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Help Conrod bearings - MC22

Discussion in 'Honda 250cc In-line 4's' started by Krompot, Mar 13, 2020.

  1. Krompot

    Krompot Well-Known Member Premium Member

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    Hey.

    Stripped engine apart and need to replace Conrod bearings. In the manual is see set 'A', 'B', 'C', and 'D'. What's the difference between the bearing sets? Does is really matter if i just use set 'A' for all 4 conrods? Asking because it's quite expensive to buy a b c d separately rather than just buy 4 'A' sets.


    Cheers,
    Kyle.
     
  2. risky

    risky risky

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    bearings have different thickness and they will be marked so do not mix up.check each pair and buy accordingly.
     
  3. thebeefsalad

    thebeefsalad Well-Known Member

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    Why would buying A B C D be more expensive than 8xA? They cost the same on the few places I've checked for any size. Have 2xA 2XB, 2XC 2XD in the cart, same price as it was when there were 8xA
     
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  4. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    No you cant just buy 4 x "A" unless they are all marked as "A". That is how Honda worked the sizes of their bearings...
     
  5. Murdo

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

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    What sizes do you have now?
     
  6. gregt

    gregt Well-Known Member Premium Member

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    Some interesting replies. Murdo is to the point. Depending on what you have now - and the clearances they produce - you may be able to use different colour code shells.
    For myself, the factory codes are a starting point. I aim for .0016in clearance on mains and .0018in clearance on big-ends.
    There's approximately .0002in thickness variation between colours.

    On a side note which is relevant. Sorting through the shells which came with the RC30 engine I did recently, I made up a jig to measure shell thickness. The colours had gone off most. Anyway, the thickest and thinnest shells were both unused greens....
     
  7. Krompot

    Krompot Well-Known Member Premium Member

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    Hi. Thanks for replies.

    Have attached a photo of what the best looking bearings look like. Can't tell what they're marked as. Can only read '018H'.

    Bike ran without oil for a long while and completely wore them out. Bought as project. They're so loose that the pistons jiggle around on the crank, piston 3 is polished on top where valves have been kissing it.


    Worst set (chucked in bin) were worn probably 1.5mm deep. was a noticeable lip on the side of the bearing where i assume the conrod wasnt pressing on it. quite scary.


    Can only find set a x8, b x8, c x8 etc on ebay (genuine honda supposedly) that fit my price range. Just finished high school, no money. Want to ride this bike. How much does it matter to have A/B/C all accross the crank considering the wear already done?

    Thanks.
    Kyle

    20200313_210010.jpg
     
    Last edited: Mar 13, 2020
  8. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    How are the crank journals? If it was run low or out of oil it's likely there is damage. You cannot just slap new shells in and run it, it will die again in short order.
     
  9. gregt

    gregt Well-Known Member Premium Member

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    Where are you in NZ ? I may be able to point you to someone local to you who could have a look at the crank and give an opinion.
     
  10. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Damn, I hate to burst your bubble but I would say that engine is going to need a lot of money spent on it before it loves again.
    You will find that there is damage to the crankshaft, damage to the main bearings. Pistons already have damage as you mention which would mean bent valves most likely and if it has run like that for a while the gearbox bearings will all be in need of replacement as well.

    As for bearing sizing, Honda used to have the sizes stamped into the bottom casing on the early SOHC 4’s, not sure on the little CBR250’s though.

    You might be better of trying to find a 2nd hand engine that needs less work than this one.


    Sent from my iPhone using Tapatalk Pro
     
  11. Krompot

    Krompot Well-Known Member Premium Member

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    The journals seem fine. Everything spins smoothly, transmission etc. Doesn't look like much wear on journals.

    If the engine is so damaged as claimed to be i figure there's no harm in messing around with it. Will buy a set of B bearings and keep you lot updated on how it runs.

    Gregt, im in Auckland. North shore.
     
  12. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Have you split the cases? Have you measured and inspected the crankshaft big end and main journals?
    Have you inspected the camshafts and bearings?
    All of these will have suffered from oil starvation if as you say is correct... not to mention the mainshaft in the gearbox etc.
    You can pretty much guarantee with Big End bearings in the state you describe that engine if just reassembled with standard parts wont run for long at all.
    To be able to know which big end bearings to use you need to split the crankcase, the bearing codes for big ends and mains are on the crankshaft.
    I suggest spending a few of your hard earned $$ either getting a Workshop manual or joining as a Premium member here and downloading the manual... you will need it even if only for the torque settings when reassembling.
     
  13. Krompot

    Krompot Well-Known Member Premium Member

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    Crankshaft is split. I'm already premium member. Big end and journals don't have any obvious scratching. The only bearings in the whole engine that seem damaged are the conrod bearings. Everything else looks fine, even camshafts. Dont have the tools to measure anything, REALLY don't want to buy any.
     
  14. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Have you downloaded the Workshop manual? If you have then look on page 151 and you will see where to find what your big end bearing codes are... it is on the end of the crankshaft. It is pointless buying any old bearing size if they are not correct.
    If you dont have at least some basic measuring equipment (verniers ) or proper tools (tension wrench?? Do you have one?) then why spend good money on bearings that may or may not be correct?
    These engines are not low revving big clearance machines... they are precision machined high revving (up to 18,000 rpm) and need to be assembled with the appropriate level of care and attention...
    Do you have a new gasket set for it?
    Do you have any Honda-bond to re-seal the crankcases when you reassemble it?
     
  15. gregt

    gregt Well-Known Member Premium Member

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    At least take the crank to an engine reconditioner and ask him to check the bigends are still round.
    If he says no, you at least know where you stand.
    If yes, ask for it to be linished - a polishing process on the bearing surfaces - and checked for straight.
    The linishing will remove any old bearing material stuck to the surfaces.
    Won't cost much.

    My North shore contacts are all vintage types sorry.
     
  16. Krompot

    Krompot Well-Known Member Premium Member

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    Yeah, got a torque wrench and high temp silicone. Will buy a new head gasket. Will buy verniers tomorrow.
     
    Last edited: Mar 14, 2020
  17. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    PLEASE do not use High Temp Silicone or any Silicone for that matter... use the correct gaskets and products ONLY.
    Honda-Bond or Yama-Bond are not High temp silicone but are specialist products used to seal mating faces on the crankcases... If you use Silicone there is every chance some of it will end up in the sump and then find its way into oil galleries etc.. or it will be too thick and you will have too much clearance on the case halves and too much clearance on the main bearings etc etc...
     
  18. Krompot

    Krompot Well-Known Member Premium Member

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    https://www.amazon.com/Hondabond-High-Temp-Silicone-Liquid-Gasket/dp/B006YTTV4W

    This stuff? Says it's high temp silicone.
     
  19. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    As long as it is Honda-Bond... it is different to your average High Temp Silicone... and only smear it on.. it really does not need much at all...
     
  20. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Verniers are +/- 0.02mm not appropriate for use on crank journals and rods.
     

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