Seized power heads, mixing and matching parts

[nabiul]

I've got two seized powerheads for a johnson hd25, what is the safest method to free the pistons and remove them for examination? Can I disconnect the pistons from the crank shaft and then hit them on the head? Once I free them, is it okay to let them scrape off the rust on the walls on the way out? Is it advisable to mix and match the better looking parts from the heads?

Power head 1: part of a donor frankenstein motor, serial number in the 90 thousands, missing carb, lightly rusted cylinders and piston rings, crankshaft doesn't look too great and lateral motion caused one of the 'lobes' to grind against the casing, crankshaft bearings look good, exhaust residue is light and dry

Power head 2: part of a complete motor, serial number in the 19 thousands, has a carb, rusted cylinders that may have pitting underneath, crank shaft condition is a mystery but the drive and flywheel portions look good, broken off screws in the cylinder head, exhaust residue is heavy and oily

I suspect powerhead 2 was a good motor which some one botched the cylinder head removal on and then left open for years, it might have a better crank shaft which I will get into tomorrow and right now power head 1 is sitting with paint thinner in the cylinders.

Also while I have your attention, the gas tank cap from the earlier motor is seized in place and is made of plastic. How can I safely remove it?

 

[HighTrim]

Soaking in an acetone/atf bath, then tapping the pistons with a wooden dowel should do it. May need to heat them up then cool off couple times to break t he bond.

Small powerheads I soak in an old crock pot with anti freeze in it, then cool off when I pull it out. Works well, but don't let your wife catch you using her good crock pot. Been there, done that.

 

[Chinewalker]

Yep, use the best of both. Pretty simple motors, and they run great. Drop me a PM if you need parts...

 

[nabiul]

Well I soaked in ATF bath and managed to recover 3 pistons. The donor power head cylinders are alright except for at the very top on one of them, there is some rusting and slight pitting which I scraped a few times with 2000grit sandpaper to get the piston out. Do I have to hone these guys out or can I go over the rusty areas lightly with some high grit sand paper and leave it at that? There is no visible cross hatch anywhere, both cylinders are smooth.

 

[Chinewalker]

A brake cylinder hone would work on those tiny bores. You've got it apart, might as well.

 

[nabiul]

I opened up the lower unit to take a look and most of the oil appears to have congealed into grease, I'm guessing it's not supposed to be like that. I was also surprised to see a lobe type of pump instead of an impeller, is the pump assembly supposed to have grease or lubrication, or do I just clean it as much as possible and assemble dry?

 

[Chinewalker]

Pump is assembled dry. Grease is used in the gearcase, lubriplate 105.

 

[nabiul]

I snapped one of the piston rings trying to remove it from the cylinder and this was one of the non rusty ones, are there any modern equivalents to these rings?