Low Tech, Lightweight 4-stroke engines?

Discussion in 'Some Assembly Required' started by tdvt, Jan 30, 2013.

  1. tdvt

    tdvt Been here awhile

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    So, still thinking about this project & I have a line on an '83 XR200, but looking at available performance part it seems '86-on is the division. I DID find limited info on the 84'-85' twin carb versions which are not well-liked.

    Any thoughts about the '83?
    #21
  2. jesusgatos

    jesusgatos fishing with dynamite

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    Here's something I started building a while ago and have been too distracted with other projects to finish. CRF450R chassis with an XR250 engine. Had previously put together a few big-wheel CR80/85's with pumped-up XR100 engines. Super fun little trailbikes. Almost exactly the same size as a mountain bike and 150-160lbs. If you want to build a hybrid that CR80/85 chassis is a great way to go. Takes quite a bit more work to stuff a CRF150F, XR200, CRF230 engine in there, but think that would be the hot ticket. Dave Miller at DMC sells custom-built conversion frames and if I remember right, they cost right around $2000. Have one that we haven't built-up yet, and bought another un-built kit at the same time (which he normally doesn't sell). Don't think I'll get around to building another one any time soon, so if you want to build your own, can hook you up with all the parts (laser-cut & formed brackets, billet aluminum carb adapter, etc.) you'd need to do it right. $500?

    [​IMG]
    #22
  3. sonic reducer

    sonic reducer Been here awhile

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    Can you elaborate on that, especially in comparison to say the xt225? Xr250r? Klr250?
    Also for the sake of this thread can anyone with the knowledge share the weights, dimensions, and power potential of the engines that could be useful in a build like this?

    Considering the cost of something like a blown up yz125, this type of project is very intriguing.
    Which late 90s early 2000s 125 chassis would be the pick of the litter for a project like this? I'd favor a steel frame for ease of chassis mods.
    #23
  4. nuggets

    nuggets Fries with that?

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    I am interested in this too.
    #24
  5. Luke

    Luke GPoET&P

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    I used a '99 YZ125 chassis, which was the last generation of the steel frame for the ease of modifying. If you have an Aluminum welder the point is moot, but I don't. I really like how it turned out, I think it handles well. The MX suspension desperately needed revalving for trail work though. I'd expect any MX bike would.

    Something to note is the shape of the engine cradle. On the yz frame it curves back more on the 125 frame than the 250. Looking at the picture of CharlieT's bike makes me think that you might want that space when using an xr200 motor. His bike shows nearly no curve back at the bottom of the cradle and the motor is using that space.

    The other issue is the headroom for the motor. 4t motors are generally taller than 2t motors and the center spine of the steel frame may cause problems. In my case I was staying 2t and the motor fit but I had to fabricate a goofy wrench to get the spark plug out without pulling the motor.
    #25
  6. JerryH

    JerryH Banned

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    I have to recommend the XT225 motor. I have put over 30,000 hard miles on one, and nothing has ever broken. Simple, air cooled, 2 valves, kickstarter option, and you can replace the cam chain without tearing the motor down. I've adjusted the valves twice in those 30,000 miles, and they were just a hair off. it's not an MX bike, but it has enough power that I have ridden it hundreds of miles on the freeway. And it still even has the original clutch. I have never seen a small displacement air cooled motor hold up this well before.

    In AZ, you can plate any production 4 stroke with a VIN, by only adding a few things. No instruments or turn signals required. But a custom frame would mean registering it as custom built, and that is a real hassle.
    #26
  7. Pete-NZ

    Pete-NZ Been here awhile

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    May 8, 2011
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    I have a striped out TTR250... Simple & bullet proof..
    [​IMG]

    TTR250 with a WR250F Rekluse EXP clutch & EBC heavy duty springs...
    [​IMG]

    Has a GYTR tail pipe with a 125mm shorter header pipe...

    Next mod is a set of 05 YZF250 USD forks...





