Shim Spitting

In the past, I've never bothered too much with shim spit worries. Since Branden spit one out of his motor with mild street cams, I decided to take an opportunity today to test a few things.

This test is only to see how easy it would be to dislodge a shim. It's not intended for anything else but that.

I had a perfect candidate on the bench, 81 J that I was degreeing cams in. So here's what I experimented with.

Head assembled with light springs [won't really matter for this test though].

Opened up the exhaust valve to about .150" lift. Just far enough to expose the leading edge of the shim so I could touch it with something.

Took the Kawasaki shim removal tool, reached down in there to the leading edge of the shim and just pushed on that edge a little.... Shim would pop right out with amazing ease. And I'm talking about pushing down on the front...not prying up on the rear like you would be during removal process....

Now you'd think the lobe would hold it down but in reality, it's not near the center of the shim enough to do so.

While I was setup, I figured I'd show you about using magic marker on the shim to inspect where the lobe rides. This is with a .390" net lift cam with 216* duration @.100" lift.

it doesn't take much does it half of what holds the shim in place is stiction from the oil that is between the shim and bucket. if that shim and bucket are dry of oil then all bets are off just about anything could pop it out.

Come on..........dry or not. I have never had a shim pop out of a bucket. Can't say it won't but seems unlikely.

i was thinking about this today....if there is a film of oil on bucket, that shim would stick pretty well...im gonna guess poor oil pressure up top which in turn inhibited bucket spinnage and aided in excessive wear in shim and eventual chuckage....of course , i could be totally full of crap.....:laugh:

That or an extremely tight valve.

that too.....

We where talking about this and I was thinking as well....

With the Motion Pro tool, those shims are a sonsabitch to get out... and unfortunately for Branden, they flew out at 10,000 miles per hour through his cover.

But as normal, my mentor informed me this, these cams are really moving and if the shim is dry, not seated properly, and clearance is loose you name it, you think that hardened steel isn't going to grab that shim and spit it! :blink: Think again...

Of course his wisdom made sense.... Bastard! :laugh:

keith1 wrote:

i was thinking about this today....if there is a film of oil on bucket, that shim would stick pretty well...im gonna guess poor oil pressure up top which in turn inhibited bucket spinnage and aided in excessive wear in shim and eventual chuckage....of course , i could be totally full of crap.....:laugh:

Not one bit of crap in that theory

arai59 wrote:

Come on..........dry or not. I have never had a shim pop out of a bucket. Can't say it won't but seems unlikely.

It is unlikely to happen. With stock or drop in aftermarket cams, very, very unlikely. Takes the right cam or right conditions to make it happen. But, every once in a blue moon....it happens.

If you don't think oil under that shim isn't a major player in it sticking in there, think again.