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Help ZXR250C - Rebuild V2

Discussion in 'Kawasaki 250cc In-line 4's' started by DanoHosko, Oct 21, 2022.

  1. jmw76

    jmw76 Well-Known Member

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    As a general rule sealing faces that form the clamping face for bearing shells typically use a silicone sealant rather than a gasket to allow better control of the bearing clearances.
    You do not put sealant near the shell bearings. Just use silicone on the areas that seal to the external side of the motor.
     
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  2. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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  3. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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  4. DanoHosko

    DanoHosko Well-Known Member Premium Member

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  5. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    And the verdict....

    Toast.
    24.45mm old mate reckons....
    He used verniers though because his micrometer wouldn't fit either. :confused:
     
  6. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Service manual gives the range of big end journal diameters as 24.984 - 25.000mm
    Something seems amiss there because ~0.4mm is a lot of material off of a crank
     
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  7. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    Hmm, I'll chase up my mate and see if he has decent micrometers that will fit
    Apparently though once you get past the hardened outer layer the inner is softer so might explain why its worn so bad?
     
  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    It is possible, but it doesn't strike me as probable, happy to be proven wrong, not that that would be a good thing for you
    But it's case hardened crank pin material versus soft bearing shell material or did it all disintegrate and end up gnashing against the conrod bore?
    That would have made one hell of a noise though ~3mm of clearance
     
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  9. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    Haha i will definitely get a second opinion as I would be very happy to save the crank!

    Well one half spun underneath the other, and she was very noisy, a little tap initially that quickly became a knocking when i pulled up :/
     
  10. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I suppose if it ran far enough with conrod bore to big end journal contact it could have worn down 0.4mm of material, but given the rotation and contact pressure points on the strokes I would have expected there to be a discernible flat spot on the crank unless the conrod jammed into the open wedge available because of the spun bearing

    Inquire with those guys that supply the metal spraying equipment if there's anyone up your way that does that as it's used a lot in the heavier industries like mining etc to put hard outer surfaces onto things like mining equipment.
     
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  11. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Get an accurate measurement before you go spending big dollars on new bits.
     
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  12. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I believe so, which is when people think they can have the crank ground down and fine shells to suit, good luck.
     
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  13. Alumascoupe

    Alumascoupe Member Premium Member

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    It is possible to have a crankshaft hardened again once its turned down to fit undersize bearings, (but less than ideal)& not cheap either. A good machinist can even build it back up with weld & turn it down to stock & re harden it either with heat or chemically. But It is usually better to source a good used crankshaft at that point unless its beyond rare.
    Once tore down a mitsubishi 4g64 engine that had thrown a rod right thru the side of the block & also thru oil pan...amazingly the case hardened crankshaft did not even have so much as a scratch ! Had I not seen it with my own eyes I still wouldnt believe it (& still not sure how it was untouched judging by the block i could literally see straight thru to daylight & all the shrapnel !)
    But I have also had ones that managed to spin a bearing, just like yours did, that then badly scored the crank rod journal in just seconds.
    You should also have your builder check the connecting rod journal opening. if the bearing spun it may also need resizing or it may just spin the next bearing no matter what the crank journal size is. The rod end may have warped or hammered in the process of knocking itself to death on the old crank.
     
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  14. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    Ok so second and third opinions are the same haha, toasted. Not even round anymore...

    I'll be purchasing a new crank and I'm thinking new conrods to go with it :cool:
     
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  15. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    So Megazip reckon if i buy a crank and conrods off them, they will provide the correct bearings based on the service manual.

    Reckon thats reliable enough?

    The service manual onlu specifies thickness of crank main bearings based on the crank journals, doesn't mention about the casing itself...
     
    Last edited: Nov 16, 2022
  16. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    Yeah i think getting the crank repaired is going to be silly money, one bloke said he wouldn't even turn his machine on for the price of a new crank...

    Going to replace the rods too, I'm in this deep may as well go more!
     
  17. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    I think they're talking about getting the correct rod bearings to match the crank, which would be nice to have ready to go for you. You'll still have to measure the new crank and figure out which bearings you need for each main journal.

    Don't forget shipping costs, a new crank and rods weighs a bit and will be expensive to air mail. You could put it on the slow boat from Japan but you'll be waiting weeks to months.
     
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  18. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    Ah yep ok, so the clearance between the main bearings and the journal is going to be dependent on the casings

    I'm going away for a couple months so boat probably won't matter too much ;)
     
  19. DanoHosko

    DanoHosko Well-Known Member Premium Member

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    Hey y'all

    Little update, since the crankshaft was ruined, I took the easy option and ended up buying a donor bike that was in bits, have plugged the engine into mine so we're back in business ;)

    Luckily the donor bike came with a starter as the second hand one I bought off Facebook didn't work lol...

    Cheers for all the help and advice as always!

    https://youtube.com/shorts/8ITohG42dRM?feature=share
     
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    Last edited: Feb 26, 2023
  20. David Gayford

    David Gayford Member Premium Member

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    Use to do that for a living....
     

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