Strange engine fault due to timing chain tensioner defect

sam2019

sam2019

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I saw a Hunter with open engine, the piston had been destroyed - but only on the top. the liner was flawless. also one of the valves was damaged and the valve guides too. How did this happen? The timing chain tensioner had "locked up". normally it moves in and out but this one was stuck in the maximum extension position.
apparently the chain jumped a few teeth and consecutively the valve ran against the piston
really a freak defect. never seen anything like it before.
 
Common when a timing Belt slips.
 
If the Tensioner was in the full out position it would indicate excessive cam chain stretch, the tensioner can only take up tension:).
As cam timing is related to the chain the valve could have been hitting the piston.
It was probably quite noisy at some stage for some time before the big bang.
 
Dool said:
It was probably quite noisy at some stage for some time before the big bang.
Click to expand...
it was as was reported to me later but of course Indians, they only stop when the engine explodes
:cool:
 
Happens at all the times with any bike from any manufacturer when the tensioners fail.
Actually, I've read of several Himalayan 411 BS6 sold in Italy suffering catastrophic engine failure due to the tensioners. It seems at some point RE updated the design of the Himalayan tensioner (worldwide) without updating the spare part number which remained 574128/E.

A tensioner might have multiple failures: remains locked in place and fails to add tension OR runs out of its maximum lenght (cam chain should rattle like hell as it wears down and gains slack); retaining mechanism fails or gets too wore down so the tensioner can then retract (this is way more treacherous because the tension and so the cam chain is then ensured in place just by the residual force of the tensioner main spring).

... if it ever happens to me (and I hope not) it will be time for an upgrade to a big bore kit (and a manual tensioner if available aftermarket at that time).
 
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