Triumph Bonneville T140E 1978 750 Repair

Triumph Bonneville T140 E 750 1978 Repair & Ride Project

The Original Advert

The original advert for the Triumph Bonneville T140 on ebay.

Should I buy, or should I not?

I spotted the listing for this Triumph Bonneville T140 on my phone when I was walking around Scarborough on a shopping trip with my wife.  Having looked carefully at the images, and having read the text, but also having bought a previous bike from the same person I felt it looked like a good quick project.  Not for a full restoration but as an oily rag rider! My other Bonneville project was going a little slow, and I wanted something to ride!!

I think most project bikes are a little overpriced at the moment.  Probably because like me there are a lot of people who are very into restoring or customising, sometimes more than riding 🙂  So when it looks like you can buy and restore/customise within what the bike will be worth, it always makes it a more attractive proposition.

It was a late seventies (therefore would not need MOT, or be subject to road tax ) Triumph Bonneville T140. It was a reimport on Nova so would need registering. Not the most popular colour, brown, when new, so a little bit unusual. Non runner, but not with the engine seized.

here were a few parts missing, parts of the carb and the front mudguard stay were immediately obvious. The fork stanchions looked a little bent, and there was a small dent in the back of the front mudguard.  But I knew the frame on these bikes are pretty strong around the steering head, and the stanchions nearly always need replacing on a bike of this age, so didn’t feel it was a big issue.

I contacted the seller to ask if delivery could be included in the price, and after a couple of interactions a deal was struck.  My wife said I had been looking a little “shifty” staring at my phone, probably relieved that it was another bike, and not something more nefarious 🙂 The seller agreed to include delivery into price so I deal was struck.

Delivery of the bike

It took a couple of weeks for the bike to arrive.  It was the same courier that had previously delivered a bike to me.  We had a lovely chat about his new van, and the fantastic lift on the back of it.  Once we got the bike out I couldn’t wait to give it a good looking at, so was quite pleased as I watched him drive off.  

First Impressions of the T140E

Once the courier had gone, I had a chance to look at my purchase.  I really do recommend that you go to look at a vehicle before buying, but I have bought a few (Speed Triple, Fireblade, TTR 600, Bonneville T120R, probably some others I have forgotten) like this and haven’t been really stung yet.

Bonneville T140E front end and forks crash damaged.

Front End and Forks

Well the forks definitely have a backwards bend to them, and the stanchions have quite a lot of rust.  Most bikes of this age have well pitted stanchions, if they weren’t too bad then putting a gaiter over the top would do, but the bend does force the issue. 🙂

The brake disk could look better, but all brakes get surface rust, it depends upon how deep it has bitten, but I am sure they will clean up. The front rim seems straight, and not too much rust lifting the chrome.  All of the spokes give a nice “ting” sound when hit, so seem to be in order. But the tyre is fossilised, no chance of reusing that! Also I noticed the bottom stay for the front mudguard is missing and there is a dint in the back of the mudguard.  

I suspect that this is why the bike stopped being used.  A front end shunt, then left in the garage and they never got around to repairing.  Forks bent, mudguard dinged, and the stay bent, but nothing else really wrong with it.

Bonneville T140 fuel tank and engine.

Tank and Engine

The paint on the tank if very faded, and there are a lot of scratches etc, but no major dents, and it doesn’t seem too rusty.  The petrol taps are both seized, this seems to always happen on the unused bikes I see. This is a Triumph Bonneville T140 E so it has Mk 2 Amal carburettors.

The one on the left side is missing the carb top and the slider and all associated bits and bobs. They are all available new, so not a big concern other than cost.  The cases look to be in good condition and should clean up OK, and the little timing cover is missing.

The exhaust headers are the strange ones that grow from 1 ⅜” to 1 ½” or bigger where they come out of the head, one of them is rusted through so it will need to be replaced.  Not looking too bad, nothing that is overly worrying, yet!!

Triumph T140 aftermarket exhaust, seat damage and drivetrain rust.

Exhaust and Drive train

It has very short silencers (mufflers) which seem to be straight through.  No chain and the rear sprocket is more worn than any I have ever seen, this is a little worrying, but overall the rear wheel seems usable, apart from the fossilised tyre.  The seat has a bad hole in the cover, and the rear grab rail is quite rusty, and there is a fair bit of rust on the frame..

