1968 L79 Harmonic Damper

[Loren L.]

Re: 1968 L79 Harmonic Damper

Well, Joe, I guess I'm just hopelessly outdated. When I look at my Fall 1993 1966 JG on page 98, under the reference to "L79 350 hp", the second sentence reads "The interior service has twelve integrally cast fins.". To make things even worse, the Spring 1993 1967 JG on page 80,
under "Crankshaft Balancer", reads in part "The L79 350 hp engines use a heavy 1 3/4 inch thick balancer with an outside diameter of 8 inches. The interior surface has twelve integrally cast fins.".
I can only assume that by now you have processed the corrections to the JG through both of these teams. I do NOT have a 1968 JG but I believe it will be some time before I attempt to inform the 3 original owners of 1968 L79s that they have the wrong balancers.

[Joe L.]

Re: 1968 L79 Harmonic Damper

Well, Joe, I guess I'm just hopelessly outdated. When I look at my Fall 1993 1966 JG on page 98, under the reference to "L79 350 hp", the second sentence reads "The interior service has twelve integrally cast fins.". To make things even worse, the Spring 1993 1967 JG on page 80,
under "Crankshaft Balancer", reads in part "The L79 350 hp engines use a heavy 1 3/4 inch thick balancer with an outside diameter of 8 inches. The interior surface has twelve integrally cast fins.".
I can only assume that by now you have processed the corrections to the JG through both of these teams. I do NOT have a 1968 JG but I believe it will be some time before I attempt to inform the 3 original owners of 1968 L79s that they have the wrong balancers.

Loren------


First of all, the current 1968 JG is silent on the subject of fins for the L-79 balancer.

Second, judging guides, including ones I've contributed to, can be wrong on certain things.

Third, 1993 is 26 years ago. 1993 edition judging guides for 1966 and 1967 may have had inaccuracies at that time. For many years folks ASSUMED that all L-79 balancers were finned. They were wrong. I think there was a certain "cachet" to these finned balancers which may have contributed to the propagation of the myth.

How do you KNOW that these 1968 L-79's you speak of have finned balancers? The fins, if present, are difficult to see with the balancer mounted on the engine and in the car.

One more thing for what it's worth: I believe the Camaro restorers have pretty well confirmed and settled on the fact that 1967-68 Z-28 Camaros were originally equipped with non-finned balancers. The 1967-68 302 engine used the same GM #3817173 balancer as 1967-68 Corvette L-79.

[Gene M.]

Re: 1968 L79 Harmonic Damper

Just to share my experience, I have not seen an original '67 L79 that did not have a finned balancer. Non finned in a '67 L79 Corvette was considered incorrect in all my dealings, even in NCRS. I have seen both finned and non finned '68 L79 Corvettes also of original condition. I have no experience with non Corvette applications. It is my understanding non Corvette L79 engine applications do not necessarily originate at Flint.

[Loren L.]

Re: 1968 L79 Harmonic Damper

Okay, the 1968 JG is silent - What do the CURRENT 1966 and 1967 JGs state?
Detection of the fins is really quite simple - with the motor stopped, reach over with a finger (either hand will do) and search the back of the balancer for fins - finding 2 will do, I have yet to find one that doesn't have 12.

[Joe L.]

Re: 1968 L79 Harmonic Damper

Okay, the 1968 JG is silent - What do the CURRENT 1966 and 1967 JGs state?
Detection of the fins is really quite simple - with the motor stopped, reach over with a finger (either hand will do) and search the back of the balancer for fins - finding 2 will do, I have yet to find one that doesn't have 12.

Loren-------


I don't know what the current 1966 and 1967 judging guides say.

With the engine mounted in the car, it's not quite as easy as you describe. But, I agree that it's very doable. However, it's not something one can tell at a glance and it's definitely not something that folks looking at an engine compartment normally undertake to do.

I'm very impressed that you go the "extra mile" to be sure that all 12 fins are there. That takes a lot of extra effort. For me, probably just finding ONE would be enough. At that point, I'd probably just assume that the other 11 were there. I guess it just goes to show how much more thorough you are than I.

[Loren L.]

Re: 1968 L79 Harmonic Damper

Joe, I guess I'm surprised that if you have an ECR making this change with an effective date that you haven't provided it to the '66 & '67 Teams. And it may not be something that "people looking at an engine compartment would do" - if only because of loss of limb by an owner - but it IS
something that a MECHANICAL NCRS judge had better do.
As for your mischaracterization of going the "extra mile" by finding "all 12" and being "thorough", I did NOT state that. If I find 2, if the other 10 are not there, it wouldn't be much of a "balancer" would it?
Do you have ECRs showing a changeover date or not?

[Joe L.]

