet it onto the cam sprocket at the top.

With the belt hooked up securely on the crank sprocket’s teeth, It’s important to work your way up the right side of the belt’s path first as this is the side that pulls the cam sprocket around so needs to be tight.

Once you’ve got the right side of the timing belt under tension by pulling it upwards slightly, you can feed the belt onto the teeth of the cam sprocket working right to left. If you’ve got the timing belt in a good orientation and pulled it taught correctly, it should be quite easy to slip the belt onto the cam sprocket.

Note that you would not be able to hook the timing belt on another tooth to the left even if you wanted to.

M40 timing belt change taking place with new cambelt.

With the belt hooked onto the crank sprocket, up past the roller and securely around the cam sprocket, you now need to ensure the timing belt is taking the correct route around the tensioner and the other roller on the slack side.

If you’ve done your job well, the m40 timing belt should be sitting comfortably already.

How to tension an M40 timing belt

Tensioning the timing belt on your M40 engine can be a confusing concept, to say the least.

There are probably very specific tools for the job, but you can also set it correctly DIY style using a simple Allen key and a luggage scale. This is an age-old method which applies to many makes and models of car.

First off, find the correct size Allen key for the hex hole in the tensioner. For this particular engine, you will need to mark the shaft of your Allen key 8.5cm from the centre line, you can do this with masking tape or a paint pen.

Luggage scale and Allen key to tension timing belt.

The method goes as follows; with the Allen key in position on the tensioner, you will put 2kg of pressure (measured using the luggage scale) at the 8.5cm mark to tension the belt correctly.

It’s a bit fiddly but with the luggage scale pulling at the 8.5cm marker on the Allen key with one hand, you can tighten the nut on the tensioner with the other to lock it into place.

Using the luggage scale to tension M40 timing belt.

Congratulations, you’ve just successfully replaced the cambelt on an M40 engine.

Now you can remove the cam locking tool and the flywheel locking pin (don’t forget to put your plastic plug back in place) and give the engine a few turns over by hand using the big spanner to ensure there is nothing untoward and make sure the belt is settled into place.

When you’re happy that it’s all right, you can move on to putting things back together.

Reassembling the M40 Engine

Start with the lower timing belt cover but don’t put the top-most two bolts in all the way as they will interfere with the top cover which you will refit next.

Put the top cover back on, slotting it into the bottom cover and tighten all the bolts up.

Now move onto the bottom pulleys, be aware that the bottom pulley with the teeth on it can only go on one way as it has a dowel. This is because the ECU reads where the cap is in the teeth to ensure the engine is running correctly.

Put the wider bottom pulley back on with the 6 fiddly bolts.

Get your new water pump out and put the new o-ring seal onto it before seating it into position and tightening in the 4 bolts that secure it.

Get your new thermostat and o-ring in position and replace the thermostat housing and tighten up the 3 bolts that secure it in.

Slip the water pump pulley on, secure it with the 4 bolts and thread your new v-belt onto the wider crank pulley, the water pump pulley and the alternator pulley.

Re-tention the alternator by levering the top side away from the engine and tightening up the bolt. The belt should have about 1-2cm of up and down slack so be careful not to over-tension it.

Get the smaller new v-belt and thread it around the power steering pump pulley and the crank pulley. This one is a fair bit tighter, so we got ours on the power steering pump first and turned the engine over with the big spanner again to ease it onto the crank pulley. Then tighten up the tensioner to re-tension the belt, again with 1-2cm of up and down slack.

Tension the aux belts by hand.

We took the opportunity to clean up our rotor arm contact and distributor cap rotor contacts with a bit of fine sandpaper and refitted them to the car.

Now you can refit that pesky clutch fan to the front of the engine. Again, bear in mind that this has a reverse thread.

Refit the plastic windage tray over the camshaft and get a clean rag to clean the face of the head surrounding it ready for the new rocker cover gasket to be fitted.

