'67 L79 alternator pulley

[William F.]

What's the correct outside diameter alternator pulley for my '67 factory air, no power steering L79?-Sorry, I haven't gotten '67 judging manual yet-had a '66 and that manual calls for a 3 3/8". Is this correct for '67also?Car now has the 3 5/8 pulley and I'm having charging problems.
Thanks in advance!

[Jack H.]

Re: '67 L79 alternator pulley

A 1/4" diameter difference for the pulley on your alternator will have virtually NO EFFECT on the charging system's integrity. It's primarily an issue of 'correct/original' during factory concourse judging.

Now, with an older generator based charging system, you 'might' see a modest difference in low end RPM + cut-through performance with a minor mis-match in drive pulley size...

[Scott S.]

Re: '67 L79 alternator pulley

What's the correct outside diameter alternator pulley for my '67 factory air, no power steering L79?-Sorry, I haven't gotten '67 judging manual yet-had a '66 and that manual calls for a 3 3/8". Is this correct for '67also?Car now has the 3 5/8 pulley and I'm having charging problems.
Thanks in advance!

The 1967 Judging Guide seems a little evasive when it comes to some of the possible engine and option combinations.

"Some one piece fan and pulley combinations with gray phosphate finish were used; 327/350hp with power steering and without air conditioning stamped 3875968AW; 327/300hp without air conditioning, or 327/350hp without power steering and without air conditioning stamped 3909815AJ and 327/300hp with air conditioning stamped 3909817 AW. The pulley and fan separate as two individual pieces for all other applications. The pulley is designed for a single V-Belt. It varies slightly in diameter and is offset based on the alternator application and additional options such as air conditioning. The pulley for two piece applications is either cadmium or zinc plated. The pulley and fan are held to the alternator with a hex-nut and lock washer with a cadmium or zinc finish. The fan is finished in either black phosphate or semi-gloss black paint." (1967 JG, 4th edition, p. 87)

I have only found four other people (besides you and me) in the archives who have an L79 with factory A/C and NO power steering. Your engine code suffix should be "HT" if it is like the other five examples (including mine) that I am aware of, although none of the books mention this particular engine/option combo.

There was a service replacement alternator on mine before we began the restoration. It had a black pulley that was 2 3/4". I think the correct diameter for the alternator pulley on the L79 with A/C and no PS is a deep-groove 3 3/8", but I am interested to hear from others on this subject.

[Mark G.]

Re: '67 L79 alternator pulley

William & Scott -



HT - L79 w/C60 - crank 3850838, and W/P 3890419
HT - L79 w/N40 - crank 3858533, and W/P 3770245

HD (K19) - L79 w/C60 - crank 3850838, W/P 3890419, and W/P add on 3883235 for A/I.R.
HD (K19) - L79 w/N40 - crank 3858533, W/P 3770245, and W/P add on 3765427 for A.I.R.

HP - L79 w/C60 - crank 8508383, crank add on 3751232 for N40, and W/P 3890419

KH (K19) - L79 w/C60 - crank 3850838, crank add on 3751232 for N40, W/P 3890419 and W/P add on 3883234 for A.I.R.




Mark

[Joe L.]

Re: '67 L79 alternator pulley

I can tell everyone this: Mark's pulley tables are the best and most accurate information ever put together by anyone, including GM, regarding 66-67 Corvette pullies. Period!

[Mark G.]

Re: '67 L79 alternator pulley

Joe -

Thank you for the kind words.
Reviewing the '65 pulley sets, I am begining to understand the cryptic L79 issues that carried over into '66.

Mark

[Scott S.]

Re: '67 L79 alternator pulley

William & Scott -

HT - L79 w/C60 - crank 3850838, and W/P 3890419
HT - L79 w/N40 - crank 3858533, and W/P 3770245

HD (K19) - L79 w/C60 - crank 3850838, W/P 3890419, and W/P add on 3883235 for A/I.R.
HD (K19) - L79 w/N40 - crank 3858533, W/P 3770245, and W/P add on 3765427 for A.I.R.

