Any tips on unseizing a old rusty piston?

Hi, i just got a minarelli engine in horrible condtition. The piston is seized in the cylinder, and looks like it has been like that along time. i want to unseize it with doing as little damage as possible. any tips? i have been soaking it in oil, and hitting it with a wooden mallet. thanks in advance.


moped army

swarm and destroy

RE: Any tips on unseizing a old rusty piston?

take it to a machine shop..

I dont think its a do-it-yourself job

RE: Any tips on unseizing a old rusty piston?

Diesel oil and brake fluid are a little better than regular oil...... but what you are doing is good... a propane torch after a few more days soaking will help..... the bad news is that the crank bearings are likely to be rusted too.... and the only fix for that are new bearings.

RE: Any tips on unseizing a old rusty piston?

Fred's right, you're going to have to do a complete engine revision, New barings, a new piston, you name it. There's no way you can get a rusted piston and cylinder to work propperly again. You'll have to bore up the cylinder and install an oversize piston to go with the bored up cylinder.

You'll have to use something that EATS rust to get the piston loose. Because you're going to have to bore up the cylinder the piston will need to be replaced for a bigger one and so you don't have to be carefull with the old piston. I suggest you drown it in WD40 and also spray plenty of it inside the engine to get the crankshaftbarings loose and get some WD40 on the downside of the piston. After letting this soak for a while I suggest you take a hammer and use it on the piston.

RE: Any tips on unseizing a old rusty piston?

When trying to drive the piston out, alternate the hits between the top and bottom of the piston. the idea is to get it loose first. If you try to hammer it out in one direction only, your chance of success is less.

To gauge piston movement, put a scratch on the piston thru the exhaust port with a sharp instrument. The line should be close to the edge of the port so you can see it's movement.

Keep adding WD-40 or Liquid Wrench as needed and take your time.


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