correct crankshaft pulleys

[Joseph F.]

I have a 350 hp 327 with air and power stearing in a 1965 vett.I am restoring the car and I need to know the correct crankshaft pulley and the correct water pump pulley.

[Joe L.]

Re: correct crankshaft pulleys

I have a 350 hp 327 with air and power stearing in a 1965 vett.I am restoring the car and I need to know the correct crankshaft pulley and the correct water pump pulley.

Joseph----


If the car is a very early car, it MAY have used crank pulley GM #3766987. Otherwise, it used pulley GM #3858533 which remains available from GM to this day (although finish and nuances may differ from original).

As far as the waterpump pulley is concerned, I believe that GM #3770245 was used. This pulley is no longer available from GM but is reproduced.

[Joseph F.]

Re: correct crankshaft pulleys

Thanks for letting me know
Joe Frejek

[Mark G.]

Re: correct crankshaft pulleys

Joseph & Joe

Crank #3827843 or #3850838; Add on #3751232 to drive the P/S; W/P #3850680 or #3890419; P/S #3868892 (rare) or #3770509; and Alt. #3875968. Three belts Alt. #3847710; A/C #3849085; and P/S #3874424.

[Joe L.]

Re: correct crankshaft pulleys

Joseph & Joe
Please consider the possibility that ’65 L79’s with C60 and N40 use the L75 300hp pulley configuration. This is because N40 could not be added to an L79 with C60 if it used deep groove pulleys. The ‘232 add on pulley will not fit into a deep groove crank pulley. So that leaves only two grooves to drive the alternator, A/C, & P/S. The “HU” and “HW” engine codes designate C60 so N40 was added or not when the option became available. Sometimes the dealer added power steering to the cars on the lot.
Crank #3827843 or #3850838; Add on #3751232 to drive the P/S; W/P #3850680 or #3890419; P/S #3868892 (rare) or #3770509; and Alt. #3875968. Three belts Alt. #3847710; A/C #3849085; and P/S #3874424.

Mark-----


I do think that 1965 with L-79, C-60, and N-40 did generally use the L-75 configuration.

I think that the crank pulley was GM #3827843, as you mention. As far as the waterpump pulley, I think it was GM #3848904. I don't think that 3850680 was used for 1965 for this application. I'm virtually certain 3890419 was not used because I don't think it existed in 1965.

By the way, take a look at the thread titled "1969 or 1979 block" and please comment on my "hypothesis" regarding pattern numbers.

Also, I missed the fact that the car had C-60 when I posted my original response. That was a serious error on my part. I need to read things more carefully. In fact, I read it THREE TIMES and I still missed it.

[Joe R.]

Re: correct crankshaft pulleys

I have been researching this issue specifically for 1967 small blocks, so I'm not sure if the situation was the same for 1965. I suspect it was, though.

The reason I have been looking into this so closely is that I have a little side project to retrofit a deep-groove pulley set on my 1967 327/300 with A/C and PS. At first I thought I could simply substitute the pulley set used for the L79 with A/C and PS, but it appears that for 1967, both the base engine and the L79 used the same standard-groove pulley set when configured with A/C *and* power steering.

Initially I found this odd, since most other L79 configurations used the high performance deep-groove pulleys of 3858533 on the crank and 3770245 on the water pump.

So, following is a short discussion with perhaps more detail than anyone really needs. It's mildly interesting, though, because it may provide some insight into what GM's engineers were thinking when they specified the pulley set for the L79 with A/C and PS.

I think the engineers found that the available deep-groove pulley sets simply would not fit on a Corvette that has A/C *and* power steering. Each groove of the deep-groove pulley set is 1/8 inch wider than the standard-groove pulleys. With A/C and PS, the PS groove is the third, most forward groove. So, a deep-groove pulley set would place the PS groove 3/8 inch more forward (toward the radiator) than the standard-groove pulley set.

