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 How to free seized or rusted piston in outboard head 
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I've got a tiny little Evinrude Junior 2hp outboard. When I got it, the pull starter would work, but now it doesn't. When I emptied the fuel tank, I found about a cup of water with a tiny bit of oil in it (or at least it doesn't smell like gasoline). I think when I tried the pull starter when my friend gave it to me a long while ago, it pulled water into the cylinder and over time it rusted the piston to the cylinder wall (that's just a guess). She also thought it was air cooled (it's not, I've already taken apart the drive shaft, impeller, transmission leg, cleaned it, drained and added new 80-90 oil to the transmission, etc.), so it's possible it's been run out of the water, but I don't know that. If I get it running, I'll replace the impeller group, but it's in good enough shape to run it as is without worry of pump failure.

I've currently got the head off and the piston is soaking in a puddle of PB Blaster:
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I've tried tapping on it with a plastic mallet to encourage it to move, but not very hard as this isn't something I have a lot of expertise in (and it hasn't budged as far as I can tell). I've also tried to spin the flywheel by hand, but it just wants to rotate the whole outboard on it's mount (I haven't tried to make it so it won't move, but that's probably what I'm going to try next). I'm also thinking about removing the drive shaft so I don't have to spin it and the propeller when I'm trying to get the piston to move.

What's the best way to free this piston up?

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Fri Jun 02, 2017 9:22 am
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get the PB Blaster out, slowly heat with a torch and use a candle to melt wax into the cylinder. The heat will separate the piston, rings and cylinder and the wax will fill in the void, when cooled the wax acts as a lubricant and eases the friction.

I have used this more times than I can count on rusty parts, works every time

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Fri Jun 02, 2017 9:30 am
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TINCANBANDIT wrote:
get the PB Blaster out, slowly heat with a torch and use a candle to melt wax into the cylinder. The heat will separate the piston, rings and cylinder and the wax will fill in the void, when cooled the wax acts as a lubricant and eases the friction.

I have used this more times than I can count on rusty parts, works every time


Nice! Do I just heat the outside wall of the cylinder and not the piston itself, or just heat up the whole assembly? I've got tons of paraffin wax, will that work? If not I can scrounge a candle from my stash of emergency candles or one of the stinky ones Rita loves (the sooner they're gone the better).

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Fri Jun 02, 2017 10:00 am
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pile a wet cloth on the piston and heat the cylinder wall all the way around. Your trying to create a temperature differential in the two separate metal pieces. This will hopefully give you a little room between the parts and allow for some movement. can also try heating the whole assembly then dousing the entire mess generously with wd40 / pb blaster etc and then let it cool. Can try this cycle several times and see if it draws some of the lubricant into places its needed and maybe free it up. Can also whack away on the piston during this process in an attempt to encourage harmonics to drive the fluid into spots that may be helpfull


Have you ever actually seen this assembly rotate since your posession?? may have to consider that this is siezed and is not gonna want to go up and down at all


Last edited by toys in the toybox on Fri Jun 02, 2017 2:24 pm, edited 1 time in total.



Fri Jun 02, 2017 2:11 pm
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toys in the toybox wrote:
pile a wet cloth on the piston and heat the cylinder wall all the way around. Your trying to create a temperature differential in the two separate metal pieces. This will hopefully give you a little room between the parts and allow for some movement. can also try heating the whole assembly then dousing the entire mess generously with wd40 / pb blaster etc and then let it cool. Can try this cycle several times and see if it draws some of the lubricant into places its needed and maybe free it up. Can also whack away on the piston during this process in an attempt to encourage harmonics to drive the fluid into spots that may be helpfull



good points, the piston being made of aluminum will heat much faster, best to heat the cast iron and let the piston get the residual heat

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Fri Jun 02, 2017 2:22 pm
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I tried heating the cylinder and water jacket leaving the flame off of the piston as much as I could. Then melted wax down on top of the piston. Nothing although the wax was disappearing in rusty bubbles, but it could have been evaporating with the flame, not sure. So I removed the exhaust inspection plate (?), and I could see the piston, which was nice & shiny, no evidence of rust at all. I sprayed it down with PB Blaster through the three 1/2" or so exhaust ports and replaced the plate. I heated the head & melted more wax several more times with the same result, no movement. So I tried heating it, then spraying the piston head with carburetor cleaner (nice & cold), same thing.

It looks to me like the piston is at TDC, as it's actually protruding from the head by 1/8" or so (or the center of the piston is, it's sort of domed) which means I have the absolute minimum leverage on the connecting rod to try to move it. I'm wondering if the connecting rod is actually what's frozen up on the wrist pin? It looks like it'll be pretty easy to get the drive leg detached from the base of the crankcase / head assembly so I could maybe see the connecting rod / wrist pin, but I'm not sure. It's certainly easy to remove the drive shaft & transmission, it's only two bolts and it slides right out. At a minimum I'm going to remove that assembly just so it's not more stuff I have to try to spin to get the piston moving.

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Tue Jun 06, 2017 10:35 am
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can you remove the crank? If so, remove it and wrap the connecting rod with a towel and drive it out the cylinder using a piece of wood and a hammer, you might break the rings, but you'll get it out

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Tue Jun 06, 2017 10:42 am
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TINCANBANDIT wrote:
can you remove the crank? If so, remove it and wrap the connecting rod with a towel and drive it out the cylinder using a piece of wood and a hammer, you might break the rings, but you'll get it out


Don't know yet, haven't tried to disassemble it that far yet.

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Tue Jun 06, 2017 11:49 am
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delliottg wrote:
TINCANBANDIT wrote:
can you remove the crank? If so, remove it and wrap the connecting rod with a towel and drive it out the cylinder using a piece of wood and a hammer, you might break the rings, but you'll get it out


Don't know yet, haven't tried to disassemble it that far yet.


Unless you know if the crank spins, trying to free the piston may be a pointless task.


Tue Jun 06, 2017 12:48 pm
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Massivedesign wrote:
delliottg wrote:
TINCANBANDIT wrote:
can you remove the crank? If so, remove it and wrap the connecting rod with a towel and drive it out the cylinder using a piece of wood and a hammer, you might break the rings, but you'll get it out


Don't know yet, haven't tried to disassemble it that far yet.


Unless you know if the crank spins, trying to free the piston may be a pointless task.


Exactly. I only know it spun when I got it, but it sat outside for at least a year (which to me an outboard should be able to withstand). The weather's supposed to deteriorate for the weekend, so maybe I'll be hunched over under my beach umbrella working on it.

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Tue Jun 06, 2017 1:06 pm
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It's almost time for a BFH


Tue Jun 06, 2017 3:04 pm
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