United Motors UM250R 2 stroke conversion
Just spotted this bike for sale and it's pretty sweet. It started as a UM250R, that's a United Motors, which I thought was a rebadged Hyosung, but the owner says it's built by Suzuki for United. At any rate, he pulled the stock 250 4 stroke V-Twin and shoehorned in an RZ350 Banshee 2 stroke, billet stroker crank yields 440cc. Forged pistons, billet clutch, programmable ignition and lots more, with modifications is now delivering 100hp. It looks very well done.
I found some details of the build online over at KO Rider and it seems he actually first had a bored and stroked RZ350 displacing 535cc in there at 125hp but pulled the engine for another project and built this engine. The 535 will be a turbo bike!
2 strokes, gotta love 'em.
Link: UM250R 2 stroke conversion
United Motors UM250R 2 stroke conversion
United Motors UM250R 2 stroke conversion - engine closeup
{ 19 comments… read them below or add one }
Well done! Simple, straight forward and mean. I’d be willing to bet that there is a slight problem with keeping the front end down when you wind it up……and the rubber hoses from the expansion chambers to the mufflers would make a fast track conversion possible……
For 49 C notes, this is probably a real bargain.
This is pretty cool. I was involved in bringing the UM line to the dealership that I worked at a few years ago. The 250R was a credible piece, as we tested one on public roads to an indicated 100mph. Not bad for a 250cc four stroke that could wind out to over 11,000 rpm if I recall.
To my knowledge from my involvement, UM was an independent subsidiary of Hyosung of Korea that was established to create a better dealership network in the North American market. The products originated from Korean plants, and the only involvement that Suzuki had was that at one time they had Hyosung build the SV650 power trains for them. When that project was fulfilled, Hyosung licensed the rights to build the SV power train from Suzuki under conditons that they would alter the product enough that would make it different from that of which Suzuki was producing. As far as I can remember, the 650cc UM/Hyosung engine utilized a different bore and stroke than that of the Suzuki mill, though architectually speaking they are very similiar.
It’s great the UM/Hyosung chassis can accept this kind of power. I rode a few at the time I was selling them and they were very credible performers when set up right, so seeing this makes me think what the Koreans may have been capable of with a 1000cc unit, though the torque and weight may have been an issue with a four stroke engine that large.
In the KO rider link I put in the post, there’s talk about replacing the swingarm with various ideas bandied about, whether he did or not isn’t clear, but it was something that entered their thoughts. He also mentions adding some bracing to the frame so the stock frame may not have been quite strong enough for full power on a 2 stroke.
Hi Paul,
Thanks for the added insight as I had not glanced at the link.
Best!
Will
awesome and pretty clean job too, it’s looking very sharp and tight.
For insurance purposes, do you check the box that says “the vehicle has been modified to alter its performance” ?
I had plans to build a Hyosung with a DRZ450 motor. I think this trumps it.
My next project was going to be a two stroke of some sort. RD400, RZ350, RD500, RZ500. something like that. Maybe an Aprilia RS250 but they are very expensive. Having said that they’re dripping in good kit. When I win the lottery I will order a TSS 500.
Thanks for the inspiration Paul…
This bike is Ultra badass!!!
Very good conversion – love it
Still miss my RD350F – 350cc 2 stroke with a fairing – would keep up with 1 litre BMWs and even my friend at the time with a 900cc Kawa GPZ900R was impressed. It was slightly tuned here in the UK by people who knew what they were doing – the speedo stopped at 125mph so no idea how fast it was but top speed was cruising speed on a Kawa 900cc – so 130mph ish
What me officer? little old me on this little bike going that fast? are you sure??
Two strokes are still great fun
The 535 had power valves…made the power delivery much flater and wider…Honest…was a bit boring to ride(to much like a 4 stroke), this 440 engine is much nastier… cruz around with plenty of power down low but go WOT and hit 6800 rpms and you better be ready to shift again because it just explodes power wise. This would not make a good track bike, it will throw you off in no time LOL. Its a muscle bike…ride it like a vmax and youll be just fine
Too awesome for words
@Dan
“This would not make a good track bike”
Unless you were interested in recreating the Glory Days. Oh my! Could those guys ride.
I agree 100% dont get me wrong, a good racer with real 2 stroke race time would do awsome!
That frame looks identical to the venerable Suzuki GS500 e.
Thats What others have said…. its a steel frame…wanted that for the strength…
Great bike though I do wonder how fragile a bored and tuned RZ350 (sold as the 350LC in Europe) would be. The RS250 isn’t that expensive here in Europe and is pretty cool. There aren’t many around now though.
the engines use so many new parts …you cannot make enough power with a stock rz barrel. You use trinity racing barrels…beefy and more modern…. reliabilty is very good… not as good as a stock rz but lets say 1/2 the life as its twice the power
The engine looks amazing, but that dodgy front engine mount ? Self tappers or pop rivets to hold the small slag welded bracket .It also looks like the bolt is missing from the bottem engine mount. If the frame fit and finish was as good as the engine,it would be a great little bike.