C2 66-67 SB Pulleys

[Mark G.]

I have some more information involving small block pulley sets. First the crank pulley centerline dimensions using the harmonic balancer face as "0".
#3850838 first groove .305" second .925"

#3858533 deep groove .370" second 1.125"


The water pump pulley measurements using the first groove centerline of the C/S pulleys to the pulley mounting surface.
#3890419 A/C pulley 2.330"

#3770245 deep groove 2.400"

The related pulley groove centerlines, alternator, P/S and A/C would be in the same relative location to the crank. My issue is the .135" (.065" + .070") difference between the '608 W/P and the '326 L79 W/P flange locations. Assuming of course, the balancer faces are common between the two engines.
The water pumps have rebuild specifications of 5 9/16" and /or 5 11/16"; could that be the reason?


Mark

[Joe R.]

Re: C2 66-67 SB Pulleys

Hi Mark:

I believe that when the deep-groove pulleys are used, the water pump flange is placed at 5-11/16", and when the standard-groove pulleys are used, the water pump flange is placed at 5-9/16".

The face of the balancer is in the same location for both the small 300 HP balancer and the large 350 HP balancer, so there is no difference there.

Given that, a simple comparison of the stack-ups of the standard-groove and deep-groove pulley sets shows why the difference in placement is required for the water pump flange. By my measurements, the difference is about 1/8 inch (.125").

The major water pump rebuilders set the flange half way between the two positions, based on the assumption that a 1/16" mismatch will not cause a problem.

[Mark G.]

Re: C2 66-67 SB Pulleys

Joe -

Thank you, that will help calculate and verify the A.I.R (K19) L79 pulley/spacer combinations. The distance between grooves is .62" on the base engine pulley set and .76" on the L79 set.

Another issue is which pulley set was used when A/C (C60) was added to an "HT" L79 engine. The "HD" code with C60 and A.I.R. does use the base engine set with the add on pulley in front of the '419 W/P pulley.

Also, Technical Service Bulletin DR #66-10 12/16/65 changed the A/C mounting brackets at SN 6S103533, around mid October, to route the heater hoses around the compressor. In doing so, the .180" spacers where discarded making the brackets standard for both engines. The spacers were a carryover from '65 SHP engines with A/C and the deep groove pulleys. This leads me to believe the "HT" L79 with only A/C uses the standard pulley set. What do you think the configuration should be?
Attached revised '66 AIM N40 page that may help.

Mark

[Joe R.]

Re: C2 66-67 SB Pulleys

Hi Mark:

For 1967, when the L79 was equipped with *both* PS and AC, the standard-groove pulley set was used. I believe that this was the reason for the special "HP" engine code for this configuration. The sole difference between the HT and HP L79 codes was the placement of the water pump flange to account for the differences between the standard-groove and deep-groove pulley sets. At least, this is my theory.

What remains a mystery to me is what pulley set was used on the L79 with AC and no PS. That configuration could have used the deep-groove pulley set, but I'm not sure it did.

By the way, I appreciate your efforts to measure all the offsets of the various pulley grooves relative to the face of the balancer. I think this is the best way to evaluate alignment, by using the face of the balancer as a reference.

I made a set of measurements of this type about a year ago with the engine in the car, but it was tedious. I now have a spare block on an engine stand and have been intending to go back and make the measurements again. Perhaps I can do that soon and compare my results to yours.

[Joe R.]

Re: C2 66-67 SB Pulleys

Hi Mark:

I have two photos that compare the standard-groove and deep-groove pulleys for 1967. These date from March 2008 so I'm not positive about the details, but I'm pretty sure that my measurements were referenced to the surface that rests directly on the balancer (for crank pulleys) and directly on the water pump flange (for water pump pulleys). Otherwise the measurements can be thrown off by the thickness of the pulley hub.

Apparently our TDB server is so smart that it won't let me post these photos a second time, but you can find them in the archives in a posting dated March 11, 2008, where I originally used them.

It was difficult to determine the exact center line of each groove, but I made a tool for the purpose, and following are the numbers I got for the various pulleys:

3850838 crank: first groove .330" forward, second groove .960" forward
3858533 crank: first groove .450" forward, second groove 1.22" forward

3890419 water pump: first groove 2.48" back, second groove 1.85" back
3770245 water pump: first groove 2.50 back, second groove 1.72" back


From these measurements you can see that for the deep-groove pulleys to line up, the water pump flange must be about 1/8 inch (.125") farther forward than when the standard-groove pulleys are used.

