Even though I believe the LT1 damper is neutral balanced, as I said above, it is easy to understand where the confusion comes about.

The factory service manual states to make sure you put the damper back on in the same position or with the arrow pointing up with #1 at TDC.
This certainly suggests that there could be a problem otherwise.
It also states to put weights in the new damper in the same location as the old.

Since I was planning to change my damper from an LT1 damper to an LT4 damper, I had to make some decisions.
First, I researched the issue -- some of which I posted above.
And, my original damper was NOT installed at the factory with the arrow up with #1 at TDC.
In addition, I decided to put an aftermarket keyed hub on -- this eliminated any possibility of me selecting the position of how it would be put on. It will only go on one way, and that way is determined by the manufacturer of the keyed hub.

So, I:
1) Have a keyed hub that negates me positioning the damper.
2) Installed an LT4, dual-mass, damper and didn't attempt to put any weights in it (what was in it, is what I got).
3) Have absolutely no balance problems.

Thus, my conclusion from research and experience with my engine is the factory manual states things that won't hurt if you do it, but probably doesn't make a difference at all.
At least, in my case it definitely doesn't.
My one suggestion is to NOT attempt to put any weights in a new damper (use it as it comes) unless you absolutely have confirmed you have a balance problem with it.

Tom Piper

 

Okay, I sent this thread to TJWong. If he says I am wrong then I will change my way of thinking. When I first put my first blower on from Carroll Supercharging, they were very specific in having me put the weights in the dampner that was modified for second belt for the blower. It was to match the first dampner so I wouldnt have any vibration. Now on my 383 that is internally balanced, I was told by the engine builder to leave weights out so the dampner was neutrally balanced. A keyway was also cut in the hub to align the arrow staight up when the 1st cyclinder was at TDC, by Thunder Racing. When I replaced the defective balancer on my Trans Am, the FSM says to put the weights back in the exact position of the original dampner. Now do you see why I think this way. Everybody to this point, that I have come in contact with, that builds LT1's have led me to believe this.

 

I understand the confusion, and I have read the same thing in the FSMs. I actually addressed those issues in my last post above.

However, logic has led me to my belief, and unless I see some highly concrete evidence the other way, I am staying with it.
That doesn't mean you will believe in what I am saying.

Some things to keep in mind:
1) If a new damper that has never been on any engine has one or more balance weights in the holes, it wasn't done to balance any engine -- it was done to neutral balance the damper alone, that you can take to the bank.
2) If an engine is out of balance, there is no reason weight can't be added to the damper to balance the engine -- that does not mean it should be done that way. In this case, the part is a combination damper and balancer -- it has two different and distinct characteristics to attack two different problems. Then, as I said, it is a damper/balancer instead of a damper.
Many people (including most of the professional bulilders) confuse torsional vibration and engine balance -- they aren't even close to the same thing. A damper is designed to eliminate torsional vibration, a balancer is designed to eliminate out-of-balance problems. A combination damper/balancer does both. You will never feel torsional vibration because it is too high in frequency, but it can destroy your engine easily. You will almost always feel an out-of-balance problem.

Read my posts at the end of this thread:
http://forums.corvetteforum.com/show....php?t=1927280

Tom Piper

 

Once again Tom, you have nailed it.


The General designed the LT1 to be neutrally balanced in the front. That is a documented fact!! Some engines, I don't think many, were fine tuned at the factory by drilling holes in the neutrally balanced dampner to cure an out of balance situation probably due to a badly balanced crank or flywheel/flexplate. In that case , they must be returned to the original position. It can't hurt to do it in any case. The FSM even suggest rotating the dampner in 90 deg increments to cure a "shaker."

The necessity to adjust the weights in a replacement dampner is surely due to the fact that the replacement may fit many applications.

 

When you purchase new dampers from GM they have zero added weight in the holes.

The weights ("pins" as GM refers to them) are purchased separately.

The FSM is very specific that weights be added to the new damper to match it with the old damper.

This leads me to the logical conclusion that the damper is neutrally balanced at time of manufacture and that the addition of the weights "match balance" it to the old damper which had been fine tuned for the engine it (old damper) was removed from.

 

Now, why would the factory drill holes in something that was already made with holes in it. Doesn't make sense. Why, if the dampner is nuetrally balanced like you said, would try rotating it in 90 degree increments, as it wouldn't make a difference, because it is nuetral. Doesn't make sense. I do believe the dampner is neutral until you put a weight in it. That makes sense.

 

What exactly is your point? Are you saying that the LTX was not designed to be neutrally balanced in the front. You are hung up with holes. The rotating of the dampner is to correct the failings of man. Do you just need to be right? The OP's original question was answered long ago.

