Yamaha 5hp 2 stroke outboard seizure

[BigART]

Hi Folks

Anyone got any advice on how to sort a seized*Yamaha 5hp 2 stroke outboard? After a couple weeks of not being used, I can't turn the engine. *It appears to have jammed up in the splined joint between the male top of the main shaft and the female socket in the bottom of the cylinder block/power head. I can undo the cylinder block mounting bolts but the head won't come off the shaft just wobbling around a millimetre or so.

Before I go in with wedges and brute force, has anyone come across this before and have a cleverer method as I don't want to damage the alloy head. *Also, what may have caused the problem?

Angus

 

[Lakesailor]

I think you are trying to separate the leg and the power head.
As long as you have undone all the bolts and before you start with wedges try shocking it off. If you can get someone (beefy) to hold the power head whilst you apply a shock load to the leg it should pop out of the joint. The best way I have found is to use a block of softwood on the part of the leg where it flares out above the cavitation plate. That;s the strongest part of the casting. Give the block of wood a sharp thump with a biggish hammer. You don't need to go ballistic. you're just trying to use the inertia of the powerhead against a force acting away from it so a steady thump rather than a banzai attack will suffice.
It's usually a bit of corrosion or gunge in the socket and the moment it shifts it will come away. If you are alone you could hang the outboard on the pushpit and do it like that, but it transmits the shock of the hammer less well.

This pic shows the place to rest the block of wood, just where the casting flares out from the leg but is still meaty. (about where that orange trailing socket on the wall behind is)

 

[macd]

You mention "cylinder head". Are you referring to what most outboard manufacturers call the "power head" i.e. the engine; or the actual cylinder head (which is probably held on by four bolts, and into which the spark plug screws)?

Is there anything in particular that leads you to believe it's seized on the splined coupling you mention, and not in the cylinder bore or main bearings?

 

[VicS]

I dont quite follow you.

the engine is siezed and will not turn... is that correct.

Most likely is that you have been using 100:1 fuel mix and have not fogged it or run it on an oilier mix after last use.

If that's the case 2T or even release oil in oil in via the plug hole allow it to soak around the piston rings and then keep trying to shift it back and forth manually via the flywheel. Gentle persistence may pay off

The cylinder head is the flat plate held with four bolts.. Taking that off to access the piston crown directly might be some advantage , at least you could tap it with a block of wood.

Possible the bearings are seized but they are all ball-races or needle rollers AFAIK;

Also possible that it is seized at the bottom in the gearcase but unlikely unless you've lost all the oil and its full of water.


Take great care unbolting anything... or you will break the bolts .. then it's probably no more than junk.

You will find useful diagrams at http://www.boats.net/parts/search/Yamaha/Outboard/parts.html

 

[KAM]

If it helps I had a similar problem with my 2HP. It turned out to be the cooling water pump which had siezed due to severe corrosion of the outer aluminium housing. The symptoms were difficulty starting, stopping whilst running and feeling very stiff. It was a very fiddly job to split the drive and repair the pump but fortunatly the repair kit included replacement stainlesss steel wearing surfaces which restored as new performance.

 

[BigART]

Seized Outboard

Sorry about the confusing terms, I am definitely no mechanic.

The symptoms were when I pulled the starter cord, the starter system/flywheel would not move - at all. I removed the starter cord assembly, and tried a few light taps directly to the flywheel, no dice.

The oil in the bottom gearbox is good (no water) so probably no problems there. On unbolting the power head (yes, sorry, that is what I meant, the cylinder block assembly, not the actual cylinder head) I could lift it about a millimetre and the piston can be seen moving inside the cylinder through the exhaust outlet, so probably not a problem with the cylinder bore or main bearings, so I am thinking it could be the bearing at the top of the shaft inside the power head. I think Lakesailor's advice is the one to follow, I will let you know how I get on. Thanks to all.

Angus

PS. Sorry about the asterisks, I am typing this on an iPad which seems to cause them to appear after posting.

 

[exfinnsailor]

The reason you cannot lift the power head any further is the gear selector clamp at the bottom of the shaft. Lake Sailors pic. Now you have undone the power head you will need a new gasket before you refit it all. So keep going but take a few pics as you take it apart. If you have never done anything like this before it maybe wise to take it to someone who knows BEFORE its terminal.

If you look at Lake Sailors picture you remove the rubber bung top right corner and then undo the bolt that holds the two lengths of rod together. If you have removed the six bolts at the bottom of the power head then it should now come away from the body after first disconnecting the throttle cables etc. Lots to undo.

 

[Lakesailor]

Good point. I haven't had the leg off that motor in the pic.
The Johnsons tend to have the clamp at the top and a sliding joint at the bottom.

 

[VicS]

Having proved that its not the piston seized in the bore I would disconnect the shift rod where suggested and remove the lower unit ( gearcase assembly).

That will enable you to check out the suggestion above that the water pump is causing the trouble. More likely to be that that the lower crankshaft bearing I would have thought.

You may well have to take the lower unit off anyway to relocate the water tube if you pull the powerhead. I think it will be difficult otherwise.

Sensible to overhaul the pump now anyhow!