Now I also noticed that the indicators are missing.  Apart from a little corrosion the shock absorbers seem to be working fine.  

T140 front wheel, disc brakes and hand controls.

Headlight and hand controls

The levers are corroded, and it is obvious that the master cylinder is seized, so they will need quite a bit of attention.  Apart from some pitting in the chrome the headlight seems to be fine. It’s great to see that the reflectors are there, not a big thing, but check out the price of them!!

Carbs

The carb on this side has all of its parts, funny that the other side has parts missing.  You would expect if somebody was taking parts from the carbs they would take both sides. I noticed that the footrest rubbers are pretty shot, but I would have expected that.

The rear brake master cylinder is seized, but the back disk isn’t quite as rusted as the front.  Oh, and I spotted that the pillion footrests are missing!

Under the seat

The seat base is in reasonable condition, but the top rails of the frame are quite rusted.  Most of the electrics seem grubby, but all there apart from the HT leads. The rear mudguard is sound, some rust and pitting to the chrome, but perfectly usable.  It is great to see that the original stickers are still there. Overall it does seem to be an honest bike.

Having had a better look at it I suspect that it was laid up after a shunt, and over time the owner, or his mates, borrowed parts off this bike to keep another one going.  If it had been left in a dryer environment it would probably have looked like new.

Checks and preparation to attempt to start the T140 for the first time

As I had bought this project with the intention of using it as a rider, I didn’t want to spend a lot of time stripping it and refurbishing.  So although some of it was a bit tatty I was going to keep the “patina” look.

I had just been reading a couple of books that were around the idea that a vehicle is only original once, and that the scars of use, and the updates and repairs over the years, all add to the character of the bike.  That and being a bit lazy as well. 🙂 So as the main deal breaker would be if it didn’t run or had mechanical gremlins, I decided to do everything that was required to get the engine running first.

I took the spark plugs out and I was pleased to note that the threads were fine.  Typically, like with the Bonneville T120R (my other project) this one had mismatched plugs. What is it with American Triumph owners? ?

Triumph Boneville T140 mismatched spark plugs extracted.
Spark plug thread condition looking good after extraction.

One of them was of a kind I hadn’t seen in a bike before, where the electrodes are recessed in the end of the plug.  I can’t see that helping with clean running! So I replaced these with Champion N3C’s they always seem to get the best press for the Triumph Bonneville T140.

Then we connected a battery up and gave it a couple of kicks. I had already given the wiring a cursory inspection to see if looked safe.  Pleasingly it produced nice strong sparks. This was looking promising. If we have spark, then all we really need is something for them to burn to get it going.  But first I needed to make sure that it had reasonable oil before I would even attempt to run it.

Filter and oil tank

I drained the oil from both the in frame tank, and from the sump.  The oil didn’t look too bad, considering it had been sat there for quite a while and the sump wasn’t full, so the seals in the oil pump must be working.

Draining the old oil from the tank and sump of the T140.

The filter although not clean, was not as bad as a lot I have seen.  There was not the usual disgusting mayonnaise type gunge that you frequently find because the oil becomes contaminated with water. 

After a good clean I replaced it with a Motao filter from Taiwan, which uses a paper oil filter.  If you have a month to spare, read the various threads on various forums about this and other filters.  I have used them before and they work a treat, saves all of the nasties flowing around your engine.

The quality is really good, but you will probably need to open up the four mounting holes to allow for Triumph’s original precision engineering work. 🙂 In truth running a slightly larger drill through the fixing holes did the trick.  They comment in their leaflet, that they have produced it to the original dimensions but you may have to adjust slightly.

Replacement Motao oil filter to uprate from Triumphs original filtration system.

This is a Motao filter, picture from another bike I was working on though, just to avoid any confusion!

I then filled the T140 up with some 20/50w classic car oil.  

Checking the carbs

The carbs are the Amal Mk 2 type, on the Triumph Bonneville T140 they are more angular shaped than on earlier bikes.  The inlet manifolds come out of the head parallel at the back, instead of the splayed layout of the pre-”E” models.  They are connected by a rubber hose rather than bolted directly to the head. This stops the heat transfer that was sometimes a problem with the “V” model.

The Amal carbs seemed to be in quite good condition.  There was some of the white powder type corrosion in the float chambers.  I’m not sure if it is dried up fuel, or because of moisture, but it cleaned off reasonably well.  The main jets were 230, which seem a bit on the large side. Maybe they were to compensate for the straight through short silencers.

