Bill Curlee

Your engine was INTERNALLY balanced when it was assembled at the engine factory with the clutch/pressure plate and flywheel installed on the test stand. MN6/MN12 OEM clutch/pressure plate and flywheel was then critically balanced further at the engine building facility to remove any small vibrations that are amplified and felt in MN6/MN12 equipped C5 drivetrains.

They installed small weights/pins in the outer rim of the FLY WHEEL and in the front damper to get the MANUAL MN6/MN12 cars drivetrains down to a nats *** zero balance.

When you removed the old flywheel, it needed to be matched marked to where it was on the crank, so the OFF SET can be put back in the exact location on the crank that it was when it was further balanced at the factory.

If your car didn’t vibrate before you pulled it apart and replaced the clutch, it was good! Even if the clutch had been replaced sometime in the past!.



Here are your options.. Find the OLD flywheel and have the new flywheel OFF SET BALANCED to MATCH the old OEM flywheel. Once its correctly offset balanced to match the old flywheel, reinstall the new off set balanced flywheel to the reference marks on the crank.

Once most people get this far and have a bad vibration issue,,, they usually didn’t reference/ match mark the flywheel to the crank and or they tossed the old flywheel.

SO,, here are some OPTIONS.

EXPIEREMENT 1. Remove the bell housing inspection cover on the bottom of the bell housing. Number the pressure plate bolts.
You can install some washers under the bolts for the pressure plate starting at position #1 presure plate bolt and see if it IMPROVES or INDUCES MORE vibrations. If it induces more, move it to the next sequence pressure plate bolt. Do that to all the pressure plate bolt locations. Figure how many washers it takes and where they need to be installed to remove the vibrations. Hey,,, Its free and it works!!

Solution#2 I helped a C5 owner in Canada fix an EXTREMELY BAD vibration problem after he installed a new clutch/pressure plate.

YES,, , he did the bad things.. No reference marks on the old flywheel and crank and he tossed the old flywheel.


I had him look in the yellow pages or GOOGLE and see if he could find a local MACHINERY BALANCING COMPANY. He did and the guy came out and hooked up his balancing equipment and told him EXACTLY where to add the exact amount of offset washers under the correct pressure plate bolt.

NOTE! He had to get a longer grade 8 fastener and incorporate the added weight of the longer bolt into his stack of washers calculations.

It worked 100% and he couldn’t have been happier..

Hope this gives you some ideas and it helps you resolve the issue.


Bill

wcsinx

I have heard (but never personally seen) that in some cases GM would counter balance the PP as well.

racebum

that's the thing bill, his flywheel was only off 3g. have you ever heard of gm balancing the pressure plate with weights or drilling? beings his plate was 12g off that may have been the deal as 12g is enough to create a driveline vibration especially if it was used as a counterbalance and this new assembly he has on is off xx grams in a totally different location

btw: your experiment 1 idea is golden for the OP

randyfl

I had the same problem with my Monster. I took the old clutch and flywheel & the new clutch and flywheel to a machine shop and the them balanced to match. This solved my problem. As it turned out, my factory clutch and flywheel were NOT neutral balanced. Hang onto you factory clutch and flywheel. You may need them for reference in the future.

Good luck

Bill Curlee

The flywheel and pressure plate are balanced as an assembly dynamically on the engine. When I did my SPEC Dual disk, I just matched balanced the Flywheel and took SPECs word that it was zero balanced. It worked out fine! NO VIBES.

Bill

racebum

well OP

you could try the washer idea and get 12g of washers and go bolt to bolt till you find the location that solves your vibration. if adding the 12g at first makes the vibration worse, go 180 from that point and fine tune from there a bolt at a time either direction until you find the location that gets you back in balance

option B is pulling it all and having the new set balanced exactly like the old one

PRE-Z06

As we said on the phone, if the unit is out of spec we'll pay the machine shop to rebalance it for you.

I apologize for the issue, things happen from time to time out of our control.

The original clutches are not manufactured by GM, they are sent to GM to assemble with vehicles. In order for the clutch to actually be balanced with the engine the setup would have to stay with said engine throughout the entire build process as the rotating assembly/clutch/dampner would all have to be done together.

Regardless, keep us posted whether on this thread or via phone and we'll stick to what we told you in the beginning. If it's on us, we'll make it right.

thbwlZ

Lots of pretty good info in this thread, but some that is still kind of close
Please take a look at this thread:
http://forums.corvetteforum.com/c5-t...ion-twice.html
within it I attached many links to articles describing the engine build process, and the HOT BALANCE PROCEDURE performed by GM for LS engines used in manual transmission vette applications.

