Valve shim adjustment for max performance

[500rider]

How does the valve shim adjustment affect performance?   :dunno:

Is there an advantage to running the exhaust valves closer to the max clearance vs min clearance (ie more low end torque)? or vice versa?  Intake valves I would think better to have closer to min clearance (except that it may make the next adjustment sooner).

I have to check/adjust the shims this spring anyway so I thought I would see what you guys think!

Rob

[KevinC]

I suppose minimum clearances would give you the most valve opening duration, and that would be best for performance. But the difference from max to min clearances will be very tiny.

You'd get way more benifit from degreeing the cams. Of course that requires new expensive parts.

[JamesG]

yep. If you try to toe the line like that its very easy to burn a vavle.

Megacycle can modify the GS's cams to be slot-able. I have a set that have been done.

[JLKasper]

Adjusting valve clearances for "maximum performance" depends on quantifying what you consider performance.  If you want maximum horsepower at higher rpms, then you want to maintain your valve clearances as low as possible within specs (.03 mm).  Like KevinC said, the valves will open sooner and stay open longer.  But, there is no free lunch.  Having valves that stay open longer mean they spend less time closed, which is where heat from the valves is disippated to the cylinder head.  Hotter valves, even if kept within tolerances, will wear out more quickly.

In my book, there are less-risky ways to obtain what little gain you obtain from running valve clearances on the razor's edge.  My goal is to retain clearances within the standard of .03 to .05mm, and leave it at that;  but my ideal of maximum performance is to have the engine lead a long and happy life, not peak horsepower.  YMMV.

[500rider]

OK thanks guys     .. not much to be gained I guess.

Rob

[Bob Broussard]

In order to get the valve cleartences exactly where you want them would take alot of effort. You are limited by the thickness of the shims to begin with.
To get them exact, you'd need to grind the tip of the valve so the stem length
brings everything to the right spec.
This means calculating everything and disassembling the head. Then, the trickiest parts is grinding the exact amount off the stem AND keep it square.
I've managed to rig my milling machine with a grinding wheel. Using a vice to hold the valve straight up, I can come down on the tip and take off what I need without beveling the tip. When valves are lapped in the seats it affects the clearences, so I have to do this if I don't have the exact shim I need.

I would just use a micrometer to find the closest shim to get you in spec. You might get lucky and find one that's really close. Even though they are marked, they do vary a bit. Hopefully your dealer has a selection to go through.  

As far as degreeing the cams go. All you need to do is slot the bolt holes on the cam sprockets and remove the pin so the sprocket can be moved.
With the pin in, take a punch and mark the cam and sprocket in the stock position. Then remove the pin and degree the cams. If you have trouble you can always go back to the stock marks. :mrgreen:

[Blueknyt]

What would you charge to mill slots into cam sprokets bob?

[Bob Broussard]

I'll do a couple I have laying around and send them to you in exchange for the stock ones + shipping. Send me your address. bobbroussard@x.cx