The Stovebolt Site Forums The Shop Area Engine Shop Engine balancing..Worth it?

My 235 is at the machine shop. It's just getting a rebuild with stock internals and a mild cam. I'm going to be running dual carbs and Fentons. Would it be worth the $250 to have this thing balanced. I've heard no since all the internal parts are very close to stock weight. But I've also heard yes. So, would it be worth it? Thanks in advance

If you are having the crank turned or cylinders bored & intend on doing some serious driving I would say yes. Just a minor ring valve job it wouldn,t be nesessary. Nothing is more pleasing to drive than a well balanced engine. You will probably want to include the flywheel, damper, & clutch.

I wish I had mine balanced. I have been chasing a vibration since I got it running. I think its the crank. I can live with it, but if it was any worse I would tear it down again. Wrenchbender is right on with the flywheel & clutch too. I had them balanced and it helped but still have vibes.

My vote is no. These are low speed engines and it will not gain you anything significant in drivability or engine life. A waste of money for a 4000 RPM engine.

Incidently, I am running the exact setup you describe.

I forgot to include that the crank is cut .010/.010 and it's being bored .080 over.
I'm still torn as to what to do... It's kinda funny that everything makes sense. Balance it so I know it's all perfect, but don't since it will rarely see anything over 4000 rpm... Ugh, decisions decisions...

Yes! Every little thing helps!

Joe

It would be good if Hot Rod Lincln would jump in here. He has built a lot of engines.

Southtowns27,

Seems to me that a lot of decisions like this go back to the person asking the questions. Life is about tradeoffs. RPM, potential vibration, cost, how many miles you drive per year. 6cyl touches on something I've believed for years (no matter what the subject), lots of little things make up one big difference. It's rare that you can fix a big problem with just one change.

If you're made of money, or you're gonna drive fast, or you're gonna drive lots, then balance it.

Rance

I have an unbalanced 235 with the M4F cam. It has turned 4,500 rpm, which is about 95 mph with my gear/tire combo. My friend has a hot 261. No comparing the engines, his is fully balanced, professional ported head, MSD-6 box, Unilite distributor, full race cam and dual 2 bbl carbs. He had the engine at 6,000 rpm doing burnouts.

It comes down to what you want to do. If I were doing mine again, it would be balanced. If you want to do it later, the price will be a full rebuild.

way esier to do it now than when it's all together!
my dad SWEARS by it.
his is a flathead f__d though and turns a little faster
Jim

Well, I decided to go ahead and have it done. Getting the balancer, flywheel, and pressure plate all done at the same time too. Thanks for the replies

An inline 6 is inherently balanced, so unless you've done something oddball, like installed super-light pistons, etc., it won't be absolutely necessary. Oversize pistons are purposely lightened a little to match the weight of a standard-bore piston, so just overboring is not a compelling reason to do a balance job.

If you decide to go ahead with the balance job, make sure the machine shop includes everything that rotates in the job, flywheel, harmonic balancer, pressure plate, clutch, etc. I weight-match all the moving parts of a Chevy V-8 before sending the crankshaft to my balancer operator, down to 1/10 gram. (That's 1/10 the weight of a dollar bill, BTW). He computes the "bob weight" from the reciprocating and rotating weights of the piston/rod/wrist pin/ring assemblies. I-6 engines do not need bob weights during balancing, because the reciprocating and rotating weight is equally spaced 120 degrees apart. Your engine will probably run a little smoother if it's balanced, but it's not necessary for reliability.
Jerry

What exactly does the machine shop do to balance it?

The crankshaft is spun up in a machine with a strobe light and some very sensitive switches. If there's a measurable amount of shake, the light flashes, "freezing" the motion at a particular position. A meter indicates how far out of balance the part is. When a "heavy" spot on the shaft is found, a big drill press built into the machine drills a little weight off one of the counterweights to minmize the vibration. If the counterweight is too light, sometimes material is welded onto the shaft. For really radical weight changes, a hole is drilled through a counterweight, and a piece of "Mallory Metal",heavier than lead, is riveted into the hole. By adding or removing weight at the right places, the vibration of the shaft when it turns can be minimized or eliminated.
Jerry

Hotrods right again.

But because it's all tore down now is the time if you have the extra cash. Have everything balanced ..... together. Because it rotates together. The clutch matched w/ flywheel and pressure plate are joined/ located together via a locating pin. So everytime that assy comes apart it goes back together in the same indexed position. crank w/ harmonic balancer same same.
my $.02

I'm assuming that the shop would balance the parts separately, right? If not, then if/when you replaced a part (clutch for instance) then the 'whole' assembly could be unbalanced again. This could happen even if you balanced the new part before installation.

Rance

yes you're correct
all clutches & pressure plates are balanced as a matter of course when new, by them selves. so you could either remove your flywheel and do those pieces all over again when you replace the clutch & disc OR not, and simply replace the clutch & disc w/o the balancing. Southowns27 has everything all apart now so if he's going to do it he'll get 75K+ out of it b4 he goes thru this process again.

I'm in the same spot, got my engine at the machine shop and am debate. My machinist told me that it wasn't necessary to balance the crank on a l-6, but that the pistons/connecting rods should be done. He said that in reciprocating engines, like a v-6/v-8, you've got to balance the crank. But the l-6 is inherently balanced. He went on to say he would spin my crank if I wanted him too but I would be wasting my money. This guy has been in the business 30 years, builds 8s for racing and has done hundreds of 6s.

Is he wrong?

I tend to agree with your machinist. If the crank was in balance when it was made, there's little if anything, including regrinding, that will make it unbalanced. Just weight-match the pistons, rods, etc., and reassemble things. The flywheel and clutch will need to be checked, and balanced if necessary to be sure this assembly doesn't create a shake.
Jerry

Jerry, that balancing procedure sounds just like the ancient Alemite wheel balancer I picked up for $10 a few weeks ago.

NM52,who do you use for machine work?