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Triumph T120R engine rebuild from start to finish

This is the full engine rebuild I carried out on my bike, it is long over due a rebore and regrind but to get those few extra miles and another season out of it it got big end shells a set of rings and a clean sludge trap.

pt1,Roughly speaking this vid goes thus; drain oil tank, disconnect battery, remove fuel tank, foot rests, exhausts remove the crank case drain plug, carburettors, clutch cable, suppressor caps, rocker oil feed, head steady and finish off by removing the tappet covers


pt1, oil, battery, fuel tank, exhausts, rear foot rests, crankcase plug, carburettors, rocker oil-feed, head-steady, tappet cover


The last time I did the bottom end was in 1994 around 90,000 miles ago, it got all new bearings two new con rods and a new set of barrels with 10.5:1 pistons I did not re-grind the crank as by eye and feel it was acceptable to me just to renew the big end shells, I also fitted a new clutch and primary chain. Back to this rebuild, I noticed my oil warning light flashed a few times on my previous journey over the Dales, the weather had been hot and my rpm around 4-5000 most of the time but when getting down to around 2000rpm I noticed the oil light gave a few flashes this said to me it was time to have a look again at the bottom end. This video starts with a short intro of the “why's and what for's” and then onto draining the oil from the frame, disconnecting the battery and removing the fuel tank, rear foot rests and exhausts. I then take a look around the motor, looking for tell tale oil leaks around the rocker boxes, cylinder head and push rod tubes, also checking around the crankcase, primary case, timing and gear box casings. Then onto draining the oil from the crankcase and removing carburettors, clutch cable from handle bar lever suppressor caps and the rocker oil feed pipe then the head steady the video ending with the removal of the rocker box inspection caps.

pt2 Roughly speaking this vid goes thus; remove spark plugs, rocker boxes, cylinder head, drain the gear box oil remove gear box outer case, clutch cable, boyer stator and rotor ending at the timing chest.


pt2 Removal of spark plugs, rocker-boxes, cylinder head, gear-oil, gear-box outer casing, kickstart, push-rods, Boyer stator and rotor


Rocker box inspection caps off, I remove the spark plugs a quick look at the colour then kick the motor over until the exhaust rocker arms are level with each other then proceed to remove the exhaust rocker box, exposing the valves and push rods. The process is repeated for the inlet rocker box; kick the motor over until the rocker arms are level (this releases valve spring pressure) then remove the inlet rocker box, on removing pushrods it is very important to keep them in order and the correct way up as they should go back in, exactly as they came out and the right way up. Getting old stuck gaskets off can be a pain, you will notice I use a large sharp hacksaw blade sharpened like a wood chisel, using sloped side up at a shallow angle it is by far the best tool I have found over the years, care must be taken not to damage the facings whatever you use.Removing the cylinder head, bolts should be slackened in the same order as you would tighten them; this brings the head off square, removing the cylinder head studs you will notice the small washers have recessed into the head slightly. There is a Triumph Parts Bulletin # LFH 84-8 stating the 4 washers on centre studs and the 4 on the outer bolts should be changed for the larger washer # 82-2184, the larger washer increases surface area therefore improve retention. As my washers have already recessed the head a larger washer would only make contact around the edge of the recess until it sunk to the same depth, on a flat face large washer great idea. With all bolts and studs removed the head is pulled off trying to leave push rod tubes stuck on the tappet block, with the cylinder head off I take a look at the bores and pistons well worn but no marks or scratches, then I drain out the gear box oil pointing out the level plug while the oil is draining, the front foot rests and the outer gearbox casing are removed and the clutch cable disconnected. Then onto the timing chest the first thing to be removed is the ignition cover this allows access to in my case Boyer ignition, disconnect and remove stator plate and the rotor allowing removal of the timing cover.

Pt3 Roughly speaking this vid goes thus; remove timing cover, oil pump, primary chain case, clutch pressure plate, pushrod and plates, the alternator stator and rotor ending with the removal of the clutch basket and engine sprocket.