PRE-Z06, Monster clutches by all accounts are very good clutches, with great customer service. Your clutches could be perfectly zero balanced, and still have vibrations in a manual vette, because of their sensitivity to small imbalances. Just paying to have the unit balanced, unfortunately may not solve the vibration issues, and no one is any closer to a solution.

GM gets the flywheels and Pressure Plates from the manufacturer, having already been balanced to within certain balance tolerances. The flywheels are actually at a smaller tolerance than the pressure plates. The flywheel and clutch is then assembled on the engine and the whole engine is run on the balance stand, using natural gas, and it is fine tuned balanced down to a smaller degree than needed in other applications. Small imbalances that could be present from internal rotating components would be fine in other applications, but can transmit vibrations in a manual vette. So they balance it closer down to zero by installing balance weights in the flywheel, damper, or both, as needed. some don't need any weights, but all are run in the balance stand and checked. Since the flywheel and pressure plate are assembled together, and weights are only added to the FW (for the rear plane), those weights are "counter balancing" effects from the FW AND pressure plate AND the internal rotating assembly. So the only way to accurately maintain this original factory balance, is to have a replacement FW/PP together as an assembly match balanced to your original FW/PP together as an assembly. (of course you can match the FW to original FW, and PP to original PP, but that is more work ).

The bottom line is, if you put on a zero balanced FW/PP combo, you might have some new vibrations that you can now feel, but they are from the as built small imbalance of the internal rotating assembly only, and the engine is still fine. They don't hot balance the engines going into automatics. So they share the same build tolerances.

if the OP is already taking out his original factory FW and PP, the easiest thing to do is put them together and have a machine/balance shop measure the state of balance of the unit. then add weights or mill balance holes to make the replacement UNIT (FW/PP) MATCH the state of balance of the original.

think about it logically. if you removed you original FW/PP, put it in your garage for a few days, and then turned around and put it RIGHT BACK ON, (in the same exact orientation), you'd better have the same smooth operation as before, with no vibrations. SO, the only way to definitely duplicate that same scenario, with a replacement unit, is to have the new unit (FW/PP together) have the same state of balance as the original. Any thing other than that is taking a chance.

Racebum and Bill, good advice as always.

now isn't this fun??

thbwlZ

well, it looks like most of the links I had put in that other thread are dead. Some are still active. I apologize if anyone tried following the dead ones. I can find several again if anyone needed to see "proof" of a hot balance procedure.

PRE-Z06

Fun topic indeed.

I've heard of what you're describing on the hand built setups, IE LS7, LS9, dry sump LS3's but not the standard production units. Obviously as a company we do what we can, but, considering the OP wasn't a hand built setup as said above we directed him to a machine shop to have the setup "zero balanced" to match the internal balance of the production engine.

Here is the AllData version of the installation on a Corvette -

Engine Flywheel
* The RPO-LS3/LS7 flywheel, clutch disc, and pressure plate are each individually balanced components and are available separately. The pressure plate mounts, or locates, onto the flywheel dowel pins in the flywheel. If the pressure plate is not aligned properly onto the dowel pins and tightened down, the pins may bend and the plate may be incorrectly positioned, which will affect component balance.

* The RPO-LS9 clutch discs and pressure plate are a balanced assembly and not available separately. The pressure plate mounts, or locates, onto the six flywheel dowel pins. If the pressure plate is not aligned properly onto the dowel pins and tightened down, the pins may bend and the plate may be incorrectly positioned, which will affect component balance.

* Existing flywheel, clutch, and pressure plate onto the existing engine: Pressure plate position to flywheel must be marked prior to removal and installed to the original position. Flywheel position to crankshaft must be marked prior to removal and installed to the original position.

* Existing flywheel, clutch, and pressure plate onto a new engine: Pressure plate position to flywheel must be marked prior to removal and installed to the original position. Flywheel position to crankshaft must be marked prior to removal and installed to the similar position on the new engine. Do not remove balance weights from flywheel, if applicable.

* New flywheel onto an existing engine: Install the same size balance weights into the new flywheel in the same location as the old flywheel. Install the new flywheel to a similar position on the new engine.

* New flywheel, clutch, and pressure plate onto a new engine: Do not install balance weights.

