VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Re-build - Balance

Going thru a re-build on a 1940 216, Am curious about getting the crank, pistons, rods, flywheel and damper balanced. Does the extra cost warrant the added value ? I've always related balancing to High Performance, High Horsepower Engines.

Thanks, Wes

In my opinion the extra cost makes it perform much better. If you are using new cast iron pistons or new aluminum, it is really required. Too late to decide when it is assembled and test runs demonstrate vibrations.

I've rebuilt (i.e. I have the machining done and reassemble the enginge myself) many engines over the years and ALWAYS have them balanced. Any reciprocating mass runs smoother with less wear, after being balanced. The balancing costs aren't really all that excessive in the long run. Do it once - do it right, IMHO.

Balance It ! I have driven my 1940 Chevy for 39 years without being balanced. My car runs great at 60 mph. 2 years ago I went on a 6 cylinder VCCA tour in upstate New York. I drove a fellow VCCA member's 1940 Chevy 216 on the highway. Wow, what a difference. My next engine in my 1940 will be balanced 216.

Thanks a lot, I got the message loud and clear. It will be balanced, Just wanted to be sure I'm on the right track.

Wes

I am sorry to ask such a stupid question (obviously I have never balance one of my many re-built motors), but exactly what is done in balanceing the motor and how is it done. I am in the middle of re-building a 1938 Chevy 216 and would like to do a better job if I can. Is the crankshaft drilled or ground with rods and pistons on it? Are all the rods and pistons weighed and the crank spun to dynamically balance it. Just what part(s) of the engine is/are operated on? Thanks for the education.
Mike

The crankshaft is balanced, the front damper, the flywheel and all rods with pistons installed.

You may be able to weigh the pistons and rods, but the other items need special equipment.

After the crankshaft and flywheel are balanced it is necessary to mark the mating place. Had one of my 4-cylinder engines balanced, and the flywheel was removed without marking. Unfortunately this was not noticed until the crank was laid and came time to assemble the flywheel.

Mike,
I can give you a short version. In my case the balance guy gave me a hands on tour. They use a digital scale and weigh each piston and match to the lightest one within a half a gram. then weigh the rods (both ends) to the same spec as above. Then spin the crank to 500 rpm an balance (similar to a wheel balance)he said with the flywheel and damper. In my case they bored the block to 20 thousands over and are honing each cylinder to match each piston to cylinder. Someone else may add to this, but that's what I know.

Wes

Wes and Ray,
Thanks much for the comments. I am still am a bit confused as to how corrective action is taken to bring the parts to a better "balance". I know the crank is blanced at the factory as I see the grind marks on the counter weight ends that removed material after the forging and initial machining of the journals. So the crank is first balanced w/o the flywheel. The flywell is balanced by itself during casting and final machining. Then the 2 are assembled and balanced together (by drilling the flywheel near the outer radius beyond the clutch friction area). This much is all done at the factory before assembly. The pistons are also made to fit within a narrow weight limit +/- a small amount (1/2 gram sounds about correct) and the same for the rods. Now the fly wheel on most model years only can be assembled one way. This may not be the case in 1938 I will have to check my flywheel and crank. However, I always mark mine upon dissamble to be sure to reassemble in the correct bolt pattern arrangement. I know there is an extra hole to mark the postion (5 hole in flywheel and 4 bolts, but in later models there are 6 bolts for the flywheel with 7 in flywheel and 6 in crank). As far as the vibration damper goes, I saw that it was also drilled and balanced at the factory and can only go on in one position (there is a keyway and key to lock it in). So what am I down to now? How much does it cost to "balance" the engine? How much do they ask to do the "balance"? Are they not trying to improve on the factory work?
Mike

Mike, Your comments make good sense in general, as for me, I'm putting new alum pistons and the rods were machined to accept insert type bearings instead of babbit. So to me it makes sense to balance. At least I have the odds in my favor as I only want to go thru this once. Hopefully at my age, I get a life time warranty. Costing me approx $500.

Wes

Back in the "olden days" the factory selected a set of pistons that were with in 1/2 ounce of each other , the same with the rods. The other rotating parts were dynamicly balanced, thus the holes drilled. This is from a 1948 Film that I have.
I have weighed new rods and pistons and found them to vary in weight greatly. When you purchased a new set of Genuine Chevrolet pistons, all the pistons in the box were of equal weight (they said)...often one or two pistons were replaced and a rod or two and there went any balance that existed, Note that the pressure plate should be balanced while attached to the flywheel.
I have never had an engine balanced but have compared weight of the rods and piston with a baby scale. I would consider all of my engines smooth, but perhaps I am just lucky. I would advise a professional balance.

The balancing on my '38 is $200. I thought I was being a bit overkill by requesting it. The machinist reccomended it as the rods and pistons are non-original plus the tolerances from the factory were a bit looser 70 years ago. I was going to pass on it but my machinist said these run stronger and almost as smooth as the Ford flat head V8's once they are balanced. I think it was a cheap shot by a Ford guy!