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.
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.
The top end needed de-carbonising anyway.
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.
I use Norman Hyde clutch friction plates and they work well.
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.
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.
After a couple days work, the engine was removed. Being a pre-unit, the gearbox stays in the bike.
Now to strip the engine.
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.
Impact driver to snug the bung up and secured with a drop of red loctite and a single centre punch mark.
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.
The camshafts were fine, although the journals are worn slightly undersize.
The wear in the big end shells was minimal with a couple of pitting marks.
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.
Some wear on the clutch basket teeth, but a new one can wait a while. The teeth were not hooked.
While the engine was out, I replaced the gearbox sprocket as the teeth on that were hooked.
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.
The crankcases cleaned up nicely.
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.
A new pair of L F Harris +0.040" 7:1 pistons (made in Taiwan to UK specs) were to be fitted.
Also purchased a set of new conrod bolts & nuts
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.
I fitted a new set of camshaft bushes and used a home made tool to "ream" to size.
Freshly polished conrods. I also weighed the rods and pistons to match for the best balance.
The rocker box stud holes were worn, so I had the holes welded up, then re-drilled them and fitted new stainless studs.
The tappets were slightly worn but serviceable.
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.
Crankcases, crankshaft and camshafts, going back together.
Camwheels pinions back on. I also have a Morgo high flow plunger oil pump on this bike, which works a treat.
Pistons on. The trick is to warm the pistons with a hairdryer first, then the gudgeon pin slides in by hand.
Also, a halved plastic chopping board resting on the studs is better than pieces of wood resting on the gasket, when fitting the barrel.
The copper head gasket was annealed and then cleaned up with scotchbrite.
Cutting pushrod tube seals to the right thickness.
Rockers boxes on
I used annealed copper washers for the oil drain pipes and fibre washers for the rocker spindle oil feed banjo nuts
Made a thick 1.4mm gasket for the inner primary cover.
Inner cover fitted with temporary holding arrangment while the gasket sealant sets.
The alternator wire insulation has gone brittle with age.
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.
Clutch plates going back in.
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.
Happily back on the road after about 3 months. A few niggly things to sort, but basically running well.
Hopefully, I can do another 50,000 miles before the next major rebuild....
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.
The top end needed de-carbonising anyway.
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.
I use Norman Hyde clutch friction plates and they work well.
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.
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.
After a couple days work, the engine was removed. Being a pre-unit, the gearbox stays in the bike.
Now to strip the engine.
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.
Impact driver to snug the bung up and secured with a drop of red loctite and a single centre punch mark.
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.
The camshafts were fine, although the journals are worn slightly undersize.
The wear in the big end shells was minimal with a couple of pitting marks.
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.
Some wear on the clutch basket teeth, but a new one can wait a while. The teeth were not hooked.
While the engine was out, I replaced the gearbox sprocket as the teeth on that were hooked.
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.
The crankcases cleaned up nicely.
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.
A new pair of L F Harris +0.040" 7:1 pistons (made in Taiwan to UK specs) were to be fitted.
Also purchased a set of new conrod bolts & nuts
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.
I fitted a new set of camshaft bushes and used a home made tool to "ream" to size.
Freshly polished conrods. I also weighed the rods and pistons to match for the best balance.
The rocker box stud holes were worn, so I had the holes welded up, then re-drilled them and fitted new stainless studs.
The tappets were slightly worn but serviceable.
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.
Crankcases, crankshaft and camshafts, going back together.
Camwheels pinions back on. I also have a Morgo high flow plunger oil pump on this bike, which works a treat.
Pistons on. The trick is to warm the pistons with a hairdryer first, then the gudgeon pin slides in by hand.
Also, a halved plastic chopping board resting on the studs is better than pieces of wood resting on the gasket, when fitting the barrel.
The copper head gasket was annealed and then cleaned up with scotchbrite.
Cutting pushrod tube seals to the right thickness.
Rockers boxes on
I used annealed copper washers for the oil drain pipes and fibre washers for the rocker spindle oil feed banjo nuts
Made a thick 1.4mm gasket for the inner primary cover.
Inner cover fitted with temporary holding arrangment while the gasket sealant sets.
The alternator wire insulation has gone brittle with age.
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.
Clutch plates going back in.
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.
Happily back on the road after about 3 months. A few niggly things to sort, but basically running well.
Hopefully, I can do another 50,000 miles before the next major rebuild....
