Triumph Bonneville T120R 1972 650 Restoration Project

Triumph Bonneville T120 R 650 1972 Restoration Project

The Original Advert

The original ebay advert for the 1972 Triumph T120.

The Long Wait

I originally did a write up of my Triumph Bonneville T120 on a Triumph forum, but it would be a shame for you not to have an overview of what I wrote there with the latest activity here.  So if some does seem familiar I apologise.

It was probably not the best starting point for a first (ish) full restoration, but having looked for a project bike for a couple of months, and feeling that the price of projects were going up daily, I bought this one. A 1972 Triumph Bonneville T120 in pretty poor condition. I now think that it was a mistake, not the bike but the price I paid. 

However I learned so much doing this bike, and developed so many new skills and ideas that it was really a good investment. The last bike I had bought in a similar condition were some boxes full of a Triton for £90, but that was 35 years ago!! I didn’t make as much progress with that one before I sold it on for around £400 to help finance a house move. Happy days!

Buyer’s Regret

Having agreed the purchase remotely, it took nearly 2 months to actually get the bike to my home, Christmas and Winter weather intruded. In the meantime, regret had set in. Examining the photos forensically I started to spot more and more that made me question the purchase.

At some time been painted in Captain America (Easy Riders, Panhead) colours, although this wasn’t at all obvious through the rust, which appeared to be commensurate with having been stored outside for a decade or two! I noticed the non standard Keihin carbs, not to worry, they look completely shot at.

The more I looked the less I thought I had made a good decision. However the price wasn’t horrific compared to some of the other projects I saw sold around the same time, and it did look like the frame and engine were usable, but I realised the forks would need replacing, but it did have new rim and spokes on the front wheel. My son discovered a likely reason for the new wheel when I got the bike, but more of that when I tell you about stripping it down.

Oh, and the engine had been apart, probably a few times 🙂  But more on that later.

It’s Arrived!

My new Bonneville arriving at home in the back of a van.

After what seemed like an age, and after two broken delivery promises because of the weather, the bike finally turned up. Not having a connected front brake, added a little excitement into getting it out of the van. However without accident it went straight into the workshop I have built. 

I spent some time sitting on a seat that coordinated with the tank, check it out, surveying the bike. I didn’t spot anything that gave me more concern, than I already had. If anything some parts seemed a little better than I expected, but my expectations weren’t that high.

My new bonneville T120 in its new workshop home ready to be worked on.

First look

The pictures hadn’t lied, the bike was a wreck 🙁  I had seen worse, and at higher prices, but some of it was worse than I had hoped, but had expected!  But I was excited as well, and I couldn’t wait to get started.  

With hindsight the bike wasn’t too bad considering it was a full project. The major parts were there and did look mostly useable.  I think that the only mistake was perhaps the model, it takes the same effort and money to do a lot of the work on a more valuable bike, so the chances of recouping your expenditure is better.  I always try to do projects within what the final vehicle will be worth (less labour of course 🙂 ).  

The OIF Oil in Frame 650 Bonnevilles are not the most desireable, so this will impact the final value of the bike.  Having worked on and found out more about this bike and model I think they have a lot more going for them than the press they get.  The frame is strong and handles well, and there are a lot of little detail things that Triumph had improved from earlier models. And some of the parts specific to this Triumph Bonneville T120 model look fabulous.  I will do a write up about them for another set of posts.

Front end

Triumph Bonneville T120 front wheel and drum brake.

Lovely chrome rim, and a new Chinese tyre, so the wheel looks good to go.  The brake will need attention but the alloy looks OK. There is a lot of corrosion on the sliders, and the stanchions are toast, the same colour and texture 🙂  The mudguard has a lot of surface rust but is pretty sound. All of the headlight assembly and front controls are pretty poor, as are the handlebars and risers.

Tank and engine

Triumph Bonneville T120 project petrol tank and engine.

The tank has been painted in Captain America stars and stripes, badges and trim are missing, and there does appear to be some areas where the rust has gone through.  This is a shame because these tanks were only used for 2 years so it will be more of a problem to find a replacement. Luckily virtually every tank off Triumph Bonneville 650s and 750s from the 70s and 80s will fit the T120.  

All of the alloy has a white crust of corrosion, but seems reasonably sound.  The carbs look like they are so far beyond redemption that it is almost amusing.  The engine is seized, but at this time I was hoping that it might just be the rings slightly stuck in the bore, and that I might get it to free up easily.  I was WRONG!!! But more of that when I get to it. The header pipes would work, but would take too much effort and cost to be viable for the rebuild, so more for the junk list.  

The footrests and foot controls were there, and could probably be redeemed with a bit of work.  Not the rubber items though, rubber always turns to crap when bikes are left to fester.

