USAFPILOT

While in neatral, if I rev to 3200 RPM it starts vibrating, then again at like 5500...smooth in between and below 3200. The car has a brand new factory flywheel installed with a new clutch about 2 weeks ago. I cant fathom why that could be the problem, but maybe? Would a new harmonic balancer do the trick? Can anything else get out of adjustment that I could take a look at?

Zix

Oh boy...there are some issues with balancing some LT4 engines. By any chance at all do you have access to the original flywheel? There was a batch of LT4 engines that had to be specially balanced, these engines were marked with white paint on the flywheel...putting in a stock flywheel could throw the balance way off. Was there anything wrong with the original flywheel that it needed to be replaced?

USAFPILOT

They resurfaced it and then it was way off.

USAFPILOT

The side of the flywheel that would be uap against the engine itself has some white numbering around the edges. I'm not sure if that is what you were talking about or not. I can take a picture of it?

Zix

Post a pic if you've got one, I'll compare it to mine! I'll talk to a couple people here that know more about the issue than I do and see if they think that might be the cause of it.

jsaunde2

Did they match the out of balance of the old flywheel? The LT4s (maybe LT1s too) were externally balanced on the flywheels so you must be sure to match the balance, or out of balance, of the new flywheel to that of the old. Any competant machine shop should be able to handle this.

It would suck for your transmission to have to come out again though.

The balance weights go in little holes around the perimeter of one side of the flywheel, you should be able to see this on your old flywheel.

Jason

Bluewasp

Ok. Every LT1/LT4 6 speed was balanced at the end of the assembly line. Yes that is what I said. There is a Fine tune balancing procedure that GM did to get the vibration out of these engines. It wasn't 100% effective in some cases but most of the time it worked. I have the GM procedure and I'll post it when I find it. I just moved a few months ago and it's inside some box.

First thing you need to do is get your hands on the old flywheel.

Then you need to look at the side that faces the engine.

You will see little holes that go all around the outer edge. If any of the wholes are FILLED then you need to buy a set of flywheel weights and place the weights inside the holes in the same spot on the new flywheel.

If the old flywheel has been trashed then I would try GM flywheel balance procedure to get rid of the vibration. GM did this “balance procedure” on EVERY LT1 LT4 as it came off the line.

how do i know this? I talked to Gordon Killebrew about my LT4 vibration issue. He sent me the procedure and it worked for me. 80% went away. He said I could share...

hope this makes sense.
robert

Zix

This is true, however, not all LT4's were balanced by GM. Here's the deal...because GM lightened the LT4 crankshaft it was hard to find a matched set of rods to balance it in some cases with the DM flywheel, in fact GM could not get some of them balanced right. So they outsourced the balance procedure to another company in Detroit...Dynatech (or something like that) who specializes in balancing (engines to turbines...you name it). They created a specialzed balancing machine for the Corvette LT4 because of the dual-mass flywheel. If you ever see an LT4 flywheel with white paint markings on it that is one of the engines that was sent out for balancing, and that flywheel is VERY specific to that engine. This came from one of the engineers at Dynatech a few years ago when some people were ordering drive-shafts from them...the subject somehow got turned to a problem LT4 engine that refused to balance.

To get it to go away 100% you would need to (and people hate hearing this) have the engine removed and have the rotating assembly balanced using heavy metal. You can try to match the balance with the weights, but it won't go away completely because the minor adjustments to each weight and its position on the original flywheel. And some of these engines are worse than others.

Mine was one of them, I replaced mine clutch with a single mass aluminum flywheel and only noticed a slight vibration while in neutral when revving the engine...very little to nothing at speed. I've seen others that actually shake because the vibration is so bad.

Bluewasp

Interesting. I was talking about after the car was fully assemble and ready to roll off the line. GM came up with this fine tune balance procedure. I think it was the last or second to last station before the car was rolled off the line. It was the final check to see if there was any vibration present. If a 6 speed did vibrate they tried correct this the problem with the procedure and if couldn't be fix I guess they would pull the motor. I never got that far into the discussion with him. Gordon can tell you all about it. he will e-mail the 4 page doc. if you call him up. Nice guy. It worked for me.

USAFPILOT

I definetly have one of those engines then. Should I take it back to the dealer and make them try again? I bet they would mess it up more. Whats happening now is only slight, at 3200RPM. I'm not sure if it will cause any further damage down the line or in the engine?

Maybe if I ever have some head work done and stuff I could have the engine balanced/blueprinted. Would that be the thing to do? I assume an engine shop could get it right.

Until then I might just drive it like it is.

Does anyone have contact information to the dynatech engine balancing company? I will need proof that my engine was sent there, if I am to have anything done about it.

Thanks for all the good info yall

Bluewasp

Give them a call and see if they have the old flywheel. The cheapest way make the car feel like it did before you took it to the dealer would be to balance the new flywheel with the out of balance of the old.

Still looking for the hard copy (printed doc). I had it on my desktop but the movers dropped my desktop computer off the back of the truck. Well it doesn't work anymroe!

bogus

This is some serious information.

I think I will add it to the Tech FAQ.

USAFPILOT

I have the old flywheel...I just dont think I want to let them in there again, unless I have to. I've got a 12 month warranty on there work, so I might drive it for a while and see if it gets worse.

Bluewasp

Are any of the holes filled around the edge that faces the engine?????

Take a picture of the flywheel and post it or send me the picture...

bluewasp@yahoo.com

Bluewasp

here is a picture of my old flyhwheel. You can see in the photo the weight that was added.







You can add the weight by taking off the inspection cover and hammering in the weights. No need to remove the trans or anything.

Bluewasp

This is the cover you need to remove to see if any weight was added to the new flywheel.





YOu are going to have to turn the engine over to see the entire flywheel... You can remove the injector fuse and just crank it but someone else might have another suggestion..

USAFPILOT

here is my flywheel

/

are those the white markings we are talking about? I also see three of the outer holes are plugged with weights. I have no way to tell if the new flywheel has them or not.

Also, can it only be bolted on one way? Could it have been bolted on rotated out of position?

Bluewasp

If three holes are filled then three holes in the SAME SPOT on the NEW Flywheel MUST BE FILLED.

You need to remove the inspection cover and look.

GOod LUCK

Zix

Yep, that's one of them...looks exactly like mine!

Bluewasp

Only one way to bolt in.