Need pulley expert!!

[Steven S.]

What pulleys (crank, add on, and water pump) do I need for a 1965 L79 with PS and AC? Also, do I have the correct balancer? 3817173 ? I'm having the old alignment issue. Thanks!

Steve

[Joe L.]

Re: Need pulley expert!!

What pulleys (crank, add on, and water pump) do I need for a 1965 L79 with PS and AC? Also, do I have the correct balancer? 3817173 ? I'm having the old alignment issue. Thanks!

Steve

Steve----


Well since no one else has stepped in on this one, I'll carefully "wade" into it. First, though, understand that the year, engine, and installed equipment makes your application one of the most "enigmatic" as far as correct pulley configuration goes. I just don't have any "for sure" information on this application; I've never been able to cull it out from available literature and I've never inspected the pullies on a known-original installation. However, I'll provide what information I have:

waterpump pulley----GM #3848904. This is a 2 groove pulley of 6-9/32" OD. I'm fairly sure this is the waterpump pulley used for your application. May or may not require spacer/reinforcement GM #3720616.

alternator pulley----GM #3846180. This is a 3-3/64" OD machined steel pulley. I'm fairly sure this is the alternator pulley used for your application.

power steering pump pulley----GM #3868892. This is a 5-23/32" OD, stamped steel, "pancake"-style pulley. I'm virtually certain this is the correct power steering pump pulley for your application. It's rare.

harmonic balancer pulley----Here's where it all breaks down for me. The pulley may have been a GM #3827843 or it may have been some other part number. Considering the power steering pump pulley, I would THINK that an add-on pulley was also used. If so, though, I don't know what it was.

ALL of the above pullies are GM-discontinued but may be available in reproduction.

GM #3817173 is the correct balancer part number for your application. However, there are different configurations of this balancer so the one you have may not be NCRS-correct. However, if it's of that part number, it will be FUNCTIONALLY correct.

[Joe R.]

Re: Need pulley expert!!

Hi Joe:

I think that all midyear L79s equipped with BOTH power steering and A/C used the standard-groove pulley set from the similarly configured base engine (with the exception of the alternator).

Based on my research of midyear small block pulley applications, there were two families of compatible crankshaft (CS) and water pump (WP)pulley sets:

1) Standard-groove pulleys used on all base engines.
2) Deep-groove pulleys used on high performance small blocks such as the L79.

The dual deep-groove pulleys have a wider center-to-center pitch for the belt centerlines, so you can't mix standard-groove and deep-groove pulleys on the CS and WP combination.

When the engine was configured for both PS and A/C, an equivalent triple-groove pulley was required on the CS, with the PS belt in the forward-most position. On the 1967 base engine, this was accomplished by adding the standard-groove 3751232 to the standard-groove dual CS pulley 3850838.

The 3751232 does not fit properly inside the deep-groove dual CS pulley 3858533, because the mounting face is not deep enough to reach the bottom of the dual deep-groove pulley. I think this would be true for any dual deep-groove CS pulley.

As far as I can tell, GM never produced a deep-groove PS pulley set for C2 small blocks equipped with BOTH PS and A/C. That would have required a deep-groove CS add-on pulley and a special deep-groove PS pump pulley with the belt centerline moved slightly forward. This configuration would have had clearance problems with PS pump pulley hitting the frame rail.

Interestingly, the 1967 Z28 Camaro did have such pulleys. The crank add-on was 3916385 (which fits nicely inside the dual deep-groove 3858533), and the PS pump pulley was 3873847, which lines up nicely with the add-on CS pulley. The only problem with using these on a C2 is that there is insufficient clearance between the PS pump pulley and the C2 frame rail, at least for production tolerances. I think this is why GM didn't use these on the C2.

I agree with you that the situation for the 1965 L79 with PS and A/C is very confusing in the parts books. However, the 3848904 WP pulley is a deep-groove pulley. If this pulley was actually used for the L79 with PS and A/C, that means that all the other pulleys would have to be deep-groove as well, including the add-on crank pulley and the PS pump pulley.

I would be delighted to learn that the pulleys for this configuration were, in fact, deep-groove pulleys, because I have a side project to equip my 67, which has PS and A/C, with deep-groove pulleys. So far, the closest I have come are the deep-groove PS pulleys from the 1967 Z28.

[Joe L.]

Re: Need pulley expert!!

Hi Joe:

I think that all midyear L79s equipped with BOTH power steering and A/C used the standard-groove pulley set from the similarly configured base engine (with the exception of the alternator).

Based on my research of midyear small block pulley applications, there were two families of compatible crankshaft (CS) and water pump (WP)pulley sets:

1) Standard-groove pulleys used on all base engines.
2) Deep-groove pulleys used on high performance small blocks such as the L79.

The dual deep-groove pulleys have a wider center-to-center pitch for the belt centerlines, so you can't mix standard-groove and deep-groove pulleys on the CS and WP combination.

When the engine was configured for both PS and A/C, an equivalent triple-groove pulley was required on the CS, with the PS belt in the forward-most position. On the 1967 base engine, this was accomplished by adding the standard-groove 3751232 to the standard-groove dual CS pulley 3850838.