Frame and forks

Rusty Triumph T120 restoration project.

Rust, rust everywhere and not a drop of paint!!  Yes it had been painted red in the past, just like the vendor had said, but there wasn’t much left of it.  However the metal of the frame did seem pretty sound, and I couldn see anything that needed repair, yet.

Back end

Rusty Triumph T120 rear mudguard tail light and suspension.

The shock absorbers were well past their best, and the spokes and rim looked well knackered.  But parts like the chain adjusters were still there and looked like they could be reused. The grab rail has a little rusty but most of the chrome was holding up.  Tail light was lunched, but the bracket was there. The rear mudguard looked like it might still be OK.

Under the seat

Rust under the seat of a Triumph Bonneville T120 project bike.

Most of the electrics were still there, but I doubt that any will be saveable.  I could now see that the rear mudguard was very weathered, and there were some holes that went through, depends how thick the rest of the metal is, it might still be saved.

It is pretty much as the pictures in the listing, and it wasn’t mis-described.  Overall I have no complaints, and I did buy another from the same seller, so I must have been happy enough.  

Ho hum, time to spray it with releasing oil, and get it stripped!!

Getting started on stripping down the Triumph Bonneville T120

When I started the main idea was to work towards a stereotypical Triumph Bonneville, rather than a fully authentic nut and bolt restoration. Ideally I wanted to reuse as many parts as I could salvage or refurbish. Following this I realised that I would have to make use of some reproduction parts, and probably mostly new fasteners.

I was definitely looking forward to learning new skills along the way.  A project like this is like a set of puzzles that you have to work out. Sometimes they are interconnected, and all too frequently you find that you have got to back track, sometimes a long way.  It adds to the fun that the parts list for this bike has some bits that are wrong, and some parts that were never produced for a bike that they sold.

An example of this is the head steady which changed for the production models and if you look up the way to assemble the rocker washers you will find enough reading to fill a couple of weeks! 🙂 

The photos above are part of a set I did of of everything from a number of angles so that I had some reference to how it was put together when I received it.  Although I didn’t intend to restore it back to the Captain America look it had. I then roped in my young niece to squirt releasing agent on everything that looked like a nut or a screw. Took her a while, but she did a good job.

Stripping down a rusty Triumph Bonneville T120 project in the workshop.
Using WD40 to penetrate rusty nuts and bolts when stripping the project bike down.

We already knew that the engine was seized, aren’t they all!!! The kickstart partway through its stroke looking a little limp!!   I was worried that the spark plug threads in the head would come out with the plugs, so it was with some trepidation that I started to remove them.  However, after a little careful application of force, they actually came out pretty easily. I was surprised to find that they were two different makes, one looked new, the other pretty old.  

Mismatched spark plugs removed from the bike, one looking pretty old and rusty.

This bike would have some very interesting tales to tell, mostly of torture from what I have seen so far!!

Triumph Bonneville project with the tank removed exposing the head of the engine.

Then I put some light oil (I know everybody recommends diesel or Mystery Oil, but I had this to hand 🙂 ) in through the plug holes, hoping that it might just free the pistons up in the bore if I left it for a while.

Pouring oil in through the spark plug holes to free up the pistons on the T120 project.

Next the silencers came off, they were totally rusted through.  The header pipes were solid, but I didn’t think that they would have a place in the plans for this bike. I thought that maybe they could be used with a wrap if it was some kind of custom, but I knew that new ones would be needed. 

Even “Young Spanner” got in on the act, wielding spanners like a pro’. He is a dab hand with a set of tools, and soon had the mudguards off. To be honest there weren’t many other parts to take off. Triumph’s of this era don’t have many superfluous parts, and the seat was missing anyway.

We removed the tool tray, the housing for the air filter and side panels. Then took off the coil brackets and all of the other electrics. Although very unlikely, I did think at the time that the wiring was a little better than I expected and thought I might reuse some of it.

Removing the tail light of a Triumph Bonneville T120.

The releasing agent that my niece had liberally sprayed everywhere had soaked in well, and most fasteners came off reasonably easily.

Removing the rusty rear mud guard from the Bonneville T120 project during strip down.

It looked like this bike had been very exposed, but interestingly, the underside of the mudguards were really clean. I mean really really clean, no mud, no rust, no stone chips,  just the paint, metallic blue. It looked like the bike may have been painted in the stars and stripes scheme then just left outside to rot. Seems very strange!!

Underneath the mudguard showing intact blue paint. Evidence of the bike not having been ridden much after paint.
The underside of the rear mud guard showing blue paint also.

