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One flywheel or two?

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Old 11-01-2002, 10:33:21 AM
Norm S
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Default One flywheel or two?

After visiting Coolsprings a couple weeks ago and seeing all the amazing engines there in the museum, I have been pondering a question that I have no theories on. Many of the "fancy" and very well built engines there had only one flywheel as opposed to two as the masses of engines one normally sees do. Also, some of the steamers there and half-breeds only had one flywheel as well. How come? I'm stumped, maybe some of you know the answer or at least have a good theory or can make something up that sounds good

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Old 11-01-2002, 11:03:31 AM
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Default Re: One flywheel or two?

On the Coolspring video that I have, they explained that the single flywheel design started in Europe. The US engines adopted a two flywheel design. Not sure if this is the rule or simply a theory.
Old 11-01-2002, 01:39:02 PM
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Default Re: One flywheel or two?

This is all theory or BS.

I would think that a single flywheel was initially used as that was all that was needed, plus it made adjustments or repairs to the non-flywheel side of the engine easier to do.

There may have been some choice between having a single large flywheel on a engine or having two smaller flywheels. Having two flywheels would make the engine more balanced by not having so much weight on one side of the engine.

Hmmmm... wonder if part of the difference is in stationary vs portable engines. Obviously a more balanced engine would be better for portable uses.
Old 11-01-2002, 05:12:12 PM
Posts: n/a
Default Re: One flywheel or two?

The one flywheel desing is reminiscent of earlier steam engine designs. Obviosly the early gas engine engineers would borrow some designs from the steam engine. One of those was one flywheel. Although having one flyhwheel did create a sorta unbalanced engine the benefits outweighed the negatives. One positive would be reduced weight, cheaper costs and less room needed for the engine. Most halfbreed engines use one flywheel because almost all of the steam engines used only and needed one flywheel. With steam, a balance is not really needed to counteract the force of the explosion. However when a gas cylinder was put on it was not uncommon to see bolt rings on the flywheel with weights attached to help add more momentum. Of course a clutch pulley was also added.

I hope this isn't BS, but who cares!


Nothrup using a single flywheel and weight.
Old 11-01-2002, 06:49:57 PM
Posts: n/a
Default Re: One flywheel or two?

Momentum and Balance is the driving issue. Steam engines only need the flywheel for the two dead spots at the end of the stroke. Since a steamer was double acting (steam expanding on both sides of the piston) momentum was maintained by increasing the diameter of the flywheel and reducing the mass of the flywheel to save $$$$$. Most steam engines followed this with exception of those engines requiring a heavy flywheel (alot of momentum) to power certain types of equipment like generators. As engines became into exsistance, many pricinples of the steam engine crossed over. The dead zone on eninges are much longer and the addition of the compression stroke requires much more momentum. Halfbreeds are steam engines with the heads replaced with gas types, a cheaper cost than replacing the whole engine, and that's why most retained the single flywheel. I believe that they discovered very quickly how fast the bearings were tore up with the single flywheel; and then came the double flywheels.!!!!! Ain't engines grand!!!! Ron
Old 11-02-2002, 02:05:10 AM
Posts: n/a
Default Re: One flywheel or two?

Single flywheel engines aren't that uncommon, at least on early tractors which were nothing more than engines on wheels. IHC 8-16 Mogul and larger, Hart Parr 30-60 and all the rest, Titan 10-20, Eagle tractors, all of the early Case tractors, all the Rumelys and Avery tractors had a single flywheel. I have worked on a number of these engines and not a single one had a bad main bearing on the flywheel side. The amount of "lift" developed in a properly lubricated bearing is incredible and can exceed 800psi and remember ALL these engines have enormous bearing surfaces. That's why they're still here for US to play with!!! :-) Craig


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