HP - L79 w/C60 - crank 8508383, crank add on 3751232 for N40, and W/P 3890419

KH (K19) - L79 w/C60 - crank 3850838, crank add on 3751232 for N40, W/P 3890419 and W/P add on 3883234 for A.I.R.

Mark

Hi Mark,

Thanks for the charts and the article. I found the part numbers you referenced in the AIM (for pulleys on a L79 with C60 but without N40), and I have a couple of questions.

1. It seems that every example of "HT" engine codes with C60-only that I have seen pictures of or read about has the deep-groove pulley set-up. Assuming the information to the contrary has always been in the AIM, why has there been any previous doubt as to the correct pulley configuration for L79 "HT" with C-60 only?

2. The power steering pulley is located close to the crankshaft (short belt), with the belt covering half the circumference of both pulleys (at the CS and the PS pulley). The A/C compressor pulley to the crankshaft requires a much longer belt and that belt is in contact with a smaller area of the respective pulleys, both of which would suggest that deep-groove pulleys for the L79 with C60-only equipped cars makes more sense than the L79 with N40-only equipped cars. Why would an L79 with power steering (N40 only) get a deep-groove pulley application, but not an L79 with air conditioning (C60 only)?

Regarding the pulleys that were on the '67 we are restoring (L79, "HT", C-60 only), it had the "3858533 BJ" crankshaft pulley and the water-pump pulley was "3848904 CS" (stamped on the outside of the pulley).

I would rather use deep-groove pulleys, but putting that aside, I am interested in understanding the subject better, and whether there is any functional downside to using deep-groove pulleys on the L79/C60-only option combo.

Thanks,

Scott

[Joe R.]

Re: '67 L79 alternator pulley

....It seems that every example of "HT" engine codes with C60-only that I have seen pictures of or read about has the deep-groove pulley set-up. Assuming the information to the contrary has always been in the AIM, why has there been any previous doubt as to the correct pulley configuration for L79 "HT" with C-60 only?

....Regarding the pulleys that were on the '67 we are restoring (L79, "HT", C-60 only), it had the "3858533 BJ" crankshaft pulley and the water-pump pulley was "3848904 CS" (stamped on the outside of the pulley).

I would rather use deep-groove pulleys, but putting that aside, I am interested in understanding the subject better, and whether there is any functional downside to using deep-groove pulleys on the L79/C60-only option combo.

Thanks,

Scott

Hi Scott:

Have you found other examples of 1967 L79 cars with A/C only having the deep-groove pulley set (3858533 crank and 3848904 water pump)? The 67 L79 with only A/C seems to be a rare factory configuration, so there are few known-originals to look at.

I have a theory that this configuration was equipped with the deep-groove pulley set, since it was easy to use and there was no incentive for GM to do otherwise.

Fitment problems only crop up in deep-groove configurations that have *both* A/C and PS, due to the triple crank pulley and the forward placement of the pump pulley. For this configuration, I think it has been well established that the L79 used the standard-groove pulley set. I believe this configuration had its own unique engine suffix, since the water pump needed a different hub spacing than the normal L79 water pump used with deep-groove pulleys (5-9/16 inches for standard-groove, 5-11/16 inches for deep groove).

Regarding the functionality of the deep-groove pulley set you have, I think it will be fine, and in fact, preferable to the standard-groove setup. The main benefit of deep-groove pulleys is their increased resistance to throwing belts at high rpm. There is no difference in tractive power with identical belts.

The ratio of crank-speed-to-water-pump-speed is about the same with both pulley combinations mentioned above. I believe that a 3.0 inch deep-groove alternator pulley was used in this configuration to keep the alternator speed ratio about the same as the standard-groove pulley set for A/C. In general GM spun the alternator faster on A/C cars, probably due to the increased electrical load.

[Mark G.]

[Joe R.]

Re: '67 L79 alternator pulley


Hi Mark:

I am away as well. I'll be home next week and can look at my files and my collection of pulleys.

I had forgotten about the idler pulley on the 65 configuration. That may affect some things. Regarding the alternator, though, I thought it was on the driver's side when the 65 SB was configured with A/C.