I decided to put 200 jets in, which is the standard, and I had them to hand. One of the exhaust header pipes has rusted through, so I am likely to go back to a more standard type system.  For now I put some aluminium tape around it so that it would at least route the exhaust gasses towards the back of the bike.

Missing Amal Carb Parts

The right hand carburettor was complete, and seemed fine, the left hand one had parts missing.  To be honest it looked like the the top had just been unscrewed, the slider pulled out, along with the needle jet, spring etc and maybe put to one side.

It seemed strange that these were missing from just one of the carbs. I suspect that they had been removed for some reason then just never replaced. I think it would be unlikely that they had been taken to use on another bike, but who knows. 

The parts missing were, the plastic top and adjusters, the slide, the needle jet and clip, and the spring.

All of the parts are available new from Amal so it wasn’t a big deal. The only real issue is that if you start buying lots of parts to rebuild a carb the cost soon rises so you might as well buy a whole new carb.  For this bike I managed to find some good condition second hand parts so I didn’t have to make that decision.

So having the carbs together, I could put them back on the bike.   The throttle cables where still in place and looked to be in usable condition.  I cleaned the air filters out, one had an infestation, long dead, insects, but cleaned up OK.  So the next thing to look at was the tank and fuel lines.

Amal carbs removed fromt he Bonneville T140.

The carbs then went back on the bike and some new fuel lines joined them up.

Triumph Bonneville T140 – First Start

We wheeled the bike out of the workshop, and strategically placed the fire extinguisher. 🙂  As we only wanted to see if the engine would run, we didn’t replace the fuel tank, just added fuel to the carbs.

Kicking over the Triumph Bonneville T140 for the first time since the 80's to see if it would start.

I don’t think that this Bonneville had run since some time in the ‘80s when it had been left to fester.  So with the little work that we had done so far, we didn’t have high hopes. We took turns in kicking it over and after a while, we did start to get the odd cough.

I have experienced this before, just when you are thinking of giving up, something works.

Anyway, it did burst into life. It had a few backfires, and hiccups, but after a little fiddling with the idle screws, it did settle to a reasonable tick over.  I checked that oil was returning to the tank. It was so that was a good sign.

Video of us starting the bike for the first time

Now we had a running Triumph Bonneville T140.  The next steps were to get it roadworthy and looking reasonable.

Rust treatment

Having bought this Triumph Bonneville T140 as a rider I was embracing the patina, but I didn’t want it to deteriorate and rust further.  I have seen a number of “Rat Rod” cars, vans and bikes with what appeared to be a stabilised rust finish.

When I researched them there seemed to be lots of different advice, most of which would have been harder than stripping the bike, and painting the parts normally.  I wanted something that kept the current finish but didn’t bring a big overhead of effort with it.  

I decided to try other avenues of research, and I hit pay-dirt while looking at bathrooms.   Apparently some high-end bathrooms have contemporary rust finishes for some parts of the furnishings, and I found an Australian Plumbing Forum (I kid you not) that had quite a bit of information.

They used a product that was really intended to make brush painting easier, I think it is based on Linseed Oil. The manufacturers seem to have spotted the market now though, and it does say rust inhibitor in the advertising.

The product is available under a number of different brands, but in the UK the main one seems to be Owatrol.  I bought a can and used it on all of the rust. It stabilises the existing rust and then dries to a hard finish.  It takes a few days to fully dry, but once it does it seems to have a durable surface. If you look at the before and after images, you will see that it does leave a good finish, without losing the patina.

Owatrol rust inhibitor coating,

Here are some before and after Owatrol rust treatment photos to show the results.

Before Owatrol rust inhibitor was applied.
Before Owatrol rust inhibitor was applied.

Triumph Bonneville T140 after Owatrol rust treatment, be advised that the sprocket is a new part.

Before Owatrol rust treatment.
After Owatrol rust treatment.

Refurbishing the switchgear on a Triumph Bonneville T140 E

The switches on Triumph Bonneville T140’s do suffer from corrosion.  The surfaces get a white powdery layer, which continues inside and the copper parts start to go black and green. To add to the pleasure, the plastic parts also get brittle and break.  However I have had quite a lot of success in refurbishing them.

