Big block mail cap casting numbers

[Steve Antonucci]

Here's a fast question:

Can any member(s) tell me the correct casting numbers for the Mark IV
4-bolt main caps? I need the numbers cast on the 1-4 caps and the rear
main cap as well. Are 4-bolt truck caps different than 396,427,454 caps.

Thanks for your help,

Steve

[Mike M.]

Re: Big block mail cap casting numbers

if you've not got the caps for your mark 4, info you're requesting is irrelevant as the donor caps will have to be fit to and then align bored the block with new caps in place. good machine shops can handle the problem.pretty cerain the 396 and 427 vette/pass car main caps will interchange. not sure about trucks and the 454's. good luck, mike

[Steve Antonucci]

Re: Big block mail cap casting numbers

Mike,

The reason I need to know the numbers is that I evidently have a coulpe
of sets with different numbers cast on them. Not sure which set is correct.

Steve

[Clem Z.]

Re: Big block mail cap casting numbers

i have a 439 block and the #s cast on the caps look like 984. the part # for the caps is 334 and it could be that cast in number is 334, but they are not very clear

[Joe L.]

Re: Big block mail cap casting numbers

Steve------

There were several different casting numbers used for main bearing caps for Mark IV engines. However, ALL Mark IV 4 bolt caps (or, even, 2 bolt caps, for that matter) are interchangeable. You can even purchase brand new 4 bolt caps from GM. These caps are semi-finished and require machining to be fit to the block and align bore/hone afterwards. Used caps will have to be machined, too, and may not have enough material remaining to be useable for your block. The new caps will. These are GM #14015334 for the 1-4 positions and GM #14103156 for the #5. These caps are really not all that expensive. The 1-4 caps GM list for $22.76/ea and the rear main GM lists for $77.84/ea.

If you use one of the sets you have, inspect them carefully for a "wagon wheel" casting symbol followed by a "D". Caps with this marking are nodular iron and are stronger than gray iron caps. Caps without the markings described may or may not be nodular iron.

[Steve Antonucci]

Re: Big block mail cap casting numbers

Thanks Joe,

Is there any correlation between the 3 digit number cast on the cap and the
nodular/gray iron variants? BTW, what are the correct 3 digit numbers to
look for? I have found a couple different numbers in my collection.

As I mentioned previously, some may be truck 4-bolt caps. I just don't
know how to tell the difference. Perhaps you do though.

Steve

[Joe L.]

Re: Big block mail cap casting numbers

Steve-----

I've forgotten the coding system for the big block main caps. As I say, there were several part numbers and codes used. The 4 bolt caps used from 1965 through 1971 for most big block engines were GM PART #3877470 (#1-4) and GM #3877472 (#5). Later, these became GM #14019825 (#1-4) and GM #14103156 (#5). However, these numbers do not appear on the caps and I'm not sure if the "code" used was even a derivative of these numbers.

GM #14015334 (#1-4) and GM #14103156 (#5) are, I believe, SERVICE-only main caps. I have no information that they were used in PRODUCTION, but they may have been so-used. Nevertheless, they're out there, too, and completely interchangeable.

There may also have been other part numbers and codes for the big block main caps.

The Mark IV truck block caps are exactly the same as passenger car. However, many trucks used 2 bolt caps (same as passenger car 2 bolt caps, too).

Mark V and VI big blocks all use 4 bolt caps. I believe that the #1-4 caps are interchangeable bewteen all series big blocks. The Mark V and VI rear main cap is different, though, and WILL NOT interchange with Mark IV due to the fact that the latter engines use a 1 piece rear seal. There are other differences, too.