Shim conversion - crazy idea???

Doing some valve work on my 1100 a weird idea entered my head.

When running high lift cams in the 900s/1000s/1100s it's not uncommon to convert to shim on bottom using 650 buckets/tappets, retainers and shims.

But has anyone ever done (or heard of) the opposite, converting a 650 to shim on top using 900/1000/1100 parts?

I can't see why it wouldn't work, what do you think, crazy or...

I wouldnt see why someone couldnt, but why? to make it easier to adjust valves?

The purpose of shim under bucket valve train is to prevent the engine from spitting out a shim at high RPM. Pretty much all of your modern motorcycles use this method of valve adjustment because they all are made for high RPM. There are still a few bikes that use screw and nut adjustment and the only other bike that I'm aware of that uses shim over bucket adjustment is the older BMW K bikes but those are pretty rare these days. I've personally seen what happens when a shim lets loose and it's not pretty. While it's definitely easier to do adjustments on the shim over bucket type it's just not meant for the high rpm's that more modern engines are capable of.

dejavoodo41 wrote: The purpose of shim under bucket valve train is to prevent the engine from spitting out a shim at high RPM. Pretty much all of your modern motorcycles use this method of valve adjustment because they all are made for high RPM. There are still a few bikes that use screw and nut adjustment and the only other bike that I'm aware of that uses shim over bucket adjustment is the older BMW K bikes but those are pretty rare these days. I've personally seen what happens when a shim lets loose and it's not pretty. While it's definitely easier to do adjustments on the shim over bucket type it's just not meant for the high rpm's that more modern engines are capable of.

If you include quads, The bombardier ds650 uses the exact same sot buckets with 29mm shims. I adjusted the valves on one and used a couple of my shims from the kz stash.

The main idea was to avoid having to remove and reinstall the cams every time with the risk of stripping cam cap bolt holes or getting the cam timing wrong.

I realize the risk of spitting a shim, not something you would want to happen, but a stock 650 has 8 mm lift and shim on bottom, a stock GPz 1100 (KZ1100-B2 in this case) has 9mm lift and shim on top, both bikes redline at 9000 rpms - if shim on top works for the GPz I think it should work for the 650 too.

But like I said, just an idea...

WOW!
Now that NEVER crossed my mind.
IF it works ,,,,let us know please,,,

Yes, you can convert it to shim on top with stock cams. Shim on Bottom was total over kill for that engine.

Good points made here, but keep in mind. Bikes with shim over bucket are designed that way and even make necessary clearance to slide it out past the cam caps once it pops loose from the bucket. If you go with shim over on that engine, make sure you can pull the shim completely out without having to remove cam caps anyway. Just a thought. You can install one shim over bucket (make sure plenty of clearance(valve shim) install the cap and try removing one, but each gap between caps might be different. Do your homework first.

Shim swaps are a non issue. The drawback is swapping out retainers with the head still on the bike. Personally, I'd leave it alone unless the head was already off and someone gave me free retainers.