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FasYankee

Valve Timing issue, Pic's included

5 posts in this topic

Hey all, went to do a valve check the other day, and noticed something weird....

I put the engine to TDC as per the manuals instructions, and the cams look like this:

6410x.jpg

6410049.jpg

Now keep in mind that I've done all the free mods, including the yzf cam timing mod, in which I retarded the exhaust cam by 1 tooth.

In these pictures the crank is PRECISELY lined up at the TDC mark (flywheel/case), and I checked before and after each pic.

I'm only concerned because the manual depicts the cams being in a different orientation, i.e. the lobes should be EXACTLY lined up with the head/valve cover sealing surface, and the "I" and "E" should be in the 3 and 9 o'clock position and the dots should be at the 12 o'clock...again, understanding that I've done the yzf cam timing mod the exhaust cam should be slightly (1 tooth) different than the picture in the manual.

The bike runs mint, starts 1st/2nd kick cold, with choke, 1st kick hot, every time. Has a slight rough running condition at steady throttle, noticeable "hit" in power in the midrange, the plug reads perfect.

I should also mention that this bike is a street legal motard, I am the 2nd owner, except for the throttle stop and removal of the peashooter cap from the exhaust, the bike was bone stock when I got it.

here it is now:

4302010004.jpg

Should I fiddle with the cams, or just leave it? I'm just curious if the bike could make some more power with properly timed cams.....

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You cut off the rear edge of the intake sprocket, so I can't tell if it's lined up or not, but if it is, and that was originally a WR exhaust cam, it looks as if the previous owner retimed the exhaust by retarding it one tooth so that the bike would have YZF cam timing.

Read:

http://motoman393.thumpertalk.com/tech/yztime.html

The only difference between the cam timing of the two engines was the way the exhaust cam was indexed into the sprocket. The intake cam is the same one in both the WR and the YZ, so before auto decompression came along, this was a simple hop up trick.

I should mention that you CANNOT do this with an auto decompression WR because the timing of the decompression cycle will be altered, and the bike won't start.

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I already did the yzf cam timing mod myself.....I'm more concerned with the fact that the intake cam seems retarded by one tooth in reference to the fact that the crankshaft is in exactly the TDC position, ignoring the position of the exhaust cam for now. I think what I'm going to do is re-position both cams so that they reflect the exact orientation as outlined in the factory manual, and then rotating the motor by hand, assure that there is no interference (valve/piston), if everything is good, run it, see if there's a marked difference. I understand that if it is correct, then it should be at WR spec (stock) valve timing. At that point, I'd retard the exhaust cam one tooth (for yzf cam timing), again turning the motor over by hand, checking for interference, and then run it again.

Although I haven't fiddled with cams in years, I remember when I built my blown '78 TransAm in highschool auto shop, we degreed the cams a few different ways with different results. I'd just like to be sure that I'm getting all the power this thing has to offer, in basically stock form.

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What mark are you using on the crank? Looks like you got a bit to go to TDC. It's the last mark by the way...

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