Trashed head/cam and scored piston/cyl Looking for suggestions on next move.

Discussion in '2012+ CRF250L Tech Talk' started by MrWesson, Feb 28, 2016.


What do you guys think

  1. Bring it back to stock 250cc you just got it!

    0 vote(s)
  2. Big bore baby!

    0 vote(s)
  3. CBR250R engine.. basically a more reliable option vs rebuild

    2 vote(s)
  4. CBR300R engine

    2 vote(s)
  1. MrWesson

    MrWesson New Member

    I basically had a cam tensioner fail, made my own and over torqued it until the engine stalled hard(while riding) I'm pretty sure its what turned a failed cam tensioner into a full rebuild.. Live learn I guess.

    The cam chain tensioner I made while waiting for the replacement. I thought I was being slick...

    I read about how to set tension but the more I tightened it the quieter it got so I kept going. I put a ton of tension on it and took it for a spin around the yard... It locked up hard and stalled.. Once I removed tension it ran fine but with the noise more prevalent. After talking to some people it seemed like a manual cam tensioner would solve all my problems.. I was doubtful when doing some testing so I pulled the valve cover gasket to check valves/etc.

    Found this.. Ugh oh

    Knew at this point I was in for a new head so I figured i'd start the removal of the battered one.
    Found this..
    My finger catches the grooves.

    After removing the cyl I found the piston to be pretty scratched up on the intake side(where the cam/journal problems were).. No pic on that and currently where the bike sits.

    The crank looks good with no play(thank god).

    My options are as follows as I see them.

    Option 1 New oem head, cams, cam chain, piston, cyl, rings bringing the bike back to stock.. parts are cheap and $3-400 should do it.

    Option 2 New oem head, Big bore kit and the above cost about $700

    Option 3 Swap in a used CBR250r engine(seem to be more prevalent than CRF250l engines) this should be pretty straight forward. low mileage engine for about $600

    Option 4 Swap in a used CBR300r engine... I can get one shipped for about $800 with very low mileage.

    Option 1 and 3 are comparable with option 2 and 4 being comparable.

    I like power and i'm leaning towards at least the big bore kit since its down to the crank.

    The CBR300R engine fits based on research but presents a few quirks/problems.

    First is the lack of an Oxygen sensor bung in the head.. I also don't have a good 250l head to use If I wanted to.
    Gearing.. The CBR300r engine is geared higher but I think sprockets could mitigate.
    ECU/Wiring potential issues. I've read many people are getting warning lights from a 3 prong vs 2 prong lean bank sensor.. I would hopefully keep the CRF250l ECU if possible and run it with my EJK on the bike(either reprogrammed for 305BB or as is not sure which I need).

    It fits!
    30WHP as is with 350cc Big bore potential down the road.
    Easier than a rebuild.
    More Powa!
    Uncertain about current engine/leftover shavings low mileage engine sounds nice.

    Anything i'm overlooking about the CBR300 swap?

    Also keep in mind this bike is new to me and has stage 1 W/EJK and the power was just fine although I felt it could use a tiny bit more(tuning would have done it I suspect). I'm also moving to the CO rockies so more power = a positive.
  2. MrWesson

    MrWesson New Member

    Not sure if anyone's here but I'm doing a CBR250R swap..

    Why a CBR250r engine vs a CRF250l engine?

    Short version is they corked up the CBR250R engine to produce the down low power by simply adding a smaller throttle body/header. Header is gone for a FMF megabomb, the CBR250r is putting down much larger numbers in the mid to top end while retaining similar although slightly less down low(hard to judge based on dyno's with stock knobbie vs street tire) but most importantly they are more prevalant because of CBR owners being more "crashy" than crf250l(plus more sales :lol3). The end result is I can get a CBR250R engine for half the price or less.

    If I want the down low torque the CRF250l has its a simple throttle body swap(back to crf)

    Differences between engines are..
    Gearing.. its hard to say how it will affect real world but its as follows.

    1st 3.416 2nd 2.250 3rd 1.650 4th 1.350 5th 1.166 6th 1.038 Reduction ratio (primary / secondary)2.807/2.571

    Transmission gear ratios 1st 3.333 2nd 2.117 3rd 1.571 4th 1.304 5th 1.115 6th 0.962 Reduction gear ratio (primary/secondary) 2.807/2.857

    I plan on installing the 13t sprocket and see if that gets me where I want to be but if not i'll play with the rear sprocket. I also have a speedo healer.

    Throttle body/Ecu 36mm for the CRF250l and 38mm for the CBR250r.. basically corking the bike to produce some down low power(in addition to a tighter header). By "corking" I don't mean it as insulting it does produce the desired result for a trail bike.. Problem is my bike has a free flowing exhaust/header undoing the honda way of mid range production.. I have both throttle bodies and plan on playing with them to see differences. For what its worth the CRF250l requires modification to fit on the intake side of the 250r engine should be a simple process.

    Engine is black vs silver.

    Most everything else down to cams/piston/valve springs,etc share part numbers.

    Dyno numbers if anyone is interested(Keep in mind street tire vs oem knobby on CRF). These numbers are pulled from the same company/same dyno but at different times(unknown). The results are mostly speculative but my guess is that the CBR250r tire scews the numbers but not enough to account for all that power. Assuming one bike was dynoed in the dry cold of winter vs dead heat of summer I don't see the weather as playing that large of a role either.

    Interested in what you guys think.
    3.5/6.5 3.5/6.8 +.3

    4/8 +1 4/7 -1hp

    4.5/10.1 +.1 4.5/10 -.1hp

    5/13 + 1 5/12 -1hp

    5.5/14.8 5.5/15.5 +.7

    6/16.2 6/17.9 +1.7

    6.5/17 6.5/19.5 +2.5

    7/18.1 7/21 +2.9

    7.5/19.5 7.5/21.6 +2.1

    8/19 8/22.5 +3.5

    8.5/18.7 8.5/23 +4.3

    9/18.2 9/22.8 +4.6

    9.5/17.8 9.5/22.5 +4.7

    10/16 10/22 +6

    10.5/14.8 10.5/20 +5.2
  3. CatFlap

    CatFlap Member

    Ouch on that cam issue.

    The swap seems interesting. And it looks to me like the CBR has lower gears if I'm reading it right? (Numerically higher = lower ratio) So should be great for dual sportin'.
  4. Alex

    Alex dude

    Good luck!