Husqvarna 250 2stroke Super Single

I've been playing with the idea of this project for a while, and I was able to purchase a new dirt bike without selling my current Husky (2009 Italian built). The idea came from my friends Metrakit. I loved the simplicity of the bike but I am too big to be racing a 125. (6ft and round!)

I have sourced a wide ratio 6 speed from an earlier model that is a direct swap. I believe it will work out pretty well from the math I have worked out.

I am working on getting my front end setup. I am planning to run a 1999 GSXR600 front end. I have it laying around from an SV project and I feel like it will be better than a SV front end but not too stiff like modern inverted front. I have the husky stem being machined and pressed into the gsxr triple by a friend. (My Lathe is down.)

For the rear wheel, I'm working with a sv650 rear wheel with a gs500 drive hub (its skinnier than the sv hub). With minor mods, I believe this will fit with everything in alignment. I probably going to use the 165-630 17 Bstones. I've gone back in forth on if I think it is too much tire for the bike, but I currently don't have a smaller wheel. I'm not sure putting a 140 in the 4.5 wheel is a good idea.

The rear suspension is one thing I still need to figure out. I plan to use the factory shock but revalve and sprung. Racetech's website mentions shortening the stroke on the shock and I'm not sure I understand the purpose of this. The shock should not care if it has more travel or not?

I'm assuming I need to get the sag number more inline with a road racer. I have always shot for a % of total travel, but in the rear this will no longer be a good target. So I am assuming I need to shoot for number more inline with a modern GP bike or smaller bike like a Ninja 400.

I would love some insight from people who have built 450gp bikes before, or attempted anything similar to this.

The picture is of a rough mock up I did when playing around with the idea. The front end is from an SV and the rear wheel is just sitting on the axle with no bearings. I'll get an updated picture as soon as all the bearing come in and its rolling. (Also excuse the mess. I just moved and trying to figure out how I want to organize the shop.)

 

I'm very interested. What classes does it fit in? I'm slowly working on my 500 Swedish Husky.

 

AHRMA SOS3 and bump to SOS2, could race open two stroke for fun, but definitely not competitive (I'm not sure it will be truly competitive anywhere, but should be fun!)

WERA I believe would be Clubman and D Superbike (maybe??)

 

I really want to see this bike on the track.

 

I started down this path, donor bike was a 16 KTM 250 XC, got a set of modified clamps to mount a 3rd gen R6 front end, got a shortened swingarm, few other bits and assembled a mockup. Sent it to my suspension guy to get his input and he wanted to cut the neck off the frame to rake it out. I got cold feet and abandoned the idea. I was hoping for something I could revert back if it didn't work out. The idea is still rattling around in the back of my head, I've still got the 'challenge' pieces... if I can find a cheap enough donor bike maybe...

 

If someone specifically had experience road racing this frame you could learn from them.
I wonder if ktm did a little different with the frame set up of stuff they called XC.
I have ridden many Husky WR or XC bikes (swedish) and they are stable even at WOT in sixth in a corn field. A poor man's way to change the steering head angle is to drop the rear suspension more than the front.

 

I've road raced them in Sumo trim, the issue with the full conversion I did is R6 forks are way shorter than the stock XC forks, plus a 17in wheel is shorter, etc. So you end up with a flat swingarm and somewhere around a 20deg front rake when it's all bolted up. I did talk to someone who's done this before on a Yamaha MXer and he advised that the numbers will look stupid but it'll work, but my suspension guy who I was working with was pretty convinced it'd be a flop. I've had good luck with him in the past so, I opted not to go against his advice, and bailed on pursuing it. There are a LOT of varying theories out there on these builds, Racetech prefers modifying the stock dirt forks to keep some length, BeON uses a custom front end entirely, etc. Now that my priorities have changed I may give it another look, dunno.

