Just got back from the machine shop. Match balancing old flywheel to new flywheel. Old one spun 18 grams off neutral balance at 1 oclock new one 10 grams off neutral in the the 2 o'clock area. He stated both are neutral balanced with in gm spec. 8 grams from each other. Sounds right to me. Do you experts have anything to add? Anyone know what gm spec was?

 

This whole thing with balanced flywheels is mostly a myth. Do you honestly think you will ever feel the difference from 18 to 8 grams?! come on. lets use some common sense here.

 

I'm calling shenanigans on that statement and I'm sure a number of others will too. I put a Spec in my car and it vibrates at higher RPM. Going to take all my stuff to a machine shop as well to have balance checked/fixed.

 

It's not that 10 grams difference makes that big a deal. It's that all C5, C6, and C7's with stick shift were externally balanced by the factory getting your old and new flywheel matched balanced is very important. It looks like my old flywheel is zero balanced so I am lucky and should not have to worry about this but I do have old assembly just in case.

 

You dont have to match balance, just neutral balance. They are internally balanced, but the stick shift cars are really sensitive to vibration. I replaced my balancer with a Summit underdrive unit. Both the OE and Summit are supposed to be neutral balanced but the OE had some holes in it to further balance it. I picked up a small vibration between 2K-3K RPM. A month later I lost the slave cylinder at the track and decided to do a clutch while I had it apart. I had the flywheel and pressure plate neutral balanced as a unit. They took less than 5 grams off (even though both the Findanza flywheel and Luk clutch are supposed to be neutral balanced from the manufacturer). Vibrations went away with the new clutch.

Big point here is to just have your stuff balanced before you put it in, regardless if they are supposed to be or not. It cost like $80 to balance the flywheel and pressure plate and I dont have to take it apart again.

 

That statement is wrong for the c5 c6 and c7 stick shift cars. GM externally balanced these cars and they can have weight add to flywheel. That made them not zero balanced.

 

They are in fact internally balanced, but the stick cars needed a finer balance after the fact so they may be extra holes or weights pressed into the balancer or flywheel. If you have those then match balance, if not just get the flywheel and pressure plate neutral balanced.

 

This statement is wrong. GM hot balanced the engines to check and see if they had any further imbalance with the pressure place and disc attached to the engine. Even though the engine is internally balanced and everything "should" be zero, those components together might not be. For example, Mcloed clutches are zero balanced and so are the flywheels but they are almost never zero balance when together. Monster clutch however spins it all together to be sure its as close to zero as possible.

GM added or removed weight from the pressure plate, flywheel and even the balancer if need be. The engine is still zero balance internally.

 

Every motor from all manufacturers are internally balanced. I did not think this need stated but gm still externally balanced after flywheel and pressure plate were added all c5 c6 and c7 cars that are stick shift
My flywheel had 3 weights add but was neutrally balanced per the machine shop.

 

Practically speaking, not a single person on this site could drive two cars and tell which one has a “balanced” flywheel and which car doesn’t. Everyone concerned with a practically
nominal engine vibration are probably driving around with long tubes, cat back, cam or just cracked motor mounts.

 

Ford small blocks are externally balanced, either 28oz or 50oz depending on year. GM's hot balancing was basically a fanatical way to increase zero balance. Take the flywheel/clutch and balancer off, motor balances zero. Put your flywheel/clutch and balancer back on and it would still balance zero.

 

To semi-quote RichieRich, who runs service at a shop that has probably done well over a thousand clutches for C5s and C6s - a zero-balanced clutch assembly will virtually always result in good balance with no evident vibration at any RPM.

Yes, stock clutch kits _could_ be match-balanced if needed. I don't know how many actually were, and how much it mattered. A proper zero-balanced clutch will do you fine.

FWIW, Monster, which is often recommended here, requires match balancing. Virtually no other clutch manufacturer does. Why? You can guess: QC. Ask me how I know.

 

You can get back with us once you slap a clutch in and experience what the rest of us have.

 

JordonPoole, you should probably become familiar with what the OEM states before you make such a statement.

 

This is my problem my old flywheel has 3 weights in it but the machine shop said they are both neutral balanced and should install as it is without transferring weights.

 

Not necessarily! The 400 SBC was externally balanced. Yes, not a C5 engine. But all, like never, is a HUGE word!!

 

Your so correct also ford did back in the 60 and 70's if I recall. Just a little frustrated with the project I am doing and the lack of certainty with with my flywheel and no good answers.

 

Transferring the weights from the old flywheel to the new flywheel in the same relative positions is designed to compensate for any minor remaining imbalance that is specific to your engine's rotating assembly. I followed the tech bulletin (the same procedure is also outlined in the service manual) when I replaced my clutch and I had no drivetrain vibrations.

 

BHauber: You can't just blindly swap bob weights from an old flywheel onto a new one. You really need to start with a zero-balance clutch assembly, install it, and then see if there are balance issues. GM service manual, IIRC, says "New flywheel, clutch, and pressure plate assembly onto an existing engine: Do not transfer or install balance weights." (from googling, I don't have the service manual in front of me.)

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These flywheels are 14.00 inches, right? To the previous topic: Let's imagine an 18 gram weight placed 7" from the center of rotation (178mm), at 6000 RPM (100 rotations per second). That one little 18 gram weight as it rotates creates a centrifugal force of mv^2/r. m = 18g, r = 178mm, and v = 100 * circumference (pi * 14 =~ 44 inches) = 4400 inches per second = 366.7 ft/s = 111.8m/s. That's a force of 0.018kg * (111.8m/s) ^2 / 0.178m = 1264 newtons or 284 lb-f.

https://www.omnicalculator.com/physi...trifugal-force

284 lb-f seems like a lot of force. But of course that's massively tamped down by the rest of the flywheel. How much effect do we really have?

Let's do it a different way. 0.018kg in one edge of the flywheel means a 10kg flywheel (~24lb) has 5kg on one side and 5.018kg on another side, which means that the center of mass is 50.18% of the way across the circle instead of 50% where you want it to be. In other words, the center of mass is at 50.18% * 14 inch = 7.0252 inches from the edge instead of 7.0000 inches from the edge (0.0252" is your radius of unbalance). F = U omega^2 = mass (of the imbalance) * radius (of the imbalance) * rotational velocity in radians squared = 0.018kg * 0.64mm * (100 * 2pi)^2 = 0.018kg * 0.00064m * 628^2 = 4.54 newtons or ~1 lb-f.

A much more tolerable figure and much more in line with "this is such a small weight" but I think many people with real life experience can tell you that it's enough imbalance to cause problems.

https://en.wikipedia.org/wiki/Rotating_unbalance

Now I don't know if I've done my math right here since I've never done unbalanced-rotor forces, but I _do_ know that Monster recommends match-balancing by putting extra washers on the backs of fasteners. We're talking weights on the order of a gram or even less to achieve proper balance. That tells me that an 18g misbalance can be a serious problem in these cars.

 

Sounds like I have a few decisions to make. 1 install as is and if it vibraterates s add washers to pressure plate bolts. 2 move the 3 weights and if vibrates add washers to pressure plate or. 3 find a different machine shop to match balance flywheel pressure plate assembly and add washers if that vibrates. Anyone know of a shop in Iowa that is familiar with match balancing clutch assembly.