'67 L79 alternator pulley

[Joe R.]

Re: '67 L79 alternator pulley

Hi Scott:

I think we need to keep sight of what questions we are trying to answer, because most of the 65-67 SB pulley configurations are pretty well documented and well understood. The configurations where there is still some uncertainty are, I think, just the following ones:

1) L79 with A/C and no PS (for years 1965, 66, and 67)
2) L79 with A/C and PS (for 1965)

I'll look at my files and my pulley collection when I get home and will post some additional information. In the meantime, the following points may be helpful for framing the investigation:

* I believe that whenever GM put A/C on a midyear smallblock, they changed the ratio of the crank-to-waterpump speed to make the waterpump spin faster (probably to increase fan speed at idle). For the deep-groove pulleys, this was typically done by keeping the 533 crank pulley but making the WP pulley smaller in diameter. An example would be changing the WP pulley from the non-A/C 3770245 to the A/C 3848904. For the standard-groove puley set, the crank pulley was made larger and the WP pulley was made smaller. For example, the 3850838 crank pulley and 3890419 WP pulley are the standard-groove pulleys used on A/C small blocks in 66-67.

* Providing just A/C and no PS introduces no special problems for fitting the pulleys, so I would expect that when an L79 was equipped with just A/C, the pulley set that GM used was probably deep-groove for the L79 and standard-groove for the 300 HP. However, this has not been completely confirmed.

* Where things get complicated is when both A/C and PS are installed. This requires using a triple pulley on the crank and moving the PS pump pulley to the forward-most groove. A standard-groove pulley set fits okay, but it is very tight to get a deep groove pulley set in there, since the deep-groove pulley set stackup is 3/8 inch thicker and frame rail clearance in front of the PS pump is marginal.

* As I understand it, 1965 was the first year that Corvettes could get PS, so this was the first year that both A/C and PS could be installed on the same car. I have heard that PS was introduced mid-way during the model year. So, the GM documentation in both the AIM and the parts books for this combination is sparse and conflicting. It can not be taken as gospel.

* I believe there is general agreement that for 1966-67, the standard-groove pulley set was used when the L79 was equipped with both A/C and PS. It is not yet clear what type of pulleys were used in 1965 on the L79 with both A/C and PS.


I think we are pretty close to sorting out these last remaining pulley mysteries. Hopefully we will reach a consensus through the discussion in this current thread.

[Mark G.]

Re: '67 L79 alternator pulley

Joe -

1) L79 with A/C and no PS (for years 1965, 66, and 67)
2) L79 with A/C and PS (for 1965)

* I believe that whenever GM put A/C on a midyear small block, they changed the ratio of the crank-to-water pump speed to make the water pump spin faster (probably to increase fan speed at idle). For the deep-groove pulleys, this was typically done by keeping the 533 crank pulley but making the WP pulley smaller in diameter. An example would be changing the WP pulley from the non-A/C 3770245 to the A/C 3848904.

For the standard-groove pulley set, the crank pulley was made larger and the WP pulley was made smaller. For example, the 3850838 crank pulley and 3890419 WP pulley are the standard-groove pulleys used on A/C small blocks in 66-67.

* Providing just A/C and no PS introduces no special problems for fitting the pulleys, so I would expect that when an L79 was equipped with just A/C, the pulley set that GM used was probably deep-groove for the L79 and standard-groove for the 300 HP. However, this has not been completely confirmed. The A/C change started at VIN 6S103533.

* Where things get complicated is when both A/C and PS are installed. This requires using a triple pulley on the crank and moving the PS pump pulley to the forward-most groove. A standard-groove pulley set fits okay, but it is very tight to get a deep groove pulley set in there, since the deep-groove pulley set stack up is 3/8 inch thicker and frame rail clearance in front of the PS pump is marginal.

