Genset engine seized

[Sinbad1]

My Onan 6.5 genset barely moved and then seized. Taken head off and two pistons are at/near top and one at bottom. (3 cylinder Kubota) There was not enough inertia in flywheel to overcome the friction between pistons/bore and so it has jammed in this position.

I have covered the pistons in a mix of engine oil and white spirit.

How do I free the engine without getting in a great big crane and a skip!

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[vyv_cox]

I assume you have checked that it is still seized, i.e. it was not a bent/stuck valve that stopped it? I think the only thing you can do is to drop the sump, take off big end caps to identify which is the seized piston and find out why. If the cause is relatively minor, like rusted bores, you should be able to persuade the piston to move with light tapping via a piece of wood. On the other hand, if two pistons are at the top and one at the bottom, you may have more to spend your money on.

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[ccscott49]

Shouldn't two pistons be at the top and one at the bottom on a three cylinder engine?

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[brianhumber]

Something major has stopped your engine from turning. This is either due to a mechanical or hydraulic problem.
You have taken off the head so I assume all looks ok with head and valves and no signs of a hydraulic lock up from water/oil/fuel in the head. Any signs of valve/piston contact?
I therefore assume pistons will not move with head off.
Not had the head off a 3 cylinder Kot before but two pistons up and 1 down would work for a 4 stroke 3 cylinder engine.
Afraid you must look at big ends etc. How long was engine stood for before you tried to turn her over?

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[Sinbad1]

Brian

She has stood for 12 months without being turned over after giving her a complete oil and filter change and flushing thru the engine whilst running.

She hasn't 'hydrauliced'. There was no water inside and no water in oil. The bores aren't rusted tho they are rather crunged up with carbon etc.

The head has been taken to motor engineers today to have valves reseated but they look like new after cleaning up with a drill powered wire brush.

In hindsight I should have removed injectors and lubed the bores with diesel before attempting to start it. But I didn't.

The positioning of the pistons...2 up and one down are of course correct for a 3 cylinder engine.

Any ideas.

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[ccscott49]

if the pistons themselves are seized, a can of plus gas, in liquid as opposed to aerosol, will go along way to freeing them, have you tried rocking the pistons in the bores, to see if there is any movement? Try that, if a tiny amount of movement can be seen, then it may well be the rings, lots of easing oil and a big spanner on the crankshaft pulley, rocking the engine back and forth should free the pistons, with a little tapping of the tops with a lump of wood or a hide hammer. You should be able to turn the crank a small amount, due to a thing called ineffective crank angle, which will show if the bearings are seized, which I doubt very much, if you changed the oil and pumped the new around. Let us know how you get on, there are other things to try, but try these first. By the way, the starter is not jammed is it? I've seen engines diagnosed with seizure, only to find a jammed starter.

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[Jules]

Are you sure its the engine? I would drop of the genset bit first (couple of bolts)and try it then. Moisture over a long period will make the more exposed bearings in the generator seize quite quickly. As a quick fix give them a tap with a drift first without dismantling too much.

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[Sinbad1]

Thanks everyone for the ideas. I am leaving pistons to oak for a couple of weeks whilst I take half term off! Then I will try your recommendations.

many tks.

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