fbpx

 

Hi. Does anyone have any thoughts on the cause of these scratches and carbon deposits on the exhaust side of my 503 pistons? I'm thinking maybe oil failure. I don't recall the engine getting hot but the oil was 4 years old. Can 2 stroke oil 'go off'? (The other piston is similar but not as bad.)

Many thanks

Tom

8305_1_IMG_1986.JPG (You do not have access to download this file.)
  • Re: Piston inspection diagnosis

    by » 4 years ago


    Just to update this post, I have shown the piston to an experienced 2-stroke mechanic who said that this is the result of blow-by. Carbon particles gettingtrapped between the piston and cylinder wall cause the scratches.

    He also pointed out to me that there were marks at the bottom the skirt that indicate the beginning of piston slap. (I'm not sure if you can see them in the photo.)

    The flakiy nature of the carbon on the head of the piston is caused by infrequent running. Apparently the inital carbon layer absorbs moisture while the aircraft is laid up, crystallizes and then the next layer has limited adherence to it. 


    Thank you said by: RotaxOwner Admin

  • Re: Piston inspection diagnosis

    by » 4 years ago


    He also agreed that 2-stroke oil can go off with time if the container is open to the atmosphere. Mine was stored in a 10 litre barrel.

    However, if there had been an oil failure one would see seizure marks rather than scratches.

    Edited: to add that the label on Shell VSX says, "Shelf life: 4 years from the date of manufacture if kept covered, stored ina dry place and protected from heat."


  • Re: Piston inspection diagnosis

    by » 4 years ago


    Here is a better picture of the early-stage piston slap on the bottom of the skirt.

     

    28020_2_IMG_2034 - early stage piston slap MAG.JPG (You do not have access to download this file.)

  • Re: Piston inspection diagnosis

    by » 4 years ago


    Here is a better picture of the early-stage piston slap on the bottom of the skirt.

     

    28021_2_IMG_2034 - early stage piston slap MAG.JPG (You do not have access to download this file.)

  • Re: Piston inspection diagnosis

    by » 4 years ago


    There is also a small cold seizure mark on one 'corner' of the piston on the intake port side.

    I hope this information is of use to people in future.

     

    28022_2_IMG_2035 - cold seizure mark on MAG.JPG (You do not have access to download this file.)

You do not have permissions to reply to this topic.