ENGINE BALANCING

I SEE ALOT WRITTEN IN HERE ABOUT ENGINE BALANCING, AND HOW IT'S ABSOLUTELY NECESSARY.
ON A BUDGET ENGINE, IF YOUR ROD AND PISTON BOB WEIGHT IS WITHIN 50 GRAMS OR SO OF WHAT THE CRANK WAS ORIGINALLY BALANCED FOR FROM THE FACTORY, YOU DON'T HAVE TO BALANCE THE ENGINE. A PRECISION BALANCED ENGINE IS SMOOTHER THAN A NON-BALANCED ENGINE, BUT A NON-BALANCED V-8 WILL STILL HAVE GENERALLY LESS VIBRATION THAN A STOCK 4 CYLINDER, AND THE FOUR BANGERS LAST FOREVER.
SO, IF YOU ARE ON A BUDGET, AND YOU'VE GOT A STOCK CRANK, AND STOCK TYPE RODS AND PISTONS, CHANCES ARE YOUR MONEY IS BETTER SPENT ELSEWHERE. IF YOU'VE GOT THE DOUGH, KNOCK YOURSELF OUT, IT DOES HELP SMOOTHNESS, BUT IF AN ENGINE IS NOT PRECISION BALANCED WITHIN 1/2 GRAM, IT'S NOT GOING TO COST YOU ENGINE LIFE OR HORSEPOWER......... LET THE BULLETS FLY!!!!!!!

Hello nairb" I have been reading your messages and I am impressed with your knowlege and eagerness to share it, and so far I cannot disagree with anything you have written! I stress good balancing due to the fact that rebuilds often require new parts and as you know new pistons are almost always used and somtimes new flexplates and the like and can be different from stock? and also from experience as one engine i did was basicaly a stock rebuild with new cast pistons and was not balanced! it threw the stock damper of the car during street driving and after the engine was pulled found a crack in the #4 main bearing cap, so since then I balance all engines and have not had a problem since!

50 grams, thats almost two ounces. I'm not saying that what you say isn't right, but that sure seems like a lot. I mean 50 grams is probably like a gazillion lbs at 5,000 RPM.

most v-8s are over-balanced , which means the crankshaft counterweight has more mass than the rod/piston bob weight. This is usually done to help counter-balance gas pressures applied on the rod piston when its a BDC. So, if your new rods and pistons are say, up to 50 grams lighter than the old ones, you probably won't even feel any vibration difference, any more than that and you might, but it doesn't spell doom for your rotating assembly.If your stuff is a little heavier, that's easily fixed yourself. Of course a big difference with big ol' heavy rods or super light-weight parts will require a crank spin-balance, and the whole nine yards.
A perfect example is of a 360 Dodge I built when I was a kid, I had a donated block, picked up a crank at one junk yard and two rods and pistons at another. The machine shop said I couldn't do it, it worked just fine, and I only had 600 bucks in the whole thing. headers ,cam ect.

Right on, I thought you were talking 50 grams difference between one rod to another. Say you did have that amount of difference between rods, would it be real noticeable? I know a weight on a flywheel will, but they are also further from the axis of rotation. But then again, a weight on a driveline can be very noticeable and it's real close to the center of rotation. I think you answered that though. How far off from each other can they be without any vibration/destruction?

again I do not have any problem with what you say! however I have reached the point that I no longer take chances with anything! be it my job or my hobbies, for the most part? the guy`s or gals on this forum all seem to be talking about performance but do not want to think about the cost of doing it right? Money is always an issue! I say that if someone doe`s not have the money? then go to the local auto parts and by a $650.00 engine? HOTRODING IS NOT A CHEAP HOBBY!

I've posted this before - horsepower costs money, RELIABLE horsepower costs ALOT of money.

Generally, what does a machine shop charge to balance an engine?

depends on how much has to be done add or remove material? usally between $100-200.

Yes, It's important to remember that the rod, piston, rings and bearings and an oil allowance make up the bob weight, but the mass of the rod and piston is only part of the mass of the rotating assembly. So if we add weight to a counterweight, say three inches from the axis of rotation of the crankshaft, it's affect on the entire reciprocating assembly is not the same as if it were a rotor {like a flywheel}.
As far as one rod being heavier than the other, or piston, I bet you couldn't tell the difference sitting in the car, but I always try to weight match my parts, and you don't need a hines balancer to do it. And, yes , a balanced engine is better than one that's not for sure, but to what extent is the improvement? Most replacement, street replacement pistons and rods only vary just a few grams from the stockers, and many times so do the rods, so balancing the crank is not that big of a deal
Case in point, I have a little 283 Chevy that has a set of .060 TRW forged slugs, a stock set of rods with the beams polished, and the stock, steel crank. I balanced this thing, but I hardly had to make any correction on the crank, because it was damn close as it was. I really didn't need to balance it. Now, if I had added a big set of Oliver parabolic beam rods, that were really heavy, I would have had to add metal to the counterweight on the crank. Just weigh your old stuff, and compare it to the new, if it's apples for apples, your crank should be okay.