The carbs were Keihins, and looked pretty poor, and the debris in the inlet manifold (look at the picture, don’t laugh) didn’t bode well for the rest of the engine.  I hoped that it was general workshop dust and rubbish that has found its way in to mix with a little rust. Maybe sawdust and paint spray.

I started to be very worried that the inside of the engine might just be too full of water and rusted to redeem. So I was even more keen to get it apart.

Aftermarket Keihin carburettors on the T120 showing signs of corrosion.
T120 inlet manifold looking very rusty, a bad sign for the condition of the internals.

Removing the Cylinder Head

The head came off the Triumph Bonneville T120 quite easily, although taking some of the upside down fasteners on the rocker covers did give me a bit of a challenge.  I kept losing track of which way I was going, you know how it is when you can only get a few degrees of turn on a spanner because of poor access.  So I spent some time turning the spanner taking it out, then accidentally changed direction tightening it for another few times until I spotted what I was doing, did this three or four times. I must be getting old!!

T120 head and valve springs during an engine strip down.

The oil that I had put in to try to help free up the pistons started to come out through the head gasket faces quite quickly.  I was pleased that I had second guessed this and already had paper towels in place to catch it.

Oil leaking through the head gasket faces on the T120.

With the head off it was clear that the left cylinder had been more exposed to water, probably coming in through the inlet.  There was plenty of surface rust on the valves. I was hoping to reuse them so this was a concern. Overall the head looked in good shape, there was surface corrosion, but there were no broken fins or other damage that I could see.

Triumph Bonneville T120 engine strip down, rust in the left cylinder following exposure to water.
Corrosion in the left cylinder due to water discovered when stripping down the T120 engine.
T120 right cylinder's head looking in good condition during engine strip down.

First impressions of the T120’s pistons

Both piston crowns and bores were a red swamp of oil, rust and whatever other gunge had found its way in. It looked pretty ghastly, but cleaned up better than I would have expected. The bores were very rusty and the pistons firmly stuck in place. On the head of the seized pistons it was marked +30, that seems to indicate that it has had at least one cylinder rebore in its life.

Triumph Bonneville T120 seized piston.

Cleaning the engine and frame on the T120

I got the pressure washer out and gave the underside of the bike a good degreasing with Gunk before washing off the encrusted grease and grime. I assume that the bike had been given a wash before being repatriated to the home of its birth.  It always makes sense to get things as clean as you can before dismantling them, it saves a lot of mess.

Cleaning and degreasing the T120 before further strip down.
Letting engine degreaser dwell on the T120 before further strip down.

I didn’t get all of the gunge off, so I had to do it again when I had removed the engine.

Cleaning up the Bonneville T120 frame with the engine removed.

Bonneville Centre Stand Removal

When I got it back in the workshop for further dismantling the centre stand bolts proved to be quite a challenge to get out.  This involved more tools than I expected, including a reasonably big hammer and a punch.

When the nuts had been removed I was nearly convinced that the bolts were welded in. Eventually with a lot of persuading they did come out, and as expected the stand did have quite a twist to it, and the brackets on the frame were not in the best condition.

Removed Bonneville T120 centre stand.

Draining the oil tank

When I drained the oil from the oil tank, I felt quite positive because I could see through it and it looked relatively clean. Positivity went a little down-hill when I pulled the plug from the engine sump and a pint or so of rusty water came out! There was some oil in it but it I was seriously concerned about the bottom end!

Draining the sump on the T120 of rusty water and oil.

I realised that as there was no chain I couldn’t put the bike in gear and press the brake method to lock the engine. So I decided to take advantage of the engine being seized to undo more of the engine fasteners.

Stripping the primary case off the engine

When I looked at the primary side of the engine on the Triumph Bonneville T120 I spotted that it had been repaired with some filler in the past.  Looked like the bike has fallen over and the footrest has been knocked into the primary case, denting and cracking it.

Previously repaired damage to the Bonneville T120's primary engine case.
Inside the T120's primary engine case showing the crack damage.

It made me realise that stripping a bike is a little like an archaeological dig.  But you keep finding broken things of no value instead of treasure! It is interesting trying to work out what has happened to it in the past and piece the story together.

Having inspected the crack from the inside I decided to try using the low temperature aluminium welding/brazing that you see demonstrated at classic bike shows. I don’t want to spoil their pitch, but the rods which I think also have some Zinc in them are available elsewhere and at a much lower price.  It is like brazing for aluminium rather than welding. The primary case isn’t a very stressed part, so if I can make it oil-tight and cosmetically OK I will still use it.

Besides the crack is on the underside so even if it is still visible it shouldn’t be too obvious.

