I have a cunning plan......

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I have a cunning plan......

Post by Polybus »

Will I either:
a) Kill myself? or
b) Kill my engine?

I have a little Mariner 2 stroke outboard - sure its not a mighty Seagull, but the concept should be just as valid (or invalid) for a Seagull. It obviously won't work on a 4 stroke - unless the valves are stuck shut very tight, but a 2 stroke, if the piston is above the ports, it might work.

The engine is seized - don't know how, but the piston is VERY stuck! I have managed to move it about 16mm down the bore, but it is still very tight.

This is what I have done so far.
  • Soaking in Diesel for 2 weeks - the diesel level never changed - so not getting by the rings/piston)
  • Belting piston with wooden dowel through the spark plug hole (failed)
  • Taking the head off and soaking for another 2 weeks
  • Belting the piston with a piece of wood and a dumpy hammer (failed)
  • Filled bore with petrol and set fire to it
  • More belting with wood - failed
  • Heating with propane torch then
  • Belting the piston with a thick length of steel bar (ye, I know - a VERY bad idea - but it was that or give up)
  • Piston moved 2mm
  • More soaking, but just overnight - this time diesel level dropped overnight - must be getting by the rings/piston
    • More bashing - moved about another 10mm, but still a real effort
    • More soaking - overnight
    • More bashing - another 5mm

    Anyway, I feel like I have used up all my luck - so far I have not driven the steel bar through the piston - but I really don't want to keep bashing it with the bar or the inevitable will happen and I will smash the piston.

    What do you think of this? I've not read anything about it, so maybe it is too stupid for words....

    The piston is still above the ports - so there is still a closed chamber - except for the spark plug hole.

    What if I put the head back on, torque it down, pour some petrol donw into the cylinder and then put the spark plug back in - closed chamber right?

    Then generate a spark at the spark plug!

    Obviously I can't generate the spark by pulling the starter rope, the thing is seized, but I can use an external magneto, hook it up and fire it.

    Will the combustion blow the piston down to the end of its travel? Blow the spark plug out? Blow the head off? Destroy the COVID-19 virus?

    I'm thinking it might be OK - after all, that's what the combustion chamber is for - but then again - under normal running the pressure won't be anywhere near as high, because the piston will be driving down the bore quite easily. In this case, if the piston won't move, when the petrol combusts - something has to give....

    I guess the best case scenario is it will blow the piston down to the point where one of the ports is uncovered - but that will help a lot.

    I guess the worst case scenario is death - for both me and the engine.

    Does this have disaster written all over it?? :shock:
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Charles uk
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Re: I have a cunning plan......

Post by Charles uk »

Is the piston the only moving part in your Mariner that can seize & prevent rotation?

Now take the crankcase apart to inspect the crank shaft.
Make it idiot proof and someone will make a better idiot.
Posts: 37
Joined: Sat Oct 21, 2017 3:42 am
Location: Port Douglas

Re: I have a cunning plan......

Post by Polybus »

I sorta came to the same conclusion.

Despite the fact that the piston is really hard to move - the bore seems to be in surprisingly good condition. And that made me think it isn't the piston that is stuck.

So Charles, thanks for being "the voice of reason" - I will pull the leg off it, and check the gearbox, and I think there is a better than even chance corrosion will have locked one of them up and I am doing way more harm than good by attacking the piston.

I don't want to look at the crank shaft - I'm scared! I fear it will be very, very ugly. :oops:
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Re: I have a cunning plan......

Post by andrew »

I’ve been there before! You’re lucky it’s still above the ports. I have successfully used a grease nipple/gun every time this happens. Amazing the pressure a simple handheld grease gun puts out, something like 10,000 psi or more. Before I discovered this trick I messed up really seized piston/cylinders every time trying to free them. The thread below shows the approach.

viewtopic.php?f=4&t=6609&p=60707&hilit= ... ple#p60707
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