Hey, why wait any longer? Yamaha made a beautiful 3-cylinder double overhead cam 750cc
motorcycle engine that would work great in a Sportsman. 3 cylinder in line 4 strokes are inherently balanced unlike inline twins and V's. In fact there are lots of wrecked motorcycles out there with great engines
guys like us could be putting in our quads.
And they're cheap! Of course it takes a lot of guts to start chopping up a new Sportsman.
Then there's the Sportsman trans-axle/I.R.S.
sub assembly on a DS-650 Bombardier! It adds 4x4,IRS,Reverse,even auto trans, all in one package...with a 3 cylinder 750 DOHC Yamaha.
Oooo new post!!
Silly later,,,,Fourlix

 

Fourlix ,
I remember that engine a little , I believe the problem was getting the cam journals lubed right .
I recall something was up in the lubrication of the valve train.

At trail speeds I have doubts on how effectively the aircooled motor would cool itself .

EDIT--> Now you have me thinking , wasn't it the crank that had trouble getting oil on the far side rod on the big end on the early ones ? My , those things have out of production for about 20 years , I guess thats why I don't recall many details .

 

Good point on the air-cooling. Hmmm.. there must be a more modern engine that would make a good Quad motor. The great thing about the Sportsman chaincase is that it includes reverse as well as independent suspension, inboard disc brake, front axle drive, and a Hi/lo, so almost any non-quad motor could be used with this stand alone "transaxle". Some kind of water cooled ninja motor or something. Then put the whole mess in a Lonestar Frame, with a custom rear subframe of course. 50 hp, 500 lb Sportsman. That's the ticket!!
Silly later,,,,,Fourlix

 

When I saw your heading "750cc 3-cylinder Sportsman" I figured that someone had finally found a good use for those piece of crap Polaris Storm motors. They sure weren't worth a crud in the snowmobiles they came in compared to the rest of the market.