To remove the primary case I used an impact driver on all of the screws first then removed the two dome nuts at the front. I noticed a little “liquid” coming out around the thread of the bottom stud after I removed the bottom nut. This made me remember to put a tray under the cover before undoing all of the screws. Which turned out to be a really good idea, when it started raining out of the bottom of the primary cover as I undid the screws! Another mixture of oil and water, quite a bit more than I expected.

Draining the oil and water out of the primary case of the Bonnevile T120.

When I got the cover off surprisingly the main corrosion seemed to be on the top of the clutch chain wheel. I assume it is corrosion from the inside of the cover, but it looked like bird droppings on the top of it.  I became a little concerned that it might all be scrap 🙁

T120 clutch chain wheel corrosion.

Stripping the primary drive 

Taking out the alternator and clutch is not particularly hard, but it does require some special tools or it will be a real struggle.  To undo the alternator you simply remove the 3 nuts and slide it out. You will probably need to cut the bullets off the end of the wire to get it through the engine casing, but the are easy enough to replace when you put it back together.

Removing the alternator from a Triumph Bonneville T120

Carefully removing the alternator from the T120 using a puller.

To remove the rotating magnet you need to use a three legged puller.  I always try to put a penny or something on the end of the bolt that screws in so that it protects the end of the crankshaft.  You can see it in the picture. 

Using a three legged puller to remove the alternator fromt he T120.

Removing a Triumph Bonneville T120 clutch

To undo the clutch retaining pins you need a special tool.  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 a special tool, in fact there is a whole variety of them. Or you can make (bodge) something up yourself which will do the trick.

I made mine out of an old tyre lever, but if I was doing it again I might use a wood chisel as my starting point. The blade needs to be quite thick, so a lot of screwdrivers are too thin.

Making a special tool to remove the clutch retaining pins from a Triumph Bonneville out of an old tyre lever.

Before going any further I took the opportunity to undo the clutch centre nut.  Once the plates are removed there would be nothing to stop the gearbox rotating, remember there is no chain!

Removing the clutch centre nut from a Bonneville T120.

With the centre nut undone and the pressure plate removed the actuating rod can be taken out, and then the clutch plates.  There are 12 in all, 6 plain steel ones and 6 with friction material plates used on a Triumph Bonneville T120.

The have tabs on the appropriate sides to slot into the drive (clutch centre) or driven (duplex sprocket and clutch housing) parts of the clutch.  The plates on this bike were very stuck together. This is a thing that happens to an extent on all clutches of this type. The user manual even recommends kicking the bike over with the clutch pulled before starting the engine.

That wouldn’t have freed this clutch up though.. It took a bit of poking and pulling to get them all out, and even then they were stuck in groups of 2 or 3.

Removing the clutch plates from the T120, they were stuck together.

To finally remove the front sprocket and the clutch housing and centre on the Triumph Bonneville T120 two different special tools are required.  A clutch puller and a two legged sprocket puller.

Two legged sprocket puller tool.

Removal of the front sprocket and clutch housing is quite easy when using one of these tools. 🙂

Using the two legged clutch puller to remove the front sprocket on the T120.

It all comes out as one, well not quite, you will find the clutch rollers all drop out on the floor.

Clutch, front sprocket and chain removed from a Triumph Bonneville T120.

And that’s the primary chain case stripped, apart from the tensioner.

Bonneville T120 primary case with internals stripped and removed.

Removing the Points and Advance/Retard

Before I could take the timing case cover off I had to remove the points and the advance/retard mechanism.  The points come out easy enough, just a couple of pillar bolts. Then pull the wiring through the hole at the front of the engine case.

However, the advance/retard mechanism is pushed on to a taper at the end of the camshaft. This needs a little more work. I used a tool that I think is actually for use on valve guides as a puller. I have a number of Triumph engine tools which I bought as a job lot.  It took me a while to identify the valve guide tool for the Triumph Bonneville T120. I have still got some tools that are a complete mystery so far.

Triumph Bonneville T120 points and advance retard mechanism.
Bonneville points stripped out for refurbishment.
Removing the points and advance retard fromt he Bonneville T120 with a special threaded tool.
The advance retard mechanism removed from the T120.

Removing the timing chest cover

When I looked at which tools I needed I was surprised to find that all of the screws were cross headed so I suspect that they were probably the originals.  I was expecting a bit of a fight, so gave each of them a tap with an impact driver first. They all came out quite easily after that. I gave the cover a couple of taps with a rubber hammer and it came off quite easily.

Removing the timing cover from the Bonneville T120.

There was some very light corrosion on the exhaust pinion, but otherwise it looked fine.  Next to come off was the oil pump. At that time I was not sure if the pump would be OK, but I knew I would check it over carefully if I was going to re-use it.

