Removing Stuck Pistons

[justind]

I’ve got a fairly old Mercury 2 cylinder that’s froze up. On the top, looks to be a pair of some type of valve. I see an access plate on the back where I can access the rods. What can I use to press the pistons forward enough to get movement to pull back? Can’t see the back but the cylinder walls from the piston up is clean still and the lower unit turns freely. I’m guessing moisture.

[garry-in-michigan]

If the ports are closed, you can fill the combustion chamber with Transmission fluid and using a spark plug converted to hold a grease fitting, pressurize the cylinder with a grease gun. This puts equal pressure on the piston so you won’t punch a hole in it. The fluid seeping into the rings should loosen the rust. If you can get it the move a little, you may be able to move it back and forth and loosen the rings.

Good Luck –

[The Boat House]

• This reply was modified 5 years, 5 months ago by The Boat House.
• This reply was modified 3 years, 2 months ago by The Boat House.

[fleetwin]

I like Garry’s plan! Adding the grease on top of the tranny fluid will help force the thin fluid down past the rings and loosen up the piston!

[jw-in-dixie]

You might try air pressure first – less messy. Weld a tire valve onto a sparkplug base.
Applying pressure and letting it sit might force some solvent past the rings.

JW in Dixie

[Steve A W]

Justin
The biggest tool used to break a motor free is Patience!!!
Give the penetrant time to work.
If You get in a hurry you might break something.
Good Luck with Your motor.

Steve A W

Member of the MOB chapter.
I live in Northwest Indiana

[dbkski]

quote jw in dixie:

You might try air pressure first – less messy. Weld a tire valve onto a sparkplug base.
Applying pressure and letting it sit might force some solvent past the rings.

JW in Dixie

I found a stash of these in Gram’s basement. I have four types plus fittings and connectors of all sorts. If there
is interest then I can send them out to you cheap.

Sea Kings Baby!!!

[crosbyman]

took me 3 weeks of soaking a late 50s 7.5 Evinrude I paid $65 CDN

periodically and alternately wacking the piston faces moderately with a one inch piece of broom handle and a hammer

then magically….. small movements began and in a few days total movement

with new coils, points impeller I got me smooth running engine trolling for days for canadian perch without a hickup ! 😆

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[20mercman]

My 58 Fleetwin was frozen also. I was able to get it free with out too much difficulty, and you’re correct, they are wonderful little motors. Not very much power, but great motors none the less. As for stuck Mercury’s, and other brands, I have used the Zerk fitting welded to a spark plug and a mixture of ATF and some Acetone to force the lube into the cylinder if the piston is above the port. Once you have the cylinder full add a couple pumps a day, and it will break free. This method works well, and it is less impactful instead of driving them out with a hammer. With this method, you can usually salvage the pistons as it does not damage them.

Steve

crosbyman, we usually throw those little ones back! 😆

[outbdnut2]

I start by positioning the motor with the top of the cylinders facing upward. Put transmission fluid, liquid wrench penetrating oil, Kroil, or other suitable penetrating oil in so the tops of the Pistons are covered – some may run out the ports. Let it sit and every few days try to move the flywheel back and forth to free the rings and pistons. Moving back and forth is key, as it may not move all at once in one direction only. This works for most of the motors I’ve come across.

Dave

[Author]

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