I was reading Lingenfelters book on modifying small block chevy engines. On page 145 chapter 17 Engine blueprinting. He talks about a 1/2 oil passage plug under the rear thrust main cap. If not replaced it can cause an internal oil leak. you can lose up too 20 psi because oil is leaking past this plug before reaching the rest of the engine.

He says that most shops remove it to thoroughly clean the block.

Ive built three 400s and dont ever remember this plug being there Or installing it. I have my present 400 on the stand with the main caps torqued down. I havent had a chance to pull the rear cap yet to see.

Anyone know anything about it?

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

 

Yes, he is right. I have an assembled 357 short block which I verified had it (it did ), and a '76 4.00" bore, bare block which also has it (rusted, but has it). HTH

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George P. Lara
1994 Z28 LT1 T56
1984 Z28 High Output
Member: SCCA, SCFB, SC3GFB

[This message has been edited by MRZ28HO (edited September 30, 2000).]

 

Thanks George....I just pulled the cap and there is no plug there.
Mike

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

[This message has been edited by MikeH (edited October 01, 2000).]

 

Yes, that's where it at.

 

Thanks...

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

 

That little plug is pretty important. It's the oil filter by-pass plug. If not installed, most if not all, oil will by-pass the oil filter. That is why the oil pressure will be lower if it is not installed. No restriction from the the filter.

Make sure you get it passed the port that takes a right angle turn to the filter. And yes it's on the filter boss side of the engine (driver's side).

Mike

 

So long as its slightly below the surface IM okay?

I had the Machine shop install the freeze plugs before. I guess thats why I never noticed it. I thought I had a good understanding of SB chevys. This time I bought most of my parts ahead of time. I know thats the wrong thing to do. I had some Brass freeze plugs so I thought I would install them myself. Glad I found out now instead of later.

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

 

When you look down the hole under the cap you will see another hole/passage that takes a direct turn to the filter boss. It's about 1 1/2" or so down. The plug must be past this passage. If not, the oil flow will be dead-headed and not go anywhere but through the pump's internal by-pass. That would be a real bad thing. The plug is there to facilitate cleaning of the oil passage from the pump to the galleys. Sludge and crap will build up on the other side of the plug. It's important to remove the plug to get that crap out of the passage. Make sure you get the plug properly seated and not ****ed or crooked. A 3/8 socket extention usually works well to seat it squarely.

Johnies book has the best description of the SBC oiling system that I have seen. It's fortunate that you read the book.

Take care, Mike

 

MD...Thanks I was just looking into the passage you were talking about and the plug is there. Its Just below the passage that angles over to the oil filter like you said. Boy do I feel stupid I was looking for a plug slightly below the surface. I learned something new today And its good to know its been there the past 10,000 miles.

Thanks guys for your help!
Mike

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!