Engine balance - Cast vs forged
 

I read on a post a while back which said that flywheels and balancers used on BBC engines with forged parts are different (and not interchangeable) with flywheels and balancers on BBC engines with cast parts. I am currently running cast part long blocks with flywheels and balancers from forged part engines. I haven't noticed a problems, but have both engines out now and if I need to do something, now is the time. What do you guys think?

BT :cool:

Cast or Forged does not really matter. Weight of the pistons or crank is the key. If the weights are different then you should have the complete assembly reballanced to the new parts. It will live longer if balanced correctly. :)

Gen 4 no difference, Gen 5 and Gen 6 BIG difference

When changing pistons the reciprocating assembly should be rebalanced, no matter what pistons you have purchased. Do I know of people that have not rebalanced after a piston swap? Sure. But quite a few of those engines had a noticeable vibration. Besides, the balancing expense is very minimal when compared to the amount of money that you'll spend on machine work on the rest of the engine at a qualified shop. Don't be a cheapskate.

You could always buy a book:D

BIG BLOCK CHEVY MARINE PERFORMANCE
call 626-675-3548 with credit card #

Dennis Moore

I hope I get away with this!:D

Thanks fellas. I have a gen IVs that have run about 50 hrs now so I'm hoping all will be ok. Doesn't sound like an overwhelming need to change what I now have. I am shooting to spin these at 5000-51000rpm in the spring.

I have your BBC marine book Dennis, and think I am beginning to know it by heart. I haven't seen anything that discusses this particular question though. Maybe I missed it somewhere??

BT :cool:

A quick plug for the book, eh Dennis? I think it'll pass the censors. By the way, KAAMA loaned me his copy while I was down with a total knee replacement last March-April. As you can imagine, I try to stay out of engine compartments now. Good to see you here. BT, what are the engines and how'd they run this year? If you ran them without any problems I sure wouldn't want to pull them down just to balance them. Just my opinion though.

Thanks Crazyhorse. Engines ran great this year. Have them pulled now for other reasons. Not really looking for things to do, but if necessary I will. The original engines were 365hp magnums, 1988. These are remanned engines now with what I assume to be cast parts. They were garaunteed sp? 330hp and have the ovals.

Found the page in your book Dennis (pg 27) talking about flywheels. The part I am missing is how could a mark IV engine balance out ok at the factory with cast or forged, and the gen V and VI could not? Was the balancing a middle of the road deal on the mark IV?

I'm sure Dennis can clarify this but it's my understanding that the crank counterweights on the GENV and VI are different due to the one-piece rear seal. The MkIV engines had a two-piece seal, and also had a counterweight on flywheel-end of the crank. Do you still have the 365 engines?

BT I am not sure what you are talking about but the main differance between the IV and V or VI motor are the crank. One piece seal or 2 piece and the weight is changed. Like the book states the flywheels will not enter change and keep everthing balanced. Everything is balanced as a group or rotating assembly. Different weight pistons mean a new balance from old pistons. Same is true if rods or crank is changed. They are dealing with grams of weight so it does not take much of a change. I to would not want to tear them down just to rebalance.

Ever been around a BBC with the wrong fly wheel installed you know they are not right. :D I would not do it but I have seen - know of a BBC with a .030 over piston is one hole and nothing else done. Still running today. :rolleyes:

Crazyhorse types faster! If you are tearing them down I would have them balanced since they are apart anyway.

I like to get a copy of the balance sheet from the machinist so I can match a component weight if I need to replace something later on.

I still have 1 365hp short block crazyhorse. It had a valve dropped in number 1 hole and split the cylinder.

Paradigm.. I think I am alright too. I once installed an eight cylinder flywheel on an in line 6 accidentally. Wow!! Suprised it didn't walk off the jack stands when it started. I'm going to look into balancing and if not to out of line get them done for peace of mind.

Thanks to everyone for their replies.

BT :cool:

I'd be interested in the shortblock. Let me know what you want for it.

Crazyhorse... I was planning to tear down for parts for a later hp engine, but have no particular plans. What would it be worth to you? Or better yet, got anything to trade?

BT :cool: