Pablo's DR350

[3uba296]

Or... try to find a core plug in the right size?

[Pablo83]

Originally Posted by 3uba296

Or... try to find a core plug in the right size?

Yes, I was really wondering if these are available.

[Pablo83]

Originally Posted by BikePilot from DisTech's DR350 build thread

IIRC the primary drive ratio (crank to clutch basket basically) is different between the 350 and 250. I know that for a given final drive ratio my '94 250SE turns more rpm than my '96 350SE. Also note that your 250 motor is a 250SE. The plain S was kick start only.

primary drive ratios:
DR350 20:64 (3.200)
DR250 22:62 (2.818)

I'm led to believe that the lower ratio (from the 250) will be easier on the tranny and harder on the final drive. I'd rather be replacing chains/sprockets than trannies, so I'm going with the 250's primary.

[HeadTrauma]

Yeah, what the numerically lower ratio does is transfer less torque through the geartrain by making it spin faster. A numerically higher final drive is then required to multiply the torque back up again. That's why Honda's HRC kit for the XR600 included an NX650/XR650L primary drive set with a lower ratio.

[Pablo83]

Originally Posted by HeadTrauma

Yeah, what the numerically lower ratio does is transfer less torque through the geartrain by making it spin faster. A numerically higher final drive is then required to multiply the torque back up again. That's why Honda's HRC kit for the XR600 included an NX650/XR650L primary drive set with a lower ratio.

I reviewed your comments on my NX build when I was deciding what promary to use. Thanks for all the help. BTW, since when are you into DR's?

[HeadTrauma]

I was considering one as a possible alternative to an XR250.

I was also thinking about DR650s until I saw the thread about some grenading the gearbox.

[Pablo83]

Originally Posted by HeadTrauma

I was considering one as a possible alternative to an XR250.

I was also thinking about DR650s until I saw the thread about some grenading the gearbox.

So far, the bike's been real easy to work on. I love the engine, it's very simple; much easier to work on than the RFVC. There are big bore kits available up to 460cc and with the 250, 350 ,street, and offroad versions, there are a number on interchangeable engine components.

The flexible chassis is an issue, but maybe I can get that sorted out. I'd love to have this engine in a CRF250 chassis; that'd be a lot of fun.

[Pablo83]

The neutral switch looks like it's missing a cover. I checked the fiche and it doesn't show one, so I guess this is right.

[Pablo83]

One tranny down, one to go...

[Pablo83]

I did some measurements on the different bores I have. "Sleeve" means the overall height of the sleeve.


The pins with two thicknesses are tapered on the inside; they get thinner towards the edge. Notice the pin dia is different between the 250 and the 350, so you can't put the 350's piston on the 250's rod (I was told you could).

[Pablo83]

this is the counterweight drive gear on the crank. Jesse Kein says there is a problem with the pin slipping out and causing catastrophic damage. I can't remember what Jesse's solution was. I decided to weld mine.



I did a fusion weld (no filler rod) so I wouldn't upset the balance.

[Pablo83]

And the second engine's apart. Now to see if I can get them back together.

[Pablo83]

Flywheel weights:
91 DR250S: 4lb, 3oz
98 DR350: 3lb, 15oz

The manual suggests jamming a penny between gears to stop them from spinning when you're trying to torque things down. I tried this to torque the flywheel bolt down (95 ft/lb) and I broke a tooth off the oil pump drive gear ($30 replacement). So don't try that.

When swapping the trannies I swapped all the internal parts (gears, shafts, forks, and drum). The reassembled trannies both bound up. I spent a long time trying to figure out what was wrong. I finally swapped the drums back and they worked. I examined the drums closely and couldn't find anything different about the two, but it appears the drum needs to stay with the case it was meant for.

[Pablo83]

In order to get the primary drive ratio I want, I need the 91 DR250S's clutch basket. So I put in the whole clutch from the 250. Does anyone know if there's a difference between this clutch and the '98 350 kicker's?

[Pablo83]

DR350 valve sizes (these are not exact)
intake: 30mm
exhaust: 26.5

DR250S
intake: 28
exhaust: 24.5