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

UL Frames

Post Sat Jul 16, 2005 6:32 am

Posts: 240
Location: Kirkland, WA, USA

I have a friend that picked up a “1947 U motor and transmission, completely rebuilt, zero miles". He is looking for a frame to put it in, and wanted to know if there is a difference between a UL frame and a Knuckle or Pan frame? Will the motor mount in either? Will it mount in a later duo-glide frame? He wants to make it a runner, and look old but does not want to get all the parts and or money together to build a stock bike.

Thank You!

Post Sat Jul 16, 2005 7:02 am

Posts: 630
Location: belgium
Yes a U frame and a knuckle frame are the same. It will go in a newer frame if you put a 3/8" spacer under the front motor mount.

Post Sat Jul 16, 2005 3:02 pm

Posts: 240
Location: Kirkland, WA, USA

Thank You Steph. I got to thinking about it, and then got out my What Fits What book, and found about the same information, except in that they were talking about butchering nice old frames for shovel head motors. Scary now, but in the 70's that was hip.

Thanks for the conformation and the right spacer size, if he has to go that route. I will give him a link to Anders site.


Post Sat Jul 16, 2005 3:40 pm

Posts: 85
Location: Honolulu/Kahului, Hawaii, USA
Bear in mind the info. in "What fits what" should be taken with a grain of salt. Not always correct or the most accurate at times.

Post Sat Jul 16, 2005 3:56 pm

"WFW" is better known as "WTF?"

Mr. Arman was once present when the word "motorcycle" was spoken aloud - this is the extent of his qualifications.

Post Sat Jul 16, 2005 6:14 pm

Posts: 300
Location: Roselle, Missouri, USA
Already built. Ohoouuuh . . . That’s going to make it hard to premount in the frame to check for actual fit when building from parts..

We always match the empty cases up and test the motor mounts. First bolt rear in place and check for daylight under front. Then reverse. Quite often a full length shim needs to be cobbled up to square things firmly and prevent case ears from cracking under running strain.

Paint buildup can also cause a problem so we prime the mounting member surface once and mask from there.

Just what we’ve always done. Any other tips welcome.

Ride Safe :: Helmets Kill

Post Mon Jul 18, 2005 1:55 am

Posts: 80
Location: Las Vegas, Nevada, USA
There is a BIG difference between the real original Flathead/Knucklehead frames and the Panhead frames.......espeically in their construction!

1-Flathead/Knucklehead frames were cold brazed at the factory, and they used spacing plugs intermittently in the frame to add flexibility and spring-likie strength to them. Try brazing or welding on one of these old frames without knowing what you're doing can mess things up for the frame and yourself down the road. [My advice is to let someone like Randy Simpson at Milwaukee Iron (Lynchburg,Virginia) restore or modify the frame to your likes.]

2- The original Panhead frames were tig/mig welded together. They need the 3/8" spacer for under the front motor mounts when putting a Flathead or Knucklehead mill in. These Panhead frames do not have the same flex and spring-like properties the old Flathead/Knucklehead frames had.

3- If you want to modify a Knucklehead/Flathead style frame, you also have the option of picking up one of the new reproduction items and hacking away without the worry of the old brazing and tube integrity.

Good luck and have fun!

Post Mon Jul 18, 2005 11:43 pm

Posts: 80
Location: Las Vegas, Nevada, USA
kozy- the stock one I have is cold brazed and it is a 1947 flatside bullneck frame. 1948 is when they changed over to the welded ones.

Return to Big Twin Flatties