engine imbalance

[5.0kid]

Ok, so my 347 stroker is finally up and running! but there is a problem...it seems like the engine isn't balanced correctly or something. Once I'm over about 2500rpms, it shakes badly. My tuner said that this is what it seemed to be.
It was balanced by eagle and I have missed placed the information for it, but it did originally come with a harmonic balancer part PB1070-N, which is a bower bond piece with a 28.2 oz imbalance. I also received a flexplate with the engine which was a pioneer piece, but i'm still trying to come up with the part number since I have misplaced that too. I'm calling pioneer on monday to check. Anyway, then I ended up buying a fidanza or ram aluminum (can't remember) flywheel with a 28oz imbalance. Could the 28oz vs 28.2 oz imbalance be the reason I'm getting the vibration? I don't want anything to happen to my new engine, any ideas would help!

 

[5.0kid]

forgot to add, it does this in neutral...

 

[Venomous96Cobra]

sounds like a bad harmonic balancer!

 

[orodi]

28 vs 28.2 would not create THAT noticable of a vibration. I would double check the harmonic balancer if you are using a stock style balancer it too is for a 50oz balance. I would not run the engine at all untill you figure out whats wrong.

 

[modo]

you might as well pull the motor as if its vibrating that badly and your running it the main and rod bearings are probably beat

 

[5.0kid]

ok, well i found out that it IS balanced to 28.2. I'm looking for a flywheel for that now, but i'm thinking now that the vibration could be from bad motor mounts? I did notice that they were cracked before I put them in, just didn't even think about it when I installed them since I was in a hurry as I had to leave to school the next day for college. could that cause a vibration that is noticeably worse as rpms get higher?

 

[nicostang]

Yes if they are badly cracked. Also be careful if u think about doing burnouts or beating the car too hard before u fix this up. If it's the motor mounts/transmission mounts, you could end up with a big mess

 

[5.0kid]

thanks nicostang. i haven't taken it over 2500 rpm since the problem started. its at the tuner's shop right now and i'm going to give him a call this afternoon to see what he can do about getting new mounts and hopefully thats it, otherwise i guess the engine will be coming out

 

[nicostang]

a simple test i used to do in FWD cars was to put it in gear and slightly rev the engine and check if the noise was noticeable. If it was motormounts, you shoudl REALLY feel it, even at like 2000rpm. It is a HORRIBLE noise.

I've had a couple of cars with cracked motor mounts, and it is a horrible rattling noise. Also, one cracked mount leads to more cracked mounts

 

[5.0kid]

ok, i talked to my tuner and he said its definately an engine imbalance problem. I'm really really confused because then engine was balanced using the flexplate and balancer that came with it (28.2 oz) and was balanced by eagle. I dont have the paperwork sadly since it got misplaced while I was at school this year, but I guess i'll be pulling the engine and starting over again

 

[gregbar]

It should cost around $250 for balancing. Had my 349 balanced and use SOLID motor mounts very smooth and spins up pretty good. I have a cam just up from stock not too much rumpity rump.

 

[5.0kid]

ya, the only thing about me taking it all the way out to have it balanced is that it already has been balanced! i'm going to try buying a new flywheel and checking that first i think. I can sell the aluminum one and buy a steel one for cheaper than the aluminum one...

 

[5.0kid]

ok, so I am going to go check the car out tomorrow and talk to the tuner again. He is pretty sure that it is an imbalance problem, but I'm really confused cause the flexplate I have is for sure the right flexplate and it is balanced to the 28.2 ounces. Is there anything else I should check for that could cause a vibration like an imbalance problem? its only after 2500 rpms...also there wasn't any shavings in the oil or the filter so bearings aren't getting chewed up yet.