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Big Twin Flathead

Post Sat Dec 09, 2006 12:51 pm

Posts: 3
Location: Chatham Ontario Canada
Hello everyone. I am new to this forum. I have all but made up my mind that I am going to build a big twin flathead. I had a 45 about 10 years ago so I have a little exp. with old flat heads. I now have a 1983 FLH which will have to go to make some $ for the new project. Is there any year/years to stay away from because of rare parts. ( was thinking of a 80 inch but that is not written in stone) I have also been looking at new repro frames, because they are straight from the get go. I am a little worried about building on a crooked frame and do not know how to get it tested. I also do not want to build a 100% correct show bike. I would also be worried that if I put thousands of dollars and years into it and if I had to sell I would loose alot because it is a repro frame. any info would be great. Name of books ( I have the bruce Palmer book). I was thinking about a 45 but there are several in this area and I want something a little different. Thanks in advance.

Post Sun Dec 10, 2006 8:57 am

Posts: 1676
Location: Interlaken, NY USA

Welcome, If you got hooked on flat heads with the 45, you'll just like the 74/80 more. As others here will testify, the BT flatties will definitely keep up with the pack. Parts interchange for all years, and some engine parts interchange with 45's. Oil pumps, tappets, come to mind. And a BT SV will fit in any big twin frame made, till modern times. That is to say, up through shovels. Drive train is the same as OHV. Just about any part you might end up missing is available aftermarket. There are lots of books out there, but you can't go wrong with the reprint of the Harley 41-47 big twin repair manual and the 41-54 parts manual. It's all we had in the old days and if you read them cover to cover a couple of times you'll have a good knowledge base to start from. Plus, of course, the webboard here has lots of people who have worked on these babies for years and know all the kinks.
And don't worry about the bike's value. If you build one of these babies, build it to suit you. Hell, let your heirs worry about the 20% beating they'll get on the selling value 'cause you didn't restore/build to exact stock specs!! :lol:
Dr. Dick

Post Sun Dec 10, 2006 1:27 pm

Posts: 2688
Location: Los Angeles, CA
On the other hand the reason the MoCo dropped the Big Flats was cylinder heat and excessive cylinder wear. They tried numerous cylinder designs and fin configurations, all to no avail. On the average a Big Flathead will get .001 of taper in the bore for every 1,000 miles of use. After 10,000 miles you are ready for a rebore. Is it no wonder the Big Flathead cylinders are so few and far between?

Post Mon Dec 11, 2006 7:14 pm

Posts: 304
Location: oklahoma usa
The only thing I can add is that if you're going to build a BT SV now is the time. My personal opinion is that in the future the big flatheads are going to start really appreciating in value. They already are, but not as much as knuckles at this point.

If you like the 45s then you'll fall in love with the 74/80 flatheads. I've owned a number of older Triumphs, AJSs, Sportsters, shovelheads, etc and I can without a doubt the big flat is the "mostest funner" of them all.
I've owned my current one for 32 years and would never think of parting with it. My 50FL runs second (30 years) and while many bikes have come and gone in my life, those 2 will always remain with me until I go belly up.

Post Tue Dec 12, 2006 6:25 am

Posts: 42
Location: houston, texas

I know the feeling, I've owned a 1958 Panhead since 1974 and its vehicle of choice over a 1997 Dyna and a 2002 Ford Mustang GT! There is something about it that makes it so much fun to ride, maybe its the feel, maybe its the sound, maybe its everything about it.

I've also owned a pan-shovel conversion, a 66GE trike (just briefly, 1972-1974) and a '51 Indian 80 but none were as much fun as my Old Panhead. I'll try and post a picture soon in the panhead section.

-little stan

Post Tue Dec 12, 2006 4:40 pm

Posts: 1676
Location: Interlaken, NY USA

44u, must have been a good year to by 80's that's when I bought mine also.
Dr Dick

Post Sat Mar 17, 2007 2:06 pm

Posts: 90
Location: derry nh
the only thing original on my 41 u is the motor, with the original linkert carb.and tranny.i now have disc brakes,12 volt ,mallory ignition,wide glide front end,paughco frame.easy to start and fun to what suits you.flathead always gather a crowd at bike rallies.i still cant believe that so many harley riders dont know about the flathead motor.i just tell them this is the harley that won WW 2.

Post Sun Mar 18, 2007 5:37 pm
flhwesty: don't be so sure that the new aftermarket frame is going to be straight. Some are, some are not. I recently purchased an American made "exact replica" 47 knuck frame that was far from straight - pretty disappointing really considering the high $ paid. Have heard from other colleagues in the industry that have run into the same problems. I wanted a vintage look and this seemed the best way to go (especially compared to what some oem frames are going for on e-bay). Given the chance to do it again I would probably try and find a nice original frame for a good price. Good luck with the flattie project.

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