Totally agreed NAIRB! I do usually have things balanced, just because I dont like feeling the vibration of the engine at 6000 RPM. It makes me nervous.

After just having an Eagle crank balanced, I would add that with aftermarket parts it might me more necissary. The oe crank/rod combos I have had done required little drilling. This eagle piece with light pistons and rods looks like a piece of swiss cheese and it also had heavy metal added at one end.

Chris

I used to work as a technician in a large car factory in England. Part of my job was calibrating Jackson-Bradwell balancing machines. The cranks were balanced as were the flywheels and front pulleys and the balancers could easily detect a pea-size blob of Plasticene (play doh). The whole lot was then bolted together for a "Final Balance". Connecting rods were matched for weight in sets as were pistons. Of course one couldn't get ones "private jobs" done at the factory one had to go elsewhere. I had been told that a company in Worcester was "really good" so I went to have a look. I was horrified with what I saw as it seemed to be Ford Pinto week. A grease monkey with an air wrench was dismantling engines by the dozen and rods, cranks and flywheels were all being stacked in skips! The term "Pick and Mix Engine Reconditioners" comes to mind as all the balancing and weight matching will be gone. One of my own cars used to shed its core plugs (freeze plugs) at high speed and this was so annoying that I eventually pulled the engine. It had one odd rod that was much heavier than the others. Anyhow I had the engine reworked by "Autosprint" of Birmingham and after that it was quite amazing. 6500 rpm could be pulled in top gear and the speedo needle would try to go around for a second time! Sometimes the factories do get it wrong I admit. We sent a number of engines to Italy but the Inocenti rejected the lot for rough running. When the engines came back it was found that the crankshaft balance was miles out. The foreman of the crankshaft section didn't like the "electronics people" so he had recalibrated the machines with his own "master crankshaft" which was bent! Allegedly someone didn't like the foreman so when he was out they drove a fork lift truck over his "master crankshaft". Our test crank and the foreman's crank were checked by a firm that did high class racing cars and the verdict was "Electronics Master Crankshaft spot on, Foreman's crankshaft as bent as a nine bob note" (It was sawn up and thrown into a scrap bin) Someone's grudge cost the company a hell of a lot of money and in the end Rover went bust.

A lot of grocery getter engines get rebuilt and never balanced but since they seldom see any more revs than necessary to go 70 or so they live just fine. however if one is contemplating turning the engine for all it is worth say at the strip then balancing is a no-brainer..And yes if you buy some kind of expensive car the factory most likely balanced the engine..Not necessarily so in the econoboxes..

Sam

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I have tried most all of it and now do what is known to work..

This thread is 9 years old.

The engines which were balanced by humans were the very old BMC "A" Series as used on the classic Mini and you can't get more econobox than those. The newer stuff was built on machinery by Carl Schenk of Darmstadt, Germany. The crank line was astonishing as at one end a labourer would load on rusty forgings and at the other end mirror-polished dynamically balanced cranks would come off the line. Even the journal corners were toughened by rolling with hardened rollers. These cranks also went into Hondas so it was pretty good stuff. As to the con-rods these were made in house. Antique style wooden barrels were stored near the foundry. These contained a grey powder from Russia or somewhere to the east, the powder was Vanadium and it was alloyed with the steel. Very interesting but its nearly all gone now.

As to revs, the hopped-up BMWs (cars) have the red (or is it yellow?) line at about 8000 rpm so the balance will have to be spot on.

Funny stories. Years ago a workmate bought a Ford straight 6. The car never ran properly. When he finally sussed it out he found that he was short of a piston and rod, also two pushrods! The engine had been converted to a 5! Another mate had motorbike trouble. The engine turned out to have one high compression piston and one low compression piston! The meanest trick ever was done by a miser in the bike club. He had a Honda 50 with a holed piston as he'd been running it lean. Kids were playing with a super-ball and when this bounced into his garden he hid it. The ball went into the Honda which was then sold (and it did have good compression LOL!)