Re: 1968 L79 Harmonic Damper

Joe, I guess I'm surprised that if you have an ECR making this change with an effective date that you haven't provided it to the '66 & '67 Teams. And it may not be something that "people looking at an engine compartment would do" - if only because of loss of limb by an owner - but it IS
something that a MECHANICAL NCRS judge had better do.
As for your mischaracterization of going the "extra mile" by finding "all 12" and being "thorough", I did NOT state that. If I find 2, if the other 10 are not there, it wouldn't be much of a "balancer" would it?
Do you have ECRs showing a changeover date or not?

Loren--------


I have the GM drawing for the 3817173 balancer. However, I cannot find it. I wish I could. All that I can recall about it is that it had a long list of revisions and that the change to delete the fins occurred prior to 1967. I vaguely recall it was late 1965 or 1966. Over the years I have received MANY GM parts drawings, including this one. Unfortunately, I did not catalog the drawings so they are "scattered about" here---some in electronic files on past and present computers, some in hard copy in a variety of files and locations.

As far as your not stating that you check for all 12 fins, I disagree that you did not say that. You said "...finding 2 will do, I have yet to find one that doesn't have 12". If your intention was to say that finding 2 would infer that all 12 were present, you would have left it at simply stating finding 2 will do. PERIOD. But, you went on to say that you have yet to find one that doesn't have 12. Unless you had actually checked for 12, that statement was entirely unnecessary. Actually, I don't even know why you would say that "finding 2 will do"; finding ONE is all that's necessary.

[Gene M.]

Re: 1968 L79 Harmonic Damper

Joe,
From the talk here I understand it is the same part number for the balancer be it finned or not. That would follow the general thought that GM stock and ordering would include both designs as arrival on the docks at GM for some time after issued change. No purge of current stock or modification to tooling would occur since the new and old design were considered interchangeable being that the p/n is the same. GM wouldn't spend money on tooling change that was not necessary nor a safety hazard. So is it not a more than probable situation that multiple vendors (or multiple tools) could be suppling both configurations finned and plain?

[Loren L.]

Re: 1968 L79 Harmonic Damper

Sorry, Joe. Your "memory" is not enough to cut off the finned balancers for 1966, 1967 and at least the early 1968s. Now I don't have to contact my early 1968 L 79 owners to incur their rath.
In the future, if you don't have a date for "entered production", ..........

[Joe L.]

Re: 1968 L79 Harmonic Damper

Joe,
From the talk here I understand it is the same part number for the balancer be it finned or not. That would follow the general thought that GM stock and ordering would include both designs as arrival on the docks at GM for some time after issued change. No purge of current stock or modification to tooling would occur since the new and old design were considered interchangeable being that the p/n is the same. GM wouldn't spend money on tooling change that was not necessary nor a safety hazard. So is it not a more than probable situation that multiple vendors (or multiple tools) could be suppling both configurations finned and plain?

Gene-------


Yes, that's very possible. There's one "fly in the ointment", though. There is a functionality difference between the finned and non-finned balancers (at least most of them; I'll get to this later). In fact, I've always been very surprised that GM did not change the part number. Most of the finned balancers do not have balance weight holes on the hub. This means that engines equipped with these balancers could not be final balanced. All of the non-finned balancers I have ever seen do have the balance weight holes on the hub. So, any engine equipped with these could be final balanced. I believe that GM engine build procedures changed about 1966 to include final engine balance. So, I don't understand why GM would have continued to use balancers after that time (whatever that time actually was) that eliminated the ability to final balance certain engines.

While most of the finned balancers I've seen do not have the balance weight holes, a very few that I've seen do! So, these balancers could be installed on engines and still receive final balancing. Perhaps one of the balancer suppliers to GM asked GM if they could continue to include the fins, thus obviating the need for them to produce a new hub pattern, if they could also include the balance weight holes and GM acceded. Obviously, this is just a guess on my part. In any event, if something like this did occur, then I would expect all of the finned balancers installed on the production line after GM went to the final balance would have the holes in addition to the fins.

[Joe L.]

Re: 1968 L79 Harmonic Damper

Sorry, Joe. Your "memory" is not enough to cut off the finned balancers for 1966, 1967 and at least the early 1968s. Now I don't have to contact my early 1968 L 79 owners to incur their rath.
In the future, if you don't have a date for "entered production", ..........

Loren-------

I DID NOT ask that any judging guides or judging procedures be changed. Even if I had been able to document what I said, I would not have asked that. I expressed my OPINION. I have expressed my OPINION numerous times before on the subject of the GM #3817173 balancer and my OPINION has remained consistent.

I DID NOT ask that you contact your "early 68 owners to incur their rath (sic)". Of course, I could see where you might incur their wrath for other reasons.

In order to post here no one is REQUIRED TO DOCUMENT every statement or definitively qualify every statement as an opinion. IN THE FUTURE I will continue to operate that way and I will not accept any admonishment or other instruction from you.

