Cam Chain Tensioner Fail

ReidMcT

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I removed my engine for some work including checking head flatness, installing titanium valve spring retainers, and possibly splitting the cases to renew sealant on coolant channels.

My first discovery was that my cam chain tensioner had completely failed. The spring had broken and the cap that pushes on the chain guide was dislocated.

In the attached photo, you can see the excessive slack in the chain. Who knows how long it was running like this. It is a track bike, so it runs hard. I vaguely recall noticing a change in off-throttle behavior; I guess that may have been due to valve timing changes. Fortunately, the chain did not jump a tooth - valve timing is still correct. I don't expect to find any evidence of valve-piston collision when I pull the head off... fingers crossed.

I've ordered a manual tensioner. While I've read here about the stock tensioner not working well, I do not recall reading of any failures such as mine. Having now disassembled and examined the tensioner's parts, I can see that the spring is made of poor quality metal that broke from fatigue.

I think this may be something for others to consider fixing before it breaks; not everyone may be as lucky as I was not to have any damage.

Oh, and I am very glad that I bought the KTM engine removal jig (pictured). It made the removal super smooth, and it also enables me to mount the engine in a vise while I work on it. (The vise has a turntable base.)
 

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Berto585

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This is the what just happened to me. Last season my cam chain broke and caused all sorts of damage. I bought a refreshed replacement motor and ran into the same issue you are describing. I only ran 2 practices and a race and started hearing noises. Opened it up and saw the broken pieces.
 

ReidMcT

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75029055000

The service manual shows a single floor jack under this part, but I use two scissor jacks to give me more control as I carefully lower or raise the engine. This method is particularly helpful for getting the mounting holes to align perfectly when reinstalling the engine.

And, it's also a far cheaper (albeit less versatile) alternative to the KTM engine holding stand and attachments, while working on the engine.




Engine in vise small.jpg
 
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