Pablo's DR350

Discussion in 'Thumpers' started by Pablo83, Sep 14, 2010.

  1. HeadTrauma

    HeadTrauma ¯\_(ツ)_/¯

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

    I was also thinking about DR650s until I saw the thread about some grenading the gearbox.
    #81
  2. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    Woodland Park, CO
    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.
    #82
  3. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    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.

    [​IMG]
    #83
  4. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    One tranny down, one to go...

    [​IMG]
    #84
  5. Pablo83

    Pablo83 Sleep, Wrench, Ride

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

    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).
    [​IMG]
    #85
  6. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    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.

    [​IMG]

    I did a fusion weld (no filler rod) so I wouldn't upset the balance.
    [​IMG]
    #86
  7. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    And the second engine's apart. Now to see if I can get them back together.
    [​IMG]
    #87
  8. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    Location:
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    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.
    #88
  9. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    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?
    #89
  10. Pablo83

    Pablo83 Sleep, Wrench, Ride

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

    DR250S
    intake: 28
    exhaust: 24.5
    #90
  11. 3uba296

    3uba296 Thumpcurious

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    Great work and awesome thread! :lurk

    Do you need to modify the engine block to get the cylinder with the 440 sleeve to fit?
    #91
  12. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    I don't think so... I hope not... Let me go check.
    #92
  13. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    The hole in the case is able 2.5mm bigger than the 440cc sleeve. My guess it the 460cc kit takes up the entire hole. Due to some of the bolt locations, you wouldn't be able to bore out the cases much larger, maybe a couple mm's, but it would be pretty pointless.
    #93
  14. 3uba296

    3uba296 Thumpcurious

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    Cool, good to know. What about people saying yoy could get 500cc out of the 350 engine?
    #94
  15. Pablo83

    Pablo83 Sleep, Wrench, Ride

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    People say all sorts of things. With enough time and money I'm sure you could.

    The stock cases can accept a sleeve OD of up to 93mm. With the 71.2mm stroke of the 350's crank, you would need a 93.9mm bore to make 500CCs. I don't know how thick a sleeve needs to be, but you're looking at widening the cases (and moving some case bolts) or getting a stroked crank. I've never heard of a stroked crank for this bike, but that doesn't mean someone hasn't made one
    #95
  16. yondering

    yondering Long timer

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    On your neutral switch "missing a cover". I think that's just how they are. Mine was the same way.

    I think I read about someone grinding an offset crank pin to make a stroker crank for one of these. Jesse would probably know.

    You do some nice welding, BTW.
    #96
  17. juda5

    juda5 Been here awhile

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    Subscribed, and awesome work on the swingarm!

    Keep up the great work!
    #97
  18. shearboy2004

    shearboy2004 KIWIINUSA

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    I bored mine out to 450 and the engineers that did the sleeve and boring said it would be entirely possible to go to 500 with the room that was left.

    The kit I used came from LA Sleeve and just maybe their sleeves are a bit thinner.

    I just went out and measured a set of cases I have and the case hole was 98.26 mm so with that you could fit a sleeve that was damn close to 98 don't yer think???? With your figures that would leave a 4mm sleeve thickness. Stock thickness just measured at 3.5 mm.
    #98
  19. jessepitt

    jessepitt Ride More

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    Sweet build. I would love to have the wider spread tranny, cant wait to hear how the final result works. FWIW my DR350 has an RMX swinger on it that is quiet stiff. I got it that way so I don't know if it was an easy swap but it looks to be a bolt up fix. Might be easier than welding the stock-er.
    #99
  20. frdbronco8

    frdbronco8 Been here awhile

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    I would love to hear from anyone who has done this, some people say its a pain and others say easy... Awsome build pablo, I wish I was knowedgable enough to tear that far into one. The higher 6th gear would be perfect!