Assuming the orginal factory flywheel/PP assembly is indeed supposed to be zero balance, and assuming that a new replacement assembly is zero (either by design out of the box or by an owner having his balanced), then we can assume that the weights from the original wheel are there as a "final adjustment" to balance the entire engine assembly and eliminate the stacking error of the harmonic balancer, crank/rod assembly, and the clutch assembly. So we can then assume that the weights need to be transferred to a new assembly, like the service manuals have been telling us, to maintain the original engine balance. This is all logical. But are all my assumtions correct?

We now see that the GM online info refutes this with the "Four Senarios" discussed earlier in this thread. And we know that many members have done the weight swap by the book and ended up with a shaker, while other have hung a zero balanced wheel/PP assembly on their cars and were dead smooth. And maybe there's some guys who have swapped the weights like they're "supposed" to do, and the result was fine.

So, are we any closer to understanding the truth?

I have an associate at GM Powertrain (he used to be on the C5 program) who is going to try to find the "right person".....someone who knows for a fact how the LS1/6 engines are balanced, and what's the deal on replacement wheel/PP assemblies, etc etc. If I can somehow get very lucky and "get connected", you can be sure I'll post the results.

 

Hi,
Chevy says that the LSx engine is internally balanced which means that they are balanced without an external balance weight as used on the old SBC 400 or the BBC 454’s. They also say that the flywheel /clutch and the damper are zero balanced but they seem to miss this on occasion.

Every Vette engine is final balanced after assembly by running it on a test stand that measures the total engine/damper/flywheel/clutch imbalance and shows the tech where to put standardized weights on the damper and/or flywheel. If they assemble an engine with a badly balanced flywheel /clutch assembly this may fix it. This procedure does not tell them if the flywheel/clutch was zero balanced! It can only balance the total system. This is a very sophisticated system that Chevy is very proud of and it does make our cars better.

The only way to change a flywheel/clutch and assure that your engine balance does not change from this factory value is:

1.) Mark the old flywheel and crank before you take it off so that you know where it was in relation to the crank. This is necessary because it was balanced with just this one crank, rods, pistons, etc. The stock pressure plate can only go on one way due to the position of the dowels so you don’t need to mark it.
2.) Take the old & new assemblies to the balancer and have them match the balance of the new to that of the old. This may not be zero balance but it is the best balance for the parts that were in the engine when it came from the factory.

If you use a zero balanced clutch assembly and you also take the weights out of the damper, you will have an engine that is balanced as good as a Camaro! Maybe that’s good enough. If you change the crank, rods, pistons, etc you can balance the crank for the new parts and then go to a zero balance flywheel /clutch and damper just like a SBC.
Good luck,
Steve
:seeya



[Modified by SNW Vette, 12:44 AM 2/2/2003]

 

SNW--If you are correct (and it sounds correct to me), this would explain all the odd results that we have seen on this forum from all the various combinations of replacement wheel/clutch assembiles. But it also means that a guy has NO RELIABLE WAY to install a correctly balanced assembly. It's simply a crapshoot, except to go to the trouble to balance-match the new flywheel to the old.......including matching an imbalanced factory condition. This seems like insanity to me, to design a mechanism that a dealer can't reliably replace.

Hopefully, I can confirm this if I hear from a GM Powertrain guy.

 

I too would like to see the definitive answer to this issue also. Let us know what you hear.

Robert
QUOTE]SNW--If you are correct (and it sounds correct to me), this would explain all the odd results that we have seen on this forum from all the various combinations of replacement wheel/clutch assembiles. But it also means that a guy has NO RELIABLE WAY to install a correctly balanced assembly. It's simply a crapshoot, except to go to the trouble to balance-match the new flywheel to the old.......including matching an imbalanced factory condition. This seems like insanity to me, to design a mechanism that a dealer can't reliably replace.

Hopefully, I can confirm this if I hear from a GM Powertrain guy.[/QUOTE]

 

So the LSx is internally balanced. The factory adds the front pulley and flywheel / PP assembly and checks and adjust the whole assembly and adds weight(s) in the final balance process.

You buy a replacement FW/PP zero balance and install. Now what happens if you replace the front pulley??

It really seems like GM is doing everything possible to make it impossible for the DIY'er to do anything and have it come out right.

As a matter of fact, I'd bet the dealers don't want to get involved with a clutch swap if it's really this difficult. They would like to get it right the first time so they don't have you coming back again and again during the warrenty period on the work to get it right. They'd loose money on the service.

Could the problem be changing the stock Ls1 clutch assembly for a Z06 assembly be the problem????