Having removed them from the bike and carefully stripped them down, watching out for the ball bearings with springs behind them, I first gave the contacts a soak in a mixture of white vinegar and salt for around 30 minutes.  This cleans up the copper parts really well, and doesn’t harm any of the plastics or other metals. Then a swill in a baking soda mixture to neutralise the acid, and a rinse in water.  Carefully dried then it is easier to check over.

If any of the soldered joints look like they may fail, I get the soldering iron out and give them a re-solder. All of the plastic buttons, springs and ball bearings are available in a new pack, look for a Console Switch Kit online.  If the plastic insert that holds the contacts together is broken or snapped, careful addition of a plastic strip support and epoxy glue usually can fix them.

Triumph Bonneville switch gear stripped down for refurbishment.

I use usual cleaning and polishing on the outer casing.  I use various grades of 3M mops on a polisher/grinding machine. You can get a really good polished finish, but for the patina look I only removed the corrosion.

Half way into removing the corrosion from the original Lucas switch gear.
The end result after rebuilding the Bonneville switch gear and mounting it to the handle bars.

Refurbishing a Triumph Bonneville T140 E Clutch

The clutches on these Triumph Bonneville T140’s do have a tendency to stick and seize solid.  The user manual recommends kicking the bike over with the clutch lever pulled in to free it before starting even on a new Bonneville.  After a few decades this doesn’t work any more. 🙂

The clutch was not going free up without surgery on this bike, so I took of the primary cover and stripped it out.

Bonneville T140E with the primary cover removed exposing the clutch.

The only special tool needed to check or change the plates is to undo the retaining pins. Basically it is a large screwdriver with a bit cut out of the middle to miss the end of the bolt that pokes through. You can buy one, in fact there is a whole variety of them available. Or you can create (bodge together) a special tool for your self.

I ended up making one of an old tyre iron. Given the chance to do it over I would prefer to modify an old chisel for the job. The blade would need to be fairly hefty, so a lot of screwdrivers are too small for the task.

Triumph Bonneville DIY clutch removal tool.

I took out the old plates and gave them a soak in white spirit for a while to get all of the old oil off.  Sometimes the friction material sticks and comes off the driven plates. If this happens then there is nothing you can do but buy replacements.

This didn’t happen on this Bonneville so I managed to clean them up with a 3M mop on a grinder to give them a fresh surface to grip with. The ghost imprint on the driven plate isn’t a problem, and I have reused plates that looked a lot worse than these in the past without problems.

The drive plates all cleaned up well so I was quite pleased.

Triumph Boneville T140 clutch plates after a clean up.

But best of all, there was none of the scalloped wear on the clutch centre or triplex sprocket housing that you can get.  This showed that this bike hadn’t been used much and that the 5000 or so miles indicated on the odometer was probably correct.

If there had been some wear here then this could have been cleaned up with a file.  There is no need to get too anxious about this, a little wear isn’t usually an issue, and I have seen massive grooves on some clutches that were still working acceptably.

Inside a Bonneville clutch housing with minimal wear.
Inside a the clutch housing showing minimal wear on the T140.

Once they were clean and reinstalled, it just needed a couple of tweaks on the screws to get the pressure plate to run true.  Then I adjusted the play at the end of the clutch pushrod. Once I was happy that the clutch was working I replaced the primary cover with a new gasket, and filled the primary case with the recommended 350cc of oil.

Cleaning an old Triumph Bonneville T140 fuel tank

Although very faded, and with the odd scratch, the tank was in quite good condition.  The fuel taps were seized, this always seems to happen when bikes are left for years.

The inside did have some rust, but looked like it would clean up.  I started by putting some nuts in the tanks and giving it a good shake. This is to remove the loose rust flakes and anything else that might be lurking in the far recesses of the tank.  I repeated this a lot of times, tedious but should pay dividends in the end.

I then used a mix of white vinegar and salt, which is quite cheap. There are plenty of different potions to clean out tanks, some are much quicker, and if some of them were cheaper I would use them.

I mostly filled the tank, and left it for a week or so, giving it a shake 2 or 3 times a day, and leaving it in different positions each time to get the solution to work all over the inside of the tank.  When I removed the vinegar mix, I then put in a baking soda solution to neutralise any acids. Then having rinsed it with a hose for quite some time I put in a cup full of Paraffin. I used this to chase out the water and to give the inside a coating to stop it rusting again.  

