Post valve clearance crank failure
Posted: Wed Jul 18, 2018 11:03 pm
Greetings fellow TRX'ers. My problem started when I decided to tackle the valve clearances on my '96 TRX. It was coming up to the service interval and I was starting to experience a reluctance to pull away cleanly from stationary when out riding. There was also some popping through the exhausts on tick-over. So....
Armed with Haynes' destruction manual I set to work and found most of the clearances where out of spec and would therefore require re-shimming. Cams out, replacement shims in and clearances where now (mostly) in spec. Unfortunately, when I tried to set the timing the inlet sprocket kept jumping back a tooth. The cam chain adjuster was fully extended so I replaced the chain with a genuine Yam one (nearly £60). At this point I realised I hadn't replaced the cam chain top guide (the one that also helps to bolt down the No 2 cam). Yes, I know...Anyway, new chain in, top guide on and all timing marks lined up and the chain wasn't jumping off the sprocket anymore but the horizontal marks on the sprockets would shift out of alignment slightly after rotating the engine as per Haynes' instruction. However, the punch marks on the cams still lined up with the raised lines on the camshaft holders and the "I" mark on the rotor was where it should be. I decided that the sprockets were shifting on their bolts under the pressure from the adjuster and the new chain. As long as the cams and crank were in alignment, surely that is what matters?
Anyway, everything back together and the bike started OK but was reluctant to idle till warmed up. Took it for a spin and it seemed OK though not noticeably better than before.I decided a longer ride could be risked and set off into North Wales. I noticed that high frequency vibes seemed worse than I remembered and the engine felt a bit rough under load. but it still ticked over evenly with no ominous noises.
However, after the bike had rested for an hour or so while it's owner drank tea and shot the shit with an old Welsh boy, and within a minute of leaving the cafe, the engine emitted a loud Brrrr! ing sound and cut out. I pulled the clutch lever in and coasted to the side of the road.
On returning home on the back of a low-loader I stripped it down expecting to find damage to the top end. Top end seemed fine, but when I tried rotating the crank to check the timing, the crank moved but the cams didn't (!). Removing the oil pump cover revealed half of the crank teeth had been stripped. I've yet to dismantle the rest of the engine so don't know what the full extent of the damage is.
If anyone has any thoughts on what may have gone wrong I'd appreciate the input, because the prospect of a major rebuild is daunting enough without the worry of the same thing happening again.
Thanks for reading, Bluto.
Armed with Haynes' destruction manual I set to work and found most of the clearances where out of spec and would therefore require re-shimming. Cams out, replacement shims in and clearances where now (mostly) in spec. Unfortunately, when I tried to set the timing the inlet sprocket kept jumping back a tooth. The cam chain adjuster was fully extended so I replaced the chain with a genuine Yam one (nearly £60). At this point I realised I hadn't replaced the cam chain top guide (the one that also helps to bolt down the No 2 cam). Yes, I know...Anyway, new chain in, top guide on and all timing marks lined up and the chain wasn't jumping off the sprocket anymore but the horizontal marks on the sprockets would shift out of alignment slightly after rotating the engine as per Haynes' instruction. However, the punch marks on the cams still lined up with the raised lines on the camshaft holders and the "I" mark on the rotor was where it should be. I decided that the sprockets were shifting on their bolts under the pressure from the adjuster and the new chain. As long as the cams and crank were in alignment, surely that is what matters?
Anyway, everything back together and the bike started OK but was reluctant to idle till warmed up. Took it for a spin and it seemed OK though not noticeably better than before.I decided a longer ride could be risked and set off into North Wales. I noticed that high frequency vibes seemed worse than I remembered and the engine felt a bit rough under load. but it still ticked over evenly with no ominous noises.
However, after the bike had rested for an hour or so while it's owner drank tea and shot the shit with an old Welsh boy, and within a minute of leaving the cafe, the engine emitted a loud Brrrr! ing sound and cut out. I pulled the clutch lever in and coasted to the side of the road.
On returning home on the back of a low-loader I stripped it down expecting to find damage to the top end. Top end seemed fine, but when I tried rotating the crank to check the timing, the crank moved but the cams didn't (!). Removing the oil pump cover revealed half of the crank teeth had been stripped. I've yet to dismantle the rest of the engine so don't know what the full extent of the damage is.
If anyone has any thoughts on what may have gone wrong I'd appreciate the input, because the prospect of a major rebuild is daunting enough without the worry of the same thing happening again.
Thanks for reading, Bluto.