Nrg 50cc compression testing

Discussion in 'The Workshop' started by Dolly5, Aug 17, 2013.

  1. Dolly5

    Dolly5 Member

    Messages:
    52
    Hi please can anybody tell me what the compression test should read on a standard 50cc nrg 50.
    I have done a compression test but not sure if its ok as don't know what it should be.
     
  2. Jonathan123321

    Jonathan123321 Member

    Messages:
    244
    Rides:
    Piaggio NRG Power DD
    If your reader is in PSI then it should read around 90 - 130 psi. Mine was always around that and it worked spot on
     
  3. Jonathan123321

    Jonathan123321 Member

    Messages:
    244
    Rides:
    Piaggio NRG Power DD
    Also does it start ? Does it tick over ? Does it sound a bit like a vacuum with no pressure ? Is the Piston scared or the cylinder. If the piston or cylinder is scared badly then you will have a air leak resulting in the bike not starting. 2 stroke nrg rely on Air pressure to start and keep running. If your loosing air into the combustion chamber then as i say it wont start. I Personally don't wast time with compression testers i just remove the cylinder and check the state of the piston and cylinder wall. Also what year is the bike, how has it been ridden, Is it derestricted ? there is alot that can result in a bad piston. From general were and tear to ragging the shit out of it. Just bare in mind there designed to go 30mph - not 60 like mine :p Also has it been serviced regularly. Most people think 2 strokes run perfectly and maintain them selves. Well they don't. They can be very high maintenance.
     
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  4. Dolly5

    Dolly5 Member

    Messages:
    52
    Thanks for the reply.
    The piston and barrel were only changed at a bike shop around 2 months ago but the shop is no longer open.
    I have had a look at the barrel and piston and they seem perfect with no visible scratches etc. What I did notice was the inside bit of the head gasket not the outside looked a little worn. The bike did start ok but smoked reallt bad of what looked like a mixture of steam and oil and did sound a bit like a vacuum. My compression test reading would at the most be 5.5 bar but not sure what this is in psi but will try and find out. The bike has been regulary serviced and has covered 6,000 miles. Also do you know where i check the coolant level as after removing the head I have lost all mine and will need to fill it again once I find out what the problem is. The bike did run however it wouldn't hardly pull of from a standing start. Thanks for your help.
     
  5. Nathanael

    Nathanael Active Member

    Messages:
    473
    3million psi is considered acceptable.

    Google is a good friend when wanting to convert things. 5.5 bar is just under 80psi which is a bit low.

    The symptoms you are describing are the inner head gasket not sealing properly. The coolant is leaking into the worky bits and getting explodified out the exhaust as steam.

    Check the head with a straight edge to make sure it isn't warped and replace the gaskets on it. Tighten down EVENLY to whatever it should be.
     
  6. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    give it a hone and new rings, 5.5 is a bit low, for the coolant you need to take off the front panel, then remove the radiator cap, fill it up slowly, then when you run it for the first time leave the cap off and keep topping up the coolant.
     
  7. Dolly5

    Dolly5 Member

    Messages:
    52
    Just an update, Fitted brand new head gasket today inner and outer and still no joy. The barrel and piston look perfect with no scratches on the barrel and the rings move around freeley. Not sure now why I should be only getting that compression as everything looks good.
     
  8. Nathanael

    Nathanael Active Member

    Messages:
    473
    has it fixed the coolant leak?
     
  9. Dolly5

    Dolly5 Member

    Messages:
    52
    The coolant wasn't leaking it was just using the coolant as I thought the head gasket was gone. I now have the engine removed from the bike but I can only get 6 bar max from my compression tester when cranking it over. The piston and barrel look perfect but that's all I can think it can be. I don't have the coolant hoses and carb connected anymore as pretty sure I can do a compression test without these on. All I can think of is buying a new barrel and piston and hopefully that will sort it but its a shame as this set is only 2 months old.
     
  10. Dolly5

    Dolly5 Member

    Messages:
    52
    Would worn crank seals cause low compression but not sure as its only done 6,000 miles.
     
  11. scubabiker

    scubabiker NITROJUNKIE

    Messages:
    7,321
    no, like i said, give the barrel a hone.
     

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