2001 426 cam chain replacement problem

I am in the process of rebuilding my friends 2001 WR426 and have run into a problem. It almost seems like the cam chain is too short to fit over both of the cams. The crank cases were replaced, crank, cylinder, piston, rings, cam chain, and all the bearings. The chain is riding on the geared section of the crank and everything is put together as the book says to do it. The part number on the cam chain bag was double checked and is the correct one. I have both cams out of the head, angled forward to ease getting the chain on, but no luck. One cam will seat back into the head, but the other one is too tight to fit into its slot. I rebuilt my 450 and never had this problem. All the parts were bought through Thumpertalk oem parts, is there any chance Yamaha put the wrong part into the wrong wrapper???? longshot.

Double check that you don't have a looped link "dangling" under the crank. Then position the exhaust cam in the correct timing location. Sit the intake up over the center of the head and guesstimate the relative position the chain should be in over the sprocket (here is where counting pins between the 12:00 marks can actually be useful). Then roll the intake cam down into its saddle. Check the alignment of your timing marks and adjust as necessary.

Double check that you don't have a looped link "dangling" under the crank. Then position the exhaust cam in the correct timing location. Sit the intake up over the center of the head and guesstimate the relative position the chain should be in over the sprocket (here is where counting pins between the 12:00 marks can actually be useful). Then roll the intake cam down into its saddle. Check the alignment of your timing marks and adjust as necessary.

Bingo...this is how we did it after trying a hundred other ways:bonk:

You don't have the tensioner in place already, do you?

I know, stupid question but worth asking :lol:

I also had to get creative when I replaced mine. It was very tight getting it over the gear for the intake.

I am in the process of rebuilding my friends 2001 WR426 and have run into a problem. It almost seems like the cam chain is too short to fit over both of the cams. The crank cases were replaced, crank, cylinder, piston, rings, cam chain, and all the bearings. The chain is riding on the geared section of the crank and everything is put together as the book says to do it. The part number on the cam chain bag was double checked and is the correct one. I have both cams out of the head, angled forward to ease getting the chain on, but no luck. One cam will seat back into the head, but the other one is too tight to fit into its slot. I rebuilt my 450 and never had this problem. All the parts were bought through Thumpertalk oem parts, is there any chance Yamaha put the wrong part into the wrong wrapper???? longshot.

Sounds like somebody grenaded a motor.:lol:

Mine was tough to get on but not that tough (by the sounds of it).

I did both cams at the same time - angle down and inward, then seat them together. And ditto to the looped link and tensioner mentioned.

Also check your front guide is in the keyway - it can force an unnecessary bend in the chain shortening it by about half a link.

Ended up that the cam chain had a couple of links dangling under the crank, once I fixed this it all went together nicely. Thanks for the replies.

Cheers

Chris.

Ended up that the cam chain had a couple of links dangling under the crank, once I fixed this it all went together nicely.
Yeah, you gotta watch that. That is usually the result of turning the crank without tension on the chain. The guides are set up so that the chain can't freely loop down of the crank like that, but if you fool with it enough, it can. That's one reason I like setting the cam timing with the flywheel and stator off.

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