Need dimension on 1967 L79 balancer

[Joe R.]

Hello All:

Does someone have an L79 balancer that is off the car that they could measure for me? In the photo below, the total depth of the 300 HP balancer measures approximately 2.34 inches (according to my calipers, not just the ruler in the photo).

I'm trying to sort out some pulley alignment differences among the 1967 327/300 with A/C, 327/350 with A/C, and 327/350 without A/C. I have come to the conclusion that one of the differences between the base engine and the L79 is that the front face of the L79 balancer is slightly farther out from the timing cover than the base engine balancer. I think the difference may be on the order of 0.1 inches.

If someone has an L79 balancer that they could measure for me, I would appreciate it. The dimension I need is the total depth of the balancer as indicated by the ruler in the photo, from the front face to the extreme end of the snout.

[Gary B.]

L79 balancer thickness

Joe,

For the finned pulley from my '66 L79, I measure 2.342".

Gary

[Joe R.]

Re: L79 balancer thickness

Hi Gary:

Well, that sounds like the same dimension as the 300 HP balancer, so I'm perplexed.

While the A/C versions of the 67 base engine and the L79 engine both used the same pulley set, the L79 engine had the A/C compressor spaced forward slightly with some washers (item 19 in UPC C60, sheet C1 of the 67 AIM). Also, according to my measurements, the centerline of the alternator pulley used on the L79 with A/C is about 0.1 inches forward of the centerline of the base engine A/C alternator pulley. So, for some reason, it looks like GM was trying to move the accessory belt centerlines about 0.1 inches forward when the engine changed from the base engine to the L79. I figured it had to do with the change in the balancer. If the L79 balancer position is unchanged from the base balancer, I can't explain the shift in the A/C and alternator pulley centerlines.

[Chris D.]

Re: Need dimension on 1967 L79 balancer

Joe,

I found that particular dimension, between standard and high performance balancers, to be the same for '63 also.

High performance C2 engines used wider, deep groove pulleys and a different water pump. Base and 300hp engines used narrower pulleys. My guess is the H/P belt and pulley centerlines were moved forward to allow the wider pulleys to clear other components.

In comparing '67 300 vs. 350 hp engines, you will find that same 1/8" difference reflected in the water pump hub locations. The high perfomance pump hub is .125" closer to the front of vehicle. With no mention of the actual measurement, the shop manual does detail different set-up gauges in the water pump rebuild procedure.

For the AC compressors, it would be simpler to space out the pulley and maintain the same compressor mounts across the engine options. I'm not familiar, at all, with stock AC setups so this is only conjecture on my part.

Chris

[Joe L.]

Re: L79 balancer thickness

Joe------

I'm not surprised, at all. I would have been surprised, though, if the dimensions were different. Most Chevrolet small block balancers have the same dimension with respect to the measurement from the face (pulley mounting surface) to the inner surface which seats against the crankshaft sprocket. This means that the face of the balancer is in a more-or-less "standard" position regardless of which balancer is installed. The configuration of the pullies and pulley SET is where things vary for different applications.

[Joe R.]

Re: Need dimension on 1967 L79 balancer

Hi Chris:

I agree with you about the difference in centerlines between the base pulley set and the high performance "deep groove" pulley sets. This difference greatly complicates the alignment of the various pulleys when you consider that some configurations had power steering and/or A/C.

As far as I have been able to determine, when A/C was installed in 1967, both the base 300 HP engine and the SHP 350 HP engine used the base engine pulley set. I think this may have had something to do with the fact that GM would have had to develop a third style of power steering pump pulley and power steering crank pulley if they wanted to support the deep groove pulley set on an A/C car with power steering.

What you say about the 350 HP water pump pulley being 1/8 inch farther out is new information for me. If that is really the case, it may provide a clue. Having the 350 HP water pump pulley farther out would explain why the A/C compressor and alternator pulley centerlines were moved out for the 350 HP A/C configuration.

The remaining mystery is how the crank pulley was similarly adjusted. It would seem to me that on a 350 HP car with A/C (which I believe used the base engine pulley set), there should be a 1/8 inch spacer behind the crank pulley to bring it into alignment with the water pump pulley.

[Joe L.]

Re: Need dimension on 1967 L79 balancer

Joe-----

Prior to 1962, Chevrolet small blocks used a waterpump flange that was spaced 1/8" further inward than 1962-68 and 69-70 Corvette. Once-upon-a-time, GM even SERVICED both style pumps with different part numbers even though the only difference was the flange spacing. I don't think that any 1962-68 and 69-70 Corvette pumps used different hub spacing dimensions. I would not completely rule out the possibility, but I don't think so.

I believe that all 62-68 small block and 69-70 Corvette used a hub spacing dimension of 5-9/16" as measured from the face of the flange to the block mounting surface.

[Chris D.]

Re: Need dimension on 1967 L79 balancer

Joe L.

I may well be wrong so let me share what I'm seeing and you be judge.

Item 1 - Fit Test.
I started my inquiry when I attempted to bolt up a deep groove drive system onto a base engine. I know, not a very NCRS activity, but I enjoy parts swapping on my driver '63. Original pulleys line up beautifully. Deep groove system gives you a pump pulley 1/8" rearward of the crank pulley. So the difference is either the pump or the balancer. It was easy enough to measure other balancers which showed they were the same in the relevant dimension. I assumed it must be the pump.

