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How to build the 45 Magnum Engine

Completed by Yankee Engineuity

By Duncan Keller, Yankee Engineuity

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Check this out. We are building a similar engine with a K-model top end for our Bonne Belle 45, 2012 Bonneville effort. Duncan Keller is helping Lee Clemens through the engine build process.


Duncan is the master of the Magnum engine. Enjoy the tech:

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Reader Comments

I recently bought a hardtail frame that came with, what will probably be, the only magnum 45 engine here in Belgium... The guy I bought it from started work on it. Already has the WL case welded up and partially machined, but apparently lost interest and is now selling me a half-finished Magnum 45!

As I do more research on it, I'm excited to tackle it! Also bought a small mill and lath a few months ago. I'll be trying to do most, if not all the machining myself. but just wondering, since my experience level is not that great, is there a more extensive "how-to" manual available somewhere, with exact measurements and pictures and all?


gent, Belgium
Wednesday, March 22, 2017
Editor Response Doubt if there is a manual, but I would highly suggest reaching out to Duncan Keller of Yankee Engineuity. He knows the complete drill and will help you.
Would very much like to contact Duncan Keller to build both my 45 magnum projects (K model and Ironhead). Have bulk of components for both projects. Any help you could provide would be appreciated.

Know Keller is most knowledgeable person on this subject. Please, please help me achieve my objective.

Marty Gibson
Comanche, OK
Wednesday, September 16, 2015
Editor Response Try calling 408-307-4714 or Duncan Keller . He's a great guy to work with on any project.
WOuld like to have my 38 case made into the 45 Magnus.

Danny Mullenaux
In wood , WV
Monday, April 27, 2015
Editor Response Sure, but could you send me a short description and an image. Maybe someone needs them more than I do.
Very nice article, and a better way to build the Magnum with the Sportster bottom end instead of the old 45. I was wondering what you do to adapt K Model cylinders with the factory `tipped valves` to the `straight up` style of the regular 45 cases, cams and followers.

The K Model cases are made so the tappet blocks are tipped to match the valve angle as well as the cams ground on an angle as we all know. Keep up the great work!

Erik `K` Hoopes
Fairbanks, AK
Thursday, August 28, 2014
Editor Response Thanks, we used WR tappet blocks and guides for alignment. If you have specific question. Call Lee Clemens at Departure Bike Works in Richmond, Virginia. He'll be glad to help. We are just back from Bonneville.
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