I am going to replace my original harmonic balancer on my 94 LT1 base engine. I have a new Dorman brand original replacement balancer from Rock Auto. Included instructions indicate that I may need to install weights in holes to match the existing balancer. My question......I thought balancers were neutral balanced and the LT-1 engine was externally balanced by the flexplate or flywheel, depending on transmission. Am I wrong? If so, where do I get weights to match the original balancer. Thanks in advance.

Mark

 

IIRC the weights were added to fine tune the balance if excessive NVH (noise, vibration, harshness). You will most likely find no weights. If you do the are like roll pins, don't know where you would find them but I would start with the usual suspects - Summit and Jegs

 

You can get the weights from the dealership. The problem is where to put them on the flywheel and balancer. There is a tech order out there that has several positions for the weights depending on vibrations. It's a trial and error system to find a balance. I know, weird. My fix is to internally balance the engine and neutral balance the flywheel and balancer. Remember, the balancer doesn't have a key to line it up on the crank so you have to mark it so you can reinstall it correctly.

 

I thought the tech order was for DMF field balancing and for only a couple of model years. Are you sure the front balancer isn't keyed?

I would have thought the front balancer was neutral balanced (as mentioned by the OP). And, that no add'l weight is necessary. On FW's, you can have them weight balanced, maybe the same is true for harmonic balancers? Hmmmmm.....try checking on that.

Again, for the DMF's, field balancing was to compensate for a change in design that wasn't correctly implemented before assembly. There is a thread or two on the subject (though not recently). And, its' these external-balanced DMFs that accepted dowel for balancing. Putting them in the balancer is news to me.

By contrast, some balancers have the option of adding an external weight for external front balanced engines (400ci). You shouldn't need this and may be mistaking this option for this issue.

 

In this pic you can see the holes along the outside ring of the balancer... the weights will be little slugs of metal used to plug the holes.



Lay your stock balancer next to the new Dorman replacement. If the stock one has any of the holes plugged tap it out (use a hammer & pin punch) and transfer it to the same hole in the Dorman balancer.

I found a pic so you can see a factory balancer that has a few slugs of metal here.

http://www.hashmarks.com/techtips/ca...0and%20hub.jpg

Will

 

 

Thanks for the information. I'll do what rklessdriver suggested. Thanks for the advice to all.

Mark

 

Can someone who *KNOWS* please answer the question whether the 1995 LT1
( NOT an LT-1 ) is internally balanced ( netural ) or as some have opinioned , externally balanced by the flywheel.

I'm not sure if any of the clutch builders even know, and I have four different answers from four different manufacturers.

The somewhat vague , but possibly more correct answer is to have your machine shop
"match-balance" your new flywheel to the old flywheel.

Three different Corvette shops say the engine is

( 1 ) internally balanced ... no outside compensation required

( 2 ) externally balanced by the flywheel

( 3 ) externally balanced by the harmonic balancer.

How can this be such a hard question ?????


Don in Huntsville, Alabama

 

I BELIEVE the harmonic balancer is neutral balance for 2 reasons:

1. The HUB that is bolted to the crankshaft has no keyway. The crank has a keyway slot, but the hub doesn't. Because of this the hub can move in relation to the crank if this ever happened it would upset the engine balance.

2. I have an underdrive pulley on my car. On f-body LT1 cars the pulley bolts behind the balancer and the stock balancer is re-installed on front of the underdrive pulley, which would preserve any balance imparted by the balancer. The Corvette, however, doesn't have room. The underdrive pulley is actually a completely new balancer which does not require any weight matching for installation. I've been running the underdrive pulley for years with no ill effects and I don't always drive easy.

At least this is how it works on my '92, I imagine yours would be the same.

 

Don-

The balancer is neutral balance (no counterweight).

The Flywheel is external balance (big C shaped counterweight).

I don't know why this question keeps comming up. Every SBC built since 1986 is like this. This includes the LT1/4 and the L31 Vortec, ZZ3/4 crate motors as well.

Some LT1's had factory balance problems. This was because it was GM's first prodution attempt with the PM rods and short skirt lightweight pistons.... When they ended up with one that had a vibration the factory assy line workers stuffed little slugs (weight) in the outside holes of the balancer or Flywheel (sometimes both) to stop the vibration.