Firstly, fit the rocker cover gasket securely to the rocker cover and place it back on to the head, being careful to ensure the gasket is seated properly.

Replace the rocker cover bolts and tighten them up, also reconnect that breather pipe which connects to the valve cover too.

Re-fit the plastic bracket that you removed from the top timing belt cover which secures the HT leads in place and then replace the distributor cap (which should have the leads still attached.

Reconnect the two large rubber coolant tubes which connect to either side of the radiator and tighten up their jubilee clips and make sure you screw the little drain cap you may have removed from the bottom of your radiator back on.

Now is a great time to take the oil filler cap off and pour in your Wynns Engine Flush as you’ll be letting the car run for a while and warm up while you tend to the coolant.

Replacing the Coolant and Bleeding the Cooling System

Bleeding the radiator and getting all the air out of your cooling system can be a real pain, especially if you don’t get it right and find yourself with an engine that’s overheating.

This is the method we used to successfully get the cooling system on our M40 engine fully bled in quick time.

Crack open the cap on your new coolant remove the cap from the top of the radiator and start to pour coolant in. Once you’ve poured a few litres in you may notice that the tank on the side of the radiator is starting to fill up quite a bit already.

Refilling the coolant via the radiator mounted tank.

Once it is showing max, replace the radiator cap, reconnect your battery and fire up the engine to allow the coolant to pump around the system for a good few minutes.

Get a large screwdriver and carefully slacken off the large plastic screw at the top of the radiator. If the car has been running for as little while you should notice steam escaping from here and hopefully lots of bubbles coming through too.

Allow the engine to run for a while more and let it come up to full operating temperature to allow the thermostat to open and allow coolant to flow around the whole system.

Massage the large rubber coolant hoses between the engine and the radiator to loosen up any trapped air. Be careful not to burn yourself as these hoses can get very hot.

You may notice more bubbles coming out of the bleed screw as you massage the hoses.

Check the coolant level in the tank by the side of the radiator and see if it needs topping up. If the level is still between the min and max then you can keep going.

If it’s below the minimum then you will need to stop the engine, let it cool for a short while and then remove the cap to top it up to max again.

Out of interest, we decided to see whether our clutch fan was worn out or not. When the engine is fully up to temperature, the clutch fan should be firm and not easily stopped spinning.

We got a rolled-up newspaper and lowered it into the blades and discovered that ours stopped effortlessly and could be stopped by hand, meaning that it’s ready for a new one.

If your clutch fan is working properly, be careful not to catch your hand in the blades, as it will really hurt.

Switch the heater controls in the car onto full hot for a while to allow the fluid to circulate through the heater core pipes properly.

While you’re in the car, sit with your foot modulating the throttle slightly for a couple of minutes to raise the coolant pressure and push more bubbles out of the system.

Once you’ve been through this procedure and you’re no longer seeing air bubbles coming through the bleed screw, tighten it up and take the car out for a little drive around the block, and again loosen the bleed screw to release any air.

How to bleed the coolant on a BMW M40 engine's cooling system.

If there appears to be none, your cooling system is fully bled. Switch the car off and allow it to cool for a while, then make sure the tank is topped up to max and the job is done.

How to complete an Engine Oil Service on an M40B16 or M40B18

Now the Wynns engine flush has been circulating in the oil for a good while, its time to drop the old oil and replace it with new.

First things first, you’ll want to make sure you’ve got a good-sized container to catch your oil in for responsible disposal. The M40B16 engine holds 4 litres of oil so you will need to be able to catch that amount.

We use a plastic oil can which can be filled from the side, the beauty of it is that its quite low when laid on its side, so on an old car like an E30 it can slide under the sump no problem without the need to jack the car up.

The sump plug on the M40B16 engine is nice and easy to access from the front with a socket and an extension bar too, even with the car on the floor.

Reach under and carefully crack the sump plug ready for removal. Once it’s turning it should hopefully start to be undoable by hand just using the socket on an extension bar. If you’ve been running the engine then it’s wise not to remove the sump plug directly by hand as burning yourself with hot motor oil won’t be fun.

