327 main cap size

[Boyan B.]

I need a set of main caps for a 63 327 small journal block. Can I use a set from a 283 block or do they specifically need to be from a 327? I know they will need to be align bored/honed with the new block.

Boyan

[Joe L.]

Re: 327 main cap size

I need a set of main caps for a 63 327 small journal block. Can I use a set from a 283 block or do they specifically need to be from a 327? I know they will need to be align bored/honed with the new block.

Boyan

Boyan----


The 283 and 327 caps are the same for 4 of the bearing caps. For the rear main cap, the 1959-67 283 caps are the same as 327. These may be identified by casting number 3746464.

Note of caution: caps from another block may be usable for you PROVIDING that there is enough "meat" on them to allow them to be machined to register properly in your block. Most of the time there will be, but not necessarily always.

[Mike M.]

Re: 327 main cap size

if the 327 is gonna be run hard ,i'd see if your machine shop can machine the block for after market 4 bolt main caps. its not that big a job.mike

[Boyan B.]

Re: 327 main cap size

Thanks guys, and no, it will not be run hard. Just a stock 250 hp motor.

Boyan

[Bob J.]

Re: 327 main cap size

I need a set of main caps for a 63 327 small journal block. Can I use a set from a 283 block or do they specifically need to be from a 327? I know they will need to be align bored/honed with the new block.

Boyan

Boyan,
327 main caps were a different metal than 283 caps and a different casting number.Bob

[Joe L.]

Re: 327 main cap size

Boyan,
327 main caps were a different metal than 283 caps and a different casting number.Bob

Bob-----


For any given year, the 283 and 327 main caps were the same. For 1959-62, the 4 forward caps were GM #3746337 (cast GM #3743951 and, possibly, other numbers). The rear cap was GM #3759260 (cast, GM #3746464 and, possibly, other numbers). For 1962, the only year during this period when both 283 and 327 engines were produced, the caps were the same for both 283 and 327.

For 1963, the 1-4 cap part numbers changed, but the change covered BOTH 283 and 327 engines. For 1963-1967, the 4 forward caps were GM #3829309. I don't know what the casting number was, but I would guess it was a 38XXXX number. The rear main cap for 63-67 was the same as that used for 1959-62. In any event, for 1963-67, the main cap set was the same for both 283 and 327. Also, the 3829309 replaced the 3746337 for SERVICE in October, 1963.

I don't know what the difference was for the 3746337 versus 3829309 main caps. It's possible there was a material change. As far as I know, the only 2 materials ever used for small block main caps were gray iron and nodular iron. However, I am unaware that any 283 or 327 used nodular iron, the stronger of the 2 materials.

Addendum:

The 3829309 caps were nodular iron. It is possible that they were only used for 340 hp and above engines for 1963-67 and it's also possible that they were used sporadically for other engines. Apparently, after October, 1963, only the nodular iron caps were offered in SERVICE for all 283 and 327 engines, even though gray iron caps (the 3746337) may have been used for some engines, including 283's and lower HP 327's, in 1963-67 PRODUCTION. In any event, all of the 1959-67 small block caps are functionally interchangeable.

[Clem Z.]

Re: 327 main cap size

Bob-----


For any given year, the 283 and 327 main caps were the same. For 1959-62, the 4 forward caps were GM #3746337 (cast GM #3743951 and, possibly, other numbers). The rear cap was GM #3759260 (cast, GM #3746464 and, possibly, other numbers). For 1962, the only year during this period when both 283 and 327 engines were produced, the caps were the same for both 283 and 327.

For 1963, the 1-4 cap part numbers changed, but the change covered BOTH 283 and 327 engines. For 1963-1967, the 4 forward caps were GM #3829309. I don't know what the casting number was, but I would guess it was a 38XXXX number. The rear main cap for 63-67 was the same as that used for 1959-62. In any event, for 1963-67, the main cap set was the same for both 283 and 327. Also, the 3829309 replaced the 3746337 for SERVICE in October, 1963.

I don't know what the difference was for the 3746337 versus 3829309 main caps. It's possible there was a material change. As far as I know, the only 2 materials ever used for small block main caps were gray iron and nodular iron. However, I am unaware that any 283 or 327 used nodular iron, the stronger of the 2 materials.

when the main bearing size changed frlom 2.300 to 2.450 i would guess that is when the caps part #changed

[Bob J.]

Re: 327 main cap size

1963 and later 327 caps are nodular iron and have a "N" cast in. If Boyan wants correct caps for his 63 327 the earlier cast iron 283 caps fit but are not the same.Bob

[Joe L.]

Re: 327 main cap size

1963 and later 327 caps are nodular iron and have a "N" cast in. If Boyan wants correct caps for his 63 327 the earlier cast iron 283 caps fit but are not the same.Bob

Bob----


What is the casting number on these caps? Any other markings besides the "N"?

[Timothy B.]

Re: 327 main cap size

Joe and Bob,

Here are pics of main caps from a 1963 Impala SS 327/250 HP built at the Tonawanda plant. The block is trashed from sitting outside but I got the caps, forged crank and rotating assembly.

The car had 200,000 miles and still the original bearings in fair condition..

[Joe L.]

Re: 327 main cap size

Joe and Bob,

Here are pics of main caps from a 1963 Impala SS 327/250 HP built at the Tonawanda plant. The block is trashed from sitting outside but I got the caps, forged crank and rotating assembly.

The car had 200,000 miles and still the original bearings in fair condition..

Tim-----


Thanks. It looks like the casting number is "7178". This might be a derivative of a 7 digit number, but I don't know what it is.

[Tom P.]

Re: 327 main cap size

I need a set of main caps for a 63 327 small journal block. Can I use a set from a 283 block or do they specifically need to be from a 327? I know they will need to be align bored/honed with the new block.

Boyan

Boyan,
Email me at home. tparsons6@cox.net
I MAY have a set, but I'm at work and can't check until I get home tonight.

[John H.]

Re: 327 main cap size

Here are pics of main caps from a 1963 Impala SS 327/250 HP built at the Tonawanda plant.

Note that out of eight original main cap bolts, there are four different headmarks; excellent example that shows how engine plant fasteners were stocked/binned by part number, with no attention whatever paid to headmarks. The same was true in the car assembly plants.

[Clem Z.]

Re: 327 main cap size

Note that out of eight original main cap bolts, there are four different headmarks; excellent example that shows how engine plant fasteners were stocked/binned by part number, with no attention whatever paid to headmarks. The same was true in the car assembly plants.

are you saying "don't believe everything you read"

[John H.]

Re: 327 main cap size

are you saying "don't believe everything you read"

Yes, you might say that. After 38 years in manufacturing and assembly plants, it's almost humorous seeing some folks obsess over having to have "all matching headmarks" for full judging credit.