SP1000 cam-chain tensioner failure

[thomas]

Hi everyone
After some 120 000 km of use, spread over 20-odd years, this spring-loaded blade-type aftermarket camchain tensioner broke.
What undoubtedly brought the bike to an abrupt stop was that the tensioner spring got jammed between the camchain and the oil-pump sprocket. Fortunately we were just idling out of town on a dirt road and the bike was only doing about 20 km/h - revs at about 1500 rpm or thereabouts?
The actual tensioner blade will have broken some time before because I found most fragments in the timing chest and two fragments in the sump and it would have taken time for them to get there.

I didn't experience the engine as being more clattery, probably because I ride with earplugs, but my GF mentioned that it seemed a bit noisier.

Collateral damage seems to be quite minimal but the LHS exhaust valve and the piston definitely did kiss (mildly) - there are witness marks on each, in the right places.

I've never heard of such a failure; do these tensioners fail at all? Are they something to be replaced every so often?

Regards
Thomas

PS I would post a photo of the remnants but I can't figure out how to do that. Using the "Insert Image" button gets me no where.

[Antietam Classic Cycle]

74,400 miles - pretty good service life IMO.

I've seen the spring break, but not the shoe itself.

[fotoguzzi]

PS I would post a photo of the remnants but I can't figure out how to do that. Using the "Insert Image" button gets me no where.

your pics must be hosted on the web somewhere else then you put the URL link in the insert image brackets.

 

[jacksonracingcomau]

Happened to me to, a long time ago, can't remember mileage on it but possibly as low as that, but in 3 years not 20
I went for alloy timing gears, would never go back, that tensioner fail is one of biggest issues in my 38 year ownership, I was travelling in NZ (from UK) and had to have bits sent from all over the world and rebuild it on verandah where I was staying, I bent at least 2 valves but think I got away with pistons, can't remember, was in 82-3 I think.
Others like em, not me, only seen half a dozen others broken but almost all high mileage ones I know now have ago gears.
If you think about it, the pressure from spring loads the chain, causing wear, when chain is totally knackered you can't hear it, something has to give.
Changing chain earlier would've stopped the break but another maintenance hassle I can live without, esp travelling.

MH

[thomas]

Thanks everyone.
I've cleaned the thin layer of carbon off the pistons and they show no sign of damage at all. I will be ordering a new timing chain and tensioner. I don't really want to go to timing gears but they do offer definite advantages.

[thomas]

Here's a question that's just occurred to me: could a worn timing chain have caused the tensioner blade to break? A chain with more slack will allow the spring to bow the tensioner blade more - could that bow have been too much for the tensioner blade?