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Piston Ring Collapse

  1. #1
    KB KB's Avatar
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    Piston Ring Collapse


    Can anyone explain it? In English so that I can understand.

    Back this season I had an engine that was smoking like a 2stroke. I bought a crashed one from some dude in Concord NH and did the motor swap. Now I have the old motor to put back into the crashed one.

    I was talking to a guy that said that an engine can show no signs of compression loss and pass a leakdown test but still have a collapsed oil ring which would cause oil burning because the oil ring isn't scraping the oil off the cylinder causing it to be burnt off in the combustion chamber. He also stated that on downshifts with a closed throttle that the crankcase pressure is great enought to cause even more oil to get into the combustion chamber causing wicked smoke on deceleration.

    I understand the theory but can anyone quantify it?

    KB

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  2. #2
    Just Registered TLRMan's Avatar
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    Piston Ring Collapse

    The oil rings get stuck in the piston lands and can't do their job.

    They get stuck usually from a build up of black carbon and crap.

    This explain it?

    So instead of expanding, and wiping the cylinder, they allow the oil to get past, and into the combustion chamber.

    Oil rings consist of 3 parts. They are stacked in this order...
    Top side rail, spacer, and a bottom side rail.

    Behind the spacer, there are small holes that are cut thru the piston, in order for the oil to come and go.

    If the side rails get stuck, and can't expand into the cylinder wall, the oil is allowed to get by.

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  3. #3

    Re: Piston Ring Collapse

    Had the same problem. Oil rings did not seem to be stuck just collapsed or too small. After I took oil scraper ring off piston, put it in empty cylinder and it was too small or collapsed to scrape cylinder wall. Wonder why this would happen.
    Quote Originally Posted by KB View Post
    Can anyone explain it? In English so that I can understand.

    Back this season I had an engine that was smoking like a 2stroke. I bought a crashed one from some dude in Concord NH and did the motor swap. Now I have the old motor to put back into the crashed one.

    I was talking to a guy that said that an engine can show no signs of compression loss and pass a leakdown test but still have a collapsed oil ring which would cause oil burning because the oil ring isn't scraping the oil off the cylinder causing it to be burnt off in the combustion chamber. He also stated that on downshifts with a closed throttle that the crankcase pressure is great enought to cause even more oil to get into the combustion chamber causing wicked smoke on deceleration.

    I understand the theory but can anyone quantify it?

    KB

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  4. #4
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    Re: Piston Ring Collapse

    how long did you run it?

    had few cases where exhaust got loaded up with oil and smoked like a MoFo for 10 or 20 miles of hard riding, common problem when bike ends up laying on the side for a while and oil get in to places it shouldn't

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  5. #5
    Day late, dollar short carsick's Avatar
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    Re: Piston Ring Collapse

    Thread date, people. Welcome to KB's world circa 2004

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    99 + 02 SV650 ex-race - 91 FJ1200 street - 03 KDX220R woods - 12 WR450F motard/ice

  6. #6
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    Re: Piston Ring Collapse

    doh!

    2 replies (and 3 beers) made me think it was recent

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  7. #7
    Lifer isaac_'s Avatar
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    Re: Piston Ring Collapse

    Quote Originally Posted by carsick View Post
    Thread date, people. Welcome to KB's world circa 2004
    At least they're using the search function?

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    Isaac LRRS/CCS #871 ECK Racing | Spears Enterprises | GMD Computrack Boston | Pine Motorparts/PBE Specialists | Woodcraft | Street & Competition | MTag-Pirelli | OnTrack Media
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  8. #8
    Lifer Chippertheripper's Avatar
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    Re: Piston Ring Collapse

    But to answer dude's question, kb is still running it, 12 years later, I'm sure.

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  9. #9
    Lifer Stromper's Avatar
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    Re: Piston Ring Collapse

    Put in Seafoam down the spark plug hole

    Wait 12 years..... wala

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