Board index Flathead Power-Technical Questions, Answers, and Suggestions Morthodites-"Non Factory" sportster case, flathead cylinders

sportster case, flathead cylinders

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Moderators: Curt!, Pa

Post Mon Oct 15, 2007 1:21 pm

Posts: 6
i'm building a custom bike, we could call it my dream bike, i love flathead style, and i wanted something that really stands out, i have been doing some homework, research and what not, i've been thinking about the possibility of marring a sportster case with a 74inch flathead top end, i was wondering if anyone out there has ever heard of this being done, knows any reason why they don't think it will work or have any advice on the matter?

Post Mon Oct 15, 2007 10:43 pm

Posts: 6
************* shovelhead was grafted to a 883 sportster block in the 71 or 2 easyrider or big bike magazine, it was called the shovster

Post Tue Oct 16, 2007 8:36 pm

Posts: 2677
Location: Los Angeles, CA
That was Sonny Raslowski's machine.

Post Tue Oct 16, 2007 9:20 pm

Posts: 6
excactly, and i think that with some machining you could put flathead cylinders on a sportsters case, the newer big sportsters have the same bore and stroke as the flathead, you could even use the sporster cams you would just have to ground them down, the only real issue is the connecting rods wrist pins on the flathead pistons, i believe they are a different size, well anyway i'll be looking for a 91-up sportster case so i can take advantage of the five speed transmission

Post Thu Oct 18, 2007 7:52 am

Posts: 56
Location: Central Fl.
I say there is no reason why it can not be done. Components from two or more different engines mated together will require
a lot of thought, fabrication, and modification of parts but it can be done. No, I have not done it myself so I am not speaking
from experience, but as long as the cylinders can be mounted on the cases all of the other problems can be worked out.
The biggest problem I see is the tappet/valve alignment.

Post Thu Oct 18, 2007 8:16 pm

Posts: 376
Location: Lebanon, CT USA
Does the fact that the cam centers are diff seem to negate this whole discuddion? 8)

Post Thu Oct 18, 2007 8:24 pm
Pa Site Admin

Posts: 5552
Location: Ohio USA

Hey Bro !!! Long time no hear from ya ? Glad to see ya back Man !!! Pa

Post Thu Oct 18, 2007 11:29 pm

Posts: 6
**************************************************************************************************************************************************** couldn't you machine the cams or have new ones made?

Post Sat Oct 20, 2007 1:39 pm

Posts: 56
Location: Central Fl.
I saw somewhere that the bore and stroke on the UL is 3 7/16x4 in.. Zimalady aka Bills Custom Cycles on ebay has a pair of
UL cylinders with new valves and pistons. They say the bore is 3 5/16. I do not know what the bore is but your cases should be
Ok to bore out to accept the UL cylinders. As long as the tappet to valve alignment is not too drastic you can have new
adjustment screws made with a bigger contact area than the stock screws. It would be a good idea to have the tappets
bored out on a lathe so that the tappet can be tapped for a larger bolt, say a 5/16 with a fine thread. I do not have my
book handy, something like 5/16x24 would be good. Short of being able to mount a cylinder on the Sportster cases so
that tappet to valve alignment can be checked, you need to get a UL cylinder and do some measuring of the cylinder and
cases to see how they line up.

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