* As I understand it, 1965 was the first year that Special High Performance Corvettes could get PS, so this was the first year that both A/C and PS could be installed on the same car. I have heard that PS was introduced mid-way during the model year. So, the GM documentation in both the AIM and the parts books for this combination is sparse and conflicting. It cannot be taken as gospel.

* I believe there is general agreement that for 1966-67, the standard-groove pulley set was used when the L79 was equipped with both A/C and PS. It is not yet clear what type of pulleys were used in 1965 on the L79 with both A/C and PS.

I think we are pretty close to sorting out these last remaining pulley mysteries. Hopefully we will reach a consensus through the discussion in this current thread.

Joe, I tried to answer some of your questions. I think I have the configurations complete. Changed the '66 L79 N40 page, hope it's clearer.

Mark

[Scott S.]

Re: '67 L79 alternator pulley

Joe -

1) L79 with A/C and no PS (for years 1965, 66, and 67)
2) L79 with A/C and PS (for 1965)

* I believe that whenever GM put A/C on a midyear small block, they changed the ratio of the crank-to-water pump speed to make the water pump spin faster (probably to increase fan speed at idle). For the deep-groove pulleys, this was typically done by keeping the 533 crank pulley but making the WP pulley smaller in diameter. An example would be changing the WP pulley from the non-A/C 3770245 to the A/C 3848904.

Hi Mark,

When you said "", did you mean '533, as in 3858533?

* I believe there is general agreement that for 1966-67, the standard-groove pulley set was used when the L79 was equipped with both A/C and PS. It is not yet clear what type of pulleys were used in 1965 on the L79 with both A/C and PS.

I'm lost (again!)

Under RPO L79 in the 1965 chart, I see where you're getting '533 (CS), 3770245 (WP) and 3834720 (PS), all in the "N40-only" row. Where does '904 (i.e., WP pulley 3848904) come into play in any L79 application (I only see 3848904 noted as an optional WP pulley under L76 with C60-only)?

On your 1965 pulley chart (post 4 pdf, and post 13 jpeg), it shows that Water Pump Pulley 3848904 was an optional water pump pulley referenced only once (below the chart, with a '2' superscript). The only matching "2 superscript" I see in the 1965 chart is for Water Pump Pulley 3850979 under RPO L76 with C60 -- the "2 superscript" showing that WP pulley 3848904 was an optional substitute for WP pulley 3850979 in the L76 with C60 application.

Should the 1965 chart show that WP Pulley 3848904 is ALSO an optional/applicable pulley for RPO L79 with C60-only, or is that a "given" unless otherwise specified, because it was listed previously with a "superscript" for RPO L76 with C60-only?

Thank you, sorry if I'm making this more complicated than it ought to be,

Scott

[Scott S.]

Re: '67 L79 alternator pulley

I was able to remove the old alternator pulley with the help of a 75lb. vice to hold it steady. Good exercise lugging that hunk of metal home, it's probably 100+ years old, but it hasn't lost any weight

For reference, the car is a '67 L79 with "HT" engine suffix, has C60 but no N40. Pulleys on the car were:
3858533 BJ (crankshaft)
3848904 CS (water pump pulley)

Can anyone identify this alternator pulley by the markings on the back side, or the measurements? Or rule it out as being incorrect for the period/era?

The alternator was a service replacement, receipt dated 11-9-78 ($40.90). I suspect that whatever pulley was on the car was transferred to the new alternator, but I don't know. There was an alternator belt ($6.95) and labor ($12.50) charged on the same receipt, from Ludlow Automotive Service in Dayton, Ohio.


Markings on the back of the pulley:
"P"
"C9AF 10A352-A3"


Measurements:
Diameter: looks like 2 3/4" by tape measure, digital caliper says 2 103/128"
Width/cross-section (outer edge to outer edge): looks like 13/16" by tape measure, digital caliper says 103/128"

[Mark G.]

Re: '67 L79 alternator pulley




Attached is the 3846180 alt. pulley layout.

Mark

[Joe R.]

