Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Flywheel balancing

Flywheel balancing

Post Mon Dec 20, 1999 8:57 pm

Posts: 54
Location: cumberland WI USA
I'm looking for information I'm about to rebuild my HD45 it'll be bored out to .070 over ported and revived with a 33 toth moter sprocket and would like to cruse about 60-65
i read some where that the 45 with a stock stroke was balanced out with only a 50% factor on the recipating weight any information would be helpful Thank you

Post Tue Dec 21, 1999 3:23 am

Posts: 3158
Location: Central Illinois, USA
Can you scan that literature that sez 50%? And send it to me? I am trying to sort all of the extremes, but in the meantime most people who know more than me say 60%...And before I forget, you will have better luck at that huge overbore if you bolt torque plates to them to simulate the stress of installation BEFORE they are honed for piston fit..Cotten

Post Wed Dec 22, 1999 6:45 pm

Posts: 54
Location: cumberland WI USA
Cotton I've don't have equpment to scan but where i got that figure was from Victory libary's "The 45 Book" I know that S&S say to use 60% and I once figured that the way the oldtimers did Indians with fylwheels all to gether and one piston and rings come out to be 63%. I haven't got a set of tork plates for the 45 and havent found any one around here that has have been looking for a set of junk iron heads to maybe make some thing out of them. Do you have some and I belive that you have Libberty cycle but i have lost your address

Post Thu Dec 23, 1999 4:51 am

Posts: 3158
Location: Central Illinois, USA
I would respect Victory's information, yet the factor of 60% is pretty much carved in granite for big twins H-Ds (and yes, Chiefs back-calculate to about 64%, yet some Scouts may have been much higher; there's info at [URL=] As I said in my direct post, I haven't made up plates for 45s, so it would still be more convenient for you to whip one up locally. Just worry about making one bottom plate out of 7/16' thick or better stock of anything: steel, cast iron, even aluminum for the bottom. I cut my first ones from steam pipe flanges. Have someone lathe cut a hole that the spigot will slip through, and tap four holes for studs=youre there!
If you look at vintage Clymer literature or "Essentials for Speed" you will see that the fixtures suggested for securing the cylinder for honeing are in fact torque plates...Cotten

[This message has been edited by Cotten (edited 23 December 1999).]

Post Sun Dec 26, 1999 12:29 pm

Posts: 136
Location: oxford, NC USA

I would agree on the 60% balance and the torque plates, but .070 is a pretty drastic cut (although I've seen bigger, my U for example). I think you might run into heating problems and possibly a fragged cylinder some time down the road. .

Have you thought about sleeving the jugs?



Post Mon Dec 27, 1999 12:12 am

Posts: 540
Location: Kansas City, Mo USofA
Can I add to this: The HD 45 was supposed to be the perfect "square" borexstroke. HD racing recommended that the cylinders be sleaved when the standard bore was no longer servicable. I grant that more cubes is more power, however I raced a 302 Chevorlet in the mid 70's and anything you did didn't do as well as if you left it alone!

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