Re: Flywheel

Posted by Mike Flanagan on December 03, 1997 at 09:25:53

In Reply to: Re: Flywheel
posted by scott on December 03, 1997 at 01:05:35

You don't. It all depends upon what you want from the engine.
The flywheel is intended to provide inertia to keep the engine turning smoothly between power strokes which occur every 180 degrees of crankshaft rotation. When one piston is on power that piston, when not powering the automobile, is opposed only by another piston coming up on compression. Obviously with compression of 4.2:1 there is very little resistance to the power stroke. The flywheel provides this resistance. This resistance also serves to maintain momentum between power strokes. Witness the old "Hit & Miss" stationary engines that powered pumps and other industrial machines way back when. They were a single cylinder with a piston sometimes in excess of 12" in diameter and they only fired once occasionally when the governor told them it needed power to maintain RPM. A LARGE flywheel provided the momentum to smooth the operation and provide a uniform transmission of power to the work. Can you imagine a piston 12" in diameter with a stroke of 5' (6786 cubic inches displacement) being fired without a flywheel to push against. A graphic example but appropriate none the less.
When pulling a steep hill in the Model A the flywheel is what provides the startling lugging capabilities. Lighten the flywheel and you will diminish this and find yourself in second gear.
If however you are building a race motor this is a different story altogether. If you are building an engine to rev quickly, go like crazy and then slow down then rev like crazy once again you need to lighten the flywheel. And have a large influx of cash to rebuild often. I am reminded of the Chev motor we built in the Hot Rod Days that was built for one run and one run only. And that's what we got, we set a record for the 1320' motor meltdown. 11.92 seconds quarter mile in a stock bodied (well almost) 55 Chevy that stood for almost a year. And the motor lasted 1325'. Then everything went to heck. I use this example to drive home the point that the Model A engine is not a high TBO engine as designed. Unless a complete redesign is undertaken including inserted mains and rods, pressurization of the oil delivery to the mains and rods, counterbalance of the crankshaft and all the R&D that goes with it simply changing one part of the equation seldom is rewarded with durability. The crankshaft is one of the major weak points with 3 main bearings. The center main must carry the load of two pistons. This cannot be changed.
A fellow at Laughlin last year had a nice Roadster Pickup with a Pinto engine running thru a Model A muffler and I swear if he had not lifted the hood no one would have known. It sounded just like an A. Before I spent the bucks to redesign the little four banger I would go that route.
But you'll never see this Fool in anything but a stock as a stove Model A...
God Speed Under 50.
The Model A Fool.
: Thanks for the respose, but I'm still wonering why the opinion that you need to counterbalance the crank if you lighten the flywheel significantly?

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