Removing the E30's sump plug to drain the engine oil from the M40.

With the oil container in place, proceed to carefully wind out the plug with washer hooked on. The trick here is to avoid dropping the sump plug and washer into the oil container to avoid doing the messy job of fishing it out later.

With your oil draining into the container, now is a good time to start work removing the filter, not only will you be changing it, but removing this also releases the vacuum which may be holding some of the old oil in the engine.

The oil filter on an M40 engine is conveniently placed beside the dipstick in a very well-designed filter housing found on many types of BMW right up to M3 models produced decades later than this E30.

The central bolt is very long and can be easily undone allowing for the removal of the lid. It’s advisable to lift the lid off with bolt still in place to make the least mess.

Put the lid to one side and carefully lift out the old filter and place it in a bag for disposal later on.

Get some old disposable rags and wipe out your oil filter housing and the inside of the lid ready for the new filter.

Cleaning out the oil filter housing with a clean cloth.

While you’re waiting for the last few drops of old oil to drip out, remove the old and fit the new large O-ring to the filter housing lid and the tiny O-ring that goes on the end of the long bolt to seal it, these should have been included with your new oil filter. It’s nice to get a dab of oil on your finger and work it into the new O-rings to ensure they fit into place easily without snagging and becoming damaged.

If you’ve got a surplus of the correct oil or at least more than 4 litres, I usually like to pour a little into the top of the engine and observe it running out of the sump cleanly to pull any remaining deposits through and confirm that the old oil has completely drained.

Once you’ve done this, get your new sump washer and refit your sump plug to the correct torque spec, don’t over tighten these, the copper washer only wants to be slightly crushed to seal effectively.

Put a dab of oil on your finger and run it over the rubber seals at either end of the cylindrical oil filter and put it in place and pour some of the new oil into the housing to soak the new filter. This way your engine won’t be without oil when you first start it up due to the filter housing and filter needing to fill up first.

Make a note of how much you put in here, then replace the lid securely, tighten the bolt, and move on to pouring the rest of the oil up to the 4 litre capacity into the top of the engine where the oil filler cap lives.

Pouring engine oil into the M40 via the filler cap.

Once done, pull your dipstick and check the oil level is correct and top up further if needs be. Then give the engine a start and let the new oil circulate around the system for a minute or two before checking again.

Ideally, your oil level will be just below the max marker on the dipstick.

Oil dipstick showing the perfect oil level, just below max.

Replacing the air filter on a BMW E30

Now your oil service is complete, you can move on to changing the air filter which is a quick and easy job.

The air filter lives in the large plastic airbox above and to the right of the alternator as you’re stood facing the front of the car. There should be 4 clips holding the top and bottom half together which can be popped off by hand.

With them popped off you can lift the top half and put it to one side. You can do this with the unlet pipe still attached between it and the engines plenum chamber thanks to its design, but on such an old car with tired rubbers, it’s always worth checking that you won’t tear it by doing so first. It only takes a moment to remove the jubilee clip fixing it to the MAF anyway.

Replacing the air filter on a BMW E30.

With the top of the airbox out of the way, you will see the exposed air filter. Carefully lift it out and give it a quick inspection to see how ready to be changed it was.

A vacuum cleaner can come in handy here, but either way, get a damp rag and wipe out the lower half of the airbox which is usually harbouring dust and various other grimy deposits, then follow up with a dry rag to dry it off.

Place the new filter in and clip the lid of the airbox back on securely. Your air filter is now replaced.

How to replace the fuel filter on a BMW E30

You’ve probably spotted the silver cannister below and between the brake booster and the power steering pump header tank, this is indeed your fuel filter.

The fuel filter is a bit awkwardly placed despite being visible. It’s mounted in an upright position to the engine bay on a bracket, secured by two jubilee clips. There are also two smaller jubilee clips on either end sealing on the rubber inlet and outlet.