One of the problems when you clean the rust off something, then use water to remove the de-rusting  agent, is that you can get flash rusting. This is where the metal is clean and exposed to air and moisture so that it can start the rusting all over again.  Putting some kind of coating on straight away stops this. I used Paraffin because I have it to hand, it leaves an oily coat, and if a bit mixes with the fuel eventually it won’t cause a problem.

I am not a fan of coating the inside of the tank with some form of epoxy.  If there are pin holes that you are trying to cure then maybe does have a place.  But I have heard too many horror stories about lumps of the coating coming away, and the problems of getting that out, to feel happy about using it.  If a tank has rusted through it needs proper surgery, with welded or brazed repairs.

What came out of the T140's fuel tank after the nut rattling rust remover technique.
Authentic Triumph Bonneville patina on the fuel tank.

Then apart from a wipe over outside, new taps and a new filler cap gasket, I put the tank back on using new fuel lines, and some new stainless clips.  It always seems that whatever hose you buy with the right internal diameter, they are always either very tight, or too loose.

These were tight, so in the spirit of the name of this site, a few grazed knuckles were gained trying to squeeze them on. 🙂

New fuel lines between the carbs on the T140.

Refurbishing the Forks of a Triumph Bonneville T140 E

The original inspection showed that the forks on my Triumph Bonneville T140 were bent.  The stanchions had rust pitting anyway so they would have to come out anyway.  The bend wasn’t too bad, and carefully checking the head stock and fork clamps (triple trees) it showed that they weren’t damaged in anyway.

Bent Bonneville front forks.

To take out the forks you first need to remove the wheel, mudguard and front brake.  The only thing I needed to be careful of was not to damage any of the fasteners. The little screws for the brake cover can be really seized so due care is required when removing them or they will easily strip.

Bonneville 1979 with the front brake cover removed.

The fork top nut on Triumph Bonneville T140’s is really just a cover, the top of the stanchion has an allen hex headed screw in it.  Triumph in their wisdom made this 11mm, or some imperial size that works out the same. Not in a standard set, so initially I wrapped some metal tape (amazing what you can find in your tool box) around a 10mm key which took up the clearance enough to remove them.

I ordered an 11mm key for reassembly, if these aren’t reasonably tight they can leak fork oil in use, and I wouldn’t have trusted my bodged tool to tighten them enough. You might spot the 12” adjustable on the seat that opens just wide enough to remove the top nuts, this saves removing the handlebars to get clearance for a large socket.

Remove the top nuts before loosening the clamps, they may put up some resistance and it is best to have them secured firmly.  If you read this too late a strap wrench will help, but expect a bit of a struggle. You might also consider the screw at the bottom, but I leave this until later.

One fork stancion removed from the T140.

Make sure that you put some good support under the front frame rails while you are playing with the forks.  It may take some force, twisting, cursing, swearing, to get them to free up. If possible strap the bike to a bike lift as well. If it falls off you may get hurt, and other parts may get damaged.

Both front fork stancions removed from the T140.
Bonneville T140 forks removed from the bike.
Triumph Bonneville front fork dampener assembly internals removed.

To remove the damper assembly you need to undo the allen hex screw at the bottom of the forks.  There is a drain plug on the side as well, it’s up to you if you want to drain them first, if you are fully stripping them you don’t need to disturb the screw which may be seized in.

The screw at the bottom can cause a problem, it threads into the bottom of the damper rod, and the whole lot may turn, rather than the screw coming out. There is a lot of different advice on this, and there is a special tool you can buy.  My solution can be seen at the bottom of the image a flat screwdriver bit on the end of a lot of ¼” extensions. This can be used to catch the slot in the top of the damper rod, while you undo the bottom.

Other methods include; leave the fork top nut in and use the spring pressure; use an impact driver, not the ones you hit with a hammer; take a break and think about it for a while before getting too heavy with it.

I gave everything a good clean, then replaced the O ring and fork seals as I installed the new stanchions.  Triumph fork seals have a pretty bad rep, and you frequently see gaiters used to hide a slight leak, there are also “leak proof” more expensive seals you can buy.

I like the clean look of the forks so I am careful when putting them together and haven’t had too many problems. The Triumph Bonneville T140 spec fork oil is ATF fluid and each fork leg requires 200cc of oil.

I personally use proper fork oil and I tend to go with 10w or maybe 7.5w. I have heard that some respected Bonneville experts use 20/50 engine oil, I haven’t tried that myself, maybe next time.

