excessive blowby

Discussion in 'Engine, Fuel and Exhaust' started by nascar7613, Jan 14, 2013.

  1. nascar7613

    nascar7613 Active Member

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    1997 Road King, FI, Evo engine. This is a customers bike. According to him, the bike suddenly started smoking out the exhaust while on a long ride. There is a lot of smoke coming out of the crankcase breather hose and a noticable amount coming out the right side of the exhaust and a little bit coming out of the left. Pulled the spark plugs. The front plug looks normal, the rear plug is oil fouled. The bike has 58K on it. Probably rings?
     
  2. Jack Klarich

    Jack Klarich Expert Member

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    Could be bad umbrella valve and or valve seal in rear cylinder, do a compression test of both cylinders, if the rear is low pump a few squirts of oil in and recheck to confirm bad rings
     
  3. nascar7613

    nascar7613 Active Member

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    Yea, I loaned my compression guage to a friend, getting it back tomorrow. So, an umbrella valve could cause this condition?
     
  4. Jeff Klarich

    Jeff Klarich Well-Known Member Contributor

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    From what you described and with that much blow by it sure sounds like weak rings. Looks like a compression test is in order.
     
  5. nascar7613

    nascar7613 Active Member

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    Did a compression test. Rear cylinder, warm, throttle open, 70psi, with a shot of oil in the cylinder 100psi. Front cylinder, same conditions, 100psi, with a shot of oil 125psi. I think the top end needs to be refreshed.
     
  6. Jack Klarich

    Jack Klarich Expert Member

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    Looks like you found your problem:s
     
  7. nascar7613

    nascar7613 Active Member

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    Tore the rear cylinder down. The cylinder is badly scored on both left and right sides. The piston is worn down into the rings on the right side, not really bad on the left side, just a little shiny spot. When looking down into the crankcase, the inside of the piston rod right where the fork starts looks shiny. I don't know if that is normal or not. I don't want to refresh the top end if there is something wrong down below causing the problem. Have you ever noticed the piston rod being shiny or is that definetely a problem.
     
  8. nascar7613

    nascar7613 Active Member

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    Upon further inspection, I found that the piston pin retaining ring on the left side is missing. I pushed the pin out with my finger. I suppose that was the begining of the problem. It looks like the pin was rubbing on the left side of the cylinder wall.
     
  9. Jack Klarich

    Jack Klarich Expert Member

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    Check the bore for scratches or groves due to the rubbing, might be looking at boreing it out. now your looking at more $ with new pistons ect. If it's not to bad you might get by with just a hone job.

    Pull the cam cover off and see if you find any material in the bottom of the case. Remove the overhead tappet screen and check the breather cavity for scoring, the wrist pin keeper got chewed up and went through the motor is my guess
     
    Last edited by a moderator: Jan 18, 2013
  10. nascar7613

    nascar7613 Active Member

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    The cylinder and piston have to be replaced. I just hope that the pin keeper came out and caused the problem instead of the piston getting so hot that keeper fell out.