Just got my forged eagle 383 setup running and have a nasty vibration between 2500-3500rpms.
Heres the specs:
Eagle 4340 3.75 stroke crank
6.0inch H-Beam Rods
Forged SRP -3cc pistons
Zero-Decked block
~11.3.1 compression
Zero Balanced and resurfaced stock flywheel
New Dorman Harmonic Balancer
Scanner picks up false knock, and a '26 quad driver module fault'. Still tracking down the module fault code but its not showing hup in any of our books (i work at a garage).
The topend consists of 210cc trickflows from AI, custom hyd roller cam.

Ive been told that I need another flywheel for it, ive been told eagle parts arent pre-balanced correctly and I need to tear it down again and have it all balanced, flywheel and harmonc balancer included???
Just wondering what opinions I can get from those of you who have had simular issues.
Any thoughts on this would be greatly apprecieted

Thanks guys.
Aaron

 

pretty sure you need to get your entire rotating assembly balanced.

or you could just replace bearings every 10k

 

Did somebody balance the engine assembly without the flywheel and dampener, or did you just trust eagle's word?

 

I trusted Eagle's word like a dumb@ss.

So I figure new bearings and a balance is in order then. I Should have it balanced WITH the flywheel and harmonic balancer correct?

 

if you bought it as a "balanced" rotating assembly then its balanced. the 'pre balancing' they usually talk about is just that the components are fairly close to minimize time balancing the assembly at the machine shop so it costs less money and doesnt require heavy metal.

 

Isnt a LT1 flywheel external balanced from stock., is your assembly internal balance if thats the case the flywheel needs to be nuetral balanced.

 

Is it suppose to be a "zero balance" rotating assembly? If so, then you need to ensure the other parts are for a zero balance motor IE. flywheel/flexplate and harmonic balancer. But, as others have posted, I wouldn't trust Eagle or anyone else for that matter when they say the assembly comes "pre-balanced". I always have the rotating assembly balanced myself.

 

my eagle crank was so far off it wasnt funny, I had to put mallery slugs in mine to get it right,no matter what when you get an assembly you should get them checked.

 

there still seems to be some confusion here. there are rotating assemblies that eagle sells and then there are balanced rotating assemblies. the regular RA's need to be spin balanced with your flywheel and damper. the balanced rotating assemblies from eagle usually include a flexplate bearings rings etc etc.

cranks as they are sold from eagle are not balanced. they only have a target "bobwieght" which is usually on the heavy side therefore allowing you to remove wieght and save money on heavy metal. things which will cause you to need to add wieght, are heavy pistons and rods or ordering a crank that is designed to be used with an externaly balanced setup (causing you to put heavy metal into the crank because the wieght is not on the damper).

perhaps the thread starter can tell us what part number exactly that he ordered so we can check to see exactly what we're dealing with here, and give him a definative answer .

 

You need to run a neutral ballanced flywheel if your motor is internally ballanced.

 

All you need is to have your flywheel balanced as stated...I ran into this exact problem with my internally balanced eagle rotating assy...I put a few hundred miles on the car and I ended up pulling the flywheel and taking to a nearby shop and had them nuetral balance the flywheel...$60 later and my car was running smooth...

 

When I had my engine built I told Eagle not to balance my assy. I had my machine shop balance the crank and flywheel seperately. I also had the damper and pressure plate to my clutch spun to make sure they're zero balanced.
It's quite possible your crank is off balance. I'd have all external rotating parts like your flywheel, damper and PP spun to make sure it's not them before tearing into the engine.

 

Whoa sorry guys, I forgot i had email notification turned off so I didnt notice anyone replied.

I had my stock flywheel zero balanced and re-surfaced before everything went together. However, I did nothing to the harmonic balancer.
I will go thru my paper work and try to find the part number of the rotating assembly I got. It came with rods, pistons, bearings, rings, etc etc everything for the bottom end.
The person on the phone asked me if i wanted it balanced for an extra amount of money and I said yes. By the way this was thru Jegs.

The way I understand it, a stock lt1 is internal balance up front and external at the rear (via flywheel weights) and since I now have an all internal balance setup I need to have all external rotating parts zero balanced.
The reason I didnt bother with the harmonic balancer before is, I was not told to , and I assumed it didnt matter since it was already internal balance up front.
Should I check the harmonic balancer? I have since bought a new stock dorman balancer and put on there with no change but I did not have it spun or anything.
I really hope I can get away with it being an external problem. We all know how fun it is to remove an lt1 once its down in there Ive done it so many times now I know the tricks but it still sucks ya know...

Thanks for ALL of the replies, you all have been very helpfull. And I appologize for the long delay in my reply. I will check this post more often now.
Thanks again !

Aaron


*EDIT* Dumb question here. If it could be my harmonic balancer causing this, would pulling it off the motor and running it be a way of checking?

 

You do not have a balancer. It's just a dampner. Don't run the engine w/out the damper in place. The dampner is zero balanced so it really shouldn't be suspect. I just had all mine done because I wanted to be that thorough.
From what it reads like it seems it would be your crank more than anything else.

 

Here is the part number on my reciept from Jegs: 0356b12111-030 (balanced rot assy 383 com) is what it shows up as on my bill.

Iam starting to wonder if the shop didnt zero balance my flywheel. I never bothered to double check my reciept from them when I got it, but I do remember the flywheel not having any weight added/removed or any holes drilled like iam being told it would.
I looked for my reciept from the shop and didnt find one. I turned it into the garage I work and they added it to my bill from there and all it says is "flywheel work $xxxxx" so Iam not sure if iam gonna be able to look it up.
All the local engine guys around here tell me I need a 400sbc flywheel and damper for it to work and that its not possible for it to be internal balance and have a zero balance flywheel for some reason? ? ?

Anyway, iam not driving it untill its right. With the exception of across town this weekend to a car show.
Next step is to check the flywheel and see if thats the culprit. I might put my old flexplate from my auto on it and see if that changes anything and just fire it up without the tranny on it.
if the flywheel was not zero balanced, it would cause these symptons yes?
Again, thanks for all the help guys really