GM Crank Pulley Numbers

[Jim Schone]

I'm a member of the Corvette forum and have a question about GM part numbers for Joe Lucia. Joe, I have found that GM still stocks at least three crank pulleys for a BBC with a short water pump. The GM part numbers are; 3921923, 3858533, 3863108. My question - are any of these pulleys different in dimensions or do they just have different numbers corresponding to say make, model or year. If they do have different dimensions how can I find out what the differences are in each pulley.

Thanks, Jim

[Joe L.]

Re: GM Crank Pulley Numbers

Jim-----

First of all, GM #3858533 is not a big block pulley. At least, it's not a big block pulley in the sense that most folks of a big block. It was used on some Mark I big blocks (i.e. 348 and 409), but it was never used on a Mark IV big block (the only series big block ever originally installed in a Corvette). Primarily, the GM #3858533 is a small block pulley and it was used on many Corvette small block applications. This pulley is a 2 groove, stamped steel pulley of 6-5/8". It may be stamped either "3766987" or "3858533".

GM #3921923 and GM #3863108 are Mark IV big block pullies. The 3863108 is a 2 groove, nodular cast iron pulley. It is 6-3/4" OD. It was used for all 1965-67 Corvette big blocks. It was also used for later 1969 L-88/ZL-1 and 1971 LS-6. It MAY have found its way onto some, or even all, 68-E69 L-71s and 1968-E69 L-88s, too.

The GM #3921923 is also a 2 groove pulley of 6-3/4" OD. However, it is of stamped steel construction. It was used on 1968-69 L-36/L-68, possibly some L-71 and all 1970-74 Corvettes with big block, except 1971 LS-6.

The GM #3863108 and GM #3921923 are functionally interchangeable. Any application that uses one of these can use the other.

[Jim Schone]

Re: GM Crank Pulley Numbers

Thanks Joe,

Could you tell me what GM, two groove short water pump pulley would work for either the 3863108 or 3921923 crank pulleys.

Jim

[Joe L.]

Re: GM Crank Pulley Numbers

Jim-----

There are at least several 2 groove waterpump pullies that will be compatible with either of the 2 referenced crankshaft pullies when used with the "short" big block waterpump. These are as follows:

GM #3864480---7-3/16" OD; long-discontinued; hard to find; expensive

GM #3906656---7-3/16" OD; discontinued; expensive; available in reproduction

GM #3848904---6-9/32" OD; discontinued

GM #3995641---5-7/8" OD; remains available from GM

There were also other 65-68 big block passenger, Chevelle, Chevy II and Camaro pullies that will work, but none of these are available.

Also, keep in mind that when pullies of various OD are used with either of the 2 big block crank pullies, the fan/waterpump speed will be correspondingly different.

[Jim Schone]

Re: GM Crank Pulley Numbers

Joe,

Thank you for all your help.