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umu24013

new timing chain problem

7 posts in this topic

I’m in the process of replacing the timing chain in my yz426.

The problem is that I cannot get the new chain on the exhaust cam gear.

I’ve spent 2 hour so far with no luck.:p

The chain tensioner is not installed!

It feels like the new chain is too tight/short

But it is identical to the old one! It is a Yamaha original chain 94591-50120

Compared to the old chain, they are of the same length and pitch, I measured before installing.

When I just removed the cams several times in the past, getting the old chain back on the cam gears was never a problem and took about 2 minutes or so.

Please advise

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I just did the cam chain on my 426 last week and had the exact same issue. It boggled the mind. I also used an OEM cam chain that was identical to the old one except for a minuscule amount of stretch.

Unfortunately, I don't have any magic words of wisdom. I eventually installed the exhaust cam first keeping the chain tight between the crank and the cam before installing the intake cam. Its important to keep all the slack on the tensioner side. Even doing this it took me a while to figure out how to get the intake cam on and I can't give you a step by step on it. Just go slow, pay attention, make sure the chain is seated fully on the teeth of one cam before starting the next, and that all the slack is to the rear of the motor. It doesn't completely make sense, but to get the intake in, I had to put it in at a bit of an angle and rotate it down the chain into it's seat (after I had the exhaust cam already in place).

Good luck!!

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Be sure you get all of that red shop towel lint out of there or it will clog up your oil screens. You should be using lint-free "paper" shop towels.

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Just located the cause of the problem. It was chain slack at the crank.

http://img15.imageshack.us/img15/7795/slack.jpg

I had that exact same problem when putting together my 426, and it ticked me off until I pulled everything apart to check it out. New procedure for me: Timing plate goes on last, after cams are installed.

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Be sure you get all of that red shop towel lint out of there or it will clog up your oil screens. You should be using lint-free "paper" shop towels.

Thank you for bringing this to my attention!

Also I'd like to clean the oil strainer and replace the oil filter after reassembly

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