Pt3 removal of timing chest case, oil pump, clutch pressure plate, push-rod, springs, plates, center, alternator stator, rotor, engine sprocket


With all the screws removed the timing cover is pulled off to expose the timing gears and oil pump in my case a Morgo replacement, a quick look at the oil seals remove the oil pump and its round the primary side. Starting by removing the brake rod which allows the foot brake lever to drop, clearing the primary case for easy access, all screws and nuts removed the primary chain case is pulled off exposing the primary drive chain, clutch and alternator. Removing the clutch pressure plate, pushrod and a few plates allows the clutch locking tool to be fitted; this tool can be made by bolting an old friction and steel plate together, and then with the bike in gear the rear brake rod reconnected and brake applied the motor can be locked up enabling the crank shaft and camshaft nuts to be undone when these are slack the clutch nut can be slackened. With the clutch nut, pushrod and large washer removed a puller is fitted for the eventual removal of clutch hub. Three nuts are removed and the alternator stator is pulled off, slackening and slightly turning the fixing studs can ease this operation, the crank shaft nut is removed and the rotor pulled from the shaft then the clutch hub puller is used to crack the hub from the gearbox main shaft and another puller is used on the engine sprocket after removal of key and spacer, the clutch, primary chain and engine sprocket can then be removed as a unit.

pt4 Roughly speaking this vid goes thus; remove primary trap-door, final drive sprocket, drive chain, engine plates, breather, g/box outer-case, inner-case, gear cluster, selector forks, cam-plate, then explain cam timing, timing marks.


pt4 removal of breather, cover plate, gear-box sprocket, inner casing, final drive chain, brake lever, gear-box leaf-spring, selector rod, selector forks gear cluster, layshaft, mainshaft, camplate, timing marks, valve timing


With the primary drive removed access to the final drive sprocket trap door is gained undo the six screws and the trap door can be pried from the primary case allowing access to the front sprocket. As my sprocket nut here is slack I had no need to lock up the wheel, if the nut had been tight I would of applied the rear brake and undone the nut with a large box spanner after knocking the tab washer flat the final drive chain is split and removed the front sprocket can then be worked through the hole in the primary case and removed from the main shaft this allows access to the main gearbox oil seal. After removing the foot break lever the engine plate removal is next, then onto removing the engine breather and disconnecting the rev-counter drive cable all done on the primary side I move round to the timing side of the bike. Starting by removing the outer gearbox cover I explain a little about the springs and pawls located in this casing, and then remove the kickstart ratchet mechanism then go on to remove the timing side rear engine mount enabling the gearbox inner casing to be removed exposing the inner workings of the gearbox. To remove the gear cluster the selector shaft is remove first then the lay shaft and then the main shaft and lastly the camplate, we now have an empty gearbox. I then set to and explain a little about the cam timing marks on the pinions and how they are set to factory STD.

pt5 Roughly speaking this vid goes thus; removing oil lines, junction block, cam pinion, engine mounts, engine out, and ends splitting the crankcase.


pt5 removal of oil feed, return pipes, junction block, crankshaft pinion, barrels, crankcase, conrod


With the gearbox now disassembled I set too and remove the flow and return oil lines from the motor then using another puller I remove the crank shaft pinion then slacken the front and underneath engine bolts. Too make the motor as light as possible I remove the barrels, not forgetting to lock up the cam-followers (I use split petrol pipe) take care not to bang the rods on the crankcase edges after a quick check for play in the big and little ends I packed cloth around the rods then lift the motor from the frame. Then with the motor on the bench I remove all the crankcase bolts and with all bolts and studs removed a few taps and the crankcases are separated and the primary side conrod is removed.

pt6 Roughly speaking this vid goes thus; remove conrods and crankshaft, primary side main bearing and finish with the sludge trap plug.