It turns out that this works fine for the crank pulley, provided that you use a deeper add-on than the standard-groove 3751232 add-on. The 3751232 does not fit into the deeper 3858533 crank pulley. However, the 3916385 add-on used on 1967 Camaros works fine.

For Corvettes, the problem is that the pulley on the power steering pump must also move 3/8 inch farther forward to use a deep groove pulley set on a car with A/C and PS. This brings it into very close proximity to the frame rail kick up in front of the PS pump.

The situation might be okay if GM had made a PS pulley that was the same 5.7 inch diameter as the standard-groove 3770509. I think there would be enough room to move a 5.7 inch diameter pulley 3/8 inch forward and still avoid the frame rail over the full range of PS pump positions.

Unfortunately, the high performance deep-groove pulley sets used on other configurations typically had a larger diameter PS pulley, to slow down the PS pump at high engine RPMs.

For example, the 3834720 used for non-A/C L79 engines was 6.1 inches in diameter. For this application it fit okay because the PS belt was in the second groove. The 1967 Camaro Z28 with PS did use the third groove for PS, with pump pulley number 3873847 that was 6.2 inches in diameter. Apparently there was more room in the Camaro than the Corvette.

So, in 1967, GM had all the parts in their parts bin to make a triple deep-groove pulley set for the L79 with A/C and PS:

Water pump: 3770245 (or the smaller diameter 3995641), 2 grooves
Crank: 3858533, 2-groove
PS crank add-on: 3916385
PS pump: 3873847

The reason that I think they did not use this combination on the Corvette is that the 3873847 PS pump pulley would be too close to the frame rail to guarantee no interference over normal production tolerances.

To my knowledge, there is no standard GM PS pump pulley that provides the necessary 3/8 inch forward offset relative to the standard-groove 3770509, *and* has a diameter of 5.7 inches or less. I have been searching for such a pulley and have recently expanded my search to include other GM cars that used the same PS pulley. So, far, no luck.

So, if anyone knows of such a pulley, I would love to know about it.

To my knowledge, though, GM did not use a deep-groove pulley set on C2 Corvettes that were equipped with both A/C and PS. If they had, my little retrofit side project would be much easier than it has turned out to be.

[Joe R.]

Re: correct crankshaft pulleys - addendum

In my earlier post I referenced a set of deep-groove pulley part numbers that hypothetically, GM could have considered for use on the 1967 L79 Corvette with A/C and PS. In reviewing my post, I see that I used two part numbers that are a functionally equivalent successors to the corresponding parts that would have been in the GM parts bin in 1967:

Water pump pulley 3995641 replaced 3848904
PS crank add-on 3916385 replaced 3765947

I'm not sure of the exact dates of these two transitions, but the earlier versions all pre-date 1967.

In my project documentation I have been using the newer part numbers because they are still available from GM or from reproduction vendors.

[Joe L.]

Re: correct crankshaft pulleys

Thanks for letting me know
Joe Frejek

Joe----


I'm sorry. Please not that I erred when I posted my first response to your question. Somehow, I missed the fact that the car had C-60 (air conditioning). That changes everything. Note my follow-up responses to Mark Gorney's post.

My REVISED list of pullies for your application:

crank-----GM #3827843

water pump----GM #3848904

power steering pump-----GM #3868892

[Joe L.]

Re: correct crankshaft pulleys - addendum

In my earlier post I referenced a set of deep-groove pulley part numbers that hypothetically, GM could have considered for use on the 1967 L79 Corvette with A/C and PS. In reviewing my post, I see that I used two part numbers that are a functionally equivalent successors to the corresponding parts that would have been in the GM parts bin in 1967:

Water pump pulley 3995641 replaced 3848904
PS crank add-on 3916385 replaced 3765947

I'm not sure of the exact dates of these two transitions, but the earlier versions all pre-date 1967.

In my project documentation I have been using the newer part numbers because they are still available from GM or from reproduction vendors.

