YZ250F tear down, re-build & interesting issues

Discussion in 'Thumpers' started by dbur971, Feb 21, 2015.

  1. dbur971

    dbur971 Been here awhile

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    I'm starting to tear down and hopefully re_build a 2104 YZ250F. I'll post photos and issues in this thread as I go.

    It had a cam bushing failure and filled the motor up with metal grindings. Besides the cam bushing there are some things I see after removing the head and accessing the crank timing chain sprocket.

    1. Intake valves have come so close to the head there is no room for even carbon build up. It looks like there has been some very slight valve to piston contact. Notice the dull carbon on the ex valves and the more burnished look to the intake valves.

    [​IMG]ValveFaces by dbur971, on Flickr

    [​IMG]PistonTop-1 by dbur971, on Flickr

    [​IMG]PistonTop-2 by dbur971, on Flickr

    The compression was good before tear down, and the valves look OK with the solvent seepage test. After ~1min there is just barely any solvent film visible around the valves.

    Think these valves are OK to use?

    2. I can feel a little roughness and stickiness in the can chain drive teeth. The crank sprocket shows some signs of stress, though all teeth are intact.

    [​IMG]CrankSprok-3 by dbur971, on Flickr

    [​IMG]CrankSprok-telecentric-1 by dbur971, on Flickr

    And here's a special treat, sprocket in stereo! View as cross-eyed stereo. look at the left image with your right eye and the right image with your left eye. Google 'viewing cross-eyed stereo' for some help with this. Can take some practice.

    [​IMG]CrankSprokStereo by dbur971, on Flickr

    Would you say this crank is still good to use or not?

    Follow the flickr links to see more details if you like.

    Thanks!
    #1
  2. Kawidad

    Kawidad Long timer

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    To me, the teeth on the cam chain sprockets look good enough to run them, which what I would do.

    As to the valves. Having them even kiss the piston makes me squeamish. If you're sending the head off to a professional to be renovated, then he'll give you the best answer to that question. If not, then you'll know more when you pull them out. You can't tell anything much, unless horrible bad, while they're still in the head.
    #2
  3. dbur971

    dbur971 Been here awhile

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    I completed the tear down and found the clutch basket has a broken off prong. Apparently the broken piece was removed and then the basket continued to be used. They also probably did not clean out the metal pieces from the motor so that's where all the debris came from and probably why the cam bushing went out. The oil stainer was heavily obstructed.

    The crank bearings all feel good, but there's crap in others. I'll need to get them all cleaned out to see what's good and not. Two clutch friction discs are broken. The remaining clutch discs all look good. I wonder if I can find individual Rekluse clutch discs?

    There is some bluing on the crank but that looks like it's not caused by the rod bearing overheating.

    The wrist pin and rod bushing show some scoring. Not enough to feel but you can see it in these closeup photos. Can that still be used? More photos with different lighting here:
    https://www.flickr.com/photos/dbur971/sets/72157648417318625/

    [​IMG]Wrist Pin by dbur971, on Flickr

    [​IMG]Rod Bushing-3 by dbur971, on Flickr

    [​IMG]Oil Screen by dbur971, on Flickr

    [​IMG]Clutch Basket (1 of 1) by dbur971, on Flickr

    [​IMG]Crank Blueing by dbur971, on Flickr
    #3
  4. Kawidad

    Kawidad Long timer

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    WOW :eek2 That's crazy to run it with that kind of damage to the clutch basket.


    The scoring looks significant. I wouldn't reuse it, but I suppose you could get away with it. As to the bluing. In my experience that looks normal and part of the heat treating process done during manufacturing.
    #4
  5. mcma111

    mcma111 Long timer

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    That rod is toast. The bluing on the crank is normal.
    #5
  6. Argus16

    Argus16 Long timer

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    What year is the yzf?
    You wrote 2104... assuming a 2004.
    #6
  7. larryboy

    larryboy Stable genius.

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    Find another engine or throw the whole thing in the trash, it's not worth the time or money.
    #7
  8. BIG ED XT FAN

    BIG ED XT FAN Long timer

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    That motor is about 1 hour tops going into a complete melt-down!! It cost about $3200 us to rebulit a 250f here local. I look for a low hour motor. Good Luck!!:eek1:eek1:eek1
    #8
  9. Argus16

    Argus16 Long timer

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    +1
    I broke the rod on mine and.spent just about that replacing piston, rod, etc. even the flywheel.

    I'd wait for a used one to show up if I had to do it again. Jist my .02
    #9
  10. dbur971

    dbur971 Been here awhile

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    Thanks for the comments everyone. I'm on the fence about repairing this, though maybe it will depend on how good of a deal I can find on decent used parts. Yes it is a 2004.

    $175 min for head repair
    $7-$30 for wrist pin
    ??? for replacement crank. I may have a line on a used one or a cheap Wiseco new one.
    $30-$40 ebay for clutch basket.
    $25 for a couple new clutch discs.
    ~$85 for timing chain and guides

    Maybe ~$500 could get it done, though certainly not with new parts.

    I suppose the rod could be replaced on this crank, but that's probably going to be as much as I'd pay for a good used crank anyway.

    The rod and wrist pin photos actually look worse in the photos than to the naked eye, since they are blown up way large and taken with contrast enhancing lighting as well. Still I recognize that rod should be replaced.
    #10
  11. larryboy

    larryboy Stable genius.

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    Looking at eBay it seems these things explode like KLR's, plenty of used parts...you'll do alright going that way.
    #11
  12. dbur971

    dbur971 Been here awhile

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    Looks like the advice is the intake valves should not be re-used since they have kissed the piston. That add's probably >$300 to the repair cost so in all likelihood this bike will end up parted out rather than repaired. Thank's for the comments you all have given.

    David B
    #12
  13. mcma111

    mcma111 Long timer

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    #13
  14. dbur971

    dbur971 Been here awhile

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    But according to Kibblewhite they must be used with Kibblewhite spring sets and a spring set is $230-$250. I assume it would still be 3/5 that if I could find just an intake valve set.

    With all the other things to repair it just doesn't add up to be an economically feasible project. :-( It would have been nice to have defeated this thing, I was beginning to see it as an enticing challenge, but practicality must be considered at some point.
    #14