I might add that you have offered many opinions on this board, many to the dismay of others.

[Gene M.]

Re: 1968 L79 Harmonic Damper

Gene-------


Yes, that's very possible. There's one "fly in the ointment", though. There is a functionality difference between the finned and non-finned balancers (at least most of them; I'll get to this later). In fact, I've always been very surprised that GM did not change the part number. Most of the finned balancers do not have balance weight holes on the hub. This means that engines equipped with these balancers could not be final balanced. All of the non-finned balancers I have ever seen do have the balance weight holes on the hub. So, any engine equipped with these could be final balanced. I believe that GM engine build procedures changed about 1966 to include final engine balance. So, I don't understand why GM would have continued to use balancers after that time (whatever that time actually was) that eliminated the ability to final balance certain engines.

While most of the finned balancers I've seen do not have the balance weight holes, a very few that I've seen do! So, these balancers could be installed on engines and still receive final balancing. Perhaps one of the balancer suppliers to GM asked GM if they could continue to include the fins, thus obviating the need for them to produce a new hub pattern, if they could also include the balance weight holes and GM acceded. Obviously, this is just a guess on my part. In any event, if something like this did occur, then I would expect all of the finned balancers installed on the production line after GM went to the final balance would have the holes in addition to the fins.

Good thought. But consider this. The holes in the hubs only allows for weight added. The weight removal was done by drilled holes on the circumference of the outer hub. The weight added on the inner hub would be of lesser effect since it is so close to the center of rotation. Now I don't know if the hubs were balanced prior to assembly as a piece part and/or drill balanced as an assembled engine. I have not seen any finned or non finned balancers without and balancing drilled holes in this time period. To be truthful I've not paid much attention to the added weight holes.

I can share when I've had my engines balanced I had everything checked including the balancer. And some did require drilling.

[Joe L.]

Re: 1968 L79 Harmonic Damper

Good thought. But consider this. The holes in the hubs only allows for weight added. The weight removal was done by drilled holes on the circumference of the outer hub. The weight added on the inner hub would be of lesser effect since it is so close to the center of rotation. Now I don't know if the hubs were balanced prior to assembly as a piece part and/or drill balanced as an assembled engine. I have not seen any finned or non finned balancers without and balancing drilled holes in this time period. To be truthful I've not paid much attention to the added weight holes.

I can share when I've had my engines balanced I had everything checked including the balancer. And some did require drilling.

Gene------


Yes, the balancers were balanced at the time of manufacture by the drilling of holes in the outer ring. These holes will be seen in many PRODUCTION and SERVICE balancers. However, as far as I know, final engine balancing was done only by the addition of weights to the weight holes seen on the hub or, in some cases (but not for the 3817173), on the outer ring.

As a matter of fact, during the Flint Engine Plant tours conducted in conjunction with the 1992 NCRS National Convention I spent quite a bit of time at the final engine start and balancing operation and I queried the operator about the procedures. Of course, I've forgotten most of what he told me but I do recall that he told me that not all engines needed to have weights added. It was only if they fell outside of a certain range that weights were added. I do recall that I was impressed at how deftly and quickly he installed the weights. I can still picture him doing it.

By the way, the weights are still available from GM under GM #274584 (which is actually an ancient part number but these weights/pins have other applications). Much later, GM repair procedures for some engines stated that if a balancer was replaced, any weights installed in the original balancer were to be noted and weights installed in the corresponding holes of the SERVICE balancer.

[Gene M.]

Re: 1968 L79 Harmonic Damper

Joe,
From your description the balancer was made neutral by drilling and I assume prior to engine assembly. I'm drawing this opinion from the replacements have drill holes also. Maybe they do not. The 327 was an internal balanced engine. But from your description it is further balanced only by weight adding. Was the process prior to this finless balancer with the holes, final balanced by drilling? Was there a process change from drilling to putting in weights or possibly was this an added process?

[Joe L.]

Re: 1968 L79 Harmonic Damper

Joe,
From your description the balancer was made neutral by drilling and I assume prior to engine assembly. I'm drawing this opinion from the replacements have drill holes also. Maybe they do not. The 327 was an internal balanced engine. But from your description it is further balanced only by weight adding. Was the process prior to this finless balancer with the holes, final balanced by drilling? Was there a process change from drilling to putting in weights or possibly was this an added process?

Gene------


Yes, SERVICE balancers often have the drilled balance holes on the outer ring. I have many NOS balancers that have these. As an assembly, they are balanced to within the specification described on the GM prints.

As far as I know, no drilling of the balancer was ever performed to achieve final balance at the engine plants. My guess is that prior to the adding of weights, no final balance, which really amounts to VERY fine tuning, was done. However, I can't say that for certain. Perhaps some member who actually worked at the engine plants "way back when" could answer this.