I searched and searched for this and can't come up with a good answer.

I rebuilt my 94 lt-1 (first timer) stupidly I overlooked getting the thing balanced with the new pistons. Didn't occure to me they could weigh any different or that it would matter.

So the problem obviously is I have a vibration but only 2k-3k RPM would this most likely be because of the rebuild or would I have vibration all of the time? I was under the impression that crank unbalance would cause worse vibration as rpm increased...

I also put in a new clutch set so I'm going to drop the tranny and strip it down to the flywheel just to see what I get.

 

I would imagine the vibration you are experiencing has something to do with harmonics. Same thing when a tire is out of balance or a drive shaft. You won't feel it at certain speeds and then the vibration will present itself. Even if you don't feel it that doesn't mean it's not there. It's possible if you don't remedy this it may end up eating your bearings.

 

Kinda what I figured, I haven't been driving it that's for sure. I might as well check the pp balance idea since I have to pull it all out to get it balanced anyway.

 

Stupid question but seeing as I don't have the engine in front of me ATM, can you take the crank and pistons out/put in with out removing the top end? I just don't want to have to pay for head gaskets and intake gaskets again.

 

In a 4th gen. it would be very difficult.

Rich

 

Taking the engine out and bolting it to a stand would be the easiest. It'd be much better than trying to do it while the engine stays in the car. That can get extremely involved.

 

Yeah, just to elaborate - it's easy to remove the rotating assy from the bottom on a tube frame car. But in a 4th gen you would have to remove the crossmember and support the engine. A PITA though maybe easier than a complete R+R if you have the correct equipment including a lift. Unless you want to reinstall the CM, the car would pretty much have to stay on the lift until it was put back together. And unless you have a neutral balance flywhel/flexplate, you would also need to remove that which means dropping the trans anyway.

BTW: I am just heading out to the shop to drop the bottom end on my tube frame race car. I figure it will take about an hour

Rich

 

sorry I didn't mean with out removing the engine, I ment without removing heads and intake.

It's actually in a thirdgen so now worries getting the engine in and out.

I certainly plan on taking that bad boy out. I gonna paint the engine bay since I didn't do it the first time.

 

Just pull the heads/intake, it is so much easier that way.

 

yea but it's 100+ dollars more to do it, and unfortunately I'm pretty much outta cash. I will most likely end up taking it all apart but I'd love to save the upper gaskets if it isn't too hard. I've got a ton more time than I have money right now.

 

So a little bit of an update...

I pulled the trans out and stripped the engine down to just flywheel and dampner. The vibration is all but gone.

Does this imply a bad balance on the PP or clutch? or would the effects of the possible bad balance in the engine be that much less?

 

So I pulled out the engine, and easy as pie I pulled the crank out heads and intake on. I'm glad I tried this first

Now the piston on the other hand I'm not sure I can get it back in from the bottom, I will see I suppose

 

Uh oh.. forgot all about that.
I can see how that would be a royal PITA. Hope you have a good ring compressor. Not to insult your intelligence, but I also hope you marked all the rod/main caps and pistons.

 

of course. the mains are stacked up in the same order they came out, besides they are already cast with the number and and are shiny from the machine shop on one side so kind of hard to mess those up.

the rod caps I put into individually numbered baggies so there is no confusing those