how to figure out which under bucket shims to use

hey all i have been trying every combination of underbucket shims in my kz 1000 1197 motor. I has 460 cams and 650 style shims. Im having a heck of a time getting the valvle clearance right. Is there a way to messure so i know which shim to use, or do i just keep doing the trial and error method with feeler guage between the cam lobe and bucket?

I have an excel spread sheet that I got from the file base here or from KZ twins forum that you can plug in your data so you can get correct shim size.

You can certainly measure the shims to determine which one is currently installed and then exchange it for one that will bring the clearance into spec.

As an example;

If you are shooting for .10mm and the current measurement is .05 and the shim currently installed is 2.50. You need to decrease the size of the shim to obtain the desired measurement of .10, so you would need a 2.45 shim to increase the clearance.

Or, using the same .10 desired clearance, but current measurement is .15 and the shim currently installed is a 2.50 you would need a larger shim to obtain the desired measurement. In this example you would need a 2.55 shim.

j236racing wrote: hey all i have been trying every combination of underbucket shims in my kz 1000 1197 motor. I has 460 cams and 650 style shims. Im having a heck of a time getting the valvle clearance right. Is there a way to messure so i know which shim to use, or do i just keep doing the trial and error method with feeler guage between the cam lobe and bucket?

(a)What problem exactly are you having? Too tight or too loose?
(b)Were big valves installed in the head?

# Those cams should have smaller than stock base circles. 1.060" perhaps, or less. Stock is 1.110".

# Do you have have thicker than stock buckets. Stock are [.099"-.100"], After market performance buckets range from .107" to .116" range.

You loose lash with thicker buckets and gain lash with smaller base circle cams. It's a combined affect that must be factored into the valve job. With 1.060 / .107, the individual affects are

Bucket +.007
Cam B/C -.025
Net Affect = -.018" [or roughly 9 shim sizes]


A a valve job setup has to take those two elements into consideration when the valve installed height is setup. If it isn't, you can end up with little lash or too much lash.

eg. Mid shim range installed height is 1.475". Now lets say you have 1.060" base circle cams with .107" thick buckets. The new installed height for mid shim range is 1.493". That's a difference of roughly 9 shim sizes. Here's how that can affect you.

So, if you did have the 1.060 / .107 parts combo, and if the valves were setup at 1.475 installed height, you would need shims in the top of the range [thick]. That's actually not a bad thing except they're not real common is guys shim collections but can be ordered.

Usually though, what happens is the opposite, you're fighting to get lash because the valves are sunk and may not have had the stems tipped. THERE'S a CATCH with tipping valves when using a shim under retainer. You can get the shim sitting so far down in the retainer cup that the bucket doesn't ride on the shim but the retainer itself. That's NOT GOOD.


With a racing engine, running very thin shims isn't preferable. Sometimes they'll fracture into little pieces. They generally don't go anywhere but sometimes you find a shim has turned into a jig saw puzzle when you go to remove it.

I use spread sheets all the time. Here's the one for valve job setup I use.

j236racing wrote: hey all i have been trying every combination of underbucket shims in my kz 1000 1197 motor. I has 460 cams and 650 style shims. Im having a heck of a time getting the valvle clearance right. Is there a way to messure so i know which shim to use, or do i just keep doing the trial and error method with feeler guage between the cam lobe and bucket?

First, with cam cover removed, and the top end otherwise fully assembled, use a thickness (feeler) gauge to determine the clearance (lash) between the cam base and the bucket when the cam is pointed directly away from the bucket.
Measure each valve's clearance, as each valve may require a different size shim.
For each valve, this measurement (clearance aka lash aka gap) will be either within factory specs, or too much (needing a thicker shim to reduce the clearance), or too tight (needing a thinner shim to increase the clearance).

At this stage, only the difference in shim thickness required for each separate valve, will be known.
Won't know the actual new shim size required until removing and determining size of the existing shim.

Not unusual for each valve to require a different size shim.
It's a mistake to think all of the shims must be the same size.

The shim's size (thickness) should appear stamped on the shim itself.
If the size stamp is illegible, may use a micrometer or caliper to measure the shim (then write it on the shim with a black fine tip magic marker).

Good Fortune!