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Valve shim adjustment measurements

  • Thread starter Thread starter mbopp
  • Start date Start date
M

mbopp

Guest
Howdy, I'm adjusting / changing the shims on my bike and am noticing something that I didn't notice before. When checking the gap to make it between .03 and .08 I am getting an inconsistent read. It seems that on all sides of the cam except the lobe side should measure the same. But I'm noticing that based on position the gap is slightly different.

To explain further.. as an example I turned the engine so that the first exhaust lobe is pointing straight forward. And then checked the 1st and 2nd exhaust valves. The #2 exhaust valve seemed a little tight, I changed the shim to a size smaller. But later I noticed that if the #2 cam lobe is turned to a different position, but still not pressing the tappet. I get a larger gap, indicating that I may have not needed to change that shim.

So... I guess the question is. should the largest gap be used in all situations if there is some deviation based on the position of the engine/cams? The largest gap should be what I am measuring and recording? That is the assumption I'm going on at the moment.

Thanks in advance for your thoughts...

Mike
 
No, do not use the largest gap.

Do not use the smallest gap.

Do not use the measurement when the lobe is pointing directly away from the valve.

Do not collect $200.

The measurements are to be taken as shown in the manuals. The exhaust lobes should have the outer lobe (#1 or #4) pointing forward and the inner lobe (#2 or #3) pointing up. The intake lobes should be arranged so the outer lobes are pointing back, while the inner lobes point up.

The reason for this is that in those positions, there is no load on that half of the cam. For example, if the exhaust lobe for #2 is rotated so it is forward (like you just did for #1), the lobe for #1 will be pushing on the valve, and possibly deflecting ever so slightly. In the designated positions, neither valve on that side of the cam has a load on it.

By the way, since you are in the process, send me an e-mail with a request, I will send you a copy of my Excel spreadsheet that will help you figure out your shim needs and will also keep track of them for next time.

.
 
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