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finglan

YZ Timing and Valve Check

11 posts in this topic

I am going to change to YZ timing. My question is does this change in any way the procedure for checking the valves. Such as the measurement or TDC.

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TDC is checked by looking at the mark on the crank/flywheel. You can be on the mark with the cam, but you'll be at BDC.

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I just went through and did this, before you start call baja designs. they sell a kit with instructions and YZ needle jet, pilot and main jet for WR to YZ timing.

While you are at it you should check your valve clearance. Just be very very careful when you remove the cam - there is a half moon circlip that can fall into the engine.

Also this site has great instructions/pictures for doing this: http://www.400thumpers.oz-au.com/wr400/yztiming.htm

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I just did check my valves and they were all at the bottom end of spec. I ran out of time to YZ it as I did the BK mod at the same time and still have the cover off of the cams.

I realize that TDC still needs to be checked by the flywheel. Changing to YZ timing would rotate the exhaust cam lobes. Would this change the measurement to check the valves on the exhaust side. Or is the rotation so slight and the fact that the measurement is taken under the round portion of the lobe the specs remain the same?

Rocky Thanks,

I will give B.D. a call.

I have not made any jetting changes since the BK mod as I was running pretty rich before it. The bike is in the basement for the winter. I was able to start it up though. It started much eaiser but when I wacked the throttle the bike would die. It may be that it wasn't warmed up enough. The house was starting to fill up from the exhaust. If I get all my projects done on it. If my son's football team ever looses ending his season and giving me some time w/good weather. I will take it out for some real tests.

[ November 01, 2001: Message edited by: finglan ]

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be very careful when reinstalling the camshaft, and follow the manual exactly when tightening the camshaft caps. Do not overtighten, even by a little bit.

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I stayed up till 1 am and did the YZ timing. After taking the camshaft cap off I see that the YZ timing will not effect the specs. on the valve clearences.

I had a heck of a time getting the chain off of the cam to rotate it ( one tooth clock wise w/12 pins between the punch marks )

Even w/the chain tensioner off there was not allot of slack in the chain.

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Careful! Sometimes the chain gets caught up under the spur gear on the crank, only by a link. This gives the impression of a shorter chain. ( Happens only when you play with the chain while the tensioner is removed )

Take care, please work patiently.

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Doc,

Just curious, what will happen if you overtighten the cam bolts??

Mu toruqe wrench does not go below 10ft/lb and the spec calles for 7.2.

I have a tendancy to overtighten things to point shearing the bolts.

thanks

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there are a few documented cases of the cam caps seizing on the cams, or visa versa...

If your T-wrench only goes down to ten ft lbs it is time to get an inch pounder...

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Assembly lube on mating surfaces of cams and caps is also a good idea. My personal preference is Isky Rev-Lube for it's high moly content.JMO

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