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Hi,

Below is a picture of the #5 cylinder springs from a 1968 390. I have two questions...first, all the other shims are more or less perfectly centered under the spring, except this one, should I be worried, do I need to do something? And second, is there any way for me to tell, test or know why the previous owner shimmed these spring without me having to pull the heads and tear the engine apart?

Did he rebuild the engine and put in a hotter cam? I'm no expert, but the idle sounded normal, not lopey in any way.

Were the springs added because the valves were sinking into the heads because someone ran unleaded gas with no additive for too long? I purchased a phone bore scope, but the angled mirror proved useless, all I could really see was down into the cylinder, and that they seemed to have a lot of carbon buildup.

Was this a "cheap fix" to freshen up old tired springs, rather than rebuild the heads? What else might it be? What is most likely?

The engine started and ran fine, didn't smoke, didn't overheat, no info on oil pressure, just a dummy light, which never came on, and might not have worked, but I did confirm it was sending oil up to the top. 390_spring_shim.jpg
 

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Did you install the springs or a shop did the work?
if the spring is fully seated on the shim, I don't think you have anything to worry about
as long as shim does not move...
Best
 

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It's the wrong shim or the guide has a problem. Shims are measured 3 ways. thickness, .015, .030, etc. OD 1.45, 1.65, etc and ID .650, .075 etc. You have to match all 3 to get the right shim. It looks like yours has to big of an ID allowing it to shift. The ID diameter keeps it in place and from shifting.
 
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