This was an assembly measure to stop the vibration on certain cars, nothing more.
Will

 

This makes good sense. I was recently looking at flywheels for my car and it said that it's balanced to factory spec and thus doesn't need to be match balanced.... how could they possibly do that unless they were all done the same.

 

Btw...glad my balancer pic came in handy

The pins are available from the dealer if you're unable to drive yours out. Some holes may have two pins installed.

 

just a dumb question, why are you concerned with replacing?

 

Because only limited number of units had the added balancing. I recall that the actual number of cars that had the weights added was in the few hundred range. Once the process was perfected, all the flywheels were the same. When you pull the flywheel off, it's pretty obvious if they added weight.

 

Makes sense to me, and calms the fears of changing the flywheel. Granted my LT1 is fairly early, actual build date was sometime in '91

 

While I don't want to confuse the issue or get into a arguing match; I do want correct information posted. All gen 1 and 2 sbc engines with the exception of the 400 are internally balanced. Th only difference between pre-86 and 86 was that they moved the weight that was on the end of the crank (which btw is external to the rms) to the flywheel. All 1-piece rms flywheels are balanced the same. Again the conterweight on the end of the crank which is outside the motor was moved to the flywheel to allow for a 1-piece seal. This doesn't change the balance of the motor. While I can understand why people think its external balanced, it's better to know the truth.

 

Thanks. First time I've heard this one. FWIW, the ZFDoc had forwarded a document about DMF FW balancing that happened as a result of a seal design change. The actual GM document (which has been posted on this site) seemed a bit fishy to me. Your explanation above makes more sense. And, if the issue you cite occurred with the earliest LT1 units, it corresponds with the document forwarded by Bill.

I agree the issue of weight balance is misunderstood by many -- especially with ZF transmissions. When I had my 383 build, most builders in my town moaned and groaned when I asked if they were sure about it's balance issues. To make sure I picked the shortblock builder most knowledgeable, I talked to Bill, Eagle, and Scat. They all confirmed that 1pc RMS engines are internal front and external rear. Though 30g was provided as the external weight for flexplates, I believe the offset weight in a DMF could be higher. Certainly, the size of the weight makes it look heavier.

I do know the perimeter weights for a DMF field balance are 1-oz per hole. This thread is the first time I've heard about the perimeter option for the front balancer.

FWIW, on my setup, Will (Recklessdriver) pointed me to a balancer option that came with a removeable balance weight. (Thanks again!) For an extra $10, it gave my builder an extra option for balancing my RA. Ultimately, he didn't use it. And, the same should be true for LT motors since the cranks are interchangeable with L98s. Plus, everyone knows the DMF for LTs did not change (ext weighting) after L98s finished production.

ZR-1's are the only ZF6 car that carried a different model DMF for their use.

 

External balance means weight is used outside the crank to balance the assembly. That's what you described above. That's external balancing!!!

Internal balance means the crank is balanced as a single, stand-along piece.

Yes, it's better to know the facts.

 

Yep...Anytime you swap DMF's, make sure any perimeter weight (perimeter pegs) on the DMF is moved to the new FW. Anyone can do this by buying weights from the dealer and populating to match a take-off unit.

If someone changes from a DMF to a SMF unit, they should take both pieces and have them weight-matched -- especially if any of the perimeter holes are populated. If not, theory says no balancing is "necessary".

The internal/external config is true for both automatics and manuals. So, you could (as people do) convert from auto to stick or vica-versa. As mentioned, flexplates have the same offsetting weight.

 

I don't know about ONLY early LT1's having the problems...

As far as I know it's a problem with random cars across all years of production. It's a tollerance stack deal on the bob weights. IMO GM further'd these balance problems when they switched the connecting rods from Forged to PM.

In the 90's when these cars were new and everybody was modifying them (we did a bunch of engine work on them) I use to have a GM paper that explained the weights and field service balance proceedures. Probally the same paper Bill has.

Back when my car was stock, I burned up the stock clutch and was forced to fix it in a hurry (it was my DD at the time).... I changed the DMFW to a Fidanza Alum unit.... of course when we got it apart, my DMFW was slugged (had 3 weights in it).....

Because I was in the process of building the current engine, I didn't bother to match the Fidanza to the stock DMFW and sure enough the car had a minor vibration at idle to just off idle. I put almost 20K miles on the car before the current engine was done with no ill effects.
Will