Remove Stuck Piston From Cylinder Bore

Article by Mark Trotta

There are several ways to remove a piston frozen in a cylinder.

remove stuck piston in small engine

The method that worked for me was vinegar and a shop press.

What Didn't Work

First, I tried soaking it with penetrating fluid (PB Blaster) for a few days, but that didn't seem to do anything. I also tried WD-40, but that didn't seem to work either. After those two didn't work, I tried Marvel Mystery Oil, but it was too thick to penetrate past the stuck piston rings.

remove stuck piston in small engine

Finally, I tried plain household vinegar, which surprisingly worked better than the other methods. Not only did the vinegar penetrate past the rings, it also dissolved some of the built-up engine sludge.

Patience Is The Key

I let the vinegar soak in the bore for a few days, checked on progress, and waited a few more days. After several weeks of letting the vinegar soak down and refilling it from time to time, I decided it was time to try the hydraulic press.

remove frozen piston from small engine

Using only minimal pressure with the press, the piston moved slightly in it's bore, perhaps 1/8 of an inch. I had to be careful, because the aluminum block could easily crack.

So I stopped and played it safe.

I let the piston and rings soak in vinegar for another week.

And then my patience paid off.

remove seized piston from small engine

Although the piston assembly came out with rings intact, the 50 year-old rings did not want to come off the piston, so I had to break them off in pieces.

small engine piston removal

The top of the piston can be cleaned gently with a soft wire brush ( it should be as smooth as possible). The ring grooves should also be cleaned, and can be checked for excessive wear with a feeler gauge.

Hone Cylinder

If your cylinder wall has a shiny finish, you want to break the glaze and leave a nice cross-hatch pattern. This allows the new piston rings to seat properly. The tiny peaks left behind by the honing process provides just enough roughness to allow the rings and cylinders wall to wear together.

remove seized piston from small engine

Clean and Oil Cylinder Walls After Honing

When you are done honing, clean the cylinders thoroughly and dry with compressed air. After they're completely dry, apply a light coating of oil (10W30, ATF, or whatever) to the bore to prevent rusting. If you're not installing the piston for a few days or a few weeks, put the oiled cylinder in a plastic bag and out of the way until needed.

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You Can't Beat Fun!


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