One thing I think is true, but have not verified, is that the when the alternator was placed on the pasenger side, it's location in the mounting bracket was slightly rearward compared to the location on the driver's side. That led to different alternator pulleys that had differing amounts of offset.

In my reserach, my overall impression is that the seemingly unnecessary number of different pulleys that GM used on the midyear small blocks is not as random as it first appears. I get the impression that GM's engineers were very concerned about optimizing the pulley ratios for each combination of accessories, and they were also concerned about maintaing proper alignment.

In other words, I think they "engineered the hell out of" the various configurations, resulting in a large number of different pulleys, and a lot of confusion for those of us trying to understand the correct factory pulley set for a given combination of options.

[Scott S.]

Re: '67 L79 alternator pulley

Hi Scott:

Have you found other examples of 1967 L79 cars with A/C only having the deep-groove pulley set (3858533 crank and 3848904 water pump)? The 67 L79 with only A/C seems to be a rare factory configuration, so there are few known-originals to look at.

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.

[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:

Thanks for the feedback. When I get home tomorrow I will take a photo of the 419 and the 8904 side-by-side with a measuring tape on the width of the grooves. This will provide an easy way for others to determine which pulley is on their car. I will be interested to learn the results.

[Scott S.]

Re: '67 L79 alternator pulley

Hi Scott:

Thanks for the feedback. When I get home tomorrow I will take a photo of the 419 and the 8904 side-by-side with a measuring tape on the width of the grooves. This will provide an easy way for others to determine which pulley is on their car. I will be interested to learn the results.

That sounds good, if you post pictures here, then I will include a link to this Thread in the PM I send. If you have a picture of Water Pump pulley 3770245 with dimensions, that might be helpful too, if it doesn't confuse things needlessly. The 1967 chart shows that WP pulley 3770245 was paired with deep-groove crankshaft pulley 3858533 for:

L79 standard
L79 N40-only
L79 K19-only
L79 K19 & N40 only

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.

Of note, according to the 1965 pulley chart, RPO L79 with C60-only used dual Deep-groove Crankshaft Pulley 3858533 with Water Pump pulley 3850979 and NO idler pulley. In the same year (1965), RPO L76 (327/365hp) with C60-only used the same deep-groove crankshaft pulley (3858533) and the same water pump pulley (3850979) as L79 with C60-only (no Idler pulley for either L79 or L76), but the L76 had the option to use Water Pump pulley 3848904 (and still NO idler pulley). So in 1965, RPO L79 and L76 (with C60-only) could both be configured with the same crankshaft and water pump pulleys (3858533 CR, 3850979 WP), the only difference was the alternator pulley (L76 alt. pulley = 3848023, L79 alt. pulley = 3875968 OR 3846180)

According to these charts, it would appear that my '67 has the pulley set from a 1965 L76 (with 1965 optional WP pulley 3848904). I don't know how to identify the alternator pulley that was on the car, but it looks like I need to find out. So far I have not been able to remove it from the alternator. It takes a 15/16ths wrench on the outer center-nut, and a 5/16ths Allen wrench in the inner center-nut/spindle. I have both wrenches, but I need to get a vise large enough to hold the alternator stationary. If I hold the center-nut/spindle stationary with the Allen wrench, will the outer 15/16ths center-nut unscrew normally (i.e., counter-clockwise), or does it have reverse threads for some reason?


According to Mark's pulley charts posted earlier and the 1966 pulley chart in the Spring 2009 Corvette Restorer (p. 16-19), the L79 with C60-only should have the following pulley sets for the years 1965-1967:

1965 (L79, C60-only, chart attached in post 4 above, picture below)
Crankshaft pulley: 3858533
Water Pump pulley: 3850979 [Note: 327/365 (L76) with C60-only shows same WP pulley as L79 with C60-only (3850979), but with option for 3848904. It is the only mention of 3848904 in the entire 1965 chart, not mentioned at all in the 1966 & 1967 charts]
Alternator pulley: 3875968 or 3846180


