valves..

No comments on this post? I'd love to hear other people's experience because I saw exactly the same thing... I measured very carefully, calculated the new shims, only to have them change substantially once installed.

There are a couple of things to watch out for, and I'm pretty certain these weren't affecting me because I was aware:

1. If the shim has been beaten up by excessive clearances, they will be dish shaped and the feeler gauge won't give an accurate indication of the actual clearance.
2. the rocker shaft will wear on one side (the bottom) and if you get it flipped around on re-installation then it will affect your clearances, generally will make them tighter if you put it in the opposite way from how it has been worn in.

Any other ideas on why these engines seem to change? I started to make educated guesses on which shim to install... choosing thicker than what I thought it should be... that seemed to help, but I still can't understand why they don't behave like we think they should.

And precise, repeatable tools are important... that goes without saying of course.

With shims, its often possible to get a tighter clearance than expected after swapping shims because of the oil film. It gets squeezed out after it runs a bit. Its also important to measure each shim to confirm its dimensions.

But why pulling a shim and then putting it back gives you a bigger clearance, dunno. Did you use the same feeler gauges, some cheap sets are not always that accurate. I like to check mine from time to time to be sure.

Was it definitely at TDC the first time, and not on the cam ramp a bit?

Steve