Inside the timing chest cover of a Triumph Bonneville T120.

Stripping the valves from the cylinder head

I have a valve spring compressor that had been in my toolbox for over 30 years, it only came out once a decade or so, and always for a car. Last time was for two burnt out exhaust valves on a Datsun (now known as Nissan) Sunny (maybe it’s two decades actually..). The sunny was still running with big Vs burnt out of two exhaust valves. Popped 2 new valves in and it was back to normal. 

Unfortunately the car type valve spring compressor won’t fit on the valves in a Triumph Bonneville T120 head, the valve guides, and thus the springs and valve stem are set too far into the casting.

I had to buy a different style of valve compressor, with enough different fittings to use with the recessed valves.

Using a valve spring compressor on the head of the T120.
Compressing the valve springs.
Triumph Bonneville T120 vale springs compressed for removal.

To keep things steady I put the head in a vice, using some wood in the jaws to protect the casting.  Compressed the springs, sometimes the fixings called collets (also heard them called keepers, and listed as split cotter in the parts manual) stick on the valves.  The trick is to give the end of the valve a tap with a hammer to free them up, works a treat. Then using a magnet to get the collets out of the way before releasing the compressor. 

Bonneville T120 valve and spring removed during strip down.

The valves looked pretty horrible. I decided to clean them up before passing judgement on whether they can be re-used.

Rusty valves and cylinder head removed from the T120.

Cleaning up the cylinder head

I gave the head a clean in a small blast cabinet using powdered glass which isn’t as aggressive as sand on aluminium.  It removes all of the corrosion and crap but leaves a clean matt surface. I am sure that vapour blasting would be better but it would have been an extra expense. To give aluminium parts a final finish and give a satin sheen to the surface I used wire brushes and 3M polishing mops. You can get a surprisingly good finish using this method.

My handy stable top sand blasting cabinet.
Starting work cleaning up the Triumph Bonneville T120's head.
The result of blasting with powdered glass to leave a clean finish.
T120 cylinder head after sand blasting.
Inside the cylinder head before blasting.
Inside the cylinder head after sand blasting.

The valve seats were not good but only one was particularly pitted.  I left the full inspection and refurbishment to a later date.

Freeing a seized Triumph Bonneville T120 R engine

When I looked at the pictures and started writing this, I find it hard to believe that I am now riding the bike with this engine. Even more unbelievable is that fact that most of the engine components were reusable. When we reached for a bigger hammer I thought, “Oh Well, there are plenty of engines available online” 🙂

Frequently in adverts for barn find bikes you see the phrase “weather seized” or “locked up”.  From past experience this is usually where the pistons have stuck in the bore and isn’t usually a big deal.  Mostly soaking in diesel or a light penetrating oil by pouring it into the spark plug holes will do the trick if left for a few weeks.

It makes sense to then split the engine and clean the bores and rings before using it, but a lot don’t bother and do seem to get away with it.  This bike wasn’t like that!

When we took the head off it was immediately apparent that water had been finding its way in.  Probably through the inlets that were silted up!!! There was thick crusty rust in the bores, I could see that these wouldn’t just clean up 🙂  They had been soaking in oil for a few weeks, it didn’t seem to have made much of a difference!

Seized pistons in the T120's engine.

Although not at Top Dead Centre (TDC), the pistons were near the top of their stroke.  This meant we could start with a little percussion straight away. If they had been at the bottom, all would not have been lost, see the socket method later.  It might even have been easier.

Initially, the wisdom is to use a good piece of hardwood as a drift, and use a hammer to start them down the bore.  Giving each a tap in turn. After we had completely destroyed a few of our improvised wooden drifts, we resorted to direct hammer on piston action!! 

Hammering the seized pistons down the bores of the Bonneville engine.

Using one hammer as a drift, striking it hard with the other one, working side to side, the pistons were not for moving!! Then we both worked together timing our blows to be simultaneous. It was only when we started to get a little irate, and using most improbable force did they start to move. Yes, we had used heat on the barrel too, not just going at it cold.

Seized pistons starting to move down the rust bores.

At last they started moving down the bore, but they didn’t give up easily.  Once we had pushed them down the bore to near Bottom Dead Centre (BDC), we had to take the next step, taking off the base nuts and lifting the barrel up.  It wasn’t a pretty sight.

Lighting the barrels up having moved the seized pistons down.

To raise the barrel up and continue knocking the pistons through, you put sockets (of the same length) over the base studs for the barrel to rest on.

By this time we were using a longer drift, a large (and I mean very large) socket on a 3/4inch drive extension.  I am sure we shouldn’t abuse tools like this, but needs must.