When I put it all back together I checked the head and wheel bearings.  If I had any doubts about them I would have stripped and replaced them. With this bike all of the bearings checked out OK, so I decided to leave it alone.

Bonneville T140E with brand new fork stanchions installed.

Triumph Bonneville T140 E Brake Overhaul

Both front and back brakes were seized, and the disks had a lot of surface rust.  Unfortunately brake fluid is hygroscopic (I had to look it up) meaning it absorbs water from the surrounding air.  This does take years to be a problem as the little vent holes don’t let a lot through. This is one of the main reasons that changing the brake fluid is on the service schedule every few years or so.

When a bike is left for decades, not only does it absorb water it evaporates as well. So not only have you got corrosion, there is also a residue that in some cases has become solid.

It is sometimes possible to recover the master cylinders, and a seal and spring kit is not expensive, these ones were too far gone in my opinion.  New ones manufactured by LF Harris are not too expensive, so I ordered a front and back for this Triumph Bonneville T140.

I ordered new brake hoses as well. Not only does the rubber become brittle and swell over time these ones were blocked.  They should be changed after 10 years and I really wouldn’t trust 40 year old rubber brake lines anyway.  

Rubber brake lines on the Bonnie.

When I stripped the brake calipers they were fine, only needing a new seal kit after a good clean.  The calipers can be split in half which makes them a lot easier to deal with. There is a little O-ring in the seal kit that goes in when you put the two halves back together.

I like to use a compressed airline to pop the brake pistons out. I use a bit of plastic bag to form a seal around the end of a simple blow gun, pushed into an appropriate opening on the caliper. A word of warning, don’t set the pressure too high, the pistons can come out a lot quicker than you expect! 🙂

Bonneville brake caliper split down for a rebuild.

The main thing of note with the master cylinder replacement is making sure that the actual cylinder is position right so that the brakes will release.  I have put images of the instructions but basically it is as below.

Setting a Triumph Bonneville front brake master cylinder

To make sure the master cylinder is adjusted properly, screw the cylinder in until it just touches the actuating push rod, then screw it in one additional turn.  If the brakes don’t release when you have completed and bled them, you only need to undo the lock screw and move the cylinder a little one way or another until they do.  It isn’t necessary to strip it all out again.

LF Harris brake master cylinder setup guide for Triumph Bonneville.
Master cylinder overhaul guide for Triumph Bonneville T140 front brake.

Setting a Triumph Bonneville rear brake master cylinder

The rear master cylinder has the push cylinder already set, but if it wasn’t you would do the same as with the front, so one turn after it touches.  However, because of the different actuating mechanism you have to set the push rod nut at the correct distance.

See the image for how I measured it. As they seem to be OK in setting the cylinder up during manufacture, I am not sure why the don’t set this as well.  But if you read the instructions it says to adjust the “diagram” not the actual push rod, made me laugh out loud when I first read it. And maybe if you have an issue you have to move it a “smidge” back or forth when fitting.

However unless you have have the wheel out you will find access for such finesse when fitted is somewhat limited 🙂

Setting a Bonneville rear brake master cylinder up with push rod nut distance at 9mm.
LF Harris rear brake master cylinder renewal for Triumph Bonneville.
Diagram with instructions on how to set up the rear brake on a Triumph Bonneville T140.

Bleeding Triumph Bonneville brakes 

I don’t tend to use a pressure bleeder for these.  We have one that works using tyre pressure and it isn’t really worth the faff of setting it up for this.  A little patience until you get the fluid coming through is all that is needed.

The main thing to note is that you need to position the caliper so that the bleed nipple is at the top.  This isn’t an issue with the front one as it is mounted that way. However the rear one will need to be re-positioned, especially if it is one of the under-slung ones like on my early Triumph Bonneville T140 E. 

Don’t forget to Put something between the pads to stop the pistons popping out.

I reused one of the sets of pads at the rear, and bought a new set for the front.  As long as the friction material is still firmly attached to the backing plate the pads should be fine with a fresh scuff up.  Over time rust can push the friction material off. I used new on the front, just to make sure.

Bonneville brake pads after years of standing.

Triumph Bonneville T140 E Brake Disc Refurbishment

The disc on the front had a lot of surface rust, but overall weren’t too bad.  I took them off and using a wire brush and then a 3m mop I made them much more presentable.  I believe that showroom models had chrome plated disks which wore off in use.