Bill Curlee

OP

See if you can look up and contact a Machinery Precision Balancing Company in your area. Discuss your out of balance engine problem and see if they can resolve it. That would be your most accurate and easiest solution other than the washer trial and error method.

The Guy I helped in Canada was VERY HAPPY with his end result and from what I remember, it wasnt all that expensive.

Hope this helps.

Bill

thbwlZ

PRE-Z06,
You are correct that all the hand built LS engines, at Wixom, go through the balance stand process. All those engines go to manual transmission vettes. One of those dead links was to an article back in 2002 about the build process for the LS6 for the Z06's built in St. Catherines. They use the same balance stand and same procedure for post fine tune balancing the LS6's and LS1's (LS1's used in manual corvettes. Not automatics, and not Camaros). They also use the same method of installing balance weights into either the flywheel or damper, all the way back to early C5 manual transmission vettes. As I mentioned in that past linked thread, there wasn't as much internet available info back then. When the build center at Wixom started hand assembling LS engines, there were quite a few articles done on them, showcasing the builds. The balance procedure was done on all manual C5's as well. The service manuals also dealt with the balance weights, like your listed Alldata info does, back then. But the language changed around 2002.

In all versions of the service manual's instructions on this topic, they are all deficient (IMHO ) about how to replicate the factory balance when changing a clutch/FW. No dealership is going to match balance a FW/PP combo as part of a clutch replacement, so they put in instructions that can get you kind of close.

The balance procedure is done to get the final overall balance of the entire assembly (rotating internals, FW, PP) at both front and rear planes (Damper at the front) to a balance at or below .5 oz∙in. When all the internals are assembled in their "as machined" state, with all the tolerance stackups, there can be an imbalance higher than .5 oz·in, but good enough for safe engine operation. But in manual vettes, the vibratory transfer path is different, and a lower imbalance is needed. If you put on a perfectly zero balanced FW/PP combo, the internals can still be above .5 oz·in, and you can still feel vibrations. Just taking the OP's FW/PP and getting their balance as close to zero as possible is fine. What it will do is make sure that any resulting imbalance is only from the internals, and the engine is fine. However, he may still feel new vibrations, because it could be above the final spec.

The goal of the post balance procedure is not to just balance the FW and PP together, otherwise they would not be adding any weights to the Damper up front. The procedure is to get total assembly balance under .5 oz·in. There are much simpler ways to balance a clutch than to build a balance stand that houses an entire engine with accelerometers, runs it on natural gas, and then indicates where to install weights. If it was just about balancing a clutch assembly, they'd use a setup like a machine shop would use, and would ignore the damper. And before someone says, "well maybe they are balancing the damper only too?" Again, its not done on automatics, and they use dampers too.

sorry that's long.
in summary:
- all LS engines used in manual transmission vettes have gone through this balance process, even before Wixom.
- the internals of his manual vette may be above .5 oz·in, so a zero balanced clutch still might have vibrations
- this is still a fun topic, and I have had a good time researching on it in the past.

Pre, you guys are stand up guys to offer to help with his situation. But I would bet that your stuff is already fine to within whatever balance tolerances you set, and just blindly zeroing them is ignoring the whole situation. If the OP has already taken out his FW/PP the hard work is already done. If the original setup was smooth and vibration free, as all are from the factory, matching the original setup is the most sure way to avoid new vibrations.

thbwlZ

Bill, if he doesn't have the driveline torn apart already, and his clutch is still in, I'd absolutely agree. They will most likely use something like a EVA2 using accelerometers to find amplitude and frequency of his vibration, and quickly get counterbalance in the correct position/s. You can even install the balance weights with just the lower bell housing removed.

if everything is already torn down, he should just match balance to original. that is very cheap.

thbwlZ

now, it's so much fun, I had to go find an old article again:

http://www.vetteweb.com/features/vem...6/viewall.html

this is from 2002. The only thing incorrect is that they say only the LS6's were post balanced. I have confirmation from folks involved that the LS1's in manual vettes were also done. Plus, the service manual talks of balance weights in them as well. And one only has to see that some LS1's had flywheels and dampers with balance weights installed. Same procedure.