Using sockets to aid in removing the pistons completely from the bores.
Using a very large socket and extension as a drift to get the seized pistons moving.

Eventually replacing the sockets with deeper ones, we got the pistons free.  Celebrations all around!!! Now we could get the engine out of the frame.

Moving up to larger sockets to finally get the pistons removed from the bores.
Using an impact gun to remove the bolts holding the engine into the frame.

It just shows that patience and persistence sometimes need to be replaced by brute force and ignorance to get the job done!!

The engine finally removed from the Triumph Bonneville T120.

Triumph Bonneville Centre Stand Lug Repair

The centre stand on the Triumph Bonneville T120 definitely didn’t work right.  So now that we had the engine out it was a pretty simple task to flip it and take a quick look.  

Bonneville frame without engine upturned to view centre stand lugs.

One of the centre stand lugs had worn completely through.  I considered fabricating a new lug and welding it on.  However, looking at it a little more I could see that there was still a lot of decent metal there.  So I decided that I would build up the missing part with weld, and grind it back to shape.

Triumph Bonneville centre stand lug completely worn through.

For this I used a simple DIY MIG welder at home. I am not the best welder in the world but I can manage to join pieces like this.

Always remember safety first, electric welders use a very high current, and the parts do get very HOT!  A mask to avoid “arc eye” is essential, and don’t let anybody watch unprotected.

Welding the Bonneville centre stand lug to repair it.

You can see that these images were taken before giving the frame a good clean.  It is essential that the parts you are actually welding are clean and free from paint or rust.

Weld built up to replace the worn lug metal.

The finished job came out great.  I now know that I should probably have put a bit more weld on the face that the centre stand stops against when in use.  Now that I have it all back together I have found that the stand comes too far forward to be able to take the bike off it comfortably.  I will take it off and build up the lugs on the stand, one day. 🙂

Centre stand lug repaired and painted, looking as good as new.

Powder coating the air filter housing

I gained a small oven (70 litre or so) when we renovated my son’s kitchen.

Originally I intended to use it to heat parts such as when you are installing or removing crankshaft bearings.  But then I thought about maybe powder coating smaller items. Plenty of Youtubing later and I had bought a simple powder coat kit and ordered some powder.

Cheap DIY powder coating equipment.

Basically to powder coat, follow the below steps:

  1. Clean the metal part of corrosion and paint
  2. Suspend it so that you can put it in the oven (wires are ideal)
  3. Put it in the oven and heat it for 10 minutes to burn off remaining grease and  oil
  4. Let it cool
  5. Attach the connector from the Powder Coating System unit to the part so that you can give it an electric charge 
  6. Use the powder gun to spray (very low pressure, 10lbs or so) the powder which sticks to the metal because it has the opposite charge
  7. Pop in the oven on gas mark 6 🙂 (180c) for 10 minutes.
  8. Job is a good ‘un

It sounds simple, and it actually is.  It is also very satisfying when you have taken a piece of scrap and turned it into something that looks new.

I will do a longer more detailed post on DIY powder coating so I’m only talking about it briefly here. In the meantime, you can check our another DIY powder coating project on our bench vice restoration post.

I cleaned the air filter housing in my blast cabinet using powdered glass first.  The alloy had the usual white powder corrosion and all of the original finish had gone.  They come up grey with a matt/rough surface ideal for powder coating.

Corroded Bonneville air filter housing.
Bonneville air filter housing after sand blasting with powdered glass.
Corroded Bonneville air filter housing.
Triumph Bonneville air filter housing blasted and ready for powder coat.

I wanted to completely coat the air filter housing.  I could have hung it inside the oven. I wasn’t too concerned about the inside finish, so although not obvious in the picture I had coated the inside first, then turned it over and put it on supports before doing the outside.

Freshly powder coated Bonneville air filter housing in black.

It worked out great.  The durable finish is just what you need for parts like this.  I now tend to powder coat most of the smaller items, it’s addictive.

Young spanner would like to get parts of his car in there, maybe we will be buying a bigger oven 🙂

Here is a video of spraying the powder coat on the fork clamps:

Triumph Bonneville T120 R drum brake refurbishment

Although the wheels had probably not turned for decades the brakes were free.  Unlike the way that disc brakes deteriorate due to the fluid absorbing water, drum brakes stay in much better shape when left unused for years. There was corrosion, but nothing that was extreme.

Bonneville T120R drum brakes after decades of standing.

I stripped the Triumph Bonneville T120 brakes down to their component parts.  Then gave the appropriate parts a clean in white spirit to remove any old grease.  

Bonneville T120 drum brake stripped down ready for rebuild.
Drum brake parts soaking in white spirit to clean and degrease them.

