anyone heard of a cam chain slipping by one tooth?

seeva · Post by **seeva** » Thu Mar 31, 2005 5:29 pm

its a long story but my r1100s had a dodgy rebuild after a minor hit and run on my right side valve cover and im in discussions with my insurer. my engine was repaired but 1000 miles later the valves failed causing extensive damage.When my engineer took it apart he found it had been assembled with the cam chain one tooth out leading to the piston kissing the valves .he,s never heard of these chains slipping but my insurer has been advised that this is known to happen on r1100s if thrashed. has anyone else ever heard of this happening before?

gus · Post by **gus** » Thu Mar 31, 2005 5:38 pm

Hi
Maybe if the camchain tensior failed,then yes it could happen.Cant see it really happening if you just tharshed it though.Unless of course something broke.The rev limiter cuts in to stop nasty things happening to the valve train,unless you have a chip which removes this or shifts it to a higher limit than standard(8200 rpm i believe).Maybe when it was damaged something in the valve train was damaged but not repaired.Or maybe the thing was incorrectly rebuilt,ie timed wrong etc etc.
gus

oyster · Post by **oyster** » Thu Mar 31, 2005 5:46 pm

I would guarantee incorrect rebuild. Jumping cam chains? Never. More chance of the rear chain slipping.

bigblackfalco · Post by **bigblackfalco** » Thu Mar 31, 2005 8:09 pm

It is pretty easy for the cam chain to slide over the bottom cog on the camshaft if the tension is not maintained on the cam chain correctly when the head is stripped down.
I have covered in excess of 300K miles on the 8v boxer engine and I have never encompassed any slippage during riding....no matter how hard....my Kiwi mate Lloyd rode from Heathrow to Portsmouth on the limiter on an 850.....bike just took it no probs!
Bailey.

Jason M · Post by **Jason M** » Thu Mar 31, 2005 9:16 pm

I'm with Gus - if the cam chain tensioner went tits up then it could happen. Must have initially been assembled correctly else they always would have hit - I think there is only 3 degrees rotation with the valves shut so I guess I tooth jump would be all it takes. When you see how much slack there is in the chain with the tensioner out you could see it could jump pretty easily. Give Daren at Motorworks a call - I seem to remember him saying somthing about failing tensioners a long time ago, maybe something to do with an oil seal or summit (don't see how the tensioner could fail though unless the spring gives up - just like the one did on my throttle body a few weeks ago)

Good luck anyway

Jason

julian · Post by **julian** » Fri Apr 01, 2005 12:04 pm

I've just reassembeled my RHS jug after having the head off and would say it would be very easy to reassemble the chain and sprocket incorrectly if they were not previously marked for correct alignment.

The chain tensioner is unlikely to be the culprit - unless the motor was run without it being fitted, or missing the piston.

Are you the Boxercup in Chiswick that doesn't move often? I'm just over the state line in Acton W3.

Cheers

Julian

Jason M · Post by **Jason M** » Sat Apr 02, 2005 7:49 am

julian wrote:I've just reassembeled my RHS jug after having the head off and would say it would be very easy to reassemble the chain and sprocket incorrectly if they were not previously marked for correct alignment.

The chain tensioner is unlikely to be the culprit - unless the motor was run without it being fitted, or missing the piston.

Are you the Boxercup in Chiswick that doesn't move often? I'm just over the state line in Acton W3.

Cheers

Julian

Julian matey - hows the bike going? I just can't see how the valves wouldn't hit straight away if it wasn't assembled correctly? The bike did 1000 miles before they touched

oyster · Post by **oyster** » Sat Apr 02, 2005 8:33 am

If the engine was rebuilt with the timing chain out by one tooth, it would still run. Even most single camshaft multicylinder engines will endure it, but they couldnt then pull the skin of a rice pudding. If the tensioner was at fault at that point it would have sounded worse than a Talbot, you would have been worried. The mistimed side would give poor performance, but would have been disguised by the other side running normally. The generally poor performance may not have been apparent. Not until the bike gets to the redline zone.... then another factor creeps in, there is probably an engineering term for it, something like lag I guess. This is the time taken for the valves to close after they have reached full open. In real terms, the valves hang for a moment after receiving the full thrust of the cam. They depend on the valve spring to shut them. At warp speed, this hang - lag is critical, it's where the valves could meet, and do. Favourite problem with racing/drag engines. It's why the desmodromic valve set up is favoured by Ducati. These valves are mechanically opened and closed, almost zero lag.
Put the timing chain back TWO or more teeth out it would probably jam the piston on the initial start attempt.

Jason M · Post by **Jason M** » Sat Apr 02, 2005 11:40 am

I put the cam belt on my Golf back on 1 tooth out once and it ran like a PIG! You wouldn't think it was running right certainly. Still - it's a bugger either way!

BTW - I've got a couple of spare pistons and a left hand head if you need one

Jason

julian · Post by **julian** » Sat Apr 02, 2005 6:26 pm

Julian matey - hows the bike going? I just can't see how the valves wouldn't hit straight away if it wasn't assembled correctly? The bike did 1000 miles before they touched

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All running now. Just need to give it a final wash and fit fairings, belly pan, Ohlins, Induct, black screen, find number plate holder ............

Courtesey of Boxerdog's tool resources I helicoiled the exhuast spigots so I could insert a bolt and penny washer to stop rthe cans falling off and aid their installation.

JK