 

From post #19 in this thread:
Some sources of information:
http://www.vibratechtvd.com/VISCOUSTECH.htm

In particular, about half-way down:
-------------------------------------------------
Elastomeric Dampers

In elastomer dampers, the outer inertia ring is fixed relative to the mounting hub through a ring (or rings) of elastomeric material (usually rubber). These units must be balanced after assembly to correct imbalance due to any offsets between the inertia ring and the hub that are created by the imposition of the rubber ring between them (note the large balance holes on many of these dampers). An elastomer damper that is not balanced out of the box is not self-correcting at any speed.
---------------------------------------------------

These people are professioinals at making dampers, notice they say that elastomer dampers "must be balanced after assembly" -- they are not talking assembly to the motor, they are talking after the "rings" are bonded together with the elastomeric material.
Also, notice the part about the balance holes.

I am not saying that some engines weren't "trimmed" by GM. To me, the engine should have been balanced correctly to begin with.

What I am saying is the smartest way to assemble the engine is to balance the front without a damper and neutral balance the damper.
That way, any neutral balanced damper will work without further adjustments.
I am also saying that, since it is more difficult to take out weights, a smart move with a new damper is to try it the way it comes before putting weights in it.

This part is just my personal opinion:
As far as the FSM saying "weights are to be added to the new damper in the same location as the old damper to maintian balance."
Anyone that tells me that, including GM, better have a method to insure the location of the damper (like a keyway in the hub) to make me thnk they are serious.
You may think otherwise.
But, keep in mind, my original damper, from the factory, on my '92, was not installed anywhere close to the "arrow" pointing up when #1 cylinder was at TDC -- so much for me believing the FSM.


Tom Piper

 

Reference: http://forums.corvetteforum.com/show...33&postcount=3

I am CFI-EFI, and I approve of this message.

RACE ON!!!

 

Off on a tangent, huh guys. My question was about the flywheel swap. Match balancing is not an option because I don't have the manual flywheel. I intend to use my original automatic flexplate. Factory balance on both should be the same shouldn't it?

 

GM neutral balances the damper during manufacture. When a new damper is purchased, one will find that it has material removed around the inside edge. This addresses the statement from "the professionals" of the damper needing to be neutrally balanced.

Since a given engine may have been trimmed by GM during assembly, one must repeat the process with the new balancer. Hence the direction to add the pin weights to the new damper. Therefore while in theory the front is neutrally balanced, reality is that they are not and require some amount of balancing.

Regarding location and needing a keyway. GM made the assumption that a tech could locate TDC and then install the big arrow on the hub at 12 o'clock. It should also be noted that the damper will only install on the hub one way, which in theory should prevent it from being installed improperly (again assuming a tech can find TDC and recognize the arrow).

We can agree to disagree

 

YES.

 

You might get lucky and have no vibrations. But, your engine was externally balanced placing weights on the manual flywheel. To get a perfect balance you will need that original flywheel to match balance your flexplate.

 

Sounds like a deal to me.

See, we do agree.


Tom Piper

 

When I built my 383 LT4 I bought a keyed hub. I installed it and my factory LT4 dampener on a neutral balanced 4.3 crank. The dampener was almost perfectly neutral. We did drill on it just a little to get it perfect. Also machined the weight off the DM flywheel and made it completely neutral. I installed both on my internally balanced rotating assembly and was good to go.

I did not touch any of the weights in the dampener and it was very close to perfect.

 

What I am interested in is how many weights were in the holes of your neutral balanced damper?

My neutral balanced LT4 damper has one weight in it -- so, the weight was never for balancing the crankshaft, it is there to neutral balance the damper.

In fact, I would like to know about any "new" LT1/LT4 dampers that were never on an engine and how many weights were in them.


Just briefly (I really don't want to start an argument on this), on another subject, since you have a 383 that has more torque than stock, you may want to consider another damper to prevent torsional vibration that the stock LT4 damper can't eliminate.
The more torque per combustion pulse, the greater the torsional vibration amplitude.
That is the reason I put an LT4 dual-mass damper on my modified LT1 -- I figure my modified LT1 has a torque curve that is about the same as a stock LT4. So, my belief is the LT4 damper will be adequate. Enough on this subject.

Tom Piper

 

That's not true. The flywheel is cast w/the "counter weight" as part of the casting.

 

This statement is what I have been trying to say all along. I guess I just didn't say it well enough.

 

Maybe, but not until long after the question was accurately and correctly answered in posts #2 and #3.



Although you didn't state, initially, that the manual flywheel wasn't available, I covered that contingency in post #3 when I said:I am CFI-EFI, and I approve of this message.

RACE ON!!!

 

Jim is correct, the small weights are to make sure that the balancer is indeed neutral. If you build a internally balanced engine, you will want both the flywheel and the balancer neutral. The stock LTx flywheel and for that matter any one peice rear main crank equipped small block has a neutral balancer and a externally balanced flywheel. Remember how the older two peice rear main cranks had a retangular shaped flange? Well with one peice design that extra chunk of steel was machined off to make the rear main a one peice design, the weight that was removed in the new design simply moved to the flywheel or flexplate.