The 3751232 does not fit properly inside the deep-groove dual CS pulley 3858533, because the mounting face is not deep enough to reach the bottom of the dual deep-groove pulley. I think this would be true for any dual deep-groove CS pulley.

As far as I can tell, GM never produced a deep-groove PS pulley set for C2 small blocks equipped with BOTH PS and A/C. That would have required a deep-groove CS add-on pulley and a special deep-groove PS pump pulley with the belt centerline moved slightly forward. This configuration would have had clearance problems with PS pump pulley hitting the frame rail.

Interestingly, the 1967 Z28 Camaro did have such pulleys. The crank add-on was 3916385 (which fits nicely inside the dual deep-groove 3858533), and the PS pump pulley was 3873847, which lines up nicely with the add-on CS pulley. The only problem with using these on a C2 is that there is insufficient clearance between the PS pump pulley and the C2 frame rail, at least for production tolerances. I think this is why GM didn't use these on the C2.

I agree with you that the situation for the 1965 L79 with PS and A/C is very confusing in the parts books. However, the 3848904 WP pulley is a deep-groove pulley. If this pulley was actually used for the L79 with PS and A/C, that means that all the other pulleys would have to be deep-groove as well, including the add-on crank pulley and the PS pump pulley.

I would be delighted to learn that the pulleys for this configuration were, in fact, deep-groove pulleys, because I have a side project to equip my 67, which has PS and A/C, with deep-groove pulleys. So far, the closest I have come are the deep-groove PS pulleys from the 1967 Z28.

Joe-----


I agree with the points made in your post. In general, there is no interchangeability of pullies designed for deep groove systems with those designed for standard groove systems.

The 3848904 pulley is a deep groove pulley and it would not seemingly be workable with a standard groove pulley system. However, there are several GM references that show it as the pulley used for 1965 with SHP 327 and C-60. For 1965 applications there is no qualifier of "except p/s" whereas for 66-67 there is. It still may be that for 1965 the "except p/s" qualifier may apply.

I wish we had someone out there with a 1965 with L-79, C-60, and N-40 that's reasonably sure their car is original. That would go a LONG way to getting this 1965 issue resolved. I'd like to get it resolved, too, since 1965 with L-79, C-60, and N-40 is one of the few applications I've never been able to figure out.

It's also possible that 1965 was the same as 1966 with L-79, C-60, and N-40. All of the pullies used for the 1966 application would have been available "in the parts bin" for 1965 and I can see no reason why they could not have been used.

CORRECTION TO ABOVE

I double-checked and there is one pulley used for 1966-67 L-79 with C-60 and N-40 that would NOT have been available for use on 1965 application. That pulley is the GM #3890419 waterpump pulley. It was not "around" in 1965 but it did have a functionally equivalent predecessor, the GM #3850680. That pulley was available for use in 1965 and was used for some Corvette applications. However, GM says that it was NOT used for 1965 L-79 with C-60. But, who knows?

The following pulley set should work for a 1965 with L-79 with C-60 and N-40 whether or not it was the original pulley set UNLESS the A/C pulley does not align. In the latter case, I don't know what to say and we're back to "square one":

balancer, rear-----GM #3850838 (2 groove)

balancer (front)---GM #3751232 (1 groove)

waterpump--------GM #3850680 (2 groove)

alternator----------GM #3846180 (1 groove)

p/s pump-----------GM #3868892 OR 3770509 (1 groove)

[Joe R.]

Re: Need pulley expert!!

Hi Joe L:

I agree that there is some chance that the elusive 1965 pulley set *might* be the only deep-groove pulley set used on the L79 when equipped with both PS and A/C. Certainly, this would have to be the case if the water pump pulley was, in fact, the deep-groove 3848904 that the parts books seem to say.

As I explained in my earlier post, it is not possible to mix and match standard-groove pulleys with deep-groove pulleys, al least for the WP, CS, and PS pulley combinations. Only the alternator pulley can be of either type.

I think the answer to this mystery could be determined if someone could locate a sample of the 1965 PS pump pulley 3868892 and compare it to the more common 3770509. In order to line up with a deep-groove pulley set on the CS, the PS pump pulley MUST place the belt center line farther forward than the 3770509.

This assumes that all the PS pumps in the C2 years used the same shaft on the PS pump. Is that the case?

Regarding compatible pulley sets for a 1965 L79 with PS and A/C, I agree that one option that would physically fit would be the pulley set used for 1966-67 with the same options. This is a standard-groove pulley set, with the exception of the alternator pulley, which was a deep groove. Following are the part numbers for this pulley set. All of these parts are readily available in used and/or reproduction versions:


1966-67 L79 with PS and A/C:

balancer, rear-----GM #3850838 (2 groove)

balancer (front)---GM #3751232 (1 groove)

waterpump--------GM #3890419 (2 groove)

alternator----------GM #3846180 (1 groove) (alternator on driver's side)

p/s pump-----------GM #3770509 (1 groove)

[Joe R.]

Re: Need pulley expert!!

