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I want to tap the front cam and lifter oil galleries on a 1970 350 truck block. Everything I can find online and on this site claim 1/4" NPT is the correct tap, but my block won't take 1/4". The bores mic to a little over .53" back into the gallery 3/4" before tapering to approx. 7/16" bores. I tried tapping the center lifter gallery to 1/4" NPT, but the threads don't cut until hitting that tapered bore behind the cam bearing hole even with the tap buried in the bore, so the plug wouldn't block oil. I tried both a Blue Point and Matco tap, so it's not my taps.
My thought is to use 3/8" NPT since that tap calls for a 9/16" bore and these bores are just shy of that.
I'm running into the same issue trying to tap the oil filter gallery. Rather than bugger that bore, and since a 3/8" tap won't fit down in there, I'm just going to use a factory soft plug there.
Has anyone run into this issue before of not being able to use 1/4" NPT on the front of the galleries? Will 3/8" work, particularly with the lifter gallery so as to not block the cam bearing hole? Thanks.
My thought is to use 3/8" NPT since that tap calls for a 9/16" bore and these bores are just shy of that.
I'm running into the same issue trying to tap the oil filter gallery. Rather than bugger that bore, and since a 3/8" tap won't fit down in there, I'm just going to use a factory soft plug there.
Has anyone run into this issue before of not being able to use 1/4" NPT on the front of the galleries? Will 3/8" work, particularly with the lifter gallery so as to not block the cam bearing hole? Thanks.