There did still seem to be some bits of chrome still on these, in the less rusty parts, again reaffirming the low mileage.  I cleaned and reused the original bolts which were all in good condition.

Rusted Triumph Bonneville Front Brake Disc.
Bonneville front brake disc after a clean and polish up.
Bonneville T140 rear brake disc rust.
T140 read brake disc after a clean up and polish.

Cleaning a Triumph Bonneville T140 E Ignition Timing Advance Retard Mechanism

I initially checked the points without thinking about the advance retard mechanism, the fact that it was sparking at all was great.  However, when we started it and I noticed that the pick up seemed decidedly flat, I knew that the points would need attention and that I added checking the advance retard to my list.

This mechanism uses centrifugal force to move the cam that opens the points. It advances the ignition so that the spark occurs further before Top Dead Centre so that the maximum power is gained from burning the petrol and air mixture. It is quite simple being some weights restrained by some springs.  

Bonneville T140 advance retard mechanism.

In this case it had just seized up.  This wasn’t through corrosion, it just seemed to have gathered a lot of dust and grime from the points cover being missing.  I checked the springs which were fine and cleaned up the other parts putting it all back together.

It worked fine after this so I could put the contact breaker plate back on and set the points.

Setting the Points Ignition Timing on a Bonneville T140 E

Although everybody rushes, including me, to put electronic ignition on these bikes, the points system is pretty simple, easy and satisfying to adjust.  The ignition timing is set so that the sparks that fire the engine happen at the right time to make maximum power.

There are a few things that need to come together so that the sparks occur at the right time for each cylinder.  Basically you first check that you can see the timing marks, then set the timing advanced, set the points gap, then set it so that the points open at the time when the timing marks are aligned.

This is how, it seems complicated but once you understand what you are trying to do and have done it a couple of times it is quite easy.

First undo the inspection cap so that you can see the timing mark on the rotor and the pointer used for timing.  Turn the engine over so that the mark is lined up with the pointer, it pays to pick out the rotor mark with some white paint or something, especially if you are using a strobe to finish the job.

Some rotors have two marks 180 degrees apart, these were used when the rotor was fitted to other bikes in the range that didn’t have an equal firing order. If yours has two make sure that the mark you use is the one before Top Dead Centre not Bottom Dead Centre, otherwise your timing will be the exact opposite of what you want. 🙂 

Setting the points ignition timing on the T140 E.

Before setting the points, you need to set the advance retard mechanism at full advance so that it is matched up with the pointer and timing mark on the rotor.  This is when the spark should come when the engine is revving at around 3000 rpm.

To do this you need to remove the centre bolt from the contact breaker mechanism, then put it back with a washer while holding the cam at maximum advance to lock it in position.

Setting the mechanism to full advance.

Rotate the engine so that the heel of one of the contact breakers (points) is against the top of the cam and the points contact should be open.  Set the points gap using the adjuster screws, using a feeler gauge so that you can just feel it dragging when you move it.

I tend to tighten them so that the feeler is clamped, then slacken off to the point where the feeler can be gently pulled out.  Then rotate the engine one full turn and the other contact heel should be at the top of the cam and you can set the points gap for that one.

There are two sets of points, make sure you know which is the one attached to the backing plate, and which one is the loose one that moves in relation to the backing plate.  You want to set the fixed one first.  

Rotate the engine so that the contact on the fixed plate (which you need to set first), is open, you should find that the timing marks are near.  Rotate the engine backwards (use the back wheel with the bike in gear) to the timing mark back past the pointer then forwards again until the marks exactly line up.  

Slacken off the pillar screws that hold the contact back plate in place so that you can move it slightly. I then use one of the test lights that look like a screwdriver with a light in them and wire with a small crocodile clip attached, see the picture.

I clip the crocodile clip to the spring on the contact being set and the other end to a good earth.  

Electrical testing screwdriver with light and earth.

Switch on the ignition then rotate the contact breaker back plate until the light just comes on. This is when the contacts will be making the ignition system spark.  Tighten up the pillar bolts so that the back plate is now held, then loosen the screws on the other, loose, contact plate.

Rotate the engine one full turn, swap the crocodile clip to the other spring and move that plate until the light just comes on, then fasten it down.  

That’s it you have statically timed your engine.  Now remove the washer that is locking the advance retard and replace the bolt.  

