Spridget- Threaded plugs for block oil gallery?

J

Joel McGinley

Well-known member
I'm going through my street Bugeye which has been parked for 12 years. It had a major oil leak behind the rear engine mounting plate at the plug for the main oil gallery- this oil made it's way out onto the car, driveway, etc... The stock plug was a brass "cork" just under 0.500 inch diameter. I think there are aftermarket plugs more like tapered thimbles, or the passage can be threaded on both ends for a threaded plug. What size is right? 3/8-18 NPT seems marginal. Do I go to 9/16-18 and use a straight setscrew as a plug? (I don't have any race engines to look at- some had such a mod but they are gone.) Joel
 
I always tapped front & rear for 3/8 NPT and used brass hex socket plugs.

I remember having to tap extra deep in back to assure the plug head was below the surface, and having to "notch" the front plate to clear around the plug threads.

Merry CHRISTmas.

RJS
 
The plugs that I used were 3/8" x 18 tapered pipe, with a recessed Allen head cavity.
A plug is about 0.44" long, with an outside thread diameter near 0.515" at the smaller end, and near 0.532" at the larger end.

Advance the pipe tap SLOWLY, remove the tap, insert the plug, determine if additional depth is needed for the threads, etc.
Cut the threads just far enough, so that the head of the plug is barely below the surface of the block.
This is especially important for the plug at the rear of the block:
If the plug is set too deep, it can block the oil passage to the rear main bearing.
Use teflon tape for sealing. Do not use liquid teflon (it will leak !).

Charlie Tolman
H/P 40 (Retired)
 
Charlie- It's actually a 1/4 NPT plug that is close to .500 diameter. I've got both ends of the block tapped now for such plugs. Joel
 
Thanks, Joel.

I measured 18 threads per inch on my pipe thread plug, but I failed to remember that 1/4 and 3/8 NPT have the same thread pitch.

Charlie T.
 
Joel, you did not mention the engine size, the 948 if I remember correctly has a larger galley hole, the 1275 for sure can be tapped directly into the exsiting hole with a 1/4"-18 NPT plug, of course with NPT plugs the engine needs to be completly apart and cleaned afterward, otherwise if together , just get a new brass plug, Moss has them. The key to doing this is getting the old brass plug out cleanly, don't attempt to drill them out, what I do is drill them 1/4"-20 in the center ofthe brass galley plug and then I've made a adapter for my slide hammer to pull them out, they come easily and clean this this way and galley hole is still virgin. Hope this helps.
 
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