Re: '67 L79 alternator pulley

I was able to remove the old alternator pulley with the help of a 75lb. vice to hold it steady. Good exercise lugging that hunk of metal home, it's probably 100+ years old, but it hasn't lost any weight

For reference, the car is a '67 L79 with "HT" engine suffix, has C60 but no N40. Pulleys on the car were:
3858533 BJ (crankshaft)
3848904 CS (water pump pulley)

Can anyone identify this alternator pulley by the markings on the back side, or the measurements? Or rule it out as being incorrect for the period/era?

Measurements:
Diameter: looks like 2 3/4" by tape measure, digital caliper says 2 103/128"
Width/cross-section (outer edge to outer edge): looks like 13/16" by tape measure, digital caliper says 103/128"

Hi Scott:

That pulley doesn't look like what I would expect for a 67 Corvette, but it is functionally quite close. According to my notes, the 67 L79 with A/C used a 3846180 alternator pulley. This was a deep-groove pulley, machined out of a solid piece of steel, with an outside diameter of about 3 inches. Paragon sells a reproduction of it.

[Scott S.]

Re: '67 L79 alternator pulley

Hi Scott:

That pulley doesn't look like what I would expect for a 67 Corvette, but it is functionally quite close. According to my notes, the 67 L79 with A/C used a 3846180 alternator pulley. This was a deep-groove pulley, machined out of a solid piece of steel, with an outside diameter of about 3 inches. Paragon sells a reproduction of it.

Hi Joe,

This is the alternator pulley on the restored 1100750, 61 Amp, dated 6 M 8. Paragon lists their 3846180 alternator pulley at 3" O.D., the one I have is a little over 3".

[Joe R.]

Re: '67 L79 alternator pulley

Hi Joe,

This is the alternator pulley on the restored 1100750, 61 Amp, dated 6 M 8. Paragon lists their 3846180 alternator pulley at 3" O.D., the one I have is a little over 3".

Hi Scott:

That pulley is very similar, but not identical to, the reproduction that Paragon sells. I don't know which version is closer to the original.

BTW, it looks like your restored alternator may be painted. This may be just the way it appears in the photos. In any event, the originals were natural cast aluminum.

[Scott S.]

Re: '67 L79 alternator pulley

Hi Scott:

That pulley is very similar, but not identical to, the reproduction that Paragon sells. I don't know which version is closer to the original.

BTW, it looks like your restored alternator may be painted. This may be just the way it appears in the photos. In any event, the originals were natural cast aluminum.

Hopefully that's just the way it looks in the photos, I'll check it for paint tomorrow to find out for sure.

[Joe R.]

Re: '67 L79 alternator pulley

[quote=Scott Smith (50839);502065]

I checked the available pulley charts (1965, 1966, 1967) and the 1967 AIM (I do not have the AIM for '65 or '66), and did not find Water Pump pulley 3848904 listed anywhere except on the 1965 chart, as an option to Water Pump pulley 3850979 with RPO L76 (327/365) with C60-only.


Hi Scott:

The AIM and the parts books are unclear on the use of the 3848904. For more discussion on this topic, see the following thread from May, 2008:

https://www.forums.ncrs.org/showthre...stion&uid=3438

[Joe R.]

Re: '67 L79 alternator pulley

Hi Joe,

Besides myself and William (who started this Thread), I have found four other people in the TDB archives who have the 1967 L79 with C60-only and the "HT" engine suffix, and one person who was asking questions here before bidding on one (located in Phoenix) that was on eBay, June 9th, 2004. I will send a PM to each of them to inquire about their pulley set-up, and if they have changed it, whether they are in a position to know what the original configuration was (e.g., original owner).

The previous owner (1972-1976) of the car I'm restoring may or may not recall ever changing the pulley set-up, but even if he's sure he didn't, he was not the original owner, so it might have been changed before he bought it. If he did change the pulleys, he would probably remember doing it, so I'll add that to the list of things I want to ask about next time I talk with him. That leaves William's car and the four others, hopefully at least one of them is an original owner or otherwise documented somehow as having the original pulley set.

