C2 SB Balancer

[Steve D.]

I have a 327 that I am setting up with the LT-1 cam. I have two part numbers for a balancer: 3817173 _described as '62-'68 HO application, and 6272222 described as a 350HO application. Would either of these be preferred over the other?

Steve

[Joe R.]

Re: C2 SB Balancer

Steve,

The balancer must be matched to the rotating assembly (crank, rods, pistons and flywheel assembly. GM assumes that the long block they are selling the balancer for is to factory GM specifications.

You should contact your engine builder for specifications and recommendations for the balancer. He may recommend a balancer and balancing the entire assembly.

I feel that any engine (built up) should be balanced for best performance and durability.

Regards,

JR

[Steve D.]

Re: C2 SB Balancer

JR

I will have the whole rotating assembly balanced, but the balancer that came off of the engine needs to be replaced.

Steve

[Michael H.]

Re: C2 SB Balancer

Steve,

The 3817173 is the 8" balancer that was originally installed on 62-68 327's with Sp. H/Per. The 6272222 was originally installed on 69-71 350 WITHOUT Sp. H/Per. and is probably a 6" balancer. If you have a 327, you should stay with a balancer designed for a 327. If the engine was a Sp. H/Per., it would have had an 8" balancer and a matching timing chain cover with the timing tab located properly for it. If it was originally a hydraulic lifter motor, you could use the original style 6" balancer.

Another problem with switching to a 69 and later balancer is the location of the timing mark. In 1969, the mark and timing tab were moved 10 degrees so if you use a 69 and later balancer, you should also use a 69 and later timing chain cover.

Unless you are going to thrash this car from time to time, I would definitely use the correct 6" balancer of the era.

Michael

[Joe L.]

Re: C2 SB Balancer

Steve-----

You should use the GM #3817173 balancer. This is the 327 SHP balancer and, if you're using the LT-1 cam, it will provide the high RPM balancing to go with the characteristics of that cam and the 327 crankshaft (as long as you're using a small journal, pre-68 327 crankshaft).

The GM #6272222 balancer is an 8" X 1-5/16" thick balancer used for 69-71 350 cid medium performance applications as well as many trucks. It's designed for use at below 5,500 RPM with cast nodular iron crankshafts. It doesn't have the correct timing mark for 327 applications.

[Michael H.]

Re: C2 SB Balancer

Joe,

Not sure if I understand why you recommend the 8" balancer over the 6". I suppose it would be a logical choice if he's going to run the engine at high RPM in competition events but for the street, wouldn't the original 6" work as well? If the car was originally a solid lifter car with 11.0 CR, I would definitely go with the 8" but if it was just a 250 or 300 HP, the original 6" is probably a better choice.

[Joe L.]

Re: C2 SB Balancer

Michael-----

The LT-1 cam, GM #3972178, is a relatively high RPM camshaft which also replaced the 64-65 "30-30" cam for SERVICE. Installing this cam in a 327, even if it were originally a 300 hp 327, converts the engine to the equivalent of a 62-65 SHP engine with a tad lower compression. Since the engine "becomes" a SHP 327, a SHP balancer is the appropriate balancer.

For 327 engines, the 6" balancer was only used for low to medium performance engines with low to medium performance hydraulic lifter camshafts. It's not appropriate for use in a SHP engine with a camshaft that produces peak power at about 6,000 RPM. Would a 6" balancer work for such an engine? Yes, it would. But, it's not the appropriate balancer. If it had been, GM would have used them for 62-68 SHP 327s. But, they didn't.

[Joe L.]

Addendum

Steve-----

One more thing. If the 327 engine being "converted" is the type which uses a crankshaft snout which is not drilled and tapped for a balancer retaining bolt, then you must add this tapping in order to use the GM #3817173 balancer. The interference fit between balancers designed for retaining bolt versus non-retaining bolt cranks is different. The non-drilled crank snout will not establish a tight enough interference fit to work reliably with the 3817173 and it is necessary to have the additional retention provided by the balancer snout bolt.

Absent the bolt, the only balancer available for use with a non-bolt-type crank is the 6" balancer GM #3896904. I don't recommend this for use with your modified engine, but it's all that's available for use with a non-drilled crank snout. DO NOT use 6" balancer GM #3896903. This balancer is designed for use with retaining bolt cranks only. Many folks who have experienced "flung" balancers used balancer GM #3896903 on non-retaining bolt crankshafts.

You can't use a 350 cid balancer with a non-drilled crank either (even if you re-mark the TDC line on the balancer so that it will be compatible with the pre-69 timing mark). All 68+ 350 cranks use the retaining bolt and, therefore, use balancers designed for use with the retaining bolt.

[Michael H.]

