Hi. My Mach .26 has suddenly "died". The engine starts when cold but stalls after a minute or 2 minutes and will not start again until ice cold again. Have changed glow plug, opened it up and checked for scratches on the sleeve and piston but cannot see any with the eye. The front bearing seems fine with the naked eye. I also sealed everything that I could i.e. carb and backplate but to no avail. Could dirt have caused very very small scratches that result in compression lost and subsequent stalls?? Any ideas or suggestions that I can try to confirm where the problem resides?

Sounds like it's worn out. Take out the piston + sleeve and check how much pinch you got left. If you can press the piston all the way to the top or beyond the top of the sleeve it's time for a rebuild.

One of my old engines was just like that. It ran for a few minutes and then it lost all power.

Compression check:

Pull the plug.

Crank flywheel with finger.

As piston comes to the top of the cylinder, you should feel resistance. On new engines, you might not be able to get the piston past the top of the cylinder with your finger turning the flywheel. This is good.

On good used engines, the piston should go up past TDC (top dead center) and while getting firm resistance, you should be able to get it past TDC and back down the cylinder.


If you spin and feel little or nothing, you need a new piston or sleeve.

When cold, the sleeve is tight around the piston. On old engines, this can mask a loss of compression. Once warm, the sleeve expands...and in a worn engine, this causes compression to drop....and to drop too much when the piston/sleeve are worn out.

On a Mach, you could get a piston and sleeve for 50 bucks and have what will run link a brand new engine (have to break it in again!). The rebuild takes 30 mins and is definitely worth it.