Engine died, Diagnosing why



  • Hi all,

    I was wondering if anyone could tell me the best process to finding out what went wrong with my bike a couple days ago. I initially thought top end/ ring failure but now am a bit unsure so I wanted to know if there was any other checks I could do before just tearing it down.

    I was going about 75mph when it just shut off so I instantly jumped on the clutch and coasted to the side of the road. let it cool down then tried pushing it in gear a little and it turned over fine.
    Then tried starting it and there wasn't even a cough of life. sounded to me like it was turning over slightly quicker on the starter motor too (low compression?) so I just got recovered straight home.

    Took the plug out and the ceramic sheath around the electrode had slid down and was in contact with the side electrode so I put a spare sparkplug in the HT lead and checked it for spark while grounded on the head. spark is fine and could smell fresh fuel going into the cylinder with no strange sounds when the engine was turning over. I then put the plug in and tried again. All I got was 1 backfire and that was all.

    Any ideas what else I could check before pulling the cylinder off? I was thinking maybe just see what I can see through the exhaust port of the rings but I have no idea.

    Anyone who could shed some light on the issue would be much appreciated haha Thanks



  • Do a compression test. If the fueling is wrong and or the wrong plug is used you can melt a hole in the top of the piston.

    But it's bog standard then this is unlikely.

    Whipping the barrel off will cost you £10 for a base gasket and some coolant. So it's no hardship.



  • @Calum Ok cheers i was thinking that. What psi will i be looking for when doing this compression test?



  • Well it differs comparing build to build.

    It won't be four stroke high, two strokes run relatively low compression.

    So I would say 70 psi???? At a guess.



  • @Calum the beauty of 2 strokes is you can take the cylinder off really quickly. I'd definitely pop the exhaust off and look up the port. You can buy and endoscope for £5 that plugs into your phone 🙂


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