Some parts needed a blast to get rid of the corrosion, some just a rub down with emery cloth. I painted the steel parts with zinc primer and polished the alloy parts.

I checked the springs and shoes to see if they needed replacing.  I know a lot of people would replace these parts as a matter of course, but it is very wasteful.

Rebuilt Bonneville drum brake internals.

There has been a change from old time engineering mechanics to modern technicians. The old timers would recondition, and pass judgement on the condition of parts, reusing where possible and only replacing where absolutely essential. Whereas a modern technician will replace parts as a matter of course, whether or not they would still be quite functional for a good length of time.

I feel that the older idea is more in keeping with the age and design of these bikes.  Plus it’s cheaper in money if not in time. 🙂 

Refinished Bonneville front drum brake housing.

Overall I was pleased with the outcome.  I originally powder coated the actuating arms with light grey, which didn’t come out too well.  But I managed to get hold of some of the longer arms that give better leverage, so I swapped to them before refitting to the bike.

I did the rear brake at the same time, it was great that I didn’t need to replace anything to get working brakes again.

Bonneville rear drum brake internals ready for rebuild.

Triumph Bonneville T120 R Fork Rebuild

I had realised right from the start, looking at the original photos and during the first appraisal, that the forks were going to need a lot of work.

The stanchions had lost most of their chrome, the sliders were covered with corrosion, and there were no signs of any movement whatsoever.  On the plus side they weren’t bent, and all of the parts were there.

Rusty Bonneville fork stanchions.

Removing the forks from the yokes was pretty easy and they came out without too much fuss.  Unfortunately I made a very amateur mistake when I took them out. I forgot to undo the top cap nuts.  

Rust front forks removed from the bike on the work bench.

It is much easier to get some oomph into moving these while they are still clamped to the bike.  If they put up some resistance then holding the stanchion is not that easy. Especially if you want to reuse the parts and don’t want to cause any damage to them.

I am not proud of this next picture 🙁

Botched Triumph Bonneville fork top cap nut removal.

At least I can take comfort in the fact That I was going to replace both of the parts.  I may not have had any better success if they were still in the yokes, but the hassle of clamping the stanchion wouldn’t have added to the fun!

Triumph Bonneville T120 R Oil in Frame (OIF) 1971 onward front forks are pretty simple affairs.

There is a tube, the stanchion, with a slider that holds the wheel.  The slider is held at full extension by a spring inside the tube, and there is another thinner tube in the middle with holes in it that restrict the flow of oil that is used to slow down how the slider moves. That and a number of seals and fasteners to hold it all together is about it.

There is only one part of working with it that may need a special tool, but there are a number of workarounds that can be used.

Although all of the parts were there once I had stripped them down it was obvious very little was going to be reusable.  I even had my doubts about the sliders, but with some patience they cleaned up fine.

Triumph Bonneville front fork slider restoration and corrosion removal.

Maybe not show finish, but certainly acceptable for a rider.  When I got the bike it had what was obviously not the original front wheel.  One of the sliders had a sticker on it that looked like it had been burnt.

My son mooted the idea that maybe the bike had been near a fire and that the original wheel and tyre had got damaged so they bike couldn’t be moved easily.  The sticker certainly looked like it had fire damage, but the dust cover at the top of the slider looked OK. We’ll never know, but I am pleased with the front wheel, and the inside of the slider was fine to use. 

Oil real removal tool being used on the fork legs.

Although there was some corrosion on the damper tube, they weren’t in too bad a shape, and with a good clean and new seals would be perfectly reusable.  The tool in the image is used for pulling out oil seals, comes in really handy.

Triumph Bonneville damper tube from the from forks.

When undoing the screw at the bottom of the slider you need to find some way to hold the damper tube from turning.  There is a special tool, but I use a modified screwdriver on the end of a number of ¼ inch extensions.

Other ways of getting around this are; you can get lucky and they just come undone; leave the fork leg assembled and the spring pressure might be enough; or use an impact wrench.  But you will need something to hold the tube when you are putting it back together, so my improvised tool will work.

Improvised tool to remove the screw at the bottom of the fork slider on a Triumph Bonneville.

Once I had got the new parts, and cleaned everything I was reusing I laid it all out before putting it back together.

Triumph Bonneville T120 front fork parts all laid out on the workbench ready for reassembly.

At this point I spotted that I was still missing something.  It happens all of the time during a rebuild, either something is missing, or there is something that can’t be reused.  You just have to have patience and wait.

In this case I had forgotten the Dowty washers.  These are washers with a rubber seal in the middle to seal the threads of bolts going into an assembly.  They don’t look that important, but if you leave them out they do cause a problem. They are used on the fuel taps as well, leave them out at your peril.

