Engine Trouble Danger Will Robinson! I have detected an air leak!

Discussion in '2-Stroke Engines' started by lazylightning@mail.r, Mar 22, 2014.

  1. lazylightning@mail.r

    lazylightning@mail.r Active Member

    When you reach top speed and rpm and experience a slight bogging effect, it may mean that you have an air leak somewhere. But not always where you think. If you are running hot with a wide range torque pipe and high compression, an air leak is instant death to your engine!!!
    After experiencing an air leak that seemed to be coming from under the cylinder (gasket leak). I decided to throw on a new cylinder and piston because the detonation had eaten up the piston quite a bit and the cylinder was old and had been gouged in a previous conrod bearings burst . It was sealing pretty good and with the wide range torque pipe it had so much balls anyway.
    Well after starting it up and trying to break it in, a horrific chattering pecking of detonation was observed. It started out just a bit and then got louder and louder.
    After dissasembly I discovered that the piston hardly moved, the walls of the cylinder were gouged and the top of the new piston was eaten up. Just like the old one was. I would have to seperate the carters.
    Then I made an amazing discovery. The chain had eaten a thin amount of aluminum from the carter and had made a hole clear into the crank case!!! To make things really encouraging, I noticed that the chain had to eat through less than 1 mm of case to reach the inside of the crankcase!!! F#@%^&%$$$**!!!
    It may be a good idea to jbweld a thin (1mm or less) steel plate onto the surface as a guard from sloppy chain play that can take it's toll over years of riding. We tried welding the hole closed with TIG, but there seems to be a problem with the quality of aluminum and I decided to use the new carters that I had bought for a special build engine. I can always pick up some more later. IMG_0229.jpg IMG_0222.jpg IMG_0221.jpg 99_EuO2keoA.jpg eos-NlP7hWc.jpg sqxEiP_l1lI.jpg

  2. jaguar

    jaguar Well-Known Member

    nice post. I never knew that was possible.
    I would second your recommendation of using JBWeld to secure a steel plate there to protect the cases from the chain. Was your chain stretched from use? How long did you have it? Stock chain or aftermarket?
  3. lazylightning@mail.r

    lazylightning@mail.r Active Member

    IMG_0265.jpg IMG_0307.jpg IMG_0315.jpg IMG_0263.jpg IMG_0318.jpg IMG_0326.jpg IMG_0329.jpg IMG_0273.jpg I think it was a stock chain. Actually my tensioner gets loose from time to time. I've been wanting to make a normal adjustment positive system to hold that roller in place.

    Here's the plate gluing process photos. I decided to do some crank stuff and open the carter part of the transfers while I was in the using a hand grinder with a small stone.
  4. lazylightning@mail.r

    lazylightning@mail.r Active Member


    Stuffings. Layer one. I had to keep flipping it over because the jbweld takes so long to stiffen up. It would run down, then I would flip it and it would run back. After a few hours it stiffened up enough to give it a straight up shape.