1966 (L79, C60-only, chart in Spring 2009 Restorer, picture below)
Crankshaft pulley: 3850838
Water Pump pulley: 3890419 [Note: 3848904 is not listed on the chart as a possible choice for any 1966 small block engine]
Alternator pulley: 3846180


1967 (L79, C60-only, chart attached in post 6 above, picture below, identical to 1966 chart with regard to L79 with C60-only)
Crankshaft pulley: 3850838
Water Pump pulley: 3890419 [Note: 3848904 is not listed on the chart as a possible choice for any 1967 small block engine]
Alternator pulley: 3846180



Attached:
1965 Pulley Chart (L79 C60-only highlighted)
1966 Pulley Chart (L79 C60-only highlighted)
1967 Pulley Chart (L79 C60-only highlighted)

[Scott S.]

Re: '67 L79 alternator pulley

I checked the C60 section of the 1967 AIM and noted the following:

UPC C60, Sheet C1
Item 5 lists a special A6 compressor mounting bolt (122145) called out for RPO L79

Item 19 lists a special washer (3706737) called out for RPO L79 only. Quantity = 2, one for each side of the A6 compressor shim (Item 18, p/n 3852876) located at the back of the A6 compressor (toward the driver compartment)

Revision Record at bottom of Sheet C1 says:
(8-9-66) "122145 RPO L79 Added"
(8-24-66) "RPO L79 Added"
(11-17-66) "327 Engine Added"



UPC C60, Sheet C2
Item 1 calls out 3890419 Pulley W/Pump & Fan, no optional pulley for RPO L79 listed.

Item 4 calls out Pulley - Generator 3846180 specifically for RPO L79 (i.e., alternator pulley)

Item 10 calls out 3850838 Pulley - Crankshaft, no optional pulley called out for RPO L79 in the C60 option section.

Revision Record at bottom of Sheet C2 says:
(7-26-66) "Was 3875968 Pulley" [Note: according to the 1966 Chart in Corvette Restorer, 3875968 was base engine alternator pulley with C60 in 1966]
(11-17-66) "327 Engine Added"



UPC C60, Sheet D3
Item 11 calls out 427559 Bolt specifically for RPO L79, this bolt goes through the lower hole on Item 12 "CLIP", p/n 3853968

Revision Record at bottom of Sheet D3 says:
(partial date legible, ?-?-66) "427559 RPO L79 Added"

I did not see any further special call outs or revisions related to RPO L79 throughout the remainder of UPC C60 (Sheet C1 through Sheet E12).


Attached:
UPC C60, Sheet C1
UPC C60, Sheet C2
UPC C60, Sheet D3

[Scott S.]

Re: '67 L79 alternator pulley

I checked the L79 section of the 1967 AIM and noted the following:


UPC L79, Sheet A1
Item 3 calls out 3858533 Pulley (note: Crankshaft). No mention of changes to any other pulleys.

Revision Record
Hose Dwg. & Dim Added



UPC L79, Sheet A2 says the following:

NOTE The following Components are not illustrated in this R.P.O. See parts list or bill of materials for part numbers.

UPC 6 Engine
ENGINE

6 Engine Assembly
6G-4 Oil Level Indicator
6H Engine Ventilating System
6K-1 Fan and Drive
6K-2 Water Pump and Drive
6L Inlet & Exhaust Manifolds & Heat Controls
6M-1 Carburetor
6M-4 Fuel & Vacuum Pump
6Y-1 Generator and Regulator
6Y-3 Distributor

[Note: I don't know how to look them up, but it seems that "6K-1 Fan and Drive", "6K-2 Water Pump and Drive" and "6Y-1 Generator and Regulator" should be checked]


UPC 8
FUEL & EXHAUST
8B Fuel Tank Mtg. & Fuel Pipes

UPC 12
ELECTRICAL
12J Instrument Carrier Panel &/or Instruments

UPC 14
BUMPERS & MISC.
14W Final Assembly Paint & Similar Materials

Revision Record
No revisions listed, end of UPC L79 section (only two pages long)


Attached:
UPC L79, Sheet A1
UPC L79, Sheet A2