Hi Scott:

Attached is a close-up photo of a deep-groove pulley (3770245) and a standard-groove pulley (3890419) next to each other with a scale between them.

This suggests a simple way to determine whether an installed water pump pulley is deep-groove or standard-groove, by simply measuring how wide the dual grooves are at the edge. Using a pair of calipers, the measured dimensions are 1.57" for the deep-groove and 1.24" for the standard-groove. Note that these two dimensions will be pretty much the same for any pulley of the C2 era, regardless of its diameter or specific part number.

For people who want to determine whether an installed deep-groove water pump pulley is a 3770245 (7.1 inch diameter) or a 3848904 (5.8 inch diameter), it may be easier to measure the circumference than the diameter using a tape measure. The circumference of the 3770245 is about 22.3 inches, while the circumference of the 3848904 is about 18.2 inches.

Regarding your reference to having an HT code on your 1967 block, that makes sense to me if the 3848904 water pump pulley was used for that configuration. If deep-groove pulleys were used for the L79 when equipped with only A/C, there would be no need for a special engine code. As far as Flint was concerned, there would be absolutely no difference between an L79 engine that St. Louis would configure for any of the following:

1) L79 without A/C, PS, or AIR
2) L79 with A/C only
3) L79 with PS only

Since Flint installed the water pump and St. Louis installed the pulleys, there would be no need for Flint to use a different engine code for any of the above configurations.

The situation changed when a 1967 L79 was equipped with both A/C and PS. In this case St. Louis installed the standard-groove pulley set, and the water pump hub spacing needed to be 5-9/16 inches (for standard-groove pulleys) instead of 5-11/16 inches (for deep-groove pulleys). In this case, the water pump installed at Flint was different, and a different engine code was needed to distinguish that configuration.

My theory is that the HP code was used for this one configuration only, when the L79 was configured with A/C *and* PS.

[Joe R.]

Re: '67 L79 alternator pulley

Joe, I tried to answer some of your questions. I think I have the configurations complete. Changed the '66 L79 N40 page, hope it's clearer.

Mark

Hi Mark:

Thanks, I was uncertain about the details of the transition to having A/C and PS together in 1965. I'm still not sure whether we have a consenus on all five configurations I listed previously. Here is where I think we are:


1965 L79 with A/C and PS:

The drawing you posted of the 3827843 add-on pulley indicates that it would fit fine in the 3858533. However, I can not seem to determine from the drawings of the 3827843 pulley and its companion 3868892 pump pulley whether they are standard-groove or deep-groove. Some key dimensions appear to be missing. I would love to see samples of one or both pulleys if anyone has them.


1965 L79 with A/C only:

Your chart indicates that the deep-groove 3858533 crank pulley was used with the 3850979 WP pulley. From the drawing, this WP pulley appears to be a deep-groove pulley that is very similar to the 3848904 WP pulley. This would fit fine and would provide the type of pulley ratios GM typically used with A/C cars, so this configuration seems reasonable to me. Perhaps we can take this configuration off the list of uncertainties.



1966-67 L79 with A/C only:

From what I have seen of the 66-67 configurations, they were mostly identical, so I will lump these two together. Your charts show the standard-groove 3850838 crank pulley and 3890419 WP pulley for this configuration. There are some indications that the actual configuration was the deep-groove 3858533 crank pulley and 3848904 WP pulley. I think this question remain unresolved.


Summary:

I think we are closing in on a consensus, and some of the questions I had previously have been answered. The two questions that remain unclear to me are:

1) Whether the add-on 3827843 PS pulley and 3868892 PS pump pulley used in 1965 for the L79 with A/C and PS were deep-groove or standard-groove. Note that under different part numbers, versions of both styles exist that are compatible with the deep-groove 3858533 crank pulley.

