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Old 07-10-2020, 02:19 PM   #19
GOSFAST
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Join Date: May 2010
Location: Long Island, NY
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Default Re: Spark plug shims

Quote:
Originally Posted by Kray_Z-1 View Post
I've built a flatty based on a 51 merc block. During the machine shop phase, my machinist shaved the decks a "little" (I don't really know how much).
I'm running the Edelbrock 74cc heads and a Potvin Super 3/8 cam. I also m sing Edelbrock's recommended spark plugs, Champion rc12yc. The problem I'm having is the valves are closing all but one of the gaps on the passenger side bank. It doesn't seem to be smashing the electrode, nor does it leave and real damage on the valve. It just seems to close the gaps. I don't want to use a shorter plug because they are MUCH shorter and the heads are aluminum. I know of several manufacturers of "indexing washer" that vary in thickness, the thickest being .064" . I believe that should be enough of a shim to keep from closing them. I have run the engine a bit (not knowing at first) and it sounded real lumpy and randomly spit fire from the pipes. After finding the problem, I re-gapped the plugs then installed them hand tight, then backed them off about 2-3 threads and fired it up again, now both banks are running but I don't think well enough to get any real tune. Has anyone dealt with these indexing washers before? or had similar problems? I guess what I really need to know is...do I remove the "gasket" from the plug before using the washer, or just leave it on?

Here's a link to it running...

https://youtu.be/rJsxl5MS4PY

Wrong plugs, no matter what Edelbrock "recommends"??

(Add) Just realized the date of this thread, missed that. Also, today there always seems to be plug length issues, more than normal for these Flatheads with aftermarket heads?

Thanks, Gary in N.Y.

P.S. We never use "extended-tip" plugs in any of our Flatheads, and we don't particularly care for that brand any longer! We use "Autolite" pump-gas plugs on almost all our builds!

Last edited by GOSFAST; 07-10-2020 at 02:37 PM. Reason: Add
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