Wots goin’ on here pls folks?

[Lobo]

Thanks gents - some useful thoughts.

Appreciate the comments Nigel, will do as you suggest, and yes, I can just buy the standard rings. Should I leave the liner scoring as-is, or risk making the bore out-of-round by dressing said scoring out?

Like the idea of sealing it up and applying a hose - thanks ka-ja. The block is designed like a bloody colander - but I’ll give that some thought today.

Sump M, yea, that’s my thinking, though eBay very thin on used parts. I’ll go as K2-K6 suggests and reuse the old piston, but with new rings.

Yep Ken; raw sea-water has been cooling this 10HP motor all it’s life. (tho hopefully followed up with a fresh-water flush after each use)

That chip is significant, but I’m hoping the head-gasket crushable component will ‘take the strain’ sealing against the liner.

Cheers all, appreciated,
Simon

[Moorey]

 Were you using a TC-W3 marine oil as outboards run a lot cooler in the cylinders than bikes and it is designed for the cooler running engine. At 100 to 1 mix as used by a lot of Yam and Suzuki outboards it doesn't pay to use the wrong oil.

[Lobo]

Thanks Moorey - tho’ the engine new to me and I’ve no idea of it’s history. From the localised blocked jacket cooling (exactly where the piston rings seized) and the fact that all else looks good internally (ie bearings / surfaces, piston skirts / crowns etc) I reckon the T2 oil delivery was likely not the issue.
I will however likely go 50:1 once I get it running...
Cheers.

[K2-K6]

"Appreciate the comments Nigel, will do as you suggest, and yes, I can just buy the standard rings. Should I leave the liner scoring as-is, or risk making the bore out-of-round by dressing said scoring out?"

If you can clean off the baked carbon/burnt oil then leave the surface as is. It's of course nowhere near perfect, but with rings free and cooling working it should be better than first appearance appearance would suggest.

[Moorey]

  The reason I asked about the type of oil which I notice you didn't actually answer is using non marine oil makes water cooled outboards
 prone to seizing on the top ring.

[Lobo]

Hi again Moorey.  I couldn’t answer you type of oil as I’ve not bought any yet - the engine is new to me, as is the 20L tank of fuel mix it came with... which is what I’ve been starting it on.

I will indeed use marine grade 2T when the time comes. (I always thought Marine 2T was about the biodegradability aspect tbh!)

Nige, have ordered a complete piston set off eBay from Singapore at < £30 landed which I’m happy with - should be here in a week or so.

As per your suggestion sanded down the various faces this arvo & pleased with the results. Thanks.

Latest pics of the block - I’m still stymied at the threaded boss within the water jacket - I can’t imagine what kind of ‘thing’ it may fasten. Certainly exploded diagrams of the block don’t show / indicate anything. The head gasket covers it all up, further mystifying the query.

Ken - you might be right that the bodge was in lieu of a chipped pot... it is actually quite extensive. I scratching my head tho’ at how any PO might have been alerted to a (presumed) gas / water leak as outboards naturally eject (cooling) water out of the exhaust - let alone everywhere else. (Ie the leg & tell tale stream)

Thanks gents...

[K2-K6]

Certainly looks better now cleaned a little, nice work.

You always have that dilemma when trying to recover things like this as to just how much metal you can remove.  It's just about there regarding getting a decent surface to seal with the gasket.  I'd use blue Hylomar on both the metal and the gasket, coated and let them dry for 30 mins before assembly to propagate the best conditions for a competent seal with it.

Interesting point on the marine oil Moorey, like Simon I knew they used specific oil,  but not the intricacy of why.

Thinking about it today, and was wondering if it could have had a sacrificial anode in that location within the water jacket to prevent the aluminium being eaten? Can find them like this https://www.anodeoutlet.co.uk/product/00831-tecnoseal-zinc-cylinder-head-anode-826887-for-mercury-mercruiser-outboard/ and looks a possibility in terms of what other's implement.

[K2-K6]

I'm sat here wondering what the small trench cut into the barrel housing is doing. It runs almost the entire length of the barrels but doesn't appear to have an exit just an entrance, shame the head is so crusty as it may be hiding the exit. The small mod and filler could be to deal with a leak from that trench, was going to say waterway but it could be something else, like an oil passage running next to the water jacket to keep the oil cooler, if there was a leakage between the 2 maybe the filler was there to stop it.

Any idea what that feature is connected to?

I was wondering too,  but looks like the port you see could be a chimney out of a chamber running underneath that "trench". If water came in at t'other end then crossed the block around the exhaust ports,  it could then come up the chimney and out via the heads.

Possibly it'd give quicker combustion chamber warm up (leaving barrels alone) to get it off choke faster.

[Lobo]

Wow Nigel, I reckon you might have hit the nail on the head with your sacrificial anode - I’ll go about looking for a zinc M6 bolt thingy and fit it regardless. Thank you. (And for your thoughts on Hylomar).

Ken, that trench is a dead area as it were, and is not used in oiling / cooling - maybe just an “is what it is” of casting?

Anyways, the hot water from the block / jacket exits via the bulged area (LHS previous photo) up into the thermostat housing. From there it is it then channelled down the length of the cylinder head (the head gasket being one side of that channel) before descending back into the oblong hole (R of previous pic) and out into the exhaust. (From here it goes down the leg and out through the centre of the prop)

FYI the head not yet been cleaned up!

Thanks again gents, really appreciate this site.
Simon

[Lobo]

Ta da! You should have been a detective!
Ordered...

[K2-K6]

Ta da! You should have been a detective!
Ordered...

Ha ha, good result then and answers the question of mystery bolt.

I had the good fortune at initial training during apprenticeship to have some very lucid outlook people teach me, significantly influenced by aaib farnborough. So in a way metallurgical detectives. 

[Lobo]

...Nige - you ever meet Phil Gilmartin (RIP) AAIB / Farnborough?
PM if ya did...

[K2-K6]

Unfortunately no Simon. I was elsewhere in RAE  with mechanical engineering,  but the whole place was informed by the investigative findings from there with knowledge and people that had worked within. 
Essentially the failures being a foundation of all works in first teir R&D and subsequent developments to avoid those eventuality.  I was toolroom which did alot of wind tunnel modelling in scale from roughly a micron up to about 5 meters.
Absolutely incredible materials knowledge base,  and skills.