2) Whether the 1966 and/or 1967 L79 with A/C only used standard-groove pulleys (3850838 and 3890419) or deep-groove pulleys (3858533 and 3848904).


The above two questions are the only areas where I remain uncertain about the 65-67 A/C pulley configurations.

[Wayne M.]

Re: '67 L79 alternator pulley

..............1965 L79 with A/C only:
Your chart indicates that the deep-groove 3858533 crank pulley was used with the 3850979 WP pulley. From the drawing, this WP pulley appears to be a deep-groove pulley that is very similar to the 3848904 WP pulley. This would fit fine and would provide the type of pulley ratios GM typically used with A/C cars, so this configuration seems reasonable to me. Perhaps we can take this configuration off the list of uncertainties.

1966-67 L79 with A/C only:
From what I have seen of the 66-67 configurations, they were mostly identical, so I will lump these two together. Your charts show the standard-groove 3850838 crank pulley and 3890419 WP pulley for this configuration. There are some indications that the actual configuration was the deep-groove 3858533 crank pulley and 3848904 WP pulley. I think this question remain unresolved. ........

.....2) Whether the 1966 and/or 1967 L79 with A/C only used standard-groove pulleys (3850838 and 3890419) or deep-groove pulleys (3858533 and 3848904).


The above two questions are the only areas where I remain uncertain about the 65-67 A/C pulley configurations.

FWIW, for the water pump pulley, in SERVICE, [P&A30], The July '65, Oct '65 and Oct'66 versions of the catalogs, the "904" is called out for '64-65 as C.A.C. w/Sp. H/Per., and (in '66) '64-5, '66 C.A.C. 327 w/Sp. H/Per., (427) (exc. P.S.), and (in '67) they dropped reference to 427 -- just '66-7 C.A.C. w/Sp. H/Per. (327) (exc. P.S.)

This "904" is described as diameter 6_9/32nds". No mention of the '65 AIM # 3850979 pulley in service (UPC C60 Sht. C2, for L76 -- which is presumably for L79 as well). My no P/S early '65 L76 C60 car has the "904"; I've never seen a "979".

Good work, guys, on this complex subject.

[Scott S.]

Re: '67 L79 alternator pulley

Hi Scott:

Attached is a close-up photo of a deep-groove pulley (3770245) and a standard-groove pulley (3890419) next to each other with a scale between them.

This suggests a simple way to determine whether an installed water pump pulley is deep-groove or standard-groove, by simply measuring how wide the dual grooves are at the edge. Using a pair of calipers, the measured dimensions are 1.57" for the deep-groove and 1.24" for the standard-groove. Note that these two dimensions will be pretty much the same for any pulley of the C2 era, regardless of its diameter or specific part number.

Thanks Joe, I'll send a PM to the other members who have a 1967 L79 with "HT" engine suffix, C60-only (no N40) and hopefully we will get some helpful data.

[Joe L.]

Re: '67 L79 alternator pulley

FWIW, for the water pump pulley, in SERVICE, [P&A30], The July '65, Oct '65 and Oct'66 versions of the catalogs, the "904" is called out for '64-65 as C.A.C. w/Sp. H/Per., and (in '66) '64-5, '66 C.A.C. 327 w/Sp. H/Per., (427) (exc. P.S.), and (in '67) they dropped reference to 427 -- just '66-7 C.A.C. w/Sp. H/Per. (327) (exc. P.S.)

This "904" is described as diameter 6_9/32nds". No mention of the '65 AIM # 3850979 pulley in service (UPC C60 Sht. C2, for L76 -- which is presumably for L79 as well). My no P/S early '65 L76 C60 car has the "904"; I've never seen a "979".

Good work, guys, on this complex subject.

Wayne------


IF GM #3850979 was ever a released part number, it was PRODUCTION-only. That part number was never available in SERVICE.