Hi Joe L:

A quick follow up question:

Was the 3868892 PS pulley that is shown for the 1965 L79 with PS and A/C unique to the L79, or was it the same part number used on the 250 HP base engine? If it was unique to the L79 with PS and A/C, there must have been something different about it, such as an offset that would align with a deep-groove CS pulley set.

I have noticed that most PS pulleys for high performance engines are larger in diameter than the pulleys used on the base engines, presumably to reduce pump speed at high RPM. However, as I recall you have said earlier that the 3869992 is the same diameter as the 3770509. So, the diameter of the 3868892 would not automatically require a different part number from the 3770509.

[Joe L.]

Re: Need pulley expert!!

Joe-----

Hi Joe L:

Only the alternator pulley can be of either type.

Only the alternator pulley can be of either type UNLESS

1) the alternator pulley is a 2 groove type (not used for any Corvette applications), or,

2) the application is a 65-74 Corvette big block with a 2 groove power steering pump pulley

I think the answer to this mystery could be determined if someone could locate a sample of the 1965 PS pump pulley 3868892 and compare it to the more common 3770509. In order to line up with a deep-groove pulley set on the CS, the PS pump pulley MUST place the belt center line farther forward than the 3770509.

I have an NOS GM #3868892 power steering pump pulley and many NOS GM #3770509 pullies. I just haven't been "brave enough" so far to dig them out.

This assumes that all the PS pumps in the C2 years used the same shaft on the PS pump. Is that the case?

The power steering pump shaft changed for the 1967 model year. However, this was primarily to facilitate a change in the seal. Functionally and as a unit, 1963-66 pumps are interchangeable with 1967-74 pumps.

Regarding compatible pulley sets for a 1965 L79 with PS and A/C, I agree that one option that would physically fit would be the pulley set used for 1966-67 with the same options. This is a standard-groove pulley set, with the exception of the alternator pulley, which was a deep groove. Following are the part numbers for this pulley set. All of these parts are readily available in used and/or reproduction versions:


1966-67 L79 with PS and A/C:

balancer, rear-----GM #3850838 (2 groove)

balancer (front)---GM #3751232 (1 groove)

waterpump--------GM #3890419 (2 groove)

alternator----------GM #3846180 (1 groove) (alternator on driver's side)

p/s pump-----------GM #3770509 (1 groove)

This is the same pulley set I described above except for the waterpump pulley. However, the 3890419 you mention and the GM #3850680 that I mentioned are functionally the same. So, for all practical purposes, we're talking about functionally identical pulley sets.

[Joe L.]

Re: Need pulley expert!!

Hi Joe L:

A quick follow up question:

Was the 3868892 PS pulley that is shown for the 1965 L79 with PS and A/C unique to the L79, or was it the same part number used on the 250 HP base engine? If it was unique to the L79 with PS and A/C, there must have been something different about it, such as an offset that would align with a deep-groove CS pulley set.

I have noticed that most PS pulleys for high performance engines are larger in diameter than the pulleys used on the base engines, presumably to reduce pump speed at high RPM. However, as I recall you have said earlier that the 3869992 is the same diameter as the 3770509. So, the diameter of the 3868892 would not automatically require a different part number from the 3770509.

The GM #3868892 was specified only for 1965-66 L-79 with C-60 and, of course, N-40. However, I don't know if it was actually used for 1966, or not.

Also, the GM #3868892 and the GM #3770509 were not the same OD. The 3868892 has a specified OD of 5-23/32"; the 3770509 has a specified OD of 5-47/64". Whether the offsets were different, I'll have to check when I dig them out. I do know that both these pullies were stamped steel, "pancake" style.

The GM #3868892 was discontinued without supercession in February, 1976

[Joe R.]

Re: Need pulley expert!!

Hi Joe:

It would be great if you could dig out your 3868892 and compare it to a 3770509. The approximate 5.7 inch diameter of the 3868892 means that it probably *could* be offset farther forward to align with the front groove of a triple deep-groove crankshaft setup.

I have found that the 3873847 pump pulley used for the 1967 Camaro Z28 lines up correctly with a triple deep-groove crank setup (3858533 + 3916385), but the 6.2 inch diameter of the 3873847 pump pulley brings it too close to the C2 frame rail. A pump pulley with a 5.7 inch diameter could have the more forward offset without hitting the frame rail.

[Wolf S.]

Re: Need pulley expert!!

hi everyone,
here 's a follow up question to crank pulleys.

what crank pulley was used on the '70 lt=1?
i know that it is a deep 2 groove one but what was the gm part number?
#3858533?
#3929697?

[Joe L.]

Re: Need pulley expert!!

hi everyone,
here 's a follow up question to crank pulleys.

what crank pulley was used on the '70 lt=1?
i know that it is a deep 2 groove one but what was the gm part number?
#3858533?
#3929697?

Wolf----


It was the GM #3858533. The GM #3929697 is a 2 groove, cast iron pulley that was SUPPOSED to have been used for 70-72 ZR-1. However, so far, I don't think an original ZR-1 has been found which was actually equipped with this pulley.