Item 2 - Shop Manual
In the '63 manual, cooling system, pages 65-6 & 65-7, there are specific, different set-up gauges to use when pressing on and locating the hub after pump rebuild: J-9608 for all except F.I. and J9648, on step, for F.I. engine. This is pretty strong indication they were different but it doesn't determine by how much. It also left out the 340 hp engine but since it shares the same pulleys w/ F.I. it needs to share the same hub dimension.

Item 3 - Parts book. (I know, not conclusive but often indicative)
The '72 parts book does indeed show service on two different pumps w/ 1/8" difference in hubs. It lists both items for years '55 - '70. Seems to me if there was an earlier, clean break point they would have used it. I think it got so fractured, they gave up, and dropped in the note that says, "...3998206 has a distance of 1/4", 3998207 has a distance of 3/8".

To my mind these are fair indications of both hub locations in some years. It would be best, of course, to have known originals to measure but the few that exist I am sure are still on cars and most the rest have been to the rebuilders a time or two.

[Joe L.]

Re: Need dimension on 1967 L79 balancer

chris------

I was aware of some of the things you point out. However, I was not aware of the differences in flange gauges specified in the service manual. That certainly would indicate that there was a difference in hub spacing. It's possible, though, that this was an "anachronism" that got into the manual from earlier editions. Still, it provides significant indication that there were 2 hub spacings as late as 1963.

It may well be that the 2 different hub spacings continued for 1962 and later. There is one "hint" of that which I failed to mention in my earlier post. There was once a GM SERVICE waterpump of GM #3848072. This pump had the 3/8" spacing with instructions to drive the hub further inward by 1/8" for those applications requiring that. This pump was specified for 55-65 applications.

At the same time, another pump was specified for 66-67 applications of GM #3890017. There were no instructions to drive the flange on further for this pump. That implies that there were no hub spacing differences for 1966-67.

In November, 1966, the GM #3890017 pump replaced the 3848072. At that time a note was added to P&A catalog that it might be necessary to drive the flange on by an additional 1/8" for 1955-65 applications.

In February, 1969, the GM #3890017 was discontinued and replaced by the GM #3929233, the pump originally specified for 1968 Corvette small blocks. There was no note about the flange adjustment for the 3929233, either before or after it replaced the 3890017.

In October, 1969, the GM #3929233 was discontinued and replaced by GM #3937996 and in November, 1970 the latter was discontinued and replaced by GM #3957981. There was no note regarding hub spacing adjustment for either of these pumps.

Then, in February, 1972 a curious thing happened. The GM #3957981 was discontinued and replaced by TWO different part numbers----GM #3998206 with 1/4" hub spacing and GM #3998207 with 3/8" hub spacing.

Based upon the above, I would say that it's very possible that the 2 different hub spacings continued through 1965. However, I think it's less likely that it continued after 1965. It's possible, though, that it continued through the end 327 use in Corvettes in 1968. If we had the engine AIM's, we'd be able to nail this down.

[Chris D.]

Re: Need dimension on 1967 L79 balancer

Joe,

Your insights on the pumps make me suspect '66 might have been the start for all the pumps set up in the forward hub location. New water pump pulley numbers start cropping up for base and base/AC when otherwise you would think the preceding pulleys would function. These new '66 base engine pulleys were perhaps designed for the forward hub location. Anyone have a base 67 pulley to measure? We could compare it to my '63. As you said, it would be interesting if someone had the engine AIMS for 65, 66 and 67 to know for sure.

Even with the pumps standardized, the crank pulleys have enough application overlap between pre- and post- '65 to suggest the two different fore/aft groove positions existed throughout.

So, back to Joe R. and his compressor spacing. If your car is 350 hp, AC, AND power steering, the parts catalog agrees that 300hp and 350hp AC engines use the same 3850838 crank pulley. Is this what you have? I'm guessing it's a narrow groove item rather than the deep groove. Is that the case?

Is there any chance the AIM note, which shows spacers for L-79 & AC, does not apply for L-79,AC, plus power steering? Would your compressor line up without the spacers? Seems to me if it uses the base/AC crank pulley, the compressor would use the base engine mounting without spacers.

Of the spacers and pulleys in hand, which are known originals and which might be in question? AIMS and parts books can only take one so far. It always gives me pause to wonder, when cars are changed to match the books.

[Joe R.]

Re: Need dimension on 1967 L79 balancer

Hi Chris:

In your post you asked for clarification about what setup I have on my car. The answer is that I have a base engine with A/C and power steering, and I am trying to swap in the deep groove pulley set, just as you are. This is what led to my investigation.

Right now I have the all the correct base engine pulleys on the car and they line up fine, but I have had some trouble with tossing belts at high RPM. Initially, swapping in the deep groove pulleys seemed like it would be a simple task, but it has turned out to be more complicated than it first appears.

Fortunately, all the little challenges involved with the swap seem surmountable once I get a clear understanding of what the differences are. That's why I was interested in the balancer dimension.

I appreciate the additional insight that you and the other responders have been able to offer. Eventually I will sort out all the little pieces of this puzzle, and I will be able to make the necessary modifications to swap in the deep groove pulleys.