Rebuilding a classic 50's Triumph twin engine

ianyonok

Ol'Timer
Dec 9, 2008
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661
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I was seeing metal particles in the engine oil and a build up of silvery detritus in the oil tank, on my 1959 6T Triumph Thunderbird.

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It was 27 years and 52,000 miles riding, since I last rebuilt this engine. So, it seemed time for a strip down and rebuild.
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The top end needed de-carbonising anyway.
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Taking note of how tight the clutch nuts are done up, as this clutch works extremely well as it is set, no slip or drag. The clutch nuts are fully home.
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I use Norman Hyde clutch friction plates and they work well.
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Also noting the position of the pinions in the timing chest. The 6T (same as the 5T & T100 ) uses the soft tune E3275 camshafts for inlet & exhaust.
There is an extra mark on the idler pinion, for use with the TR6 & T110 engines, using the E3325 camshafts. That mark is also used for the T120 which has the E3325 exhaust cam and the famous hot E3134 inlet camshaft.
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The sealing of the clutch mainshaft into the primary chaincase is quite primitive on the pre-unit engines, merely a sliding steel washer. This appears to be worn oversize, so I made a new one in the lathe with 0.020" smaller i.d. I also learned it is a good idea to use less than the prescribed 1/4 pint of oil in the chaincase, to keep leaks here to a minimum.
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After a couple days work, the engine was removed. Being a pre-unit, the gearbox stays in the bike.
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Now to strip the engine.
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I have the workshop tools for removing/replacing the crankshaft timing pinion and the camwheels. It is then easy to separate the cases.
The crankshaft sludge trap bung and sludge tube was removed for cleaning. I used one centre punch mark to lock the bung, last time.
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Impact driver to snug the bung up and secured with a drop of red loctite and a single centre punch mark.
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The pistons showed normal wear. There was also normal minimal wear in the barrel bores apart from the inside of the D/S bore which was worn and the bore was 0.008" oversize. This was caused by a piece of carbon that was found struck behind the top piston ring. I believe this was the reason for the metal particles in the engine oil.
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The camshafts were fine, although the journals are worn slightly undersize.
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The wear in the big end shells was minimal with a couple of pitting marks.
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The clutch centre was fine, the internals rubbers felt ok, hub, spider, thrust washer and rollers all within spec. Important here to check that there is no radial play between the hub and the spider within the clutch centre.
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Some wear on the clutch basket teeth, but a new one can wait a while. The teeth were not hooked.
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While the engine was out, I replaced the gearbox sprocket as the teeth on that were hooked.
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Although the pre-unit engine does not specify a tab washer for this sprocket nut ( as the old idea was just to centre puch the nut to the high gear), I modified a unit engine tab washer to use when fitting the replacement sprocket.
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The crankcases cleaned up nicely.
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I took the barrel to the big machine shop, Chiang Mai Yontrakit, just off the SE corner of the moat and got them to bore out 0.040" and hone the bores.
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A new pair of L F Harris +0.040" 7:1 pistons (made in Taiwan to UK specs) were to be fitted.
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Also purchased a set of new conrod bolts & nuts
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Plus a set of new old stock Glacier -0.020" big end shells. The crank big end journals had been ground undersize back in the 90's, during the last rebuild.
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I fitted a new set of camshaft bushes and used a home made tool to "ream" to size.
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Freshly polished conrods. I also weighed the rods and pistons to match for the best balance.
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The rocker box stud holes were worn, so I had the holes welded up, then re-drilled them and fitted new stainless studs.
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The tappets were slightly worn but serviceable.
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The 1/2" AF conrod nuts were tricky, as there was very little clearance to fit a spanner. So, I machined a socket to reduce the wall thickness, to fit the nuts.
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Crankcases, crankshaft and camshafts, going back together.
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Camwheels pinions back on. I also have a Morgo high flow plunger oil pump on this bike, which works a treat.
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Pistons on. The trick is to warm the pistons with a hairdryer first, then the gudgeon pin slides in by hand.

