'67 L79 alternator pulley

[Mark G.]

Re: '67 L79 alternator pulley

This is what I understand from the drawings and dimensional stack up for the L79 engines.

1965
Deep groove pulleys were used just like the L76
The steel P/S crank add on and pump pulleys are not deep groove, the cast 3834720 is


1966 - 67


HT- L79 with no driven options
HT - L79 w/C60 - crank 3850838, and W/P 3890419
HT - L79 w/N40 - crank 3858533, and W/P 3770245, P/S 3834720

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., P/S 3834720

HP - L79 w/C60 - crank 8508838, crank add on 3751232 for N40, W/P 3890419, and P/S 3770509

KH (K19) - L79 w/C60 - crank 3850838, crank add on 3751232 for N40, W/P 3890419, W/P add on 3883234 for A.I.R. and P/S 3770509

[Joe R.]

Re: '67 L79 alternator pulley

This is what I understand from the drawings and dimensional stack up for the L79 engines.

1965
Deep groove pulleys were used just like the L76
The steel P/S crank add on and pump pulleys are not deep groove, the cast 3834720 is


1966 - 67


HT- L79 with no driven options
HT - L79 w/C60 - crank 3850838, and W/P 3890419
HT - L79 w/N40 - crank 3858533, and W/P 3770245, P/S 3834720

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., P/S 3834720

HP - L79 w/C60 - crank 8508838, crank add on 3751232 for N40, W/P 3890419, and P/S 3770509

KH (K19) - L79 w/C60 - crank 3850838, crank add on 3751232 for N40, W/P 3890419, W/P add on 3883234 for A.I.R. and P/S 3770509

Hi Mark:

I couldn't tell from the drawings whether the power steering pulleys used on the 1965 L79 with A/C and PS were deep-groove or standard-groove. If you are convinced they were standard-groove, then that mystery is solved. It means that GM used standard-groove PS pulleys in combination with deep-groove crank and WP pulleys for the 1965 L79 application.

I agree that for cars equipped with A/C, it appears that GM used one of the following two matched pairs for the crank and water pump pulleys, in order to obtain a faster water pump/fan speed:

1) A deep-groove set consisting of the 3858533 crank pulley and the 3848904 WP pulley (or one similar to the 3848904).

2) A standard-groove set consisting of the 3850838 crank pulley and the 3890419 WP pulley.


So, the only remaining area that I think is unresolved is which of these two combinations was used on the 66-67 L79 with A/C and no PS.

My theory is that this configuration used the deep-groove set, while your analysis of the AIM suggests that the standard-groove set was used. It sounds like at least some believed-original 66-67 cars have the deep-groove set. It also seems that the P&A book shows deep-groove pulleys for this application. So, we still have some work to do to pin this one down. In the end, the determining factor is what GM actually installed on these cars, rather than what the documentation says. I think there are many known cases where the documentation does not match production.

It's not 100% clear from your post, but I think you are agreeing with me that the HP code for the 66-67 L79 was reserved exclusively for the special case of having both A/C and PS installed. In that case the standard-groove pulleys were used. I think the hub placement on the water pump was the only thing that made this assembly, as delivered from Flint, different from the HT assembly.

If, as you suggest, the HT assembly was used with both standard-groove and deep-groove pulley sets, there would be no reason for Flint to create the HP code.

[John H.]

Re: '67 L79 alternator pulley

I think the hub placement on the water pump was the only thing that made this assembly, as delivered from Flint, different from the HT assembly.

Joe -

Interesting by-product of the pulley system analysis. I've wondered for years why there was a specific suffix for an L-79 with A/C and PS, as there was no visible difference at all on the engine assembly as-shipped from Flint between that application and a plain L-79 or an L-79 with only A/C or only PS.

If the hub position on the shaft was the unique item that generated the L-79/AC/PS suffix, it would be interesting to know how Flint identified that unique pump when they assembled it so the guys on the engine assembly line could readily select it vs. the "standard" pump.

[Wayne M.]

Re: '67 L79 alternator pulley

.....If the hub position on the shaft was the unique item that generated the L-79/AC/PS suffix, it would be interesting to know how Flint identified that unique pump when they assembled it so the guys on the engine assembly line could readily select it vs. the "standard" pump.

