Motorsport 250 gearbox options

[dirtrumpy]

Does anyone here know of any gearbox/clutch modifications or replacements for the Honda 250 motorsport engine?


Mike
#278

[Swiss]

I am assuming that you are talking about the '72-'77 XL250?  There are several options, some are currently available and some are not, but might be found on EBay or in a used tranny...  First of all you can swap out the gears from an XL350 which is a little wider ratio overall.  Or you can go really wide ratio and swap in the transmission from the TL250 trials bike.  It is close ratio 1-3 and wide ratio 4th and 5th..  If you swap in the TL gears to an earlier 250 tranny you will also need to swap the shifter drum and forks because they are different on the later engines. 
There are also the "Webster" 2 gear and 4 gear sets to work with 3rd and 4th gears which were a little weak in the "dog" area and could break with high horsepower engines.  Typically this is done with the bigger engines.  One of the guys in AU is supposed to be working on a 2 gear set similar to the Webster gears but improved but I haven't heard anything in over a year about his progress.
Also there were Primary gear sets that replaced the crank gear and the clutch basket gear that were available in the late '70s.  These are no longer available but I am working with a Racer in Sweden that says that he can build the sets up.  These gear sets increase the rpms going into the transmission and reduce the Torque input into the tranny by about 30%.  You make the ratios the same by using a larger rear sprocket...

Now, what are you looking for?

Swiss

[dirtrumpy]

Hi Swiss,
            Yes i'm talking about the xl250 motor, and am looking at options for the gearbox regarding strength when used with a non cushdrive rear wheel. I'm looking at building up a Pre 75 VMX bike.

Mike
#278

[Swiss]

The stock 250 gearbox is probably the best combination for a VMX250.  It is strong enough to handle the 25-30 hp that a good running 250-290 MX built engine will put out.  The bigger engines like the 403-500cc engines will put out closer to 40-50+ hp and will eventually break gearboxes, especially if run on tracks with rough whoops where the tranny is loading and unloading.  Even the Webster gears can be broken if run hard enough/abused.  The lack of a cush drive shouldn't hurt the 250 when run on Vintage dirt tracks. 

Swiss

[LWC82PE]

Is the standard gearbox ok with the 305 kit?

[Swiss]

No one can make blanket guarantees, but it should work fine with any of the smaller engines.  It is the modern style tracks that would be hard on it with their "rhythm whoops" that load and unload the rear tire.  Basically shock loading the tranny.  Might look at one of the Kush rear sprockets with the cush drive built into the sprocket.  Made in AU!!  http://kushsprockets.com/

Swiss

[LWC82PE]

So if you had a 305 plus the XL350 cush drive hub you would be pretty right then? I would only be looking at enduro/trail type use anyway.

[Slakewell]

You always need to remember the XL rear wheel weighs in at anchor weight of 12 kilo's a YZ wheel weighs in at 4KG that a whooping 8 kilo's of sprung weight.

[matcho mick]

So if you had a 305 plus the XL350 cush drive hub you would be pretty right then? I would only be looking at enduro/trail type use anyway.

XL250/350 share same cushdrive rearwheel,(& front),i've stuck a XL350 motor in a TL250 roller,TL's have no cushdrive rear,but it's for dirt track experiment,so no probs with gearbox loads there,(i hope ),

[Simo63]

You always need to remember the XL rear wheel weighs in at anchor weight of 12 kilo's a YZ wheel weighs in at 4KG that a whooping 8 kilo's of unsprung weight.

fixed for you 

[Swiss]

I did the YZ wheel back in '74 when I built my XL350/403.  Of course I started with an engine in a wooden crate from Honda so I could pick the pieces that I wanted!

Swiss

[cheapracer]

Hi Swiss,
            Yes i'm talking about the xl250 motor, and am looking at options for the gearbox regarding strength when used with a non cushdrive rear wheel. I'm looking at building up a Pre 75 VMX bike.

Mike
#278

Mike, just as an option there was a few small Japanese road bikes pre '75 with cush drives a lot smaller than the XL, look around an older wrecker's yard?

Check out a postie bike rear wheel too, I know they have cush drive but can't remember if they are heavy or not, sure you could trim some weight out of one ...

[mx250]

  Made in AU!!  http://kushsprockets.com/

Swiss

"Kush Sprockets are Australian Engineer designed and tested."

"Q.4   Where are Kush Sprockets made?

China. Without China's competitive market, the Kush sprocket concept would not be achievable. Although Chinese manufacturing is usually associated with poor quality, we use high precision automated CNC machining, ISO certified quality controlled manufacturing. This combination of both high quality modern processing techniques and competitively priced manufacturing gives us the ability to offer the sprockets at a practical price." Sounds about right . Interesting solution though.

[cheapracer]

Kush Sprockets

Yeah, no.

I don't care what I can't see but lets keep the visual aspect of our sport correct.

I recently promoted Kush Sprockets in a bike engined car build forum so I haven't got anything against them.

[mx250]

I don't care what I can't see but lets keep the visual aspect of our sport correct.

You wouldn't be offended by the appearances of the Kush sprocket would you? .

You must have a melt down sighting some expansion chambers, black rims, blinged out chrome everything, and some shocks  .