WR426 Timing chain

So I finally convinced a buddy of mine to go blue and he picked up a clean 02 WR426. He rode it 4 times no problems, and last month we were out and it lost all compression, it kicks full stroke without the decomp lever in with very little resistance. I figured a bent valve, so I took it apart and found the camshaft timing to be out about 5 teeth. The bike had been YZ timed by the previous owner. I reset the cam timing to WR spec and checked the clearances, all appeared ok. I removed and inspected the tensioner, looked fine. The only thing I did notice was the timing chain had several very stiff links and very loose between the cam sprockets. I put it back together and it ran, but only for a few minutes and then quit. I took it back apart and found the cam timing out again.

I am assuming the timing keeps jumping due to the stiff links in the timing chain and the looseness of it (stretched that much??). Has anyone else experienced anything like this? Do you have to remove head/cylinder to replace the chain or can you sneak it through? I don't think any valves are bent because you can reset the timing and it runs. If they were bent, I should still have no compression.

I have a 02 YZ426 and love it, has given me no problems at all and I ride it fairly aggresively. I do a lot of solo rides and it's got me a bit concerned... :)

Perhaps the cam caps were torqued to tight at one time and the cam gear spun on the shaft. It's something you may want to check out. If you setup the bike like you're adjusting the valves (engine at TDC, cam marks aligned to cover, etc), then take a good look at where the lobes are pointing and compare their position to another bike or picture. There's some good pics somewhere here on TT of where the cam lobes must be pointing when the engine is at TDC with the cam alignment marks properly setup and this should give you a better idea as to whether or not your cam gear spun or not.

the chain is worn out, but if it's that bad, it sounds like its time for some new cams also. you need to remove the flywheel to get the cam chain off, but you can leave the head and cylinder on. it doesnt sound like the bike was well maintained, so you might want to check out the valve clearances and the condision of the piston. Maybe it was run w/o oil? Just replace the cam chain and check the valves to be sure. watch out for the valve lifters though, mine fell out and got lost, and it took me a long time to figure out which one I needed to get. good luck!

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