    .
    #27
  8. Lizrdbrth

    Lizrdbrth Wackjob

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    FWIW an XT225 motor weighs 75 lbs. 4 oz., all up, wet, less exhaust. And that's for an early one with both kick and electric starters. Later E-start-only XT and TTR versions have an increased number of things like plastic drivetrain gears and stuff and will be a few pounds lighter. Not sure how that compares with the Honda motors, but take it from there.
    #28
  9. mousitsas

    mousitsas Long timer

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    Is it possible to modify a trials bike to suit your needs for a light trail blazer?
    Do they have the engine and gearbox specs for such a job?
    #29
  10. shirk

    shirk n00b

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    XR200R engine is 58 lbs.

    http://www.lite-bikes.com/
    #30
  11. Lizrdbrth

    Lizrdbrth Wackjob

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    That weight is dead empty and stripped. No oil, no shifter, kicker or carb. Important considerations if you're yer gunna split hairs. The all-up weights are gunna be damned close, considering the Yammi I weighed is both kick and E-start.

    Not trying to start a pissin' contest at all. I'd like to know, myself. All else being equal 10 lbs. difference in engine weights would be significant.
    #31
  12. tjzondrz

    tjzondrz Non-Nefarious

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    I just got my 1980 IT175G plated in Pa.(antique)
    Great little bike to throw around in the dirt.Its a fantastic bike for single track.I believe it weights 208 lbs.loaded.
    #32
  13. Zuber

    Zuber Zoob

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    In the States most all the trials bikes are two stroke, except for a high dollar honda/montessa 4RT. If two stroke is ok, I'd look for a 2000-2004 Gas Gas TXT, 250, 280, 300. This is a very similar engine to the Pampera which was a 'long ride' trials bike with turn signals and a seat.

    http://www.gasgas.com/Pages/2003's/Pampera/pro-280-main-specs.html

    The TXT 6 speed trans has a good spread for trail riding, unlike some others that have a big gearing 'hole' at trail riding speed. Some sheet metals guys around here make up a gas tank/seat combo for these that add 1 gal or more.

    The newer Gas Gas Pro models would not be good for trail, they have 4 gear sets and make a 6 speed by double passing. The clutch only has about 3 plates.

    Wish KTM would bring in the 350 Freeride. Pushing 220 lbs, but all the right specs otherwise.
    #33
  14. mousitsas

    mousitsas Long timer

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    Thanks Zuber, very good info!
    #34
  15. nuggets

    nuggets Fries with that?

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    CRF250X engine. 58LBS. No oil. No carb. With shift lever, kick lever, and some hoses and wiring.

    [​IMG]

    I know it isn't super low tech, but it was just sitting there, so I threw it on the scale.
    #35
  16. scooted45

    scooted45 Adventurer

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    Low-tech light-weight is the textbook definition of a 2 stroke, just sayin
    #36
  17. scooted45

    scooted45 Adventurer

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    definite advantages to 4 cycle on tight trails near my house. just put put put... no need for serious power in sloppy rooty woods trails. my DR200 was perfect but never saw 2nd gear. I rode it for 7 years with minimum maintenance. Not sure of the weight factor but VERY torqy.
    #37
  18. jesusgatos

    jesusgatos fishing with dynamite

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    Anybody building anything? Just finished this (CRF150F/CR80).

    [​IMG]
    #38
  19. JagLite

    JagLite Long timer

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    Looks fantastic!

    I would go that route but the 85 frames are so tiny.

    Projects? Yes, several of them actually...
    Nothing major though:

    I finally found an RM85 (small wheel) roller to use the complete front end and rear wheel on my RM250 frame.
    Still looking for an XR200 engine to put in it.

    The 85
    [​IMG]

    The 250
    [​IMG]

    I need the larger frame since I am 6'-4" but I want the 14" & 17" wheels.

    Finished projects?

    I built a tool tube for my DR650 to match my GSXR muffler:

    [​IMG]

    [​IMG]

    Which one is the real muffler and which is the tool tube?


    For my Street Tracker DR650 (AJS tribute) I have experimented with various baffles in the Emgo reverse cone muffler to get the noise level down.

    [​IMG]

    This the latest and so far the best, a bent sheet metal baffle:

    [​IMG]

    Yes that bent blue, white, and yellow thing goes inside the perforated core to deflect the sound waves.
    That is in addition to the 3 perforated blocking baffles welded in the core.
    It is "less loud" but still obnoxious to me.
    Experimentation continues.
    Runs great!

    I built an engine rebuild bench for the Triumph TR6C engine that will go in my Rickman:

    [​IMG]

    [​IMG]

    Also bought a house, worked six months remodeling the house, moved, spent 4 months painting our old house and selling it.

    And finally spring has arrived in Anchorage so I go riding every chance I get and my projects wait for winter...
    #39
  20. bradrh

    bradrh Been here awhile

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    How about some details on how you built the tool tube?
    #40