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YZGazza

In over my head?

8 posts in this topic

I recently got back into riding and bought my first decent bike (had an old ag bike on the farm when i was a kid) 99 YZ400F about 6 months ago and it has been great so far apart from a few minor hick-ups (countershaft seal and water pump seal) but i have done 20 odd hours without checking valves. It died on me on the trail last weekend so i got it home and pulled off the head cover to try and check the valves and found the cam chain has stretched and one of the camshafts has slipped around 4 teeth. I've read through the manual and it doesn't seem to complicated to replace the cam chain but i'm a newbie with little motor knowlege. Is there more damage that I'm not aware of? Am I up for big $$$ ?

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Since your going to pull the cams to replace the camchain, it's not much harder to pull the head and check your valves. While you have it apart, it might be a good idea to replace valve seals. Those should be SS Valves so even if you dinged a couple, they shouldn't be too much to replace compared to the titanium valves of the newer years.

The biggest thing before starting this project is to make sure you have the right tools handy. A good torque wrench, feeler gauges, and some good measuring tools will make your adventure a lot easier.

Chad

PS- of course, if you run into any hiccups, just post on here and somebody should be able to walk you through things.

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4 teeth is a lot - you could have valve/head/cylinder damage...do you still have compression and does it turn over completely?

Replacing the cam chain is no big deal but if you're going to do that, I would DEFINITELY take the head off and verify you didn't have a valve kiss the piston - even just for the extra piece of mind.

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....pull the head and check your valves....
....take the head off and verify you didn't have a valve kiss the piston....

Check the valves.:moon:

P.S. Check the tensioner, or have a dealer do it, to make sure it is functioning properly.

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Setting the cam timing is an operation that requires careful attention to detail and two specialized tools:

http://www.thumpertalk.com/forum/showthread.php?p=3150405#post3150405

What I would do to address the damage question is to first find out why the cams slipped (chain too old or cam seized in the head?), replace the chain, time the cams, and then have a leak down test done. This will likely show a little ring leakage, but you'll be able to listen down the pipe and air box for valves leaking excessively, which would indicate they were possibly bent.

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I had a look this arvo and it seems like the tensioner is at full extension and the cam chain still has a lot of slack and movement side to side. The engine still turns over completely and has good compression. Am i right in thinking that an old, tired cam chain is the culprit and the tensioner doesn't need replacing as it is still trying to work? The bike was running a little rough and hard to start before the cam chain slipped. Would this just mean the valves also need adjusting? Cheers

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Don't 'assume'....you know what that does....make absolutely sure, even if you have to remove the head, which won't be difficult, since you are in the area anyway.

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Would this just mean the valves also need adjusting? Cheers
Why don't you check the clearances when you get the cam cover off and find out?

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