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ethlam

how does my timing look?

4 posts in this topic

hello, i recently purchased a 2001 yz426 and it was kind of a pain to start cold. so i decided to give a auto decomp hot cam a shot. the timing of a the cams seemed like no problem at all seeing as i time over head cam cars on a weekly basis. after i was finished with the cam install i tried to start it up and i could definitely tell that the auto decomp was working but it still felt good and seems to have compression. i kicked it about 20 times and decided to take it back apart because all the videos that i have seen of the auto decomp cams, they got it started on the first or second kick. so my question is does my timing look good to you guys? because the cam marks aren't perfectly in line with the case but that is how it was with the original cam too when it was on top dead center. also i noticed that my spark plug was we when i took it out, so if it looks good to you guys i might just throw a new plug in it and see if it fires.

 

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It depends on whether that exhaust cam was made for the 426 or for a YZ450.  If it has some brand name like Hot Cams , etc. on the cam, it's OK.  If it's a YZ450 cam, it's a tooth too far retarded.  

 

The 450 cam requires that you time the intake to the factory marks, then count 14 pins forward to the 12:00 mark on the exhaust cam, ignoring the 9:00 o'clock mark (because it was made for a different head).  

 

http://www.thumpertalk.com/topic/56257-yz-450-cam-mod-please-read/page-49#entry2979654

 

http://www.thumpertalk.com/topic/56257-yz-450-cam-mod-please-read/page-53#entry4458141

 

One way to know is by what kind of cranking compression you have.  If you have the YZ450 cam timed that way, you should have almost no compression.  The AD cam is designed to hold one exhaust valve off its seat until about 25 degrees before top dead center to shorten the compression stroke.  Each tooth on the cam moves the cam 22.5 crank degrees.  So, if you have the cam retarded one tooth, the valve will close 23 degrees to late, and only 2 degrees BTDC, so, no compression.  

 

Likewise, if you are a tooth too far advanced, the compression would be abnormally hard to kick through.

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