Jackhammer sound?

Discussion in 'Motorized Bicycle Trouble Shooting' started by dimentio, May 18, 2013.

  1. dimentio

    dimentio New Member

    Joined:
    Jan 5, 2013
    Messages:
    71
    Likes Received:
    0
    Hi all, I'm back with more troubles on my Genesis 29er. Got the simple LEB PK80 motor on there. For about 3 days now, my engine has been sounding like a jackhammer - like its clanking really loud on mid-high rpms. Also my top end has fallen a few MPH (About 5) and throttle response is much crappier. I took off the cylinder head and found a lot of carbon buildup. Piston had carbon build up all over the edge of the top. I took a dremel and a wire wheel and wicked away as much carbon as i could until it looked clean. I replaced the cylinder with an old one laying around as well as the cylinder head. I'm running 50:1 ratio with 93 octane gas. Got a torquer 2 exhaust and a NT speed carb on there and a thinner head gasket. everything else is stock. Even with the cylinder and head replaced it still sounds the same. Any ideas? I also cleaned out the entire clutch area (took out the clutch flywheel and cleaned the rubber/carbon deposits with cleaners, and replaced) idk whats going on but I really dont want to order a new motor unless i have to.. BTW I've had this engine for about 3 months and I ride it every single day to work and back but not as much on the wekeends... It gets plenty of use though, believe me.
     
  2. Greg58

    Greg58 Active Member

    Joined:
    May 1, 2011
    Messages:
    2,735
    Likes Received:
    22
    Does the engine make the noise with the clutch pulled in? Since you had the cylinder off and everything was ok there it makes me wonder if something may be going on in the clutch shaft / spring area. I would try running it up to speed then pulling in the clutch and killing the engine, just coast along and listen to the sounds.
     
    #2 Greg58, May 18, 2013
    Last edited: May 18, 2013
  3. dimentio

    dimentio New Member

    Joined:
    Jan 5, 2013
    Messages:
    71
    Likes Received:
    0
    I didn't really check the torque on the small gear screw under the clutch cover, I'll check it now... I think someone else in a different thread said something about the needle bearing in the piston.. I'll check it too. I have like 3 disassembled motors in my bedroom so i can strip those parts if they need replacing anyways.. It's a shame, I really love my bike, I've came so far with it lol I hope I can get it running good again I ordered a jake jug (from jakebike.com) for it so I definitely need it running before I get that in the mail.
     
  4. Kioshk

    Kioshk Active Member

    Joined:
    Oct 21, 2012
    Messages:
    1,149
    Likes Received:
    5
    First thing I thought of was one of your upper or lower needle bearings was shot; if so, you'd have ruined your rings and jug in short order. Still, I'd pull the jug, and check the piston and crank for play. You might want to use a lower octane too...87 is just fine.
     
  5. dimentio

    dimentio New Member

    Joined:
    Jan 5, 2013
    Messages:
    71
    Likes Received:
    0
    What do you mean by "play"? If you mean side-to-side play (left to right) then there is play, yes. I replaced the piston, wrist pin, upper needle bearing. I kept the rings because I only had those ones, the rings from my other spare motors were broken. I also replaced the jug and head but it's still making that damn noise. If i have side to side movement on the crank, is that bad? I pulled a crank from a spare motor and that one had lateral movement too so I thought it was normal...

    Anyways I ordered a new motor. I don't have the patience to deal with this crap if it's my daily rider. However, after I get the new motor mounted, I'm gonna use whatever info I gather from this thread and begin working on it with spare time just for the **** of it. And how do I tighten the crank, exactly?
     
    #5 dimentio, May 18, 2013
    Last edited: May 18, 2013
  6. Greg58

    Greg58 Active Member

    Joined:
    May 1, 2011
    Messages:
    2,735
    Likes Received:
    22
    Try the stock head gasket and see if it changes, if the thicker gasket helps you may have lower rod bearing wear. You will have some movement side to side but shouldn't have any noticeable movement up and down.
     
  7. LR Jerry

    LR Jerry Active Member

    Joined:
    Dec 19, 2011
    Messages:
    1,027
    Likes Received:
    0
    Here is something I was taught on this forum. If your engine compression is below 9.1:1 use 87 gas. If its around 15:1 then use 93 gas. These engines are low compression to make them easy to crank. Only by modifying them will you get high compression.
     
  8. crassius

    crassius Active Member

    Joined:
    Sep 30, 2012
    Messages:
    3,204
    Likes Received:
    10
    I've occasionally opened an engine that had a shim or two on the crank from the factory - no info on what end play should be, but seeing those shims says it shouldn't be allowed to be too much.
     
  9. dimentio

    dimentio New Member

    Joined:
    Jan 5, 2013
    Messages:
    71
    Likes Received:
    0
    Well, my engine finally gave way. I was riding it about 15 minutes ago and I heard a loud "pop" and it stopped working. I tried turning it over there's pretty much no compression. I'm gonna open it up later but I'm guessing I broke my piston rings... I had swapped them over to a new piston when I took out the old one yesterday.
     
  10. Kioshk

    Kioshk Active Member

    Joined:
    Oct 21, 2012
    Messages:
    1,149
    Likes Received:
    5
    All I can recommend for the future is that if you hear ANY unusual noises (rattling, rapping, ticking, knocking, squealing, etc.) from your engine: STOP THE ENGINE IMMEDIATELY AND PEDAL UNTIL YOU CAN REMOVE THE HEAD TO INSPECT. You're just begging for jug/piston/ring destruction if you push it. You'll also reduce your losses: replacing a worn needle-bearing will cost you less than $10, a blown upper assembly can run you more than $50, PLUS you'll need to split the case to clean out the bits. Would make better sense to just invest in a brand-new engine at that point.
     
  11. dimentio

    dimentio New Member

    Joined:
    Jan 5, 2013
    Messages:
    71
    Likes Received:
    0
    Well I opened the engine.... The cylinder has 2 big scores near one of the transfer ports, the piston is scored on one side, one of the piston wrist clips are not seated properly, and my crank has slight up-and-down movement (very little, still probably enough to damage something) So it would call for a new piston, piston rings, piston clips and bearing needle, cylinder .... to **** with it. I'll just save the bottom half for parts.
     
  12. Greg58

    Greg58 Active Member

    Joined:
    May 1, 2011
    Messages:
    2,735
    Likes Received:
    22
    Kinda what it sounded like, as we said any movement you can feel will increase dramatically at 3000 rpm. Good luck with the next one.
     

Share This Page