Moparts Tech Archive

Small Block

Main Cap Q's

charlie clark
New Member
Posts: 12
From: Maple Valley, WA
Registered: Sep 2001

I have a 340 block that I got without main caps. I have been told that small block mopar motors all use the same type caps. Is this true and can I just score a set of 318 pieces and do a line bore?
Thanks,

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beepbeep
Moparts Member
Posts: 3658
From: Orange, CA. USA
Registered: Dec 2000
posted 05-13-2002 01:52 AM

I think they are the same except for the #3 center cap. That is probably a beefier cap than the 318's is.

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PISTOL GRIP
Moparts Member
Posts: 291
From:
Registered: Apr 2002
posted 05-13-2002 03:31 AM

the 360 mains are bigger so it would have to be a 318 or 340.

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340_6Pak_Cuda
Moparts Member
Posts: 2491
From: Maryland
Registered: Nov 2001
posted 05-13-2002 09:17 AM

273, 318 or 340 caps will interchange.
I dont know about the #3 cap being different, never noticed a difference but that doesnt mean its not true.
[This message has been edited by 340_6Pak_Cuda (edited 05-13-2002).]

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Jerry
Moparts Member
Posts: 1643
From: WARREN, MI
Registered: Nov 1999
posted 05-13-2002 09:22 AM

buy aftermarket caps for your engine. it will costs you about 200 bucks to have align honed bored. you have to do this whether you use weak factory caps or stronger aftermarket ones.

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Andy Faulkner
New Member
Posts: 38
From: Truro,Nova Scotia,Canada
Registered: Aug 2001
posted 05-13-2002 10:27 AM

Caps from a 318 or 273 will work. I've done this operation a few times and it's good to have a variety of caps to pick from to get the best fit. This is especially true for two reasons. One,...ALL the caps must fit at least snug in the block registers, and two,...find a number 3 cap that is as close as possible to the machined surfaces in the block, particularly the thrust surfaces on the sides. The fit here is critical, as bearings only come in one width to maintain crank end-play.

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dogdays
Moparts Member
Posts: 1802
From: Golden, CO
Registered: Oct 2000
posted 05-13-2002 10:27 AM

YUP. By the time you get the new 318 mains put on, you will wish you had put on some new Pro-Gram caps. Even MP ductile iron caps are better, by that I mean stiffer and stronger in tension than the stock gray iron stuff.
R.

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Andy Faulkner
New Member
Posts: 38
From: Truro,Nova Scotia,Canada
Registered: Aug 2001
posted 05-13-2002 10:39 AM

Just remembered one other little detail....
If you put a 340 and 318 cap side by side the way they're installed, the 340 one is about one sixteenth taller than the 318 piece AT THE BOLT BEARING SURFACE. The 340 caps are probably slightly stronger in that regard, but no big deal unless the motor is real crazy. One little problem you will find is that a stock windage tray will hit the oil pan rail when using 318 caps so you'll have to shim a little, or trim the windage tray.

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