Rapid seizure

KREW2

KREW2

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After keeping it going for 12 years has my little 2hp mariner 2 stroke finally gone beyond economic repair.
It started okay after a being stored for the winter, but no water.
I renewed the impeller and all was fine, started and ran okay in a tub of water.
Next day it was seized. I managed to free it up put in a little neat 2 stroke oil down the plug hole turned it over a few times replaced the plug and off it went.
The next day it was seized again. Even if the head gasket has gone I'm surprised that a motor that was running fine can seize in 24 hours.
 
KREW2 said:
After keeping it going for 12 years has my little 2hp mariner 2 stroke finally gone beyond economic repair.
It started okay after a being stored for the winter, but no water.
I renewed the impeller and all was fine, started and ran okay in a tub of water.
Next day it was seized. I managed to free it up put in a little neat 2 stroke oil down the plug hole turned it over a few times replaced the plug and off it went.
The next day it was seized again. Even if the head gasket has gone I'm surprised that a motor that was running fine can seize in 24 hours.
Click to expand...

It usually more of a problem with people who insist on using 100:1 fuel mix and then don't lay it up properly.

Oil down the plug hole will get around the piston crown and the rings but not to the crankshaft bearings, big end or wrist pin. That's why when laying up one should spray fogging oil in via the intake . It gets around these places as well as into the upper cylinder ( personally I use 2 stroke oil in a trigger spray bottle). Double the oil, 25:1 instead of 50:1, is not a bad alternative in the last tankfull of fuel at the end of the season.

Don't overlook the possibility though that there is problem with the "foot", but presumably you will have changed the oil and it has not sat there half full of water for the winter.
 
Strangely enough, my Tohatsu 9.8 2 stroke has started seizing when left for a few weeks. Started happening over winter when it was left as usual on the dinghy inside a shed for 2 months. Came to start it and had to turn it over (with a struggle) with the flywheel as the pull cord wouldn't do it. After priming fuel from remote tank, it started literally first pull and ran perfectly with no smoke, steam or misfire. Initially wondered if I had forgotten to add oil so gave it a dose of 25:1 to see if that cured it but the same thing happened again after leaving for 5 weeks. Once freed, still runs perfectly and starts first pull every day.

Spoke to Tohatsu UK tech dept and they've never heard of the fault before and suggest head gasket may be the problem.
 
In both cases I'd have the head off and find out what the damage looks like. Both sound more like a rust problem than what I'd call seizing (galling of the piston/cylinder through heat/no oil).
 
Freed it again, going to run it today with a 25/1 mix.
I did fog it up and after its winter break it turned over fine, and started okay, just no water.
Replaced the impeller, ran it and now it's seizes after about 36 hours.
That's why I suspect the head gasket is letting water in.
 
KREW2 said:
Freed it again, going to run it today with a 25/1 mix.
I did fog it up and after its winter break it turned over fine, and started okay, just no water.
Replaced the impeller, ran it and now it's seizes after about 36 hours.
That's why I suspect the head gasket is letting water in.
Click to expand...

If its the head gasket you might be able to detect water on the plug if you get it turning over without starting ..... Pull the plug lead off an give it a good few pulls of the rope in a barrel of water , then inspect the plug.

Running with a blown head gasket can also produce a curiously clean spark plug ( steam cleaned!)

Alternatively as it was the last thing you did you might recheck the impeller and installation. Correct part and all correctly refitted?
 
Spark plug was very dry and had a rust colour. I have taken the head off and there is film of rusty water in the bore.
The water ways to the cylinder head were completely blocked, so I don't think any water was getting in via the head gasket.
Now I have to see if I can get the two sheared cylinder head screws out before I put it back together.
I am still surprised that after only 36 hours it can seize so much that it is not possible to turn it over.
 
Gasket not too good, cylinder head inside surface is a bit rough, but not cracked.
Bolts came out easy with a lock nut.
Before I fork out for a new gasket and bolts is there any other way water could get into the bore.
 
As far as the blocked waterway is concerned - I think read that some of these have a tell tale hole, mine didn't. You'll need to take the motor body off the leg to clear the channels in the 'interplate' and the bottom side of the cylinder wall, so while you have that plate out, I drilled a hole in the edge just before the hole where the hot water is about to fall down into the leg. At a slight downward angle it sends a weak jet out just under the plastic cowl. (I could have put the hole into the higher pressure 'cold' side and got a stronger jet, but don't know if the water pump has enough reserve capacity to waste the cold).
 
