Hello, all.

I originally posted this on a different thread, but it fits here as well.
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Gentlemen, I am going to throw some information in here concerning ANY piston connected to a crankshaft with a pivoting connecting rod. AND, this stuff has absolutely no relation to the feces of a male bovine, it is straight fact.

The problem is piston accelleration rates. When going past top dead center the piston experiences much greater accelleration than going past bottom dead center. There have been many attempts to even the rates at top and bottom, but none have been made to operate as well over all as the ordinary pivoting con rod. By lengthening the con rod the difference can be reduced, but not eliminated. In the boxer twin the same differential is there but the forces of the two pistons cancel each other. The remaining vibration in a boxer
comes from the crank itself. Commonly in boxer twins there are opposing counter weights, one at front and the other next to the rear bearing. All by themselves they induce a dynamic imbalance. The manufacturers can vary these to minimize the resultant total vibration, but since the two conrods do not run in the same plane it cannot be eliminated.

To prove to yourself that the accelleration rates are indeed different top and bottom (I heard some references out there to that male bovine) pull the backplate off any of your single cylinder engines. Pull the plug, bolt a cheap protractor on the crank, lining the center up, as well as you can, with the crankpin, bend a short wire to use as a pointer. Now get out your dial indicator, stick it through the plug hole and zero it with the piston at TDC, turn the crank and check the reading at BDC. bend your pointer to get a zero in the middle of the protractor. Now comes the proof. Turn the crank backwards until the piston comes up a bit, let's use 0.15", and note the degree reading. Turn it back the other way, let the piston go back down and come up that same distance again, note the degree reading. See how much crank rotation it took for that much travel? Now go do the same at the upper end. (You'll have to reset your pointer for TDC) Shocked? Usually about 1/2 the angle at TDC for the same distance traveled. With the crank turning at a constant speed that means the piston has 1/2 the time to go the same distance at TDC as it has at BDC. Consulting with Sir Isaac Newton we find that means the accelleration at TDC is FOUR times as great as it is at BDC. Gentlemen, this is simple mechanics, and there is NO POSSIBLE WAY TO BALANCE IT!

If you don't have that dial gauge, and your kids wont let you have their protractor the difference is so great you can use a nail and a ruler to indicate piston position, and stick a prop on the crank. Less accurracy, but the difference is so great you'll still see it.

As a side note, the only piston engine that can be set up with ALL vibration forces internally balanced is an in-line six, or a V-12. Hello, Enzo Ferrari!

If not one of your planes is not a TWIN, no body can say you're not IN!

WLR
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Hope this clears the water somewhat.

When the twins balance, the wings stay on - it soesn't become a lance.

Bill.