My small end bearing failed

Discussion in 'Motorized Bicycle General Discussion' started by biknut, Feb 19, 2012.

  1. biknut

    biknut Active Member

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    Has anybody had this happen. I was riding along and all of a sudden my motor started making a sound like the piston was hitting the head.

    The motor is my new BGF 80 with a MM gen 2 head and SBP pipe. It had about 165 miles on it.

    Tonight when I took the cylinder off, I found that the cylinder and piston look great, but the head, and piston top, have little beat marks from some kind of metallic object. First I looked closely at the piston skirt, and rings, and also the cylinder wall. All that stuff look brand new.

    Then when I took the small end bearing out of the rod, one of the needle rollers fell out of the retainer. I tried to put in back in, but it fell right out again. A closer inspection revealed that this roller was slightly shorter than the others.

    Then it all made since to me. A piece of the roller broke off and must have fallen into the crankcase, where it was sucked up the transfer port and onto the piston top.

    I can tell by looking at the marks on the piston top, and combustion chamber, that they're obviously the exact shape of the missing piece of roller made by it being crushed between the piston and head.

    At the time this happened I was in the middle playing with my new MM adjustable rotor. Initially I assumed I must have seized the piston or something by advancing the timing too far, but I've now ruled that out as the cause.

    This looks like a clear cut case of the China Syndrome

    Does anyone know where I can find better small end bearings?
     
  2. The_Aleman

    The_Aleman New Member

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    LOL! Yeah, that's happened to people. A lot of people. Some engines sooner and some engines later.

    My first HT I had in 2006 munched the small end when I tried to hit 30MPH after I thought it was broke in rotfl

    You know it's coming when they start knocking at 6K and up
     
  3. biknut

    biknut Active Member

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    I'm going to try a little harder this time to find a better bearing. I had just finished advancing the timing for a second time before this happened. I'm a little relieved that it didn't seize because it was running the best it's ever run right before it failed. How many times have you heard that lol.

    i've read where people are going to a wider 15mm bearing. i think the stock one is about 13mm. the piston is slightly less than 16mm where the bearing fits. seems like a sloppy fit for the stock bearing. that may have been a contributing factor.
     
  4. Al.Fisherman

    Al.Fisherman New Member

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    If you can't find a good one locally, I'm sure my supplier has them in stock. I thought about getting some and add to my store.
     
  5. biknut

    biknut Active Member

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    Thanks a lot. I'll let you know after I check around tomorrow.
     
  6. Al.Fisherman

    Al.Fisherman New Member

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    Some stores might be closed tomorrow. But no rush, I'll call here and see if they are open and if they have them in stock.
    Stock is 10X14X13 I'll call and see if they have the 13mm and if they have the 15mm (which I think would be better)
     
    #6 Al.Fisherman, Feb 20, 2012
    Last edited: Feb 20, 2012
  7. biknut

    biknut Active Member

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    I was able to find a source here in Dallas, but it wasn't easy. I was about to give up, but the fourth bearing house I went to, recommended a fifth one. That place found me Japanese IKO part # KT-101415 which is 10x14x15 mm. Of course they didn't have any in stock but ordered me some. I should have them in a week.
     
  8. timboellner

    timboellner Member

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  9. inked1974

    inked1974 New Member

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    I have used the Stihl chainsaw bearing # 95120032340.... it seems to me to be very heavy duty.
     
  10. biknut

    biknut Active Member

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    Thanks Tim, those are the same ones I found, and about the same price.
     
  11. biknut

    biknut Active Member

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    Thanks inked, do you know the dimensions of this bearing?
     
  12. inked1974

    inked1974 New Member

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    It is the same size as stock but of course much better construction. I too was looking for the wider size but couldn't find one. So I went to the local chainsaw store and picked up the stihl. I also ordered a bunch of the INA 10x14x13. These came with a plastic cage and tat made me nervous. If you are interested in one of them, you are welcome to give one a try.
     
  13. biknut

    biknut Active Member

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    Thank you very much for the offer. I'll wait to see what I get. The ones I ordered are 10x14x15. IKO are pretty high quality japanese bearings, and should be better than the stock ones.

    INA are chinese bearings
     
  14. inked1974

    inked1974 New Member

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    I will surely be awaiting your review of that bearing. Especially at that cost! Hope they work out well for you.
     
  15. biknut

    biknut Active Member

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    I found the missing piece of roller that broke off. It's still stuck in the head. It was a clean break. Both pieces are now accounted for, which is a relief because now I don't have to worry about any debris that might be left in the crankcase. I measured the pieces to make sure that's all of it.

    I also found the piston is damaged beyond repair. The ring land is crushed a little in one spot, and is locking the top ring.
     
  16. biknut

    biknut Active Member

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    I just got a call from the bearing house. My bearings came in.
     
  17. biknut

    biknut Active Member

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    Japanese IKO KT101415
    which are 10x14x15 mm $6.42 ea

    These bearings are great. They're exactly the same size as my stock bearings, but it's easy to tell by looking these are superior, and the stock ones are toys.

    The outer dimensions of the race is the same, but I can see several important differences. For one thing, the rollers are longer. Also the inside of the cages are a lot more robust looking, and offer more support to the rollers, but at the same time the IKO are about 1.5g lighter. They both have the same number of rollers. Looking closely at the IKO, they look Japanese precise, where the Chinese ones look, kinda close.
     
    #17 biknut, Feb 23, 2012
    Last edited: Feb 23, 2012
  18. Al.Fisherman

    Al.Fisherman New Member

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    Great...is the cage open on both the inner and outer (where you can see the bearings)?
     
  19. biknut

    biknut Active Member

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    Yes, it's exactly like stock, only better.
     
  20. Nashville Kat

    Nashville Kat Active Member

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