Engine balancing question

[astroblastin]

I had my engine balanced and I was told that the crank had to have a little weight added to it to get it balanced.The crank did not need to be turned.I'm just wondering if all motors that are balanced need weight added. This motor is out of a 1991 caprice.Thanks

[mikedamech]

A 91 motor is 18 years old, I can't imagine a journal that doesn't have some sort of wear on a motor with 100,000+ miles. To just balance a crank shaft ( Heavy Duty Special Equipment) wouldn't do the engine justice with out balancing the Pistons and rods.

[GEJ]

The factory spec for balance is pretty big.I worked at a Chevy plant and yrs ago I watched the cranks go down the line and was suprized to see what was acceptable.The material used to balance cranks is very expensive. It is the core costs of the job.What it does is it allows the bearings to live alot longer.I might want to say in race engines,it has been a long debate balanced vs unbalanced.I don't think anyone has proven balanced engines spin up any faster-but I could be wrong on that count.

[GEJ]

A 91 motor is 18 years old, I can't imagine a journal that doesn't have some sort of wear on a motor with 100,000+ miles. To just balance a crank shaft ( Heavy Duty Special Equipment) wouldn't do the engine justus with out balancing the Pistons and rods.

I agree-rotating assby's is the only real way to balance.I might add that re-balances is generally needed when aftermarket pistons are the replacements

[SoCalli V8]

Are you doing a complete rebuild on this motor or just a re-ring and fitting new bearings?

[Smiliesafari]

The answer to the question is: no, all crankshafts do not need weight added. Generally only the cranks that are externally balanced need weight. The old style internally balanced rotating assemblys will usually need weight removed.

[peter]

I'll go further by saying that in most cases, it isn't needed at all!

Most stocker v-8 sbc's spin up to about 5-5.5k. As was mentioned by Gary, the amount of out-of-balance allowed by manufacturers back then was pretty big. Replacement pistions "should weigh in at around the same weight as OEM'ers. And between us, if you were to get a slight vibe at 5k+ rpm on the rare occasion when you were up that high, would you even realize it? Prolly not.
Having said this, I would personally never, ever, rebuild an engine without getting it re-balanced. But I can pretty well promise you that most rebuilders out there don't bother re-balancing their engines. 'Cause most people would never even know the difference!

[Smiliesafari]

I agree 100%. Balanceing a stock street type daily driver engine is a waste of time and money. There's no added value. Spend the money on something that will get you to your goal.

[astroblastin]

Wow thanks for the replies. I talked to another engine builder and he said that if they added weight then it is not balanced!! This guy has built engines for alot of years. So I am glad that it is not put together and in the van. I am just frustrated a little right now.

[peter]

[Mr_Roboto]

There's a lot of factors that determine wether or not a crank needs to be balanced, such as what you're running for rods and pistons, the original crankshaft, and a few others. If you're running a 350 crank in a 305 and using stock bore pistons, you probably wouldn't need to add metal. On the other hand if you've got a 350 that's .060 over, has H-beam rods and heavy TRW forged slugs, you probably will be adding metal. If you didn't change any rotating assembly parts besides the rings and bearings, you would probably be ok just running it. This being said, if you're planning on winding it up a lot you need to do other stuff and then balance, at the minimal some ARP rod bolts. What's your power goals for this engine, and what are you doing to it?

[astroblastin]

Update...I took the motor to another engine builder.One that everybody I talked to says he does a very good job.The block was bored right,the motor was balanced right,but the rods needed to be honed bigger cause they were too small!! Also the crank was good and it did not need to be turned.

[GEJ]

Thanks for the update.Yep-that is a good policy to follow is to have as many people as you can(not connected to each other)look at your build.That builds in checks and balances to the work that was done.