Yamaha 4hp 2 stroke 4AC 6E0, impeller, cooling

[experimental]

Hi Everyone,
I am a new member, I have been reading and enjoying the advice given here.
Thank you very much.
Perhaps you could help me on this one?

I have been brave enough deciding to fix an outboard engine with no knowledge or experience.
Me being an easy target some guy sold this outboard to me telling me that it was only used in fresh water. (might be true)
It looked perfect when I lifted the cowl.
Also tested it in the bucket, it worked fine for 5 mins then I thought that was enough.

However on our first trip out to the north sea , my gf ended up in tears when the outboard stalled 5 mins in to our adventure on a very windy day near Grimsby.
After 10 mins trying It worked fine for 1 min, then stalled again, then had to wait another 10 mins to go in shore for a minute.... Desperate rowing in between, trying to keep calm. It was scary. We have managed to get back to safety in an hour or so.

After some research I thought it was a common overheating issue.
That was last year...
This year I have decided to fix it,I have been watching videos and training myself and I am hoping to complete this project in a month.

When I took out the lower part of the motor I have discovered that the impeller was destroyed (pic attached).
I can't stop thinking where the pieces are gone?? Shall I investigate further up in to the water channels?

What has caused the impeller to melt? Can it be because it was never changed since 1995? Is it possible? (I am also changing the thermostat)
Shall I use some heavy cleaners or even some sort of an acid to clean the cooling channels just in case??

Many thanks
Aydin

 

[longjohnsilver]

When you tested it in a bucket, did you see a small jet of water exiting the underneath of the engine, known as the tell tail? If not, then the impeller was already gone. I think it unlikely on an outboard that bits of the impeller will have reached the engine, but others might know for sure. There’s no harm cleaning the waterways, but if it has been used solely in fresh water, there should be no need to do that.

 

[Boathook]

Put a new impellor in and see whether there is a tell tale jet from the engine underside. If there is quite good. I would also remove the thermostat and see what it looks like there. Test the engine in calmer waters where it is easy to row back before doing anything to adventurous.
Not sure on the engine style but if you search for Malta on this forum quite a lot of advice on that and it is a yamaha 3.5hp.

 

[QBhoy]

Hi

I’d advise doing a compression test on it now, before going to the bother of changing the impeller. The engine may be cooked. That said...it’s a Yamaha 2 stroke. Takes a serious event to destroy one of them.

 

[Boathook]

Just re-reading the original post, the engine is overheating. Mine did the same a few years ago. If there is signs of salt crystals on the thermostat the I feel an engine strip down is required to clean the water channels. They are fairly small and do seem to block easily.

 

[Jim@sea]

You should check up to see if there is a small bit of metal (woodruff key) in the bits of the impeller you removed. A friend stripped the impeller out of my outboard and neither of us realised that there would have been this tiny keyway which is placed on the shaft and a small round bit protrudes into the brass inside of the impeller. You certainly cant re-fit an impeller without this small keyway which makes the impeller turn

 

[experimental]

Thanks for the advice everyone, i have changed the impeller, changed the gaskets, replaced the thermostat however 3 bolts snapped waiting for a mole grip to take them out. Not from corrosion but from age and not being greased I am guessing.

It was full of dirt so i had to remove the headcover and also removed the main block from the body. Cleaned it.

I wanted to clean inside the cylinder head as well but in order to do that i had to undo 8 bolts, they look like they have never been touched factory paint and when i tried one it was about to snap so i decided it was not a good idea.

Cleaning the water jackets, some water and gunk went into the cylinder maybe where pistons are.... As i have no way of getting in there i looked to see if i can spray anything in there to clean it... I am at that stage now....

Ps. Had to order new bolts and gaskets which are coming from the US! as i could not find the exact matching parts in the UK.
These parts can be very expensive..

Here are some images of the work so far...
i hope i can put this back together properly

 

[experimental]

the last one