BMW E30 fuel filter location in the engine bay.

The worst part about replacing a fuel filter is the knowledge that no matter what you do, you’re going to spill fuel and probably get covered in it too.

Knowing this, it’s wise to have a plastic bag on hand to put the old filter straight into once removed, rather than carrying it around and pouring it everywhere.

Start by slackening off the clips on the body of the fuel filter with a flat head screwdriver and pull the top clip upward onto the pipe and let the bottom one drop down onto the below pipe.

Now your old fuel filter should be released and moveable. Now is a good time to make note of which direction the fuel filter flows so you can put the new one in the correct way, they aren’t bi-directional.

Start by undoing the top jubilee clip and pulling that up the pipe too, once undone, give the connection a twist to get it moving and a pull to pop it apart. A good trick at this point it to pull one of the end caps off your new fuel filter and put it on the now exposed end of the old one.

This will help you avoid spillages while you’re working on the bottom clip, but will also make the filter hold a vacuum if kept upright reducing the amount of fuel that will come out of the bottom of the filter once the bottom pipe is removed.

With the bottom jubilee clip removed and the pipe popped off, bag your old fuel filter and make sure none of the four jubilee clips have gone walkabout. Check the direction of your new filter is correct as you put it in place and refit the jubilee clips to either end and secure it back on the bracket.

Your fuel filter is now replaced. Hook the battery back up and turn the key to the on position without firing up the car a couple of times to try and build some fuel pressure and saturate your new fuel filter. After a moment, fire the car up as normal.

Expect the engine to splutter and misfire a little as air escapes and fuel is pulled through to replace it.

If the engine stalls, stick your head under the car to check that there’s no fuel leaking and start it up again. It should settle down within a few seconds and run smoothly from this point forward.

Take a moment to refit the fan shroud to the radiator with the plastic rivets that you removed at the start of this procedure, as there is no longer any reason for it to be out of the way.

Replacing the Spark Plugs on a BMW M40 Engine

Above the exhaust manifold, you’ll notice the other end of the four ignition leads entering the engine, below the valve cover.

For ease, I like to leave these in place and pull them and replace one by one to change the plugs. This stops you from faffing around trying to remember which lead goes to which cylinder later on. The order is probably denoted on the ignition lead cover, but my E30 was missing this plastic part so I’ll never know.

Carefully pull the first lead out from as close to the spark plug hole as possible. Avoid pulling from the middle of the lead as this can damage it and cause the plastic shielding to separate from the connecting end.

With the lead removed, use a socket on an extension with a ratchet to carefully slacken off the first spark plug. Luckily the M40 has spark plugs on quite a flat angle and they’re not in too deep, so with a steady hand, you can undo and remove the spark plugs with a simple socket rather than a special spark plug wrench.

Replacing the spark plugs on a BMW M40 engine in an E30 3 series.

Place your removed spark plugs down on a workbench in the order they came out for later inspection and put the new plugs in one by one, be very careful not to overtighten them.

With the new plugs in place and all HT leads reconnected firmly, have a quick look at your old plugs and check them for signs of an issue.

Normal healthy used spark plugs should have a browny grey colour to the electrode end, but if the plugs are very old and worn out you may notice that the electrodes and insulator tip have eroded away somewhat.

If your plugs are black and oily it can indicate worn pistons, incorrectly adjusted valves or possibly a leaking head gasket.

If they’re sooty and coated in carbon it can mean the car is running too rich or not getting enough air, check the inlet passageways are clear.

If the plug is burned with a melted electrode or blisters on the insulator tip then it’s a sign that the engine has been overheating, or time timing has been out.

If the plug is showing signs of corrosion or oxidation, this can indicate that the engine has been sat for a long period of time and moisture has got to it.

Check your plugs and make note of any abnormalities for further investigation.

Check the condition of spark plugs to diagnose engine problems.

