Valve Guide Clearance

Hello all! Just want to take a second to say how grateful I am for this invaluable resource. My question is, does anybody know the service limit for valve guide clearances on a '52 Super?

The way I interpreted the information in the shop manual was that the figures applied to setting up/reaming new valve guides. My intake clearances range from .0027 to .0038. The exhaust clearances range from .0038 to .0061.

I'm going in to the machine shop soon, and I'd rather only have done what needs doing. The exhaust seats certainly need cut and the valves refaced. I would like to know the service limit on the valve guide clearances so that I have an idea of what is acceptable to run. Pulled the head because of an exhaust valve that was starting to burn and was causing a misfire.

Thank you for any and all opinions/information,

Generic numbers for cast iron guides are intake 0.001" - 0.003", exhaust 0.002" - 0.004".
Looking at the specs shown in the link above "Straight Eight Engine Specifications " shows
intake .0015" - .0035”
exhaust .0021" - .0039”
myself, I would always fit them tight, especially if I was using the Buick specifications. If you use a bronze guide, or liner they can be tighter. It will cost more to have a tighter fit, the tightest fits require a honed finish. Most shops quote for a reamed finish.
As far as the service limit on used parts, one 1984 college-level engine rebuilding textbook uses a limit of 50% over the published spec limits for new items. See attached pages for more details and measuring techniques.

So using the Buick Shop Manual numbers, it looks like your worst exhaust valve is barely over the textbook's in-service limit. 😀


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I'm going to be much more confident walking into the machine shop with all this information. Thank you very much! Todd- I've been scouring the internet for the last month trying to find that information. I appreciate it greatly!