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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    That's right folks...My humble, utilitarian Honda crf250l 2015 is about to receive a cbr 300r engine swap.
    My crf started making strange noises and so I went back into the Oz vendors section to find a thread for a new mechanical business on the Sunshine coast.
    Drivewell mechanical.
    http://advrider.com/index.php?threads/drivewell-mechanical-sunshine-coast.1181800/
    I took the bike over to Gerard and we had a good chat about what he's done with bike tours in the Far Nth of Australia.
    I ran my thoughts about some prospective bikes to replace my Triumph scrambler since I was more into exploring off road with the crf than road riding with the scrambler.
    Essentially the crf while being a fun bike showed its suspension and power deficits when pushed faster both off and on road. So I was thinking of just one bike to simplify things.
    Is it too soon to insert? ....Buy a KTM...which one? ...who cares which one...ok, ok ... A 500 exc!
    Ok.
    Now I've got that out of the way. I did get as far as test riding some used bikes the week before the crf signed off.
    I rode a Ktm 530 exc, a WR 250r, dr650, drz400e and a Kawasaki klx450r.
    Funnily enough I got back onto the crf thinking if it had a bit more power and I had the suspension upgraded it would be spot on for cruising around and exploring the hills and dirt roads out the back of the Sunshine coast hinterland where I live.
    I'm not looking to ride single trail or snotty terrain since I'm doing it solo.
    I have a large VW van to either wheel it into or put it on the back with my rack n roll carrier so it doesn't have to be a "adventure cargo bike". I can drive the way further afield and use it as my camping base to explore areas if I want.
    Anyway...Gerard called me with the bad news that the top end was going to need quite a few parts.
    So while looking for used top ends on Ebay I came across a used cbr300r engine with 15,000kms on it. The vendor also had the ecu, throttle body, coil and spark plug listed too.
    I started researching a prospective engine swap.
    Rick Ramsey did an excellent comparison sheet of the engines.
    http://www.rickramsey.net/CRF250Lresearch.htm
    To date I've found threads on Thumpertalk where people have swapped various parts and even the majority of the cbr's engine but none have simply done a straight entire cb300r engine swap into the crf-l.
    So Gerard also did his own research and agreed to do the work for me and document it along the way.
    I can take the bike to Full force racing suspension specialists (famous now for their plex valve DR 650 transformation) to re-valve my stock rear shock and front forks once the engine is in.
    https://www.fullforceracing.com.au/
    I'm on a bit of a budget. Probably will need a ejk fuel controller down the track too.
    The crf has an FMF Q4 pipe with power bomb header, standard airbox with K&N filter (bought it used this way) and I've put a 13 tooth front sprocket on it.
    The engine should leave Dubbo in NSW tomorrow and so by middle of next week the transplantation could commence.
    Here's the crf waiting for its donor engine.
    [​IMG]
    #1
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  2. The_flyer

    The_flyer Been here awhile

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    Looking forward to seeing this project!
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  3. wolftrax

    wolftrax Long timer Supporter

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    Sent from my XT1019 using Tapatalk
    #3
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  4. swimmer

    swimmer armchair asshole

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    Interested in weight increase if this ends up working.
    #4
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  5. adventurebound9517

    adventurebound9517 Long timer

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  6. Blossem12

    Blossem12 Adventurer

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  7. Cuttlefish

    Cuttlefish Riding to disappear.

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    Engine is on the way....due by Thursday.
    #7
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  8. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    Morning Cuttlefish.... I'm the same @shortman that is on Thumper Talk....
    I wanted to elaborate on the transmission thing a little more.... If you keep the CBR300 engine as is I recommend you go back to the stock 14/40 gearing... Because of the close ratio box in the 300 engine 6th gear (when running the stock 14/40) feels like the CRF250 engine when running 13/42 gearing.... Hope that makes sense...

    Because you already have the 250 engine out of the frame it's not too much more work to just split the cases and swap the gear box OR put the crank in the 250 cases..... You will be much happier, I promise!
    #8
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  9. Cuttlefish

    Cuttlefish Riding to disappear.