pt6 removal of conrods, bigendends, crankshaft, main bearings, sludge-trap


With the conrod removed a quick check inside the piston reveals a loose little end bush in the conrod. Then removing the crankshaft from the timing side casing, after removing the key and the spacer the crankshaft was removed by dropping the unit on a frame, made of wood and using the weight of the crank so it removes itself (almost) with the crank out and held in the vice, I removed the other conrod the timing side bearing. With the crankshaft stripped I moved onto the floor so I could remove the sludge trap plug. Using plenty of sweat, cussing, heat and an impact driver I got the plug out, eventually! Revealing the long overdue sludge trap tube.

pt7 Roughly speaking this vid goes thus; remove sludge tube and start cleaning stuff


pt7 removal of crankshaft, bigends, sludge trap, flywheel bolt


All the bashing and banging over and the plug out its back to the bench to have a look what’s in the trap, using and old baking tray to stand the crank in (stops it rolling off the bench) a squirt of oil showed me the bigends were still getting oil although the trap was ¾ full. With the crank in the vice the sludge tube/flywheel retaining bolt is removed I then examine the wear on the big end shells, then set too and dig out the sludge from the trap. Then with a large modernised tent peg tailored as a hook, the sludge tube is withdrawn and then the rest of the sludge that remains in the trap is cleaned out and it’s back down to the floor to meticulously clean the crankshaft with petrol.

pt8 Roughly speaking this vid goes thus; a good look at my con-rods then fit and part ream, the little-end bush


pt8 inspection of conrods, little end bushes


This being a budget rebuild on account of me being skint new everything is out of the question, having replaced the con-rods in the 90’s I had a spare to replace the damaged one, also my friend Jed had given me a set of STD big end shells and a set of little end bushes, so doing the rods cost nothing but time to do. So in this vid, I first remove the pistons from the con-rods using a homemade gudgeon pin puller and a bit of heat then remove the little end bushes using a similar puller, the eye in one of the rods was so badly worn it no longer gripped the bush, this con-rod I would replace using one of the old rods I had. Then it’s onto cleaning them up, to remove the carbon I use a little rust eater “phosphoric acid” which works quite well then pre reamed the bushes by hand and eye to fit the gudgeon pins before I installed them into the rods. For this purpose I used a variety of grades of wet n dry carborundum papers and cloths, oh! and a split pin and a lot of twiddling!

pt9 Roughly speaking this vid goes thus; I fit the other small-end bush into con-rod with more reaming then drill the oil hole


pt9 inspecting and reaming little end bush


First using a bit of heat and a vice to press the little end bushes into the rods and cleaning up slightly the crankshaft journals using 1000grit wet n dry. Now with the bushes fitted into the rods the gudgeon pins no longer fit the bushes which entailed more reaming until I had a satisfactory result then I drilled the oil holes through the bushes.

pt10 Roughly speaking this vid goes thus; finish con rods and fit the sludge trap then go on in fair detail about the gear-box


pt10 inspect and replace sludge tube, flywheel bolt, gear cluster, gearbox camplate, selector fork, mainshaft,layshaft


Roughly speaking this vid goes thus; finish con rods and fit the sludge trap then go on in fair detail about the gear box. Preparation, look at gearbox. Drilling the second oil hole and slightly enlarging the oil hole in the con-rod the rods are now ready to go on the crank. Then its replace the sludge tube making sure the hole in the tube is lined up with the hole in the flywheel a drop of loctite on the bolt and its job done. As the motor was on the bench I thought I would go through the process of fitting the four speed, leaf spring type gear cluster into the box and going through the process once or twice to try and dispel some gearbox nightmares!

pt11 Roughly speaking this vid goes thus; remove old gaskets and give casings a good clean then fit sludge plug and take a look at the primary chain tensioner