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Also, a halved plastic chopping board resting on the studs is better than pieces of wood resting on the gasket, when fitting the barrel.
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The copper head gasket was annealed and then cleaned up with scotchbrite.
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Cutting pushrod tube seals to the right thickness.
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Rockers boxes on

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I used annealed copper washers for the oil drain pipes and fibre washers for the rocker spindle oil feed banjo nuts
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Made a thick 1.4mm gasket for the inner primary cover.
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Inner cover fitted with temporary holding arrangment while the gasket sealant sets.
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The alternator wire insulation has gone brittle with age.
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I have ordered a new alternator stator, but for now, after separating the wires, I sealed it all up with epoxy. I'll swop alternators next time the case is opened, then should be able to repair this one by replacing the wires.
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Clutch plates going back in.
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With the outer cover on, just needed to check the alignment was correct, that the clutch drum was not touching the inside of the outer cover, with a new primary chain on.
The primary chain is a 428, 1/2" x 3/8", the same size a Honda Wave rear chain, so cheap to buy. I use DID 428 HDS chains and they last about 7,000 miles.
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Happily back on the road after about 3 months. A few niggly things to sort, but basically running well.
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Hopefully, I can do another 50,000 miles before the next major rebuild....
 

canthai

Ol'Timer
Apr 8, 2015
340
142
43
Excellent ! Liked the fact that you used new Con Rod bolts - !!!
A tip I have used for years is to use Fuel Injector cleaner. Stops the carbon deposits from forming very well.
I add a small amount every fill up - piston crown looks like new when viewed with a borescope
 

ianyonok

Ol'Timer
Dec 9, 2008
1,017
661
113
Thanks canthai, that's an interesting idea to use fuel injector cleaner, I might try that.
Conrod bolts seem a point of varying opinions. As I understand, the original Triumph conrod bolts and nuts were of high quality and the manual says to use them again. They are both centre punched after assembly and I believe the idea was that they were tightened to a stretch spec that was within the elastic limit of the bolt. So, you could undo them and then do them up to the same position and they would be good. But this is obviously questionable on an engine that has been rebuilt by someone else, where they may have been overtightened. The conrod bolts you can buy now from most vendors are of questionable quality. They have correct rolled threads but burred ends, so you cannot measure stretch without first grinding the ends to a dome shape.
I think, if doing the job again, I would probably buy some ARP conrod bolts and nuts. Not cheap, but these look to be the best you can get. I believe the nuts are fitted with lubricant and tightened to a stretch spec rather than a torque spec.
 

canthai

Ol'Timer
Apr 8, 2015
340
142
43
Thanks canthai, that's an interesting idea to use fuel injector cleaner, I might try that.
Conrod bolts seem a point of varying opinions. As I understand, the original Triumph conrod bolts and nuts were of high quality and the manual says to use them again. They are both centre punched after assembly and I believe the idea was that they were tightened to a stretch spec that was within the elastic limit of the bolt. So, you could undo them and then do them up to the same position and they would be good. But this is obviously questionable on an engine that has been rebuilt by someone else, where they may have been overtightened. The conrod bolts you can buy now from most vendors are of questionable quality. They have correct rolled threads but burred ends, so you cannot measure stretch without first grinding the ends to a dome shape.
I think, if doing the job again, I would probably buy some ARP conrod bolts and nuts. Not cheap, but these look to be the best you can get. I believe the nuts are fitted with lubricant and tightened to a stretch spec rather than a torque spec.
ARP make an outstanding product, used them for years, bikes and cars, never even heard of a failure.
I always install new fasteners if they perform a critical job - head studs, con rod bolts, main caps ... Cheap insurance.

Re: FI cleaner - when I bought my first new FI car in 1995 I talked to the service manager as to any precautions to take. He said change oil every 5000 km and use FI cleaner.
Fast forward 2 or 3 years. Chevrolet had a recall - head gasket problems. Book an appointment and we will swap for free.
I had 550 km to travel to the dealer, so made an appointment and arrived on the day early morning. They had a bunch of cars in, and 2 guys dedicated to doing the swaps.
Asked them to call me when my car was being done, and I duly arrived. My piston crowns and combustion chambers were clean as new. The other car, with similar mileage - about 70,000 km, was covered with carbon. As was the intake ports.
Convinced me, and been a believer ever since
 

ianyonok

Ol'Timer
Dec 9, 2008
1,017
661
113
canthai,
I'm with you on putting FI cleaner in the fuel tank.
What quantity would you suggest in an 18 ltr petrol tank?
Thanks
Ian
 

canthai

Ol'Timer
Apr 8, 2015
340
142
43
I use the stuff below - 196 THB at Big C
350ml - treats 40-60 liters
So 18L - I would use 100ml or 120ml - one bottle then good for 3 tanks.
Beware of those bottles - once the foil seal is broken the cap will not seal well enuf to stop leaking out all over everything.
I picked up some square juice bottles at 7-11, drank the juice, marked 50ml on the side with magic marker, pack them on the bike. No issues
I think you will find that with constant use a small amount will be OK
Don't know why the foto attached is so crappy - one on my fone is OK
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Gasoline Injection Cleaner Carretex - is the label
 
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ianyonok

Ol'Timer
Dec 9, 2008
1,017
661
113
canthai,
That's good info, thank you, I'll be looking for that or something similar.
 

