Thread: Engine Balancing

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Hey Gang,
Trying to find some answers on engine balancing. The 392 I am going to be using has been gone through once already, and has had the crank, rods, and pistons already balanced. I know the owner, and the person who did all the machine work, and he is a man of his word. The thing is, the engine did not come with a flywheel, or flexplate, and a stock harmonic balancer. I just bought a fluidamper, and flexplate from hot heads. Now from what I have read
http://www.aa1car.com/library/2003/eb10330.htm along with some other articles on the web
I probably don't need to get the engine re-balanced, but what about the flexplate? should that be checked, or will the fluiddamper balancer take care of the problem. This is in a 392 Hemi, that will have a blower.
BTW is the 392 internally or externally balanced?

Thanks,
Mike

Dinosaur hemi's are all internally balanced. The flex plate should be neutral, as will the fluidamper, shouldn't affect the balance.

Just a note for those reading this,do not use a fluid dampner when balancing,the machine shop should know this.Meaning when you have it balanced,do not use the fluid dampner,its ok to use after its balanced.

For peice of mind it wouldn't hurt to have flexplate double checked for nuetral. It's an easy job for the balance shop to do.

Will do I'll take the flexplate down, and have it checked, thanks for the other info also

Mike

eticket, just so you know. A harmonic balancer should properly be called a harmonic damper. It won't balance anything and never has. It is used to dampen harmonic vibrations that are set up in the crankshaft from the crank being twisted and then springing back after a cylinder fires and exerts pressure on it.

Tech, how does that relate to a 400sbc or 454 bbc that are externally balanced?

Originally Posted by NTFDAY

Tech, how does that relate to a 400sbc or 454 bbc that are externally balanced?

Oops, ya snuck that one in on me. Thanks for bustin' my chops Ken. You're correct, there is an eccentric balance pad on the "balancer" of those motors, as well as on the flexplate. I was answering on the 392 motor. Actually, the blower belt acts as a harmonic damper, so no damper is necessary on the crank snout. At least that's the way it is in the fuel classes. Prolonged street use may tell a different story.

I don't normally disagree with you Denny, but can you explain the difference between the dampners on sbc350's and 400's?

I understand what you are saying, but the dampner on a 400 is considerably different than on a 350 or any other gen1 sbc. Though they are the same thickness,but the 400 dampner has a slot machined about half the circumference of the dampner. It's my understanding that it is the only style that will work on a stock 400sbc an must be used in conjunction with a flex plate with added weight on the backside or a flywheel from a 454bbc. I only know this because of the problems I had when I dropped a 400sbc in a '62 pickup and hooked a 3 speed behind it.

i know of off shore blower engines making 1500 +hp with dampers . they could do any thing they want. but they run them with . i have run blower engine with dampers. the fluid deal is some what true but if it400/454 ex bal you need to run it with the counter weigth on the hub from the fluid damper the 400 and 454 need more weight so it was put in the fly/ fex plate and damper .they could not put it in side the engine the counter weights would need to be big that would of hit on the bottoms of ther pistons or long rods so$$$ you could put more counter weigth on the crank so GM just hang it to the out side of the crank with a counter weigth in the damper and on the wheel this for very hi rpms will in time hurt the crank. but have had many 454 /548 run in the 68000+ with no bad things happen the only way to fix this is with very lite pistons and rods this just will no happen or with heavy metal to get the weight in the crank counter weights about $100. per 1 inch slug to put in the crank and two slugs will not make it IN bal . so you know what gm did with the 400and 454

test have shown that the crank ratchets thru the power stroke it not as smooth has every one would like to think . what denny said is right hamonics/resonating frequency can make junk out of your engine . valves springs busted and crack cranks and sings in the bearings of the crank humming you will have nice cross lines in them just before the crank go,s south