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Help MC22 overheated

Discussion in 'Honda 250cc In-line 4's' started by thebeefsalad, Aug 2, 2018.

  1. thebeefsalad

    thebeefsalad Well-Known Member

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    Was cruising to a meetup, got stuck in traffic. looked down to see the needle darn near touching red. Pulled off the highway and let it cool off. Managed to get to the meetup and back without her getting hot again. I did notice that my fan was not spinning when I pulled off, so I'm wondering where I should start diagnosing that. I cannot say I ever checked the fan to see if it worked, but I'm assuming it did as I have been through several trackdays and never overheated it. Wondering if there is a common failure mode for the cooling. I.e. bad temp sensor, bad ground, burnt connector. I haven't touched it yet, so all options are open.
     
  2. thebeefsalad

    thebeefsalad Well-Known Member

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    I just checked the radiator. It's empty :( Pretty sure this is telling it was overheated. Hopefully I got lucky and milling the head will fix it but I don't have my hopes up.
     
  3. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    On the front of the radiator , there is a brass sensor, un plug the wire and put it to ground and the fan should then spin. The sensor in the radiator is a common failure on mc22’s

    Check your overflow bottle under the seat, these get brittle and fail , is there coolant in there ? The other check I would do is to check your radiator cap is correctly sealing
     
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  4. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

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    Empty rad means you have a leak or worse the head gasket is gone.

    Refill and check for leaks once thermostat opens. If no leak then take the rad cap off when the motor is cold, run it, look for bubbles.
     
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  5. jmw76

    jmw76 Well-Known Member

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  6. thebeefsalad

    thebeefsalad Well-Known Member

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    Thermo switch is junk, bubbles in the rad :( I guess the good news is I felt the need to order a headgasket with all of the other stuff I ordered when I first bought the bike. Tempted to drop the engine, since it will be down to fix the head anyway, and see if I can fix the neutral issue. Any simple things to check for an MC22 that's damn near impossible to hit neutral on? I'm afraid it's going to be a shift fork, but hoping there might be something easier to look at. About the only way I can find neutral on this bike is turn the engine off, then click into neutral.
     
  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The last thing I would look at would be the gearbox. It shifts into neutral easily when the engine is not running because there is no clutch drag. All of the shift mechanisms which have to convert the up and down motion on the lever into the axial motion of a selector are prone to wear and misalignment.
     
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  8. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    99/100 times it is the alignment of your shift rod , I am with @maelstrom , it is most likely not your gearbox
     
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  9. Murdo

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

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    Clutch drag will cause that too. Check the clutch plates and fingers on the basket.
     
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  10. thebeefsalad

    thebeefsalad Well-Known Member

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    Thanks again all! Will dig into...eventually. Huge sigh of relief hearing it should be outside of the gearbox. While I've split cases more than once, it's not something I want to take on with this bike!
     
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  11. thebeefsalad

    thebeefsalad Well-Known Member

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    Finally found my roundtoit... Do I really need to order a special tool from honda to pull the head? According to the manual the head bolts are '7mm dodecagon', so I went and picked up a 7mm 12 sided socket, only to find out it's too small. 8mm 6 sided is too small, 9mm 6 sided is too large. I'd throw a wrench right now, but there are innocent bikes I would hit.
     
  12. Murdo

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

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    I have only ever used a 12 sided 8mm on head bolts.
     
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  13. thebeefsalad

    thebeefsalad Well-Known Member

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    Just picked up an 8mm from the only place in town that appears to stock 12 sided sockets outside of a giant set. FWIW I'd suggest finding a 1/4 drive 8mm 12pt over the 3/8" drive for the mc22. The 3/8" gets a decent bite, but doesn't seat completely due to the taper at the top interfering with the head. Thanks for the correct sizing @Murdo!
     
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  14. thebeefsalad

    thebeefsalad Well-Known Member

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    Aaaaaaaaand **** just got a lot more expensive. Anyone bored enough to quote shipping an unrestricted year engine and exhaust to me? :prankster:
     
  15. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Oh no, how bad is it ?
     
  16. thebeefsalad

    thebeefsalad Well-Known Member

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    It's now eligible for a big bore kit. Haven't dug into it other a quick glance at CMSNL which shows the wrist pins as NLA. If my phone ever decides to upload my photos I'll post pics of the damage.
     
  17. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The Japanese auction sites have complete engines and they are usually not too expensive. One of the members here mentioned a way to get things sent by sea from Japan also.
     
  18. thebeefsalad

    thebeefsalad Well-Known Member

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    So assuming I go the rebuild route, what is everyone doing for wrist pins? I'm not having luck finding any in stock :/
     
  19. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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  20. Andych

    Andych Well-Known Member Premium Member

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    And the tops of the pistons are pre-pitted to save you detonating them later on :)
     

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