Joe-----


There was another p/s pump pulley. It was a Corvette-only piece and of GM #3868892. It was used for 1965-66 Corvettes with L-79, C-60, and N-40. It was 5-23/32" OD. In fact, I have an NOS example of this pulley [not for sale] but I really can't get at it right now. I do recall, for sure, that it's a stamped steel pulley, configured more-or-less like the 3770509.

I can't find any indication it was used for 1967 or later, though. It was GM-discontinued without supercession in October, 1976. It is available in reproduction, though.

[Joe R.]

Re: correct crankshaft pulleys - addendum

Joe-----


There was another p/s pump pulley. It was a Corvette-only piece and of GM #3868892. It was used for 1965-66 Corvettes with L-79, C-60, and N-40. It was 5-23/32" OD. In fact, I have an NOS example of this pulley [not for sale] but I really can't get at it right now. I do recall, for sure, that it's a stamped steel pulley, configured more-or-less like the 3770509.

I can't find any indication it was used for 1967 or later, though. It was GM-discontinued without supercession in October, 1976. It is available in reproduction, though.

Hi Joe:

Thanks for the tip on the 3868892 pulley. Do you have any way of determining what crankshaft set this pulley was used with? If it was used with the 3850838 dual and the 3751232 add-on, the offset is probably identical to the 3770509.

On the other hand, if the 3868892 was used with the 3858533 dual crank pulley and some other add-on pulley (possibly the 3765947 or the 3916385, which I believe are both functionally equivalent and are designed to fit inside the 3858533), then the offset of the 3868892 would have to be 3/8 inch farther forward than the 3770509. That would make it perfect for what I am trying to do.

Any help you can provide would be most appreciated.

[Joe L.]

Re: correct crankshaft pulleys - addendum

Hi Joe:

Thanks for the tip on the 3868892 pulley. Do you have any way of determining what crankshaft set this pulley was used with? If it was used with the 3850838 dual and the 3751232 add-on, the offset is probably identical to the 3770509.

On the other hand, if the 3868892 was used with the 3858533 dual crank pulley and some other add-on pulley (possibly the 3765947 or the 3916385, which I believe are both functionally equivalent and are designed to fit inside the 3858533), then the offset of the 3868892 would have to be 3/8 inch farther forward than the 3770509. That would make it perfect for what I am trying to do.

Any help you can provide would be most appreciated.

Joe----


It was used with the GM #3827843 crank pulley + (as far as I can tell) the GM #3751232 add-on crank pulley. I can find nothing to indicate the 3765947 and 3916385 were ever used on Corvettes.

[Joe R.]

Re: correct crankshaft pulleys - addendum

Joe----


It was used with the GM #3827843 crank pulley + (as far as I can tell) the GM #3751232 add-on crank pulley. I can find nothing to indicate the 3765947 and 3916385 were ever used on Corvettes.

Hi Joe:

I agree that the 3765947 and 3916385 add-on PS pulleys do not appear to have been used on Corvettes, although these are the only parts I have found that fit correctly inside the deep-groove dual pulley 3858533. The 3751232 add-on is not deep enough to seat properly inside the 3858533.

So, my working theory is that the deep-groove pulley set was not used on Corvettes with A/C and PS. Since a deep-groove triple stackup would push the PS pump pulley 3/8 inch forward relative to the standard-groove triple stackup, I think GM realized that the PS pump pulley could hit the frame rail kick up in front of the PS pump.

In any event, I will try to track down an example of the 3868892 PS pump pulley that you reference. My guess is that the offset will turn out to be the same as the 3770509, but it's worth checking.

Thanks again for your help with this.

[Joseph F.]

Re: correct crankshaft pulleys

Thanks Gentleman for all your help.I believe the correct setup is from a 300hp car with air,other wise useing deep groove pulleys will cause a nightmare with the power steering.
Joe Frejek