KREW2 said:
Gasket not too good, cylinder head inside surface is a bit rough, but not cracked.
Bolts came out easy with a lock nut.
Before I fork out for a new gasket and bolts is there any other way water could get into the bore.
Click to expand...

Sounds like you're having a fun time. I'm tempted to order a new engine and put the old 9.8 on the 'bay, let someone else sort it.
 
As said above you need to take the powerhead off the leg and clear those water galleries as those are the ones that block. Last year someone in our boat yard left a Yamaha 2HP leaning against the skip for anyone to take, so I did. The waterways beneath the power head were blocked solid but after cleaning them out it runs just fine and is the best tender outboard I've ever had by a country mile..
By the way, in 20 years of Mercury 2.5 and now this Yamaha 2 ownership I've never purchased a new head gasket after cleaning out the block waterways, just re-used the old one with out any problem.
 
Thanks for all the tips
The waterways were all cleaned out last year, I put in a new impeller and pump housing and all worked fine.
Except that two days later I couldn't turn it over, seized.
I now think I know how the water got in to seize it. To test the waterways were clear, while the leg was off I attached a hose to the inlet pipe and ran some water through it. I had the tap only on a trickle for about 2 minutes. Is it possible water was forced back in through the exhaust?
Anyway I have just cleaned out the bore and replaced the cylinder head and it started fine, but lo and behold it has stopped pumping water again. I now have taken off the leg and and checked the impeller all seems fine.
I will re-assemble today for the last time.
 
I'm not completely clear on what you've done.

Have you had the crankcase off the leg and the interplate off both, because it was the bottom side of the cylinder where the marginally worst lot of blockage was in mine? That's the way in and out for the head cooling water. I mean this year - mine was pretty bad after one season because I can't flush until I get home and the salt is all well and truly dry by then. If you have it off now, and you haven't got a tell tale hole I'd recommend that you drill one (as above and in this pic).

IMG_20180508_122430913.jpg

Next. How can water get in? Hard to see how if there's no damage in the head gasket or severe corrosion in the water pathway. If the engine were laid on its side very soon after running then it's possible that it could flow into the exhaust hole in the interplate between crankcase and leg because it doesn't offer as much protection from this as some other engines I've worked on. Was your hose also shooting water up the leg as well as the coolant tube - that would certainly do it this time. Another thought is that if you have still got a partial blockage then the engine is going to be running hot, and some of the little water that there is will be turned to vapour, which will certainly get in though an open exhaust port.

How bad is the corrosion found in the cylinder?
 
All sorted, and seems to be running fine, even though it does sound a bit industrial.
I removed the motor, and there was a blockage in the waterway from the cylinder head to where it comes out of the exhaust. I must have pushed some crudge down when I cleaned it out. A drop of rydlyme soon sorted it.
Still no idea how the water got in initially though.
 
KREW2 said:
All sorted, and seems to be running fine, even though it does sound a bit industrial.
I removed the motor, and there was a blockage in the waterway from the cylinder head to where it comes out of the exhaust. I must have pushed some crudge down when I cleaned it out. A drop of rydlyme soon sorted it.
Still no idea how the water got in initially though.
Click to expand...

The water is dumped in to the exhAust, any restriction there or thereabouts and the water backs up in to the cylinder through the exhaust port in the cylinder wall
 
skipper_stu said:
The water is dumped in to the exhAust, any restriction there or thereabouts and the water backs up in to the cylinder through the exhaust port in the cylinder wall
Click to expand...

Not on this engine. The cooling water drops out of the plate twixt powerhead and leg, as does the exhaust, so the only blockage that would cause that is one of the exhaust hole at the foot of the leg - not very likely.

It is possible that if the engine were stopped and fairly promptly laid slightly head down on its right hand side then the contents of the pump, tube, head and barrel pathways would drain into the top of the leg and find its way into the passage to the exhaust port.

But that's for actual water, and I'm beginning to wonder if a bit of rust in the barrel is actually a bit more common than we might have imagined given an open port, a little water nearby in the leg and plenty of residual heat. Following that line of thought I'd then suggest that the OP's problem has always been a blocked passageway, which is only now completely clear. But perhaps the rust he's seeing is only appearing on the surface of the bore where it's already damaged by the seizures?

Lastly, I'd again recommend drilling your own tell tale hole where I did. I have a lot more confidence in my engine now.
 
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