Honda CBR300 engine swap into a CRF250L.

Discussion in 'Thumpers' started by Cuttlefish, Jan 7, 2017.

  1. Cuttlefish

    Cuttlefish Riding to disappear.

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    With all this talk of engines have you taken your bike out for a spin yet?
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  2. Cuttlefish

    Cuttlefish Riding to disappear.

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    G'day, I noticed you used "was" when you wrote "This was intended to be a good rider and it was." No more or still running?
  3. Scutty

    Scutty Talent-limited bike builder and rider

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    Samtech now has a CB500X engine in his CRF
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  4. Samtech79

    Samtech79 Two wheeled lunatic

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  5. Cuttlefish

    Cuttlefish Riding to disappear.

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    I remember the 500 build thread of yours. The next level!
  6. Kawidad

    Kawidad Long timer

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    You mean, "the next level" of awesomeness. :raindance
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  7. Cuttlefish

    Cuttlefish Riding to disappear.

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    Michael Kozera's crf500l build, being the first one, was the groundbreaker that moved the goalposts for me. I was inspired!
    Samtech took it to the next level with a factory look cleaness to his build.
    Both awesome!
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  8. DaBinChe

    DaBinChe Long timer

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    What is the compression ratio on the 283 big bore? How about when it is upped to 325?
  9. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    I can't speak for the 283 kit when it's used on the 250 but in my configuration it's 11:8 to 1
  10. swimmer

    swimmer armchair asshole

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    There have been a few posts suggesting that one can use the 300 crankshaft in the 250 case. A few years ago Rick Ramsey stated on his website he was told "by a little bird" it would not fit. He never updated that post with any newer info. Does it really not fit?

    Also, if it does fit are you just left to buy cylinder, balancer, etc... and then use the 250 ECU? If so this confuses me a little due to it being said in this thread for this build that you need to use the 300 ECU due to timing issues. If that is the case how does the 250 ECU work with the 300 crank only mod?
    FWIW, my inquiry is based on doing a swap on a '17 250 engine with the larger TB.
  11. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    @Samtech79 has detailed pictures of both cranks, both cases and exactly what was different between the 2 on Thumper Talk.... The short answer is YES it will fit in the 250 cases BUT we don't know what Honda changed on the 2017 engine without a tear down and inspection. So... You'll have to do your own research on that...

    I tested my 250 ECU with the 300 engine and can say with 100% certainty that it doesn't work very well. It did start and did idle but would not run with any sort of throttle. I swapped the ECU and it ran perfectly.... So... I can't say what it would do if you "just" swapped the crank..... I would venture to say, because of the longer stroke, it should suffer some sort of timing issue anyway... BUT... With that said.... Using the crank position sensor from the 250 might work... After all they both spin 360 degrees... Dunno... If someone were going down this path it just make sens they would have a 300 ECU handy just in case it didn't work with the 250....
  12. Samtech79

    Samtech79 Two wheeled lunatic

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    If you want to know what changed... do a part number search. The case numbers and bearing numbers will tell you if there are any differences.
    These are parts bin engines for the most part so you'll see them pop up all over the place. Search by model and you can sort out part numbers that are different due to paint color.
    I doubt that much of anything changed with the 17 other than the flash on the CPU. The only big hard part change was with the 300 crank and balancer. The bearing size of the balancer also changed with was an update to the casting itself and the machining.
    The peripherals have a few variations but it would seam nothing is unique. The big throttlebody has been around on the 250r... with the new rebel I think it shares the same cams as the 300r, etc.
    Lots and lots of cross compatibility.
  13. swimmer

    swimmer armchair asshole

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    Thanks for the info. The only reason I have any sort of reluctance about using a 300 ECU would be if that would cause anything not to function as normal on the combo meter of a non-ABS Rally. If I was confident I'd have no issues with that I would just do a whole swap like OP but use the new, bigger 250 TB.
  14. Samtech79

    Samtech79 Two wheeled lunatic

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    EJK or PCV will give you more flexibility but also more liability if you don't know how to tune.
  15. Cuttlefish

    Cuttlefish Riding to disappear.

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    Just a heads up for anyone in Australia thinking of doing the 300 engine swap. The seller on eBay I bought my engine from still has the listing on. He is in Dubbo. Calling will get you an engine for $45 cheaper. There's also a cb300f engine in Adelaide for $500 on eBay.
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  16. Stillupright

    Stillupright Make my day

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    Looking at cbr300 engines on eBay I'm seeing prices of $1100-1800 USD

    What's going on? Is there a shortage now that more peeps are doing engine swaps?
  17. Cuttlefish

    Cuttlefish Riding to disappear.

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    When I was looking the price of used crf250l engines was $1200 USD (in the US) too.
    What about wreckers or Craigslist?
  18. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    Sounds about right... I have $1500 in my setup not including the big bore kit...

    I'll sell my perfect original 250 engine with 4K miles on it for 1K if anyone is interested....
  19. minkyhead

    minkyhead Long timer

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    acouple of questions chaps if you could help ...the o2 sensor plug is missing on the 300 apparantly its in the exhaust on the 300 ...are you running without one ? does it deal with tickover and low revs on open loop ..and then closed loop ecu afterwards

    i have a ejk controler for the 250 ..im leaving is disconnected to start with ..but ive heard snippets that folks are using this on the 300 ...

    engine arrived today thanks
  20. Cuttlefish

    Cuttlefish Riding to disappear.

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    Good to hear the engine has arrived. Running mine with no O2 sensor or ejk. It runs smoothly through the entire rev range. Dont know about closed and open loop. It also has very little popping on deceleration un-like with the 250cc engine.