 

I need to get the correct front end on the bike. I have the rear wheel fitting the axle, I need to get it centered up and spacers made. Once I get the tires on it I plan on using, I'll get to seriously measuring the suspension.

From the rough mockup with SV front and sv rear wheel. It looked like I would be around 22deg of rake and 15deg of swing arm angle. Swing arm angle was not measured with much precision but I was just curious.

I'm putting my vintage super single (Kawasaki Bighorn in S2 frame) back together for Tally with AHRMA first. If I can get this things rideable before Tally, I'll take it and ride it in practice, just to see how feasible it is. There are a ton of little details to work out in order to get there.

I'm not trying to build the bike with fancy expensive components, I'm just trying to see if it can be a fun economical race bike. I like the idea of cheap and easy top ends and bottom ends that are simple to rebuild. If it works out, I'm sure the bike will slowly evolve into something with way to much time and money in, but it wouldn't be racing if it didn't.

 

It should definitely be on the track next season. It may make a winter break trackday if I can get it done.

 

I'm so happy that there is still a two stroke following. My two strokes are a wonderful aggregation.

 

They are either an aggravation or maybe an aggregation.

 

I would probably be much better served with putting my SV together. Its fun to race but its missing something. So I will have 3 two stroke race bikes. That way at least on of them is always ready to go to the track... haha

 

Ran into a slight snag. The required front sprocket to get any top speed out of it hits the swingarm. But that should be a pretty simple fix by grinding some clearance. Once my other bike is back assembled, this one will get back on the stand and I'll get the wheel alignment strung up and make spacer accordingly. I may have to make or have made a front offset sprocket but I'm not worried about that. I'll get some pictures once I start making strong progress.

 

Rebel Gears can make offset rear sprockets, I've not had luck sourcing an offset front when playing that game in the past. How small of a rear are you mocking up with, I've got 38s for standard dirtbike (Yamaha/KTM/etc) hubs?

 

I'll likely need an offset front, but I'm not sure until I get the wheels aligned. Worse case I'll make an offset sprocket.

I'm planning on running a 35ish on a gs500 hub (same bolt pattern as a sv650), and a 16 front. I need to look back at the different primary ratios that this family of engine ran. I may be able to swap primaries and not go so big on the front and so small on the rear. I'm really not sure what mph to gear for. I wonder what mph a 450 hits at Barber?

 

@TLR67

 

No clue…. No speedo on the RMZ however a 450 can really f you up in the kink of the chicane on a rainy day…found that out 2 weeks ago and still healing…

 

Sorry, I haven't been on top of this project the last week or so. I just got my new TM en300fi. If I had the cash to buy another one, I would definitely try the super single with a TM. It is a really nice bike, and super well built.

I'll try to make some progress soon, but this TM is really fun to ride.

 

I finally spent a free weekend in the shop instead of on the new dirt bike. I'll get some pictures tonight hopefully, but I made some small progress.

My GSXR 600 forks are assembled and ready to install on the bike. I have the stem from the Husky pressed into the GSXR triple clamp. It should all slide right together tonight. Once I have the correct front end mounted, I'll be aligning the SV rear wheel with the front wheel and start looking at rotor and chain alignment. I'm kicking my self for not purchasing the Super Moto rear wheel from a guy off facebook. It would have really simplified the back of the bike. But if I can get it to use SV wheels, I'll have a lot of spares available.

 

I forgot to take pictures. But I got the front end on and started aligning the rear wheel in the swing arm. I got it strung up, and what appears in alignment with the front wheel seems very offset in the swing arm. I swing arms are not normally symmetrical due to the drive side typically being wider, but the wheel looks offset to the drive side by a good margin. I took fair measurements and 3D printed some trial wheel spacers to see how it all bolts together. I may have to modify the drive hub to get the clearance I need. It will definitely require sprockets with counter sunk bolts to clear the swing arm. If I can get into the shop tonight, I'll try to get some updated pictures. The shop pictures are also embarrassing my shop is a disaster.