With your service now complete, get your friend to help you put the bonnet back on securely and lined up back into its previous condition, reconnect the washer jet wiring and washer fluid pipe and hook the battery back up once and for all.

Resetting the Oil Service Light on a BMW E30

With your BMW E30 car now fully serviced, you will finally want to reset that annoying oil service inspection light on the instrument cluster.

Luckily, on a car of this vintage, you won’t need any fancy software or cables to do this, although it advised you use the proper plug to connect to the Data Link Connector (DLC) so you don’t short anything.

However, I like to live dangerously, so use a more rudimentary method which I’ll share with you, but please be aware of the risk to your E30’s electronics.

Locate the Data Link Connector port on the inlet side of the engine connected to the firewall beside the fuse box and unscrew the cap and find yourself a very short piece of insulated wire at around 5cm in length with either end exposed.

Bridge a connection between pins 7 and 19 and switch the key to the on position and wait for the oil service inspection lights to all light up on the dash, they usually do within a few seconds and once they have let them stay lit for around 10 seconds, switch your key back to off and your oil light is reset.

Bridge pins 7 and 19 to reset the oil service light on a face lift E30.

Remove the wire and store it safely for next time, replace the data link connector cap and close your bonnet.

You can now start the engine and take the car for a test drive to admire your work. Congratulations, your E30 timing belt and major service is now complete.

Taking your BMW E30 out on a test drive following major service and M40 timing belt change.

If you’d prefer to digest this E30 service process in video form, check out our film below for a less detailed version of how we did our m40 timing belt change, water pump and the rest of the service in our workshop.

Summary of E30 Service Work Completed

  1. Source servicing parts
  2. Remove the bonnet
  3. Remove the fan shroud
  4. Remove the distributor cap
  5. Remove the valve cover
  6. Inspect the camshaft and valvetrain oil supply
  7. Drain the coolant
  8. Remove the auxiliary belts
  9. Remove the clutch fan
  10. Remove the distributor rotor arm
  11. Remove the thermostat housing and thermostat
  12. Remove the water pump
  13. Remove the crankshaft pulley and harmonic damper
  14. Lock the timing with the camshaft and flywheel locking tools
  15. Replace the M40 timing belt
  16. Tension the new M40 timing belt
  17. Reassemble the engine
  18. Refill coolant and bleed the system
  19. Drain the engine oil
  20. Replace the engine oil and filter
  21. Replace the air filter
  22. Replace the fuel filter
  23. Replace the spark plugs
  24. Reset the oil service inspection light
  25. Take it for a test drive

If your BMW E30 with its M40 engine is a keeper, you may want to take things a step further and renew more parts before considering it a job done. My advice would be to consider replacing tired old ignition leads, although mine looked shot and the car runs well.

I’d also recommend changing your gearbox and differential oil to avoid excessive wear as this is probably ancient too.

Brake fluid would be another recommendation as this absorbs water and leads to an ineffective spongy pedal if it’s very old.

Disclaimer: This post contains affiliate links.

8 thoughts on “BMW M40 Timing Belt Change, Water Pump & Major Service Guide”

  1. I’m getting all the bits together to attempt this. This guide will be open the whole time.
    Not done a timing belt before but I have done water pumps, pulleys, thermostats, and other bits on my 2002 E46 330i so hopefully it all goes to plan.

    1. Good luck Lee, hope our M40 timimg belt guide comes in handy. If you’re used to working on an E46, I reckon you will find working on the E30 a pleasure. So much more room for activities in the engine bay with that little M40 unit in there.

  2. Many thanks! Will be doing all of this as a spring time project. Quick question – how long should you allow for the whole job? Draining and disposing of coolant, oil and fuel in my very tight and gloomy garage would be tricky. But I can’t leave it outside for too long with the bonnet off.

    1. Hi Nick, to be honest, the job took us pretty much a whole day. Make sure you have the right parts before you start and you should be fine, I suspect it could be done a lot faster now we know how, hope the guide speeds things up for you!

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