here's a thought exercise:

many people are unaware of this balance process, that's fine.
all service manuals reference the balance weights in some aspect.
what has changed over the years and directly conflict with their existing instructions are dealing with balance weights in the FW. What to do when replacing. Transfer or not to transfer, that is the question.
Well, ALL service manuals are consistent when dealing with the damper. They all say to transfer weights to a new damper, and replace in same orientation as new. This is to maintain a factory balance condition. The weights are installed as a part of the same balancing process, both in the damper, and in the FW. People won't believe that it's relevant to the flywheel/clutch replacement, but they WILL think its relevant with respect to the damper. Now consider the fact that the balance correcting capability in the holes of the damper are much much less than those of the FW, because the radius is so much smaller. Inernals are a component of this balancing procedure.

food for thought

randyfl

So here is my question?? If this balance procedure is performed on a completed motor in a stand, what type of equipment is used and why can't that equipment be used on a motor already in the car?

thbwlZ

randyfl, here is another link with a more current article, showing the whole process in more detail:

http://www.vetteweb.com/tech/vemp_10..._engine_build/

I doubt you would be able to use the same balance stand that GM used in the build facility, I don't know if anyone else even uses it. I know who I could ask to find out though.

However, if you wanted to perform balance with the engine and clutch assembly in the car, you could use an EVA2. Its a tool described in the service manual, and there are even places you could rent one. Or you could do the iterative trial and error method of installing washers under the PP bolt heads. Or you could do trial and error installing balance weights. Or you could take the factory unit, FW/PP combo to a competent machine/balance shop and have them match your new stuff to the factory stuff. Its all a matter of how much of a hassle you want to deal with. Anyone coming out to balance your engine while still in the car is going to use something like the EVA2.

The balance stand used by GM is a pretty substantial piece of equipment. Its not an engine stand with some simple tools attached. It allows the engine to vibrate in all degrees of freedom, then accelerometers identify the imbalance and tell the operator where to apply weights, if needed.

take a look through this last link I provided. Its not a dead link.

racebum

this thread should be in the sticky section. it has all the needed information for a clutch change and the balance on a c5

thbwlZ

You'd be surprised at how many people refuse to believe an external fine tune balancing is actually done, even after being shown the evidence. Not talking about people in this thread, but many others I have had to deal with. I think it's pretty cool what GM did/does to get the balance even better. It can just makes changing a clutch adventurous.

racebum

the final straw with me, besides reading the hordes of good info was speaking with a guy who was heavy in c5 racing back in 2001-2004 when they were the golden cars. the story about propane firing and what not was absolutely true, he had mentioned speaking with a GM engineer and seeing pics of the process. it's just as stated in this thread, the goal was to make the final balance in the manual cars under 1/2oz

that's why the balance was done after the clutch was installed on the engine. it's the combo of parts all having tolerances. many went through and did not need more weight added, some did.

even guys like ranger who live eat and breathe drag racing say the same thing and enough guys have had this issue that it's something everyone changing their clutch should at least be aware of even if their car is not offset balanced with extra weight

i could see how this would be an enormous problem for shops to do it the right way, you would have to get a car on the lift, pull it apart, take the old clutch assembly down to the machine shop along with the new one, have the new one offset the same number of grams, go back to the shop and install it in the marked position. that could easily be a 2-3 day clutch job that ties up lift time

thbwlZ

yep, it's hard for people to accept. Even the hand assembled engines still use mass produce rotating components. Even though they are all manufactured to very tight tolerances, they still stack up. These aren't blueprinted engines with a near zero balanced rotating assembly. They do a great job engineering them so they can be assembled as machined, with an as machined crankshaft, and the engine is great as built. The fine balancing on manuals, is only due to the vibration transfer path that is different from the automatics. The engine is still good. So I have great respect for GM engineers and all the folks at Wixom, they put out an amazing product for a very low price, with respect to the kind of performance they have.

And you're right. It makes a clutch replacement a crap shoot. When even the service manual is somewhat deficient, what is an aftermarket clutch manufacturer to do? Or a vette shop. It's not cost effective to do the match balance unless you charge for it and the extra time tying up a lift. And then, there are so many shops who don't believe in any of this, that the would tell you that shop is insane. So you wouldn't have much business doing a clutch anyway.

This could all be avoided if they would take an additional step before assembly. They could have a simple balance stand for simple rotating components, and zero balance the FW and PP separately to closer to zero than as delivered from the manufacturer. Then when they put in weights during the hot balance, those weights would ONLY be accounting fort the engine internals. Then, when changing a clutch, you could zero balance a new FW and PP separately, and then transfer the weights to the new FW. But all that cost money. so you know how that goes.

good stuff.