2-stroke Outboard Head Gasket help needed

Bobc

Bobc

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I recently acquired an old Yamaha 8A outboard, which wasn't running well.

After much mucking about with the usual bits, I noticed a drop of what looked like water on the lower spark plug.

So I removed the head and found the lower chamber with water in.

Now, I asume that it's coming past the head gasket (I don't think there's anywhere else it can get in is there?).

Anywhay, it looks like I won't be able to get a new head gasket, so I'm looking for advice from the experts on how best to nail it back together. I tried cleaning the faces up and putting a bit of blue silicone on the faces, but that didn't work (didn't expect it to).

Is there any type of gob that I can use that will work on head gaskets? The gasket is intact (no lumps out of it).

Or is the water getting somewhere else?

Your thoughts please...
 
Cylinder heads are pretty hot, even water cooled ones. I had a similar problem with an old 2 stroke bike and used Blue Hylomar. I'm well out of it these days but Hylomar was developed for use in gas turbines and can take the combustion temperatures with ease. I also run an old morris minor and sometimes have to use crappy fibre head gaskets when I can't get the proper copper sandwich ones. I use a smear of hylomar on these and it seems to work well. I don't think Hylomar is a silicon material.

IF the old gasket is solid copper, you'd be advised to anneal it before re-using it.
 
You can buy sheets of gasket material. Use some tacky stuff thats easily cleaned off afterwrds to stick the sheet to the cylinder block or head. Tap round the edges of the casting with a small (toffee) hammer only enough to mark, remove from engine part and trim out the holes.
 
Another thought...

Will removing the thermostat reduce the water pressure in the head? Just wondering if this combined with adhesive might do the job.
 
From experience the only fix is to fit a new genuine head gasket. A home made one will run or a while but i certainly wouldnt risk it out at sea.
 
It'll only be used in the river to get between the marina and the mooring (about 1/4 mile each way).
 
Hi Bob, its your call. You can get head gaskets for these . Im pretty much sure the 6hp gasket is identical. Whatever you decide its wise to check if the head is flat before reassembly. Apologies if im teaching my mother to suck eggs.:o
Bobc said:
It'll only be used in the river to get between the marina and the mooring (about 1/4 mile each way).
Click to expand...
 
steve66 said:
Hi Bob, its your call. You can get head gaskets for these . Im pretty much sure the 6hp gasket is identical. Whatever you decide its wise to check if the head is flat before reassembly. Apologies if im teaching my mother to suck eggs.:o
Click to expand...

Defifnitely flatten the head on a plate of glass and some wet and dry.I've made a head gasket out of graphyte asbestos material for an old Johnson 2hp and it worked but I don't know how long it would last as I'm not using the motor.
 
I have an old Yamaha head gasket set, 6hp I think, it's been sitting in the garage for years (it's dated 1992!), the outboard was scrapped, sheared bolts and not worth repairing. It new and still in the packet.

It's marked:

677-W0001-00
350 948-9
Gasket Kit for Power 3S6C30

No idea if it'll fit, but you can have it for a donation to the RNLI.

If it's of use, PM me with your address and I'll post it to you.
 
I once made a head gasket out of a sheet of alloy.
It was for a Harley Davidson.

It lasted about 15 minutes before firing an inch sliver of the gasket out, narrowly missing my leg.
 
Lakesailor said:
I once made a head gasket out of a sheet of alloy.
It was for a Harley Davidson.

It lasted about 15 minutes before firing an inch sliver of the gasket out, narrowly missing my leg.
Click to expand...
I remember some small two stroke bikes with ali head gaskets, and my little Gilera had no gasket at all. The cylinder sleeve projected into the head IIRC.
Water cooling complicates it of course.

Don't just check the head is flat, check the barrel too.....
 
Quick update for all who helped with this...

On removing the head and getting the gasket off it, I noticed a small amount of material missing from the head between the bottom cylinder and the water jacket. Not a big chunk missing, and producing a really tiny hole under the pot ring (just enough to let water in).

So, filled the void with chemical metal, flattened-off, and then re-built (the gasket you sent didn't fit Ian, but many thanks for your generosity). I cleaned the old gasket up, gave every face a liberal coating of wellseal, and bolted it back together.

The result is that I now have a 2 cylinder outboard again. I've put it through a number of heat cycles and all seems fine. It'll be interesteing to see how long the chemical metal stuff stays there, but for the moment I have a working engine again.

Thanks to all.

Bob
 
So just out of interest, how long did it last for?

I have a similar problem with the same engine, only the block is corroded. The head came off in pieces and I sheared three bolts, so an already resigned to replacing those.

If I could build the surface up with chemical metal rather than paying somebody to weld it, that would be useful.
 
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