Dowty washer used to seal the threads on the fork stanchions.

I put the legs together as far as I could, while waiting for the postman.  When putting the screw in I also put a little silicone sealant on the threads, a bit belt and braces but why not!?

I carefully put the new oil seals in making sure they had the open spring side down.  It’s amazing how often you find that these have been put in the wrong way.

Reassembled Bonneville fork legs ready to go back on the bike.

It was great to get them back on the bike, nothing like a lovely big bit coming together.  You feel like you are making some progress.

Painting the frame of a Triumph Bonneville T120 R

Originally I did intend to have the frame powder coated, but having got a couple of quotes and reading horror stories about grit in the oil tank I started to change my mind.

I am sure that most powder coaters can do a good job of Oil In Frame (OIF) Triumph frames, and I would always use a “Charlies” type filter anyway.  And I totally accept that powder coating gives a better more durable finish, but I decided to paint it myself anyway. It was sunny and I have the time!

Triumph Bonneville frame prior to sand blasting.

My main intention was to make sure the frame was sound and that the rust was treated.  I tend to do bigger blasting jobs outside on dry days. It causes quite a mess if you try to do it inside and you don’t have an appropriate booth.

I use powdered glass on steel items accepting that it will be a virtually total loss of the medium, although you can scoop it up and feed it through again.  I use the gun from my small blast cabinet, just running the feed tube into a bucket of powdered glass. Eye protection and a breathing mask is a must.

Bonneville frame after blasting with powdered glass.

All of the old paint comes off along with the rust.  Having blasted the frame, you need to be ready to get some coating on it straight away, or the rust will get a foothold again.

I gave the whole frame a good blowing over with an air gun, then a good wipe with panel wipe just to remove any other dust and fingerprint grease.  Then a couple of coats of a zinc primer, this is a good rust inhibitor for the future.  

Triumph T120 frame in zinc primer ready for painting.

As the cosmetics of the frame are not quite as important as other parts you can be quite business-like doing this.  Triumph didn’t bother removing weld spatter before they painted it, so I was making an improvement.

I did spray it with primer filler before colour coats, so that I could smooth the more visible parts, but I didn’t put the same effort in that I would with a tank or mudguard.

Triumph Bonneville T120 OIF frame being painted in primer and then black top coat in stages.

I was quite pleased with the final result, which I protected with a final coat of petrol resistant lacquer.  I am sure that this will hold up for a good time to come, it won’t be as durable as powder coat, and I will have to be more careful that I don’t scratch the surface.  But it is probably as good as the original painted finish.  

Triumph Bonneville T120 R rolling chassis coming together

With the frame painted I could now start to get the wheels back on.  I checked and replaced all bearings as I did so. The wheel and swing arm bearings just need a clean and fresh grease.

The steering head bearings were suffering from quite a lot of corrosion so I got a nice new set of taper bearings and fitted them.

I fitted the Matao “Charlie’s” filter so that any grit that I hadn’t managed to clean out of the oil tank would be caught.  I also think that these are a really good idea compared to the original filter system, which is basically a sieve! 

Triumph Bonneville Charlies FIlter by Matao being installed.

A new set of shocks and a tyre on the back wheel, and the bike would be ready to go. 🙂

Ne chrome rear mudguard being mocked in place.
Wife sat on the Triumph Bonneville T120R project.

Now I just needed to rebuild the engine, and do the electrics!

5 thoughts on “Triumph Bonneville T120 R 650 1972 Restoration Project”

  1. What an absolutely brilliant post, relevant to me because I have a similar project just about to start. I have numerous manuals etc. on this particular bonnie but I’ m pretty sure I can glean a lot of information from this thread. Not sure how long ago this was but no matter, also very impressed with the home powder coating kit, keen to find out more about that,……and of course the ‘interruption’ was just the best! Going to look for the next installment now many thanks.

    1. Thanks for the kind words James, I hope there are some useful tidbits of information in here for you with your own bike project. The home powder coating kit works remarkably well for small bits actually, great fun too, highly recommend!

  2. I have a 72 T120v that has the Coffin Tank but will Shortly be fitted with an Export Tank and Dummy Oli Tank and Side Panel’s so it will look like a 68/69 the original Mudguards have been replaced with Alloy ones and the rear Light has also been Changed it should be Finished around Early Spring next Year. Yours is looking good keep up the Restoration.
    If you would like Photos please email

    1. Hi andy, great job done another classic bike saved, Im doing the same on a 71 t120 oif , im at a point where i dont know weather to have my hubs painted or polished and the same with the sliders i was thinking of having them polished have you any thoughts on this ?. Regards Nigel

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