1971 Base Engine Harmonic Damper

[Michael B.]

Re: 1971 Base Engine Harmonic Damper

Joe,

I just checked the pulley that was attached to my 7701 balancer. Like Alan's, it is also part number 4858533 BJ. There is significant rust so I couldn't guess on finish yet. It's soaking overnight in Evapo-Rust so maybe tomorrow I'll know if it was painted or phosphate finished.

Additionally, after reading your post I checked the part number for the water pump pulley. It is part number 3991423 BW and appears to be a deep groove pulley as well, as does the power steering pulley.

Mike

[Joe L.]

Re: 1971 Base Engine Harmonic Damper

Joe,

I just checked the pulley that was attached to my 7701 balancer. Like Alan's, it is also part number 4858533 BJ. There is significant rust so I couldn't guess on finish yet. It's soaking overnight in Evapo-Rust so maybe tomorrow I'll know if it was painted or phosphate finished.

Additionally, after reading your post I checked the part number for the water pump pulley. It is part number 3991423 BW and appears to be a deep groove pulley as well, as does the power steering pulley.

Mike

Mike-------


Is the power steering pump pulley cast iron? If not, is there a number stamped on it?

Is there an add-on pulley sandwiched onto the front of the crankshaft pulley as the power steering driver pulley?

The GM #3991423 is not a deep groove pulley; it's a standard groove pulley. It replaced the GM #3890419 standard groove pulley used for 1967-70 standard groove applications.

[Michael B.]

Re: 1971 Base Engine Harmonic Damper

Joe,

There was no pulley on the front of the crankshaft pulley, just the two groove 4858533.

I'll check in the morning to see about the PS pulley.

Mike

[Michael G.]

Re: 1971 Base Engine Harmonic Damper

Well I thought I'd check on my Dec. '70 built '71 w/ ac, ps and find a measurement of 6-3/4" triple pulley with the balancer being a bit smaller than the pulley (guestimate 6") Poor lighting, tired eyes, and the nose pulled up tight made it difficult but this is what I found on what I believe to be an unmolested original base engine '71.

[Michael B.]

Re: 1971 Base Engine Harmonic Damper

Good Morning Joe,

The power steering pulley is cast iron with three spokes.

After soaking the damper pulley in Evapo-Rust overnight, I can say for sure that there is evidence of a layer of satin/low gloss black paint. I can't say for sure that it was applied over a black phosphate finish, but if so, the phosphate was very thin. The evidence of black paint is very apparent.

Additionally, I took another look at the damper pulley and water pump pulley side by side and the grooves still look identical to me. I'm not disputing you, only saying that there must be a very subtle difference between a deep groove and standard groove pulley. I measured the depth of the grooves on each pulley at the same 5/8 inch. I don't know what else to look for.

Mike

[Joe L.]

Re: 1971 Base Engine Harmonic Damper

Good Morning Joe,

The power steering pulley is cast iron with three spokes.

After soaking the damper pulley in Evapo-Rust overnight, I can say for sure that there is evidence of a layer of satin/low gloss black paint. I can't say for sure that it was applied over a black phosphate finish, but if so, the phosphate was very thin. The evidence of black paint is very apparent.

Additionally, I took another look at the damper pulley and water pump pulley side by side and the grooves still look identical to me. I'm not disputing you, only saying that there must be a very subtle difference between a deep groove and standard groove pulley. I measured the depth of the grooves on each pulley at the same 5/8 inch. I don't know what else to look for.

Mike

Mike------


I blew it on this one. The GM #3991423 IS a deep groove pulley. For some unknown reason I was thinking we were talking about the GM #3995643 which is a standard groove pulley.

For 1971 and later GM went to deep groove waterpump and crankshaft pulleys for all small block applications. Prior to 1971 the deep groove pulleys were used only for HP and SHP applications. The GM #3995643 standard groove pulley or its "sister" deep groove pulley, GM #3995641, would not even work for 1971 and later. That's because for 1971 Corvettes GM went to the 3-1/4" bolt circle waterpump hub pattern AND the 3/4" pilot. The 3991423 accommodates this. The 3858533 deep groove crankshaft pulley is the same as that used for 1965-70 HP and SHP small blocks.

Of course, GM could have released standard and deep groove pulleys with the new hub pattern for 1971 and later. However, I guess they figured that really didn't make much sense and just standardized on the deep groove pulleys for all Corvette applications. It probably would have been smarter if they had done this starting in 1963.

[Michael B.]

Re: 1971 Base Engine Harmonic Damper

Thanks Joe.

Hopefully we'll get some more response from 71 owners to see how far back in the production year the 6 3/4 inch dampers appear. Interesting stuff!!

Mike

[David L.]

Re: 1971 Base Engine Harmonic Damper

What is installed on the production line is generally the same as what is sold over the counter at any given point in time but there are exceptions.

My 1971 Chevrolet Passenger-Chevelle-Nova-Camaro Parts Catalog (September 1970) lists the 3947701 balancer (6 3/4" dia.) for ALL w/2BC (350) and the 3947704 balancer for ALL w/4BC (350)(exc. Sp. H/Per.). Maybe there was a temporary shortage of the 7704 balancer at the Flint engine at some point during the 1971 production and the 7701 balancer was used as a substitute.....Just a thought.

Dave