John, others --- I don't have the chart that covers '66-7, but here's the situation up to 1965 MY (check Corvette column and compare to other Chevrolet products) -- [same question] how did they know what water pumps to ship to St. Louis, with the 1/8" further hub projection ?

Obviously, with C60, they corrected for deep pulleys with the 0.180" thick washer/spacers.

[Joe R.]

Re: '67 L79 alternator pulley

Joe -

Interesting by-product of the pulley system analysis. I've wondered for years why there was a specific suffix for an L-79 with A/C and PS, as there was no visible difference at all on the engine assembly as-shipped from Flint between that application and a plain L-79 or an L-79 with only A/C or only PS.

If the hub position on the shaft was the unique item that generated the L-79/AC/PS suffix, it would be interesting to know how Flint identified that unique pump when they assembled it so the guys on the engine assembly line could readily select it vs. the "standard" pump.

Hi John:

I agree that if this was done, Flint would have had two different versions of the L79 water pump, one with a 5-9/16 hub spacing (standard-groove setting), and one with a 5-11/16 hub spacing (deep-groove setting).

Previous discussions here on the TDB have noted the conflicting values for the hub spacing that appear in GM service literature. Both values show up, but not in a consistent way.

I'm told that the water pump rebuilders just split the difference and set all water pumps at 5-10/16. A 1/16 error in either direction will work okay, but a deep-groove pulley on a 5-9/16 hub spacing can cause interference between the back egde of the pulley and the pump casting.

[Wayne M.]

Re: '67 L79 alternator pulley

d

Mark -- just a thought; is there a possibility that the change from the '64-5 small block compressor support assembly Gr 9.170 from # 3841696 (pic below) to '66-up # 3878222 encompassed more than just adding an indentation (pencil in pic points to location) to accomodate the A.I.R. (K19) ? Could they also have changed the location of the compressor mounting eyelets, to affect the need for spacer/washers ?? I don't have the '222' bracket, but could measure the '64-5 unit if someone wants to compare.

BTW, I'll expect a college-level credit for slogging through this long and detailed thread .

[Mark G.]

Re: '67 L79 alternator pulley






C60 - AL L79 conv., AM L79 coupe

[Scott S.]

Re: '67 L79 alternator pulley

Could they also have changed the location of the compressor mounting eyelets, to affect the need for spacer/washers ?? I don't have the '222' bracket, but could measure the '64-5 unit if someone wants to compare.

Here is the 1967 p/n 3878222:

[Joe R.]

Re: '67 L79 alternator pulley

[quote=Mark Gorney (35760);502928]




Hi Mark:

Yes, I had arrived at a value of 1/8 inch (.125") based on empirical measurements. This is the difference between the centerlines of the first belt track, closest to the engine, for the deep-groove pulley set compared to the standard-groove pulley set.

To get the WP pulley and the crank pulley to line up correctly, the position of water pump hub needs to be moved by this amount when changing from standard-groove pulleys to deep-groove pulleys. This is because the face of the balancer is in the exact same location in all configurations (6" balancer and 8" balancer).

Apparently the decision of the water pump rebuilders to use a compromise hub spacing of 5-5/8 inches works okay and the 1/16 error is not noticeable to the customer.

However, if you set a water pump to either of the two GM specs that seem to be in circulation (5-9/16" or 5-11/16"), you will find that one pulley set lines up perfectly and the other is off by abouy 1/8 inch. With the WP pulley and crank pulley being so close together, this mismatch would be quite visible to the customer. I don't think that GM would have tolerated this on production cars.

So, since we know that GM installed both standard-groove pulley sets and deep-groove pulley sets on the 66-67 L79, it would seem that they must have compensated somewhow for the hub spacing problem. They would have had to use two different hub spacings on the water pump or some sort of spacer.

In the case of the A/C compressor, the belt is a lot longer and it is hard to visually discern a slight misalignment. In fact, at this distance, GM may have felt that some misalignment was technically acceptable.