pt11 replacing crankcase, sludge tube, plug, primaru chain oiler


Starting this one with scraping off the inner gearbox gasket, then with a little heat remove the main shaft gearbox seal a quick check of the camshaft bushes reveals to me they are ok so I decided to leave them alone. As a bit of an experiment to remove the carbon from the inside of crankcases I used a drop of phosphoric acid and it worked a treat. A little salt due to the ingress of water was found on the mating surfaces of the crankcase this was carefully scraped off using my scraper then I cleaned out the three drain holes that go through to the primary side, if a belt drive is fitted it is these three holes that are blocked off also a seal is added to the crank shaft in the primary side. A little more scraping to remove the trapdoor gasket then I point out some damage around the crank shaft bearing housing this damage has been caused by a PO who has not had a puller for the crank shaft drive sprocket the damage is superficial so I tend not to worry about it. Although I had bought a new sludge trap plug the old one had a much deeper screwdriver slot in it so I decided to reuse the old one, as the banging with an impact driver to remove it had deformed it slightly I needed to dress it up using a thread file then I refit it using a drop of loctite after it was fully home I secured it with a couple of pop marks. On removing the primary chain tensioner I noticed the rod was worn and a potential breakage point so changed it for a better one. Also in the primary side there is a small oil feed pipe that directs oil to the engine sprocket this had also worn through and required changing I also changed the gasket on the main breather stub. With the crank cases all clean it’s ready for going together.

pt12 Roughly speaking this vid goes thus; fitting the primary side main bearing, big-end shells and fit con rods to crankshaft and crankshaft into primary side crankcase and end fitting the gearbox main shaft


pt12 replacing bigend shells, conrods main bearings, crankshaft, crankcase, primary side, mainshaft oil seal


First I refit the crank shaft bearing to the primary side end utilising a couple of sprockets as drifting implements as the bearing is going on a shaft the forces need to be on the inner part of the bearing so not to strain the bearing and then onto fitting the con-rods to the crank. After a rub off with an oily rag I fit the new big end shells to the rods it was when I was tightening the big end bolts I noticed there was a length difference between the two sides obviously because the rods I am using are not a matched pair, so I am making do with what I have and will invest in a new set of rods at a later date probably when I re-bore and re-grind the motor at the end of the season. Fitting the crank shaft into the timing side first requires a little heating of the crankcases around the bearing housing and the crank shaft was dropped home and left to cool, again heating the case “bubbly spit is hot enough” I fitted the new final drive oil seal a few taps and it was fully home. Lastly I cleaned up the crank case facings with a drop of mentholated spirits ready to drop the other crank case half on.

pt13 Roughly speaking this vid goes thus; assemble crankcases and gear box cluster


pt13 assemble crankcase, gearbox, mainshaft, layshaft, thrust washers, gear selectors, camplate, selector rod


Removing all grease from the other crank case half I smeared a little silicon instant gasket around the surface after a few strategic squirts of oil the crankcases are assembled and bolts and studs replaced, with the motor back on the bench I tightened all the crank case bolts. I’m sure by now you have noticed I do not use a torque wrench I do things by feel, If you are not confident enough to do that all the figures and torque specs are in the manual for your particular model and should be used. Onto the gearbox, as the selector forks differ slightly I show a simple way to check you have them the correct way round when assembling the box. Firstly a look at the gears and components for wear then I show the order the gears go onto the shafts, all looks well so I fit the cluster into the gear box housing, starting by fitting the selector camplate and the lay shaft thrust washer then the high gear goes into its bearing then the main shaft c/w its gears and onto the lay shaft with its gears, engaging the selector forks into the cam plate the selector rod is fitted and the low gear, gear to the lay shaft.

pt14 Roughly speaking this vid goes thus; assemble crankcases and gear box cluster index gearbox

pt14 assemble gearbox, indexing, bottomend frame, engine mounts, outer casing, cotter pin, kick-start lever


Starting by scraping off the gasket from the inner gear box cover and the using a drop of loctite to stick on the thrust washer then a preliminary indexing and fitting of the inner casing then a quick run through the gears to make sure I have them all. With the bottom end ready to go in the frame I set too to clean off the frame again Using petrol and a stiff brush when that is done I fit the bottom end into the frame using a screwdriver and bottom engine bolt to hold the motor steady I loosely fit the two rear engine plates then back to the main engine bolts to fit the spacers when all the bolts are in they are then tightened. As I am changing the kick start and gear lever oil seals its back to the bench to remove the kick start cotter pin enabling that seal and the kick start spring to be changed.