Eoin Christie

Ol'Timer
Jul 16, 2019
359
178
43
Nice work, Ian, and thanks for recording the process. Looks like a timely rebuild with general wear, but no substantial damage - Good call.
 

ianyonok

Ol'Timer
Dec 9, 2008
1,017
661
113
Modern equivalent..? Really.... I don't know.
I suppose the new Triumph Bonnevilles are similar in many ways. They are a similar height and size, petrol tank size and shape and similar looks from the side. But the new Triumphs of course have larger capacity DOHC engines and are heavier machines, with a lot more power.
There are some similarities to the Royal Enfield Interceptor 650 twins, although they too are a heavier machine I believe and also DOHC.
The old Triumphs have pushrod engines, like the Indian Chief, most Harleys and the new BMW R18.
A pushrod engine runs with a tappy-tap and a dohc engine runs with a whirr.... the two types have a very different sound and feel.
But really, I don't think there is a modern equivalent. Modern bikes are so high tech, in comparison.
The 1959 Thunderbird 650 weighs 180kgs and takes four different types of oil; Engine oil, gearbox oil, primary chaincase oil and fork oil.
It has no idiot lights of any kind, no turn signals, no neutral or main beam indicator lights, or riding modes. It only has a dip switch and horn button, plus manual throttle lock cruise control, on the handlebars.
It does have as standard; kickstart, right foot gearchange, chronometric speedometer with trip meter, drum brakes, carburettor tickler, steering damper, ammeter, manual oil pressure indicator, a large tool box and tool kit and 3- position pre-load rear shocks.
It is a quite different world in many ways.

Here is a nice picture from 1951. This is an earlier Thunderbird 650, but with the 1950 rigid frame. That is nearly 220kph.... no shirt, no gloves...
70 years ago, back in the days when men were men....!!

1615515168113.jpg
 

ianyonok

Ol'Timer
Dec 9, 2008
1,017
661
113
Fantastic pics, Gents.

Certainly, it appears the world has seriously regressed since 1969.

Amazing achievements by Silverhawk in the Two way One mile average.
I wonder what the different AMA class codes mean?
 

Eoin Christie

Ol'Timer
Jul 16, 2019
359
178
43
Modern equivalent..? Really.... I don't know.
I suppose the new Triumph Bonnevilles are similar in many ways. They are a similar height and size, petrol tank size and shape and similar looks from the side. But the new Triumphs of course have larger capacity DOHC engines and are heavier machines, with a lot more power.
There are some similarities to the Royal Enfield Interceptor 650 twins, although they too are a heavier machine I believe and also DOHC.
The old Triumphs have pushrod engines, like the Indian Chief, most Harleys and the new BMW R18.
A pushrod engine runs with a tappy-tap and a dohc engine runs with a whirr.... the two types have a very different sound and feel.
But really, I don't think there is a modern equivalent. Modern bikes are so high tech, in comparison.
The 1959 Thunderbird 650 weighs 180kgs and takes four different types of oil; Engine oil, gearbox oil, primary chaincase oil and fork oil.
It has no idiot lights of any kind, no turn signals, no neutral or main beam indicator lights, or riding modes. It only has a dip switch and horn button, plus manual throttle lock cruise control, on the handlebars.
It does have as standard; kickstart, right foot gearchange, chronometric speedometer with trip meter, drum brakes, carburettor tickler, steering damper, ammeter, manual oil pressure indicator, a large tool box and tool kit and 3- position pre-load rear shocks.
It is a quite different world in many ways.

Here is a nice picture from 1951. This is an earlier Thunderbird 650, but with the 1950 rigid frame. That is nearly 220kph.... no shirt, no gloves...
70 years ago, back in the days when men were men....!!

View attachment 140331
Love your work, Ian...

My aunt (now off in the great speedway in the sky) was the first woman in NZ to crack the imperial ton (riding a Triumph). Somewhere I have a newspaper article about her and her roadracing post-WWII.