500cc, two stroke single test/build.

dave3593

dave3593

What I know about opera I learned from Bugs Bunny
I think I'll start building another bike. I know I have thrown out various combinations but I want to try this as an addition to the three race bikes I already have. At least I have the base bike or engine.

I have had this 1985 Husqvarna XC500 for several years. I paid very little for it and it needs an engine rebuild. I already have an RZ350 that I run in V6LW and this pre 1990 500cc two stroke is allowed in there also. When new these Huskys were just a couple rear wheel HP down as compared to a CR500 Honda. I had a different 500 Husky back in the day and it was quite an armstretcher.

First thing is to rebuild the engine and ride it to see how bad it vibrates at peak HP RPM. If that looks good, I have a complete 650 Suzuki front end I can easily put on it. Then just rig up a lower rear end height and DOT tires. Another question is, can I still kick start one of these at my age. I CAN still start my 430 Husky. In this basic state, I can take it to a track practice session or two to see if its worth continuing the project.

If this all works out I would hope to go to better rear suspension and wheel along with different ergonomics and fairings. I really enjoy putting stuff together and drinking Beer while doing it!
 
Any pointers? I know there are guys that have done similar stuff here.
 
If you have any fillings be prepared to have them vibrate out within a couple of laps and also don't think that you're having a stroke when you have still got pins and needles in your feet and fingers twenty minutes after a race...
 
yeah and get a 55 gal drum of loctite. this is coming from a guy who takes a set of bolts with him on rides with his duc.
 
  • Like
Reactions: 418
You guys are scaring me. I do plan on riding it before I start the conversion.
 
Getting an understanding of all the various mounting materials ability to dampen different frequency vibrations can help isolate some of them.
I've ridden motards with 400+cc motors that were anywhere from slighly buzzy to jarring. The best ones had a combination of different materials and isolated everything.
Never gonna be smooth as a counter balanced V or inline but it will sound amazing. Like a planishing hammer on steel.
 
Very interesting
I have seen the vibration isolating aftermarket foot pegs and handlebar mounts.

Also my RZ350 has some engine torque bars (?) that are rubber mounted and only handle force in one axis.
 
Seen enough of these relatively cheap to know better.

It sounds good but reality is these big MX motors aren't designed for road racing.

I do believe the Quadzilla 500 motor is counterbalanced so three might be some hope there.
 
The hope of what this could be is so neat. I'll go ahead and rebuild the motor just to see how bad it shakes. This dirt bike has the same HP to weight ratio (including rider) of my stock RZ350. The RZ works well on V6LW.

This motor needs a rebuild crank. But as it sets it is worth very little.
 
Last edited:
I wonder if I should take the crank to somebody that might set it up for higher RPM. I know the ballance can never be very good on a single with no balance shaft. I have heard of improvements if the shop knows this kind of stuff.
 
  • Like
Reactions: 418
I race a Bighorn which is a 350 rotary valve single. (air cooled late 60s early 70s technology). It is a bigbore short stroke and can be very temperamental with vibration. My frame does a fair job of dampening it but other bighorn racers have issue with frames breaking and transmission issue due to vibrations. I have had issues with spring loaded shifter paws not staying put at high vibration making shifting difficult. I also had one motor mount bolt come loose and it vibrated so bad my handle bars felt like they were 3in diameter and I could barely hold on. My cranks hold up really well but I need to have my cases sleeved due to the main bearing pockets getting worn out. The last time I rebuilt it, I had to peene (not sure if that is quite the right terminology) the bearing pocket with a punch and apply sleeve retainer to make the next race.

I'm saying this not to scare you, racing my big single is a ton of fun! I'm hoping to build a super single out of later model Husky 250 (Italian built Wr250). Just know that vibration and sustained high rpm creates various issues. The old Husky's are awesome bikes, and I'm sure it will be fun to ride! If the frame starts having resonance issues, I can talk to you about something I discovered in my frame that I believe is helping it.
 
Thanks 90.

Something about a Bighorn. Years ago a buddy put an Bighorn engine built for flat track in a small cafe' street bike. It accelerated very well but vibrated so bad it was painful everywhere you touched the bike. The thin seat was painful and you had to lift yourself off by the pegs at high RPM.
 
I've got it apart and it doesn't look too bad. Will need the crank rebuilt and at least a new piston. The great thing about Swedish Huskys is that they are popular enough in the vintage world, wear parts are being made.
 
dave3593 said:
I've got it apart and it doesn't look too bad. Will need the crank rebuilt and at least a new piston. The great thing about Swedish Huskys is that they are popular enough in the vintage world, wear parts are being made.
Click to expand...

I have a 78 390 I'm also going through. It's really nice how easy it is to get parts for. Its actually easier than my 09 I'm building the super single out of.
 
90kacoupe said:
I have a 78 390 I'm also going through. It's really nice how easy it is to get parts for. Its actually easier than my 09 I'm building the super single out of.
Click to expand...
I had a 1979, 390. What a wheelie monster.
 
dave3593 said:
I had a 1979, 390. What a wheelie monster.
Click to expand...

It is! I've race it a few times (CC and VMX) and its a monster. I always struggled with starting it and getting the jetting right. I discovered the last time I tore it down, it had a huge air leak from porosity through the transfer port into a bolt hole. So I'm curious how intense it will be running correctly.
 
Well, I'm going to delay this engine rebuild for just a little while. My parts money is going to a crankshaft for my TZ250.

Rick of Accu-products just called and is clearing out some stock. He offered me a good and complete crank for my tz for a good price. I don't have to have it but I should not pass it up. I'll buy it then wait a little while and buy the crank parts for the Husky.

Now me and 90kacoupe are both delaying our builds. Too much cool stuff, too little time and money.
 
You must log in or register to reply here.
Back
Top