pt15 Roughly speaking this vid goes thus; remove kick start and gear change quadrants and change seals and kick start spring reassemble outer case

pt15 assemble gearbox outer case, gear shaft, quadrant, kickstarter return spring, gearchange plunger, plate oilseal, oring


Removing the gear change mechanism from inside the gearbox outer case enables the gearlever shaft/quadrant to be withdrawn and the o-ring seal can be changed. Dressing up and cleaning all components, the guide plate and gear change quadrant plungers. I also changed the seals in the outer case, then replace the quadrant return and plunger springs and reassemble the gear change quadrant. Having changed the kickstart shaft o-ring in the outer case. With the kickstart shaft dressed it and the return spring fitted can be replaced back in the case fit the kickstart lever and fit the cotter pin, job done. Then it’s on to scraping off the old gasket and cleaning the surfaces of the barrels.

pt16 Roughly speaking this vid goes thus; dress the cam followers, fit new piston rings and pistons to conrods


pt16 dressing and replacing cam followers, piston rings, circlips, gudgeon pin, barrels


After cleaning the old gasket from the base of the barrels I point out the wear on my cam followers. You may notice I have ground the corners off the base of my followers this supposedly allows more oil to the cam, I then dress up the followers with an oil stone, care should be taken and the followers should be replaced in the same holes they came out of, this rule applies to most things including the pushrods, pistons and rings. My bores are well worn and the ring gap measures at 28thou, twice the normal amount! after dressing the pistons a little I replace them onto the con-rods, a little heat in the pistons makes pushing in the gudgeon pins a lot easier. With the pistons on the rods I use my board to steady the rods in the crankcase then set too replacing the rings, all in the same grooves they come out of and the same way up I then fit a new base gasket.

pt17 Roughly speaking this vid goes thus; fit barrels, change seal in cover plate, fit final drive sprocket, tensioner blade, clutch and engine sprocket


pt17 replace piston rings, barrels, cover plate, oil seal, final drive, engine sprocket, primary chain tensioner blade, clutch drum, cush drive, clutch plates


Setting the rings so the gaps are at third intervals around the piston, the followers are held in place using split petrol pipe I replace the barrels and tighten them down. I then change the seal in the primary side cover plate and clean off the old gasket. Replacing the gearbox sprocket I smear a little silicon inside on the splines, put it on the shaft and loop the final drive chain over the sprocket and refit the split link, this way I can use the rear brake to hold still the sprocket while tightening the nut as well as the tab washer I use a little loctite on the threads when the nut is tight the tab washer is bent over to secure the nut. A little grease is used on the seal part of the shaft and the covered plate is put on. A spacer and a couple of shims are then put on the crankshaft end and the primary chain tensioner replaced loosely then the key is fitted into the gearbox main shaft this key should be parallel with the taper of the shaft. Having assembled the clutch hub, thrust washer, rollers, basket and Cush drive at the bench I fit them to the motor as a unit. To tighten the clutch centre nut the bike is put into gear and again the rear brake can be used to lock up the shaft, fitting the clutch locking plate enables the tightening of the crankshaft nut.

pt18 Roughly speaking this vid goes thus; fit alternator rotor and stator set valve timing, fit oil pump change, timing side crank shaft oil seal


pt18 replacing engine sprocket, alternator rotor, primary chain, alternator stator, timing marks, timing pinions, oil pump, crankshaft oilseal


After tapping back the engine sprocket a distance piece and the key is placed onto the crankshaft and the alternator rotor is fitted and all is tightened using the rear brake to lock up the shafts. With the clutch centre and the alternator nuts tightened the primary chain is adjusted and the plug fitted. After a little adjustment the primary chain oiler is fitted then the alternator stator is fitted assuring there is an air gap between the rotor and the stator of around 8thou, turning the fixing studs slightly can ease the fitting of the stator. Moving to the timing side I set the valve timing explaining how the camshaft pinions are fitted to the cams to achieve the standard timing setting. I then fit the key to the crankshaft followed by the pinion and the nut then the intermediate pinion is fitted and the valve timing is set. With the timing set the oil pump is fitted using the special coned shaped nuts and washers I then change the crankshaft oil seal inside the timing cover.