While I have just finished converting my 1967 300 HP engine to deep groove pulleys, I have not yet moved the A/C compressor at all. Visually, it appeared to line up pretty well with the original standard-groove pulleys, and it still appears to line up pretty well with the new deep-groove pulleys. I have not yet made the precise measurements necessary to determine whether the compressor needs to be moved, but I hope to do this soon.

[Larry M.]

Re: '67 L79 alternator pulley

This morning I received a PM from Scott asking me to provide information on my 1967 327/350 HP car with factory air. Car does NOT have power steering or power brakes. But it does have N36 telescopic steering. Car is 26,000 mile original car with the tank sticker. Built in late March 1967. VIN #14845. AOS body. Engine stamped "HT". I have owned this car since 1994.

The alternator is a 61 amp, dated so as to be original to the car. The alternator pulley diameter is 3 to 3-1/16 inch outside diameter.

The water pump pulley is a two groove with part number # 3848904 CS.

The crank pulley is also two groove with part number # 3858533 and B7 or BJ (hard to read upside down with a mirror).

The AC compressor clutch diameter is approximately 5-5/8 inch outside diameter. This is the original compressor for the car and is date coded for late January 1967. The only code(s) I can find on the compressor clutch pulley is a small "FO 32." I do not know what this means.

The AC belt is 15/32 inch wide x 57-1/2 inch long. The alternator belt is 3/8 inch wide x 52-1/2 inch long. Both fit well with good alignment.

When I replaced the belts many years ago with Quanta reproduction belts, I had a lot of discussions with Quanta
about the fit. They said I needed this, and I said I needed that. We went through a few trial and fits (returns) until I got the correct width and length. Interestingly enough, the belts are listed by Quanta as: 1964 -65 327 with AC for the AC belt, and 1964-65 350 HP and 365 HP with AC for the alternator belt. Quanta's listed 1967 belts did not fit.

When changing the belts and fan clutch, I found a 1/16 to 3/32 inch thick metal spacer behind the water pump pulley. Paragon shows this as a reinforcing spacer for 327/300 HP cars. I thought that it might have gotten installed by someone in the cars early life, so I removed it. Maybe it was originally installed by GM to improve pulley alignment. The alignment now is acceptable, and reinstalling the spacer will actually hurt alignment for the AC compressor, but will help improve alignment for the alternator. Go figure. Not a big issue either way, though.

Hope this helps the discussion.

Larry

[Scott S.]

Re: '67 L79 alternator pulley

Thank you Larry, the detailed report is very much appreciated!

[Joe R.]

Re: '67 L79 alternator pulley

This morning I received a PM from Scott asking me to provide information on my 1967 327/350 HP car with factory air. Car does NOT have power steering or power brakes. But it does have N36 telescopic steering. Car is 26,000 mile original car with the tank sticker. Built in late March 1967. VIN #14845. AOS body. Engine stamped "HT". I have owned this car since 1994.

The alternator is a 61 amp, dated so as to be original to the car. The alternator pulley diameter is 3 to 3-1/16 inch outside diameter.

The water pump pulley is a two groove with part number # 3848904 CS.

The crank pulley is also two groove with part number # 3858533 and B7 or BJ (hard to read upside down with a mirror).

The AC compressor clutch diameter is approximately 5-5/8 inch outside diameter. This is the original compressor for the car and is date coded for late January 1967. The only code(s) I can find on the compressor clutch pulley is a small "FO 32." I do not know what this means.

The AC belt is 15/32 inch wide x 57-1/2 inch long. The alternator belt is 3/8 inch wide x 52-1/2 inch long. Both fit well with good alignment.

When I replaced the belts many years ago with Quanta reproduction belts, I had a lot of discussions with Quanta
about the fit. They said I needed this, and I said I needed that. We went through a few trial and fits (returns) until I got the correct width and length. Interestingly enough, the belts are listed by Quanta as: 1964 -65 327 with AC for the AC belt, and 1964-65 350 HP and 365 HP with AC for the alternator belt. Quanta's listed 1967 belts did not fit.