To be honest this is probably as good as you need to time your engine, but you can get it “better” by using a strobe.  Basically this is a light that flashes at the same time as the spark occurs. Usually the simple ones connect between the spark plug and the HT cable, but there are plenty of other systems.

You run the bike and point the light at the timing pointer so that it lights up when the engine sparks. The revs need to be at around 3000 so that the ignition will be fully advanced. If the marks line up, bingo it is OK.

Usually the strobe shows that there is some variation of when the spark occurs anyway 🙂  If not then you need to adjust the contact breaker back plate, and the loose plate, with the strobe connected to the appropriate plug, and the engine revving at 3000.

This becomes a multi person activity very quickly, like I said static timing is frequently good enough, and I haven’t really been able to tell the difference when I have gone to the effort of strobe timing a Bonneville, over one that had been statically timed.

Fitting the tyres on a Triumph Bonneville

I know that people get very precious about tyres on everything.  And I do admit that cheap tyres on a hot car can give you a lot of fun practising your drifting on damp corners 🙂

However, unless you are the kind of rider that is frequently in the top 20% of the performance range of a vehicle then most tyres are perfectly adequate.  I am not snooty about using part worn tyres either, there are a lot available which are virtually new.

I think they must be imported from places where they have to change the tyres as part of an annual inspection, and a lot have only done a few hundred miles.  

Because originally  the tyres on a Bonneville were measured in inches people get confused about what they can fit.  For the Triumph Bonneville T140 E, I got a nice set of part worn Bridgestone Battlax BT45s, apart from the nobbles having been worn off they looked new.

I opted for alternative tyre sizes and selected 100/90 19 for the front instead of the 3.25 19, and 110/90 18 for the rear instead of a 4.10 18.

The tyres were tubeless, but I believe using them on a spoked rim of this type isn’t an issue.  The warning not to use tubes in tubeless tyres is when you use them on a tubeless rim.

In a spoked rim the air around the tube is pushed out when you inflate it. However, with a tubeless rim there is a chance of air pockets between the tube and the tyre because the rim doesn’t let the air out.  This can cause sudden failure due to the tube rubbing against the tyre/rim where the air pockets are.

Bonneville spoked wheel with Bridgestone tyre mounted.

When fitting tyres I always like to use new tubes of a good brand.  I use a G clamp to break the seal, which isn’t hard on tubed tyres. Then using some small tyre irons and sometimes the well placed heel of a loved one, to get the tyre off.

To be honest, getting your local bike shop to change them is a lot less sweaty and they have great equipment, but I am a bit old school. To balance them put them back on the bike without connecting the brake or chain, and use gravity to tell you where the heavy and light spots are, and common sense to position some weights, it doesn’t need to be perfect to be good enough on a bike like this.

Fitting a new tyre on a Bonneville spoked wheel.
Using your heel to break the seal on a tyre.

For the rear on this Triumph Bonneville T140 I did use the tyre clamps that were originally fitted to the bike, they add to the pleasure of fitting the tyre, even though I don’t think they are really necessary on a bike like this. They are more essential on trials or motocrossers where the tyre pressures are much lower so that tyre may move on the rim.

Triumph Bonneville T140 Repaired and Back on the Road

The Bonnie was ready to go back on the road so I needed to register it.  This is the one that needed to be inspected, so I was very frustrated when the process took the best part of two months, read my V55/5 post for more information on that.  Oh and the weather was beautiful day after day!

It was great when it eventually came through and I could ride the bike. With the work finished the bike starts and rides really well.  Here is Young Spanner starting it, with some joy!

Photographs of the completed Bonneville T140

Triumph Bonneville T140E repaired and back on the road.
Triumph Bonneville T140 restored and registered.
Wife sat on Triumph Bonneville motorcycle.

I was really pleased with the outcome on this T140 project, I came away hungry for the next project..

2 thoughts on “Triumph Bonneville T140 E 750 1978 Repair & Ride Project”

  1. I’ve only just brought my T140E back to life after 25 years of standing. I bought it in ’79 when it was just a few months old.
    Fresh oil, cleaned carbs and few other checks she started 2nd kick. Well happy with it.

    1. Hi John, they are solid bikes, even if not that well looked after as I found out with mine. I suppose that’s the beauty of simple machinery!

Leave a Comment

Your email address will not be published. Required fields are marked *