Thread: Hear's one ? for the small block guys

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Inside the block of a 327 motor under the rear main cap there is a expansion plug that go's in the block.every auto part store that i have talked to they don't know what this is for or even heard of this plug.so do any of you guys know what this is for and if you need to put this in.I looked on the net and cant find any info on this. thanks for your time ktm

What Denny said...... Just measure the hole and give your parts store the size they should be able to fix ya up......

Not many people are aware of that plug. Most machine shops don't remove it before block cleaning. Builds up accumulative junk that will come loose at a later time and wash through the engine and destroy bearings, etc.

Oil Passage plug should be P/N 3701638
It's about a buck at the Chev dealer
Most SBC blocks use a .520" plug, GM 3701638 or a Pioneer part number EPC-87 from your local parts store. The late 1 pc rear main seal blocks use a steel ball from the factory
New blocks dont have one installed and some
machine shops remove it to hot tank the block.

Thanks guys big help will put it in .I wonder owe many guys leave them out with
out knowing there even there? Found one guy to day at the speed shop and he
said, the oil filter bypass plug(that is what he called it) diverts oil from the pump and sends it through the filter so the bearings only receive filtered oil which is a must if you're using a modern oil filter.Anyone think he is right? still I will put it in to be on the safe side thanks guys big help. ktm