When changing the belts and fan clutch, I found a 1/16 to 3/32 inch thick metal spacer behind the water pump pulley. Paragon shows this as a reinforcing spacer for 327/300 HP cars. I thought that it might have gotten installed by someone in the cars early life, so I removed it. Maybe it was originally installed by GM to improve pulley alignment. The alignment now is acceptable, and reinstalling the spacer will actually hurt alignment for the AC compressor, but will help improve alignment for the alternator. Go figure. Not a big issue either way, though.

Hope this helps the discussion.

Larry

Hi Larry:

What you describe is what I would expect to see (deep-groove pulleys 3848904 and 3858533). The 3" alternator pulley is also what I would expect to see (3846180). This supports my theory that deep-groove pulleys were used when the L79 had A/C without PS.

Regarding the "spacer" you found behind the pulley, that part was originally developed by GM as a reinforcement for the pulley, after some customers' pulleys cracked and broke in the transition region just beyond the water pump hub. You may want to reinstall it if you continue to run the original pulley.

In later years, GM adopted the "reinforcement" part for use as a general-purpose spacer. Sevice instructions for water pump replacement often suggested adding this part as a way to compensate for replacement water pumps that had the hub placed father back than would be optimal for the application.

[Wayne M.]

Re: '67 L79 alternator pulley

Here is the 1967 p/n 3878222:

Scott -- thanks for the pics of the "222". Now, if anyone wants to compare dimensions, I've measured my '64-5 version of this bracket, 3841696, and am curious if the '66-7 revised bracket also "adjusted" the rear & front eyelets that bolt to the compressor rear and front head brackets, to possibly alter the need for the 0.18" thick washer-spacers.

Here's the "696" dimensions: from front face of forward eyelet to rear face of back eyelet (these are both machined surfaces and unpainted, on NOS examples -- they are also the mating surfaces with the compressor mount brackets) This dimension is 6.812". Now the distance from the front eyelet forward surface to the centerline of the nearest exhaust manifold mount bolt; this distance is 2.725".

If the "222" bracket has different dimensions, it may have been to shift the compressor forward without using the washer-spacers (which are a PITA to install, BTW).

[John H.]

Re: '67 L79 alternator pulley

[same question] how did they know what water pumps to ship to St. Louis, with the 1/8" further hub projection ?

Wayne -

They didn't ship water pumps to St. Louis - the water pump was part of the engine assembly; the guys on the engine assembly line at Flint V-8 had to select the correct (raw, unpainted) water pump.

[Scott S.]

Re: '67 L79 alternator pulley

Scott -- thanks for the pics of the "222". Now, if anyone wants to compare dimensions, I've measured my '64-5 version of this bracket, 3841696, and am curious if the '66-7 revised bracket also "adjusted" the rear & front eyelets that bolt to the compressor rear and front head brackets, to possibly alter the need for the 0.18" thick washer-spacers.

Here's the "696" dimensions: from front face of forward eyelet to rear face of back eyelet (these are both machined surfaces and unpainted, on NOS examples -- they are also the mating surfaces with the compressor mount brackets) This dimension is 6.812". Now the distance from the front eyelet forward surface to the centerline of the nearest exhaust manifold mount bolt; this distance is 2.725".

If the "222" bracket has different dimensions, it may have been to shift the compressor forward without using the washer-spacers (which are a PITA to install, BTW).

Hi Wayne,

If I have understood your references correctly, I think I covered them in the attached picture. My caliper is a 4" digital, so I had to use a tape measure, measuring by 16ths. I measured first, then compared to your data. It looks like the "from front face of forward eyelet to rear face of back eyelet" measurement is the same (6.812" vs. 6.8125"), but the "from the front eyelet forward surface to the centerline of the nearest exhaust manifold mount bolt" measurement may be slightly different.

When I compared my measurement (2-10/16th" or 2.625") to your measurement (2.725"), I went back to measure it again. Being as careful as I could, using a straight-edge centered under the hole for a centerline and measuring across from the "front eyelet forward surface", it was between 2-9/16th" (2.5625") and 2-10/16th" (2.625"), but it was not larger, I couldn't get 2.725", to match your measurement.

If anyone else has a 1967 GM #3878222 compressor bracket and more precise measuring equipment, it would certainly be a good idea to double-check my results.

If I misunderstood either of your measurement references, please explain and I'll re-measure.