Re: C2 SB Balancer

Joe,

Unless an engine is going to see prolonged high RPM full throttle operation, there's no reason why the 8" balancer is a necessary or even desirable item. That balancer was designed for use on competition cars and had little to do with street driven cars. On the street, an engine passes "through" the critical crankshaft flex speed briefly as it's accelerated through each gear and "through" the torque peak which is the moment of greatest C/Shaft flex or twist. In competition, especially at long tracks like Daytona, the engines would run at or near the peak of flex or twist for extended periods of time and this was the reason for the large damper.

The point of greatest crankshaft flex is generally at the torque peak of an engine so the point of greatest inertia ring activity is at this point also. This means that the higher RPM potential of the LT1 cam has little to do with C/Shaft flex. It all has to do with the actual amount of twist in the shaft and that comes from power inputs, not RPM. I really don't think the LT1 cam is going to make any drastic changes in that area.

Some of the negatives on the 8" balancer are, as you mentioned, the fact that the crankshaft may not be drilled and tapped for the retaining bolt and also the fact that the timing chain cover would probably have an incorrectly located timing tab. Also, there's the addition of absolutely unnecessary and unwanted weight and it couldn't be in a worse location, mounted near the front of the car. Any additional weight shouldalways be added to the mid section or rear. Then there's the unnecessary and unwanted additional engine rotating mass weight. Ultimately, a lighter rotating mass is much more desireable. There's absolutely zero performance gain with an 8" balancer. It doesn't do a single thing for balancing the engine, has absolutely nothing to do with that. Then there's the availability problem. The correct finned balancer is long gone and all that's available from GM is the current "unfinned" unit.

When you add up all the positives and negatives on this issue, including the money it would require for the change, I would think the 6" would be a decent choice.

[Tracy C.]

A couple more things to consider...

Don't forget about the timing tab when selecting between your 6" and 8" dia balancer, you will need to match up to the existing timing tab placement on the timing chain cover. (or be prepared to change the cover to match it to the balancer)

Also, the "173" balancer is thicker than a typical "6" unit. This will hose your pulley/belt alignment if you change from one to the other.

good luck,
tc

[Joe L.]

Re: C2 SB Balancer

Michael------

What you said being the case, I don't see why GM didn't use the 6" balancer in the first place? It would have been considerably less expensive for them. Plus, every SHP engine that GM built for Corvettes was a PRODUCTION-type engine intended for street usage, although some may have been used for racing purposes. However, GM used the 8" X 1-13/16" GM #3817173 on ALL 1962-68 SHP 327s, including 1962-63 340 and 360 hp, L-76, L-79, and L-84.

Also, GM used an 8" X 1-5/16" balancer on 69-71 300 hp engines and an 8" X 1-11/16" balancer on all 69-81 LT-1, L-46, and L-82.

As far as the "finned" versus "non-finned" balancers go, it is true that the 3817173 available for about the past 15 years, or so, is "non-finned". However, that's really only an issue for folks concerned with "squeezing out" every possible juding point. The current "non-finned" version of the 3817173 is completely equal with respect to functionality to the "finned" version. If one wants those extra few judging points for the "fins", there is available a reproduction of the "finned" unit (for about $350).

[Michael H.]

Re: C2 SB Balancer

Joe,

I think the big difference on the balancer selection is the intended use of the car. I probably should have been more specific. If someone has serious plans of running one of these old cars hard and often, it WOULD be a good idea to use an 8" balancer. I suppose I assumed the owner was just going to weekend cruise and not tangle with people at every stop light or amature road race the car. If the owner just wants to install the solid lifter cam because it sounds cool, then there's no point in adding the 8" balancer but if he's seriously going to run the car hard, then I agree with you 100%.

[Duke W.]

Re: C2 SB Balancer

This is being beat to death, but when you install a LT-1 cam in place of the medium performance 300 HP cam you raise the usable rev range to SHP spec - 6500 RPM. GM engineers determined that a special harmonic balancer (actually a torsional damper) was needed for these high revving engines and all were equipped with the "special" 8" balancer. Will it function with the original 6" balancer? Probably, but why not do the upgrade right.

When upgrading from a medium performance hydraulic cam to a mechanical lifter SHP cam I would recommend that other SHP parts be included in the upgrade. This includes the balancer and the large oil pan and windage tray.

Also, the pre-'66 connecting rods are weak, and should be at least upgraded to the '66 design, but, preferably they should be upgraded to Crower Sportsman if you want a bullet proof bottom end.

Duke

[Duke W.]

Re: A couple more things to consider...

SHP/FI 327s did use a different cover. I'm not sure why. Does the cover for the 6" balancer have the tab welded closer to the crankshaft centerline such that the 8" balancer will not have adequate clearance?

Duke

[Joe L.]

Re: C2 SB Balancer

Duke and Michael------

Plus, consider this:

GM #3817173 8" SHP balancer---current GM list price= $107.10

GM #3896903 6" 327 balancer---current GM list price= $163.42