 

[BigART]

The reason you cannot lift the power head any further is the gear selector clamp at the bottom of the shaft.....

...If you look at Lake Sailors picture you remove the rubber bung top right corner and then undo the bolt that holds the two lengths of rod together. If you have removed the six bolts at the bottom of the power head then it should now come away from the body after first disconnecting the throttle cables etc. Lots to undo.

Sorry, should have said that I have done that. My money is on the problem being the lower crankshaft bearing as suggested by Vic. A few months back, we did get some odd symptoms of some brown, possibly rusty water coming out of the exhaust, however, we weren't in a position get professional help being in the Chagos Group at the time. I think I am now paying the price of conveniently forgetting about the symptom as the engine seemed to continue running well enough.

I will let you know.

Angus

 

[pete]

Same happened to my old Yamaha 4HP 2 stroke.
After many years of reliable service I came to start it and it wouldn't turn. Thinking it would be the piston rings I removed the spark plug and squirted in a touch of oil and using a screwdriver on the flywheel I managed to get it turning and started (I assumed somehow a drop of water had got into the cylinder) over the next month this happened a few times !.

On stripping the leg down I found that it would not come off but after a lot of prising and hammering carefully (at first) it did come off. It was the drive shaft into the crank shaft bearing joint that was the problem and it was full of what looked like thick aluminium paste gone hard. I think it had been building up on top of the drive shaft and forcing the shaft down into the leg and gear box and the extra length was stopping the engine from turning.

As soon as I managed to open the lower leg joint a little everything turned over easily.

I dug out the crank shaft spigot hole and was surprised at how much crud was in there. After cleaning and greasing up the shaft and crank shaft spigot hole I reassembled and have had no further trouble.

This all happened about 5 years ago.

Hope this helps.

Pete

 

[BigART]

SNIP It was the drive shaft into the crank shaft bearing joint that was the problem and it was full of what looked like thick aluminium paste gone hard. I think it had been building up on top of the drive shaft and forcing the shaft down into the leg and gear box and the extra length was stopping the engine from turning.

Hope this helps.

Pete

That sounds about right. Here goes.

Thanks

Angus

 

[Seajet]

My father ( retired Spitfire & Harrier engineer ) recently salvaged a friends’ Yamaha 5hp 2-stroke with exactly this problem.

Stan:

"Every indication of engine seizure & the previous mechanic was unable – in the time available – to separate the leg from the engine body, it was economically a write-off but with a lot of time & patience the engine is now fine…

The cause was a build up of carbon & gunge from the exhaust gas in the deflector tube ( 3” long on the bottom of the engine ).

It only came out by using a suitable size drill & various screwdrivers, emerging as a grey powder.

Separation of the leg was achieved by inverting the engine & pouring a mixture of oil & petrol down the shaft through the gear change access bung in the middle of the leg, & thumping the cavitation plate with a wood drift.

No need to strip the engine itself down at all but change the impeller while you’re at it.

Suspect this was caused by a too oily 2 stroke mixture ( the owner reckons he uses 75:1 while it’s rated at 100:1, yes we all think we’re being kind to an engine giving it more oil ! ).

Hope this helps someone".

 

[Lakesailor]

thumping the cavitation plate with a wood mallet.

I would suggest my method is better. To hit a softwood drift with a hammer allows the point of impact to be more accurate. To hit the leg casting as I suggested rather than the cavitation plate is safer. You see lots of outboards with bits missing from the cavitation plate.

 

[Seajet]

Lakesailor,

actually I mis-translated it to be a wooden mallet, it was indeed a drift, my apologies.

Dad was a Leading Air Mechanic on Seafires & Hellcats in WW2, then worked on steam engines & Battersea power station among others, and retired as top trials crew chief on the then new Harrier GR5, I doubt there are many C.V's like that and I reckon he can handle a Yamaha 5, as I say all mistakes mine, I've always struggled to read his writing !

 

[BigART]

Suspect this was caused by a too oily 2 stroke mixture ( the owner reckons he uses 75:1 while it’s rated at 100:1, yes we all think we’re being kind to an engine giving it more.

That is probably true, thinks "Best give it a little too much than too little, hate to seize it up...."

I am having a day off today, back to battle tomorrow.

A

 

[Seajet]

That is probably true, thinks "Best give it a little too much than too little, hate to seize it up...."

I am having a day off today, back to battle tomorrow.

A

A,

I used to do the same myself with my ( near identical ) Mariner 5, and since this episode have had a bit of a rethink !

Happy New Year,

Andy

 

[BigART]

Still no joy...

...time for more brute force.

Angus

 

[Seajet]

...time for more brute force.

Angus

Angus,

please note my Father & Lakesailors' remarks, this is a job which seems to require lubrication, time & persistent small blows with a wooden drift, rather than giving into the temptation to nuke it !

On further chatting with Dad, he strongly recommends that once the leg parts begin to separate, prising rather than hitting is the way to go, with the edges of the parts being prised protected by pieces of soft metal or wood.

Also watch out as the deflector tube has very little clearance.

Good luck,

Andy

 

[Seajet]

BigArt,

do please let us know how you get on.

Andy