pt19 Roughly speaking this vid goes thus; fit oil junction box oil lines, re-index gearbox fit outer-casing and timing chest, fit boyer stator and rotor set static ignition timing


pt19 replacing oil lines, oil junction block, gearbox inner/outer case, indexing, kickstart ratchet, boyer stator, ignition timing


Now for the fiddly bit, indexing the gearbox as mine is the four speed fitted with the leaf spring and not the indent plunger, as I push on the inner casing the spring turns the camplate making the job a pain, after a few goes I get all four gears selecting nicely but firstly I fit the oil pipes to the motor, as they interfered with the inner case I had to adjust their position, then onto fitting the inner case and the indexing. After indexing was accomplished all fixings and the kickstart ratchet are replaced and tightened then the outer case is put on followed by the engine plate. Now with the gearbox finished I turn my attention to fitting the timing cover priming the crankshaft with oil as I go, care must be taken when fitting the timing cover as the camshaft oil seal can be turned inside out by the camshaft end, a special tool is available for this job but I use a piece of cellophane inside the seal that will go over the camshaft end and prevent damage to the seal all the fixing are replaced and tightened up. After setting the crankshaft to 38deg BTDC on the compression stroke of #1 cylinder (right-hand side sat on bike) using the timing plug at the rear of barrels, or you can use the mark on the alternator rotor the Boyer pickup and rotor are loosely fitted timed up and tightened.

pt20 Roughly speaking this vid goes thus; fit clutch pushrod and plates the set the wobble, the fit pushrod tubes, pushrods and cylinder head and rocker boxes


pt20 assemble clutch plates, cluthc pushrod, pushrod tubes, squishgap orings, cylinder head, rockerbox tappets


This one starts, showing the motor at TDC by the timing marks on the rotor then on to fitting the clutch plates. As I had the 4spring pri-unit clutch fitted, I explain a little of how I had to adjust the clutch pushrod, I have since fitted a new 3 spring clutch with pressure plate adjuster. I then go onto to fitting the clutch plates and pressure plate. Then adjusting the pressure plate to reduce the “wobble” this saves “clutch drag” then onto fitting the cylinder head and try to show what the squish gap is and how to adjust the pushrod cushions, as my head has been skimmed in the past I cannot use the cushions that are in the gasket set so I use two more orings. I then go on to the rocker boxes and after going over them fit them to the head.

pt21 Roughly speaking this vid goes thus; fit exhaust rocker box, top hat oil filter prime crankcase fill gear box, set tappets fit covers fit carbs exhausts and fuel tank and try to fire it up


pt21 checking filling ans setting rocker box, tappets, engine/gear oil


Starting with the fitting of the exhaust the rocker box and a rough setting of the tappets I move on to the oil side, first fitting the top hat filter inside the frame and cover with the sump plate I then put a couple of pints of engine oil into the tank and prime the motor around the rockers and crankcase. The go on to filling up the gearbox with oil using the level plug. Next on the list to be fitted are the side panels and carburettors and rocker caps after setting tappets properly then kicking the motor over until oil appeared from the rocker feed pipe. After connecting the ignition and check for spark I set too to fit the petrol tank showing the rubber support I use underneath the tank. It was so close to going! I shoved the pipes on give it a tickle and a few kicks nowt! Arghh! after a bit of head scratching and a load more unsuccessful kicks I decided to swap the wires on the boyer stator.

pt22 conclusion strobe timing and start up


pt22 conclusion strobe timing and start up


The last video of the series this one and I hope you enjoyed them. Having had the bike started and run up with static timing I now strobe the timing trying to use two cameras to show what I’m doing, strobing revealed the timing was retarded and required me to reset the rotor position. After the timing is set, I check the primary chain and fit the primary chain case and top up with oil. The next day after I had fitted the pipes and stuff I run the engine till hot (with aid of fan for cooling) and set my severely worn carburettors as best I could. I have since fitted new carbs and there are superb.

copy right to be put here when I find it again