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    G'day. Thanks Shortman. I was already thinking of going back to the stock front sprocket after what you'd said.
    Since the crf will be run on plenty of twisty hills on-road to gravel roads and 4wd tracks as opposed to single trail as its primary riding the cbr 300r transmission ratios may still be good for me.
    I will probably sell my Triumph scrambler soon so the crf will get some road rides in its use too. I'll see how it goes first.
    Will run through the transmission swap with Gerard before the engine installation. Should turn up tomorrow...or even today!
    #9
  10. mekros

    mekros Adventurer

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    I'm very interested to see how this progresses, thanks for starting the thread.
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  11. Cuttlefish

    Cuttlefish Riding to disappear.

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    For those following this thread, Shortman has already done the cbr300r swap.
    #11
  12. swimmer

    swimmer armchair asshole

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    So you can run the 300 crank and cylinder on the existing 250 case? Do you retain everything else from the 250? Sorry some of this might be repeated questions. OP said you've already done the swap. Is that documented somewhere? Thanks.
    #12
  13. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    No... I didn't have the time to document mine and really didn't think it was necessary... The engines are basically identical... The 300 has some minor internal differences with the biggest one being the longer stroke that provides 38 more cc of engine size.... I added a Bill Blue "283" big bore kit to mine before installing it to further increase displacement....

    Yes the 300 crank will drop right into the 250 cases.... I suggest the use of the 300 balancer....
    #13
  14. Sootgrinder

    Sootgrinder Been here awhile

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    Once completed this sounds like the perfect sensible dual sport, mini adventure machine. Can't wait to hear the rest of the story.
    #14
  15. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    I really think it will be... At least that's what I was thinking when I decided to buy and build it.... I have a KTM 500 for the gnarly single track and big dual sport rides I attend thru out the year so the Honda is gonna be my "go to" bike when I wanna ride from home somewhere OR maybe take a multi day trip....

    I've only ridden it enough to know the engine upgrade was well worth what it cost... I plan to log many more miles as soon as my house remodel is finished and I yank the engine back out for a transmission swap....

    I also wanna throw out there for someone reading this who is thinking they might like to do the same thing... I have the complete 250 engine that came out of my bike sitting in the basement... Would love to pass that along to someone who wants to wants to go down the same road of building up an engine then just do the swap
    #15
  16. swimmer

    swimmer armchair asshole

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    Thanks. Rick Ramsey stated back in '14 on his site that the 300 crank won't fit. I guess he had bad info at the time?
    #16
  17. Sootgrinder

    Sootgrinder Been here awhile

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    How involved is it to get the honda suspension up to an acceptable level of performance to go along with the new "big block" motor? I also have a 500exc, but someday would like to add something similar to the crf 300 for mini adventure type activities.
    #17
  18. shortman

    shortman Beta 500 RS, X-Trainer 250 Supporter

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    I can't really say... I've not made it that far but from what I've read it comes down to a new rear shock and race tech valves in the forks.
    #18
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  19. retroone

    retroone Long timer

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    "New rear shock and race tech valves in the forks"
    That's the minimum :dirtdog Shock and forks is what I would do. :ksteve
    #19
  20. Cuttlefish

    Cuttlefish Riding to disappear.

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    Talked to Gerard about the transmission gearing and he'll install it as it is with the 14/40 standard sprockets and we'll test ride the bike to see how it goes.
    This way we can give a benchmark for others who may also do this swap in the future.
    Then we'll look at different sprocket combos to adjust with the 14/42 being the next step (thanks Shortman).
    So far with my stock suspension (rear pre-load wound right up for my 185 lbs/85kgs) the ride is fine for me on road. Off road my main gripe is with the sluggish rebound of the rear shock. The terrain and pace I'm riding doesn't tax the front too much. I will have Fullforce racing re-valve the forks and look at springs/fork oil adjustments as they see fit in the future.
    #20