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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    Stoked. That 15 front sprocket will give you the relaxed legs you're looking for on the highway.
    Running 14/38 made a significant difference towards relaxing the revs at speed and fun around town/easier trails. I ran the 14/40 most recently because of the terrain I was riding being more towards enduro vs adventure touring in very hilly country.
    Giving it a fist full in 3rd on dirt and having it spin the back wheel is novel.
    I like the 1st-2nd transition with the 300 gearbox. No more yawning gap inbetween first and second.
    Easy to swap front sprockets.
  2. GSXR

    GSXR Trail Rider

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    have you got a link to 15t Pete?
  3. Cuttlefish

    Cuttlefish Riding to disappear.

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    Sorry I don't. Sick of this rain yet?
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  4. Rocking Horse

    Rocking Horse Self funded bludger

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  5. GSXR

    GSXR Trail Rider

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    I've pretty much flogged out the chain & sprockets now, so will look to get a nice combo with 15t front.

    Don't want to commit to any gearing combo untill I get the oxy sensor welded into the header pipe. Want to see what effect this has first
  6. wolftrax

    wolftrax Long timer Supporter

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    Put a few miles on after 15t swap. My Africa Single 300 is now far better than I could ever hope for. It's now better off and on road than the Stage 1 250 Still plenty of giddiup in first and second. On the highway it cruises easily at 65 with pull all the way up to 75 MPH. Love this bike. [​IMG]

    Sent from my Moto G (4) using Tapatalk
  7. minkyhead

    minkyhead Long timer

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    just wondering if your going off the crf clocks or the sat nav ..the clocks are loads out a indicated 63mph is actually 70mph on the sat nav
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  8. wolftrax

    wolftrax Long timer Supporter

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    Going off my GPS. I'm sure it'll do much better than 75. Just don't see any need to go any faster.

    Sent from my KFAUWI using Tapatalk
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  9. falcn

    falcn Squidless Soul Supporter

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    I wish these were mainstream enough for a magazine to do a comparison for the Versys-X 300 to the Rallye 324cc incarnation.
  10. jwb

    jwb Local minimum

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    Hey pals, I read through the thread and I guess I'm pretty surprised at the variety of builds going on here. It seems like some folks are just swapping in the crank kit from the 300r and nothing else? Not even the ECU? Is anybody also using the intake cam from the 300? It's different from the intake cam on the 250l, although the exhaust cams are the same part. The piston is also a different part number ...
  11. Ed@Ford

    [email protected] Long timer

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    I've studied this business for several years. By studying the parts between the 250 and the 300 (286 actually) you can make sense of what to swap (i.e. what's different between the two) important cautions is a 250 piston on a 300 crank will give you almost 13:1 compression ratio....too much!! , second, there is a chance that the 250 ECU will not provide enough fuel at WOT, and a piston might melt. Some guys do not change the balancer or the balancer gears....probably only having a little extra vibration. If you use an EJK you can add fuel, or have it custom flashed by Dobek. Look into the cam swapping business....the 300 cam is different, also, I think the rocker is different. Also the 2017 Rally & CRF-L got a bigger throttle body. Go to thumper talk and read up on technical details of what other folks have done. Also, the 2017 250 has a different speedo/tacho....some fiddling of the wiring harness is required to make certain 300 ECU work and run the tacho. Swapping in whole 300R engines is popular too.....many ways to skin the cat to get more power. Just be careful.
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  12. jwb

    jwb Local minimum

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    Yeah you'd obviously blow it up with a stroker crank and the same piston. The balancer shaft appears different but the balancer drive gears are all the same parts.
  13. Ed@Ford

    [email protected] Long timer

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    It would run REAL fine if you could get RELIABLY 94 octane or you always stayed above 8000 feet. Early CRF-L had different balancer gears....2017...I think all CRF-L/Rally 250 had 300 balancer gears....working from memory here. Also, when you get a crank kit get the kit provided for recalls of ALL 300's from '15 and '16 because they all had recallable/warranty bad cranks.
  14. jwb

    jwb Local minimum

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    Seems like I'd need the 'A' type crankshaft bearings, or I'll have to order, receive, and measure the crankshaft and get the correct corresponding bearings, regardless of which bearings are already in my crankcase.

    I've convinced myself this is a cheap and easy project. :hmmmmm
  15. jwb

    jwb Local minimum

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    The major parts all have, at least, different part numbers. Importantly, the crankcase halves and the cylinder. And of course the crank, piston, cam, balancer, and then the balancer gear looks very different on the CBR fiche compared to the CRF one, but has the same part #.
  16. Ed@Ford

    [email protected] Long timer

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    At least 2 of the reasons crankcase halves are different # is 1: paint color, # 2 is: one of the halves holds a bearing that supports the end of the balancer shaft. This bearing is larger OD in 300's compared to the 250. Probably because (noted in some documentation on Thumpertalk) the 300 balancer shaft is heavier than for the 250.
  17. jwb

    jwb Local minimum

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    Yep I woke up with the realization that they paint these different colors. You think the balancer bearing outer diameter is different than the one in the 2017 250? It’s only going to cost me $7 to find out.
  18. KLeptoLee

    KLeptoLee Adventurer

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    I put a 300 crank balancer shaft,cams in my 250l and an 81mm big bore=325. 305 reflash on the ejk. It’s a rocket compared to stock. Something must have self clearanced I found shavings in the first oil change at 250 miles. They may have been hard miles lol. Being paranoid i pulled the side covers off and inspected, either the crank or balancer shaft clearanced it’s self.
    Edited to add content.
  19. Ed@Ford

    [email protected] Long timer

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    don't buy it...in the description of the bearing there is a 4 digit number . Get each number and google bearing dimensions...you'll find the300 balancer shaft bearing OD is about 5mm more...ID of both are equal, so the 300 balancer will fit in the 250 case with bearing.....obviously honda thought the heavier balance shaft needed more robust bearings. But numerous folks have built 250's with the stroked 300 crank and kept the 250 balancer.....most said they did not notice any vibration increase.....that's about the only real technical issue stroking the 250 with honda parts...but I find it acceptable, as I have no positive opinions of the current choices available in big bore kits for more displacement.
  20. KLeptoLee

    KLeptoLee Adventurer

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    I had custom thickness gaskets made by cometics to drop the compression. To 12.5:1 if you use the stock thickness gaskets it’s 15:1
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