Hey all,
I recently bought a '92 GS500 knowing it needed the valves adjusted. I've managed to measure all the clearances and figure out the sizes for the new shims I need. According to the math, two of the shims should've been able to be relocated to provide proper clearances, but when I moved them the clearances were way off. I went from a thicker shim to a thinner one and the clearance got smaller. Is there another issue here or did I do something wrong? Any help is super appreciated!! Thanks for reading :)
A couple of basic things first:
1. Have you checked the actual thickness of the shims themselves with a micrometer? (probably unlikely but worth checking).
2. When you rechecked with the feeler gauges did you cycle the pistons around a few times first? If there's oil between the shim and bucket that isn't squeezed out
then it can appear to make the clearance smaller.
I have checked the thickness of all the shims with a micrometer, they are all within +/- .01 mm of what's actually marked on the shim. I hadn't cycled the pistons when I first checked, but I have cycled them since and it did not change the clearance.
How much clearance did you start out with? Sounds like you were trying to increase clearance on at least one or more valves, so it could be that you had "zero" clearance even though you could measure something due to binding or just the position that the valve came to rest on the seat. You might cycle the engine a bunch of times and make a bunch of measurements to find the average measurement. But if the clearances are too small to begin with, then all theory aside, my experience says you might get these kinds of results.
Have you done a compression test?
Anyway, there is a limited list of things that cause insufficient valve lash and then a shorter list of reasons why your changes didn't work as expected. I know you feel confident, but to be sure you will have to redo this so you might as well plan on double-checking your measurements and your math. Even though I have not done valve clearances adjustments on my GS, my Miata had the same bucket-and-shim type arrangement and I worked on it several times. With 4x the number of valves, suffice to say the feeler-gauge-and-math method of doing this often resulted in confusing results unless I had too-big clearances to start and went to a bigger shim to reduce clearance. Add in a receding valve seat and everything goes haywire pretty quickly.