Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties UL flywheel

UL flywheel

Post Sun Sep 03, 2017 5:39 pm

Posts: 4
Hello everyone.
i have a set of flywheels for a UL that are set up with the pinion side and pinion side, i did not know that until another mechanic pointed this out.

is this a common modification and how will this work on a UL engine??

Thank you.

Post Sun Sep 03, 2017 10:29 pm

Posts: 2718
Location: Los Angeles, CA
In other words you have two small flywheels. An old Speed Secret. Lighter weight revs faster.

Post Sun Sep 10, 2017 11:39 am

Posts: 3321
Location: Central Illinois, USA
Chris Haynes wrote:
In other words you have two small flywheels. An old Speed Secret. Lighter weight revs faster.

Yes, Chris,...

But only for light racers and race bikes.

A heavy payload demands more flymass.

...Cotten

Post Tue Sep 12, 2017 10:17 pm

Posts: 4
I was hoping for a more technical response.

So if i am building a bobber for street use should i take these flywheels apart and get a proper set and just start over.

As i sit these flywheels are completed [pinon/pinon side UL wheels] with rebuilt rods, balanced to my pistons, and the shafts have bearings fit to cases.

i just wonder if the engine will run weird and just be wrong?? i do have a stock UL i ride and am used to.

Any body out there in flathead land know how this thing would run??

Post Wed Sep 13, 2017 7:45 am

Posts: 3321
Location: Central Illinois, USA
Handshifter13!

Its all about how much "stored" torque you will need.

If you to rev up real fast to a peaky powerband, then flymass gets in the way, and that's why lightened wheels are popular with riders who like to race, particularly from stoplight to stoplight.
But if you need a stump-puller, particularly if you are massive yourself, carry a passenger, dress the machine out, and primarily cruise at a constant speed, then flymass is an advantage.

Since your assembly is complete, might as well use it; Just don't put a sidehack on it!

....Cotten

Post Sun Sep 17, 2017 11:19 pm

Posts: 120
i have a couple sets of flywheels if you want an oem pair.


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