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YZ250F Cam Chain Stretch
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Posted by: MWEISSEN---------------------
I'm checking rebuilding the top end on my son's 2001 YZ250F for next season. During checking valve clearances, I noticed that the cam chain stretch does not allow the sprocket indicator marks to line up exactly on the exhaust cam sprocket on the leading mark. This would be indicative of cam chain stretch.
Just how much stretch is too much???
Basically the top edge of the mark closest to the exaust side is showing on the edge of the head.
Since I've got the bike torn apart I figure I'll replace it anyway.
Posted by: woodsy---------------------
I dont mean to get your thread off course but is this common to YZF's? I recently helped a friend rebuild his 426 and couldn't help but notice the size of the cam chain - tiny (I am very familiar with Honda and they - the XR's anyway - have alot more substance to them).
Just curious.
Woodsy
Posted by: Rich Rohrich---------------------
Do you know for sure that the marks were lined up properly from the begining? They tend not to be even on new engines due to production tolerance differences.
Toss the cam chain with every second piston and you sould be OK.
Posted by: MWEISSEN---------------------
Rich, you have a good point. Removing the tensioner and pulling a slight amount of slack out of the chain between the cams puts everything in line.
I was more curious of what would be an expected tolerance - 1 degree, 5 degrees?? Yamaha's manuals are great, especially in listing specifications, but in this area there's not any leeway.
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