I have been planning to extend my measurements to include reference dimensions from the balancer face to the water pump mounting surface on the block and to the alternator mounting surface on the exhaust manifold. The idea was to determine all the reference dimensions and cross-check them.

If anyone is wondering why I would bother with all this, it is because I have a side project to equip my 67 A/C and PS car with a full set of deep-groove pulleys, since I have had trouble with tossing belts at high RPM.

GM used standard-groove pulleys for this option combination, but I have convinced myself I can get what I want with a combination of Corvette, Camaro, and Pontiac pulleys. I just have to make sure I address the alignment issues.

[Mark G.]

Re: C2 66-67 SB Pulleys

Joe -

This is what I have compared to your dimensions;

3850838 crank: first groove .330" forward, second groove .960" forward
First .305" second .925"

3858533 crank: first groove .450" forward, second groove 1.22" forward
First .370" second 1.125"

3890419 water pump: first groove 2.48" back, second groove 1.85" back
First 2.33" second 1.71"

3770245 water pump: first groove 2.50 back, second groove 1.72" back
First 2.40" second 1.64"

Please email me, mtgvette66@aol.com, and I will send my information.

Mark

[Joe R.]

Re: C2 66-67 SB Pulleys

Hi Mark:

I made some measurements on a spare block assembly that I have, and came up with two additional numbers that may be of interest:

Face of balancer to water pump mounting surface on block: 2.92"

Face of balancer to alternator mounting surface on 3846563 exhaust manifold: 2.72" (plus/minus .020" due to manifold mounting slop).

I think that with the 2.92" dimension and the pulley dimensions, it should be possible to calculate the required water pump flange position for alignment between the crank and WP pulleys. I'm short on time today, but I plan to try these calculations later.

[Mark G.]

Re: C2 66-67 SB Pulleys

Joe -

That was my original question; why the different lengths for the W/P assemblies. The standard pulley set calculates to 2.635" and the deep groove set 2.765" from the harmonic balancer to the W/P mounting flange; the average is 2.70". I plan to layout the A.I.R. (K19) L79 pulley/ spacer combinations from this dimension to check the alignments.


Mark

[Joe R.]

Re: C2 66-67 SB Pulleys

Hi Mark:

If I use your numbers for the centerlines of the first pulley groove and my measured 2.92" dimension for the distance from the face of the balancer to the WP mounting surface on the block, everything adds up nicely:

WP flange spacing for standard-groove pulleys = (0.31+2.33+2.92) = 5.56"
WP flange spacing for deep-groove pulleys = (0.37+2.400+2.92) = 5.69"

Since 5-9/16" = 5.563" and 5-11/16" = 5.688", this seems to confirm my theory that GM used the 5-9/16" WP flange spacing for the standard-groove pulleys and 5-11/16" for the deep-groove pulleys.

Note that this calculation ignores the thickness of the WP gaskets, but I think the original gaskets were pretty thin.

[Dale S.]

Re: C2 66-67 SB Pulleys

Mark, What is the thickness of you smog pump pulley spacer? Dale

[Mark G.]

Re: C2 66-67 SB Pulleys

Dale -

I have a '66 300hp w/C60 & K19; my spacer is the 3890425 (.607") with the 3890421 pulley mounted web forward. This standard position sets the pulley groove .200" back toward the pump.
The L79 w/C60 uses spacer 3890423 (.497") with the same pulley mounted web rearward. An L79 w/C60 & N40 uses spacer 3890427 (.339") with the web rearward. Flipping the '421 pulley mounting offsets the groove .481" total, from -.200" to +.281". The different spacers are needed because there are two different W/P add on pulleys w/C60. The A.I.M. K19 page has those descriptions.
I believe the L79 W/P mounting flange is about .130" longer than the base engine W/P. This also contributes to the spacer/pulley complications. I am currently trying to verify all the A.I.R. pulley groove locations. The metal thickness of the pulleys is tricky.

Mark

[Dale S.]

Re: C2 66-67 SB Pulleys

Thanks Mark, I also hve a base engine, C-60 , K-19 car. Spacer .600+ I have pictures. Thank you Dale

[Mark G.]

Re: C2 66-67 SB Pulleys

Dale -

That's great; send them to mtgvette66@aol.com. A pump code picture would be nice to document too. There appears to be a trend of "A" coded pumps installed in restored cars. My general understanding is '66 uses "E" and '67 along with correct service replacements use a "P" coded pump. There are several A.I.R. pump features that make then unique for Corvettes.

Mark