:cheers:

 

I have not seen a post on this forum from someone who has balanced the assembly, installed it per the service manual, and then had a problem. On the contrary they all seem to report it being very smooth. Mine is smoother than stock. Perhaps GM calculates the weight before the dampener and just prior to the flywheel install. Then they place the weight on the flywheel and install it. This would make more sense and explain the inconsistencies.

 

Due to the questions raised here I called and had the advisor ask the mech that did the work on my car what he did. Turns out he did not transfer any weight as I was originally told. They seem to be under the impression the weight is more for the clutch than the engine. Andy at A@A, who originally had urged me to do this, said he doesn't transfer the weight either. He has had same results as me.

 

Blocktrdr - It sounds like your experience says the weight(s) is/(are) GM's way of balancing the clutch assembly after installation rather then balancing the assembly before assembly.

Do you agree?

That would make sense to me, however, a dealer would have to balance the clutch assembly prior to installing a new clutch. That just doesn't sound like something a dealer would do.

Another issue might be my change from a stock to Z06 clutch. I did notice two of the three mounting arms have, what looks like rivets in them, that are missing on the 3rd arm. Perhaps there is something different, in the internals, between my early (97) LS1 and the LS6? I could buy that also. I seem to recall reading some where that the LS6 uses a different piston.

If that is true, then the only way to get a Z06 clutch smooth on the LS1, would be to zero balance, test and move the weight if needed to fine tune it to the LS1.

Thanks for all the feedback.

Steve

:cheers:

 

Before everyone jumps to a conclusion, let's review what we know.

The LS1/LS6 has an internally balanced crankshaft. This is clearly stated on the National Corvette Museum website under 2002 Z06 info - "Power Boost" http://www.corvettemuseum.com/specs/2002/power.shtml

However, the repair manual refers to the balancer on the front of the engine as a "Crankshaft Balancer". The manual also states that the pressure plate is mounted on the flywheel so the light spot on the pressure plate is matched to the heavy spot on the flywheel.

I have copied the pertinent pages from the 2000 repair manual regarding clutch removal and installation, and a section on vibration analysis to a web page at http://temp.corvetteforum.net/c5/steve_row/index7.shtml .

I do not have a copy of the document entitled "Engine Balancing" which states that the weights should NOT be transfered to the new flywheel when replacing the clutch assembly. However, I have seen and read it. And my Z06 is proof that it worked. This document applies to all C5's from 1997 to 2003.

Another curious thing is that the F-body version of the LS1 has no weights in the balancer or the flywheel and furthermore the front of the crankshaft is keyed for the balancer. For some reason the F-Body information is included in the 2002 Corvette repair manual ( and perhaps other years) which I spent some time reviewing this evening to be sure that nothing had changed from the 2000 manual. And nothing concerning the balnacing weights, etc., had changed. There have been some improvements in software and procedure for the Engine Vibration Analyzer.

It would appear that the only way to insure that you remain vibration free when changing the clutch assembly is to take the original assembly and the new assembly to a machine shop and have them balance matched so that the weights will work in the new assembly as they did in the original assembly.

I would certianly like to hear from one of our Corvette repair technicians on this subject.

 

Steve and all--

I heard from my pal in GM powertrain today......but he's still trying to get with the right guys, both of whom are on travel. He's still on the case, and has promised to get back to me next week with some credible info. [Note: my guy is not the balance guru, but he knows who they are!!]

 

What's the latest on this Tracey? Transfer weights or don't transfer weights? :confused:

Robert

 

Tx99FRC and all,

Nothing yet. I'm at the long end of a "favor" line. But, I'm supposed to harass my contact sometime this week, so thanks for the reminder.

I would LOVE to get to the bottom of this. Keep your collective fingers crossed for me. I hope to have the Straight Dope from GM Powertrain, but don't hold it against me if I fail.....it's not for a lack of wanting!

 

What do you all think of running the engine right after the new clutch is bolted on? Is it safe? I haven't changed my clutch yet, but I am very interested in this topic for the future. Doing a little brain storming, IMO the biggest pain on doing a C5 clutch replacement is dropping the transaxel/torque tube assembly to access the clutch. Therefore, it would be helpful to check for any vibration before bolting the torque tube et all back together. A dial indicator mounted to the frame or the ground and contacting either the rear of the engine or the bell housing can give some indication of vibration amplitude. Look for the total indicator fluxuations. Do it first with the original clutch, then with the new clutch. If it is possible to run the engine this way, you can also do it with no clutch. While not an absolute method of quantifying imbalance, this should give some indication of relative inbalances. The idea here is to see if you have increased engine vibration before bolting everything back together and taking corrective measures. :cheers:

 

Just give us the word when you hear. Tnx. :thumbs: