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Wots goin’ on here pls folks?

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K2-K6:
With rings stuck it will compromise most stages of running as it's effectively sucking (drawing in the cases) as well as holding compression. It's more or less like having leaky cases in a way.

Dilution of crankcase gases with burnt blow by effectively reduces the volatility of the next charge phase.  This is what they do on exhaust gas recirculation systems in car engines, but only at specific load demands.

You'd need the rings working properly to make realistic assessment of the running as a prerequisite.

Lobo:
Thanks gents. (So far 🙄)

I started cleaning all the deposits off the cylinder block today... and found the cause. Some PO has inexplicably plugged a cooling gallery with a SS screw, and then, for good measure put putty about the whole lot... causing an interruption of water to the cooling jacket in a localised spot.

Intrigued I dremelled away all the putty, and removed the screw. So far, I can see no damage to the casting, indeed it ‘rings’ consistently everywhere I tap it with a screwdriver. But I’m bloody confused as this hole is within a boss, and is tapped (M6). It’s other end is the common cooling gallery, which feeds about 4 other such cooling inlets (varying sizes, shapes, tho’ none others with screw threads.)

Honestly I’d have sworn the head had never been removed as no markings whatever on the painted fasteners. That said, it don’t look like a factory mod!

Any ideas please? Could it be a ‘hot climate’ option.... ie to supply more water to the jackets? I’ve looked the internet for flow paths, cylinder block photos etc but keep coming up blank.

Semi planning on leaving the hole clear, and having a rebore with .25mm o’sized pistons. (though the scoring not deep so will first try a bit of 600 grit sanding.)

All thoughts & ideas welcome...  it’s an engine that won’t see much use so not too critical wrt perfection)
Ta.

K2-K6:
I can't think immediately of a competent reason to restrict the water way there.

Trying to determine exactly where that is in relation to the piston damage, it looks like it's the same place?

As it's been running like that, think I'd get the rings free and gently clean the "snots" off very lightly, then put it back together and run it to further assess and answer questions.  Put it on 50 to 1 ratio and see what you've got then.

If you rebore and go with new pistons,  then any initial problems with it may take those as well. I know it's not mechanically ideal to reassemble but will tell you a lot with very low risk.

As you'd expect in an engine like this,  those combustion chambers in the head are focused on complete burn with low thermal problems,  it shouldn't intrinsically be making too much heat, making the cooling jacket modification distinctly odd.

It should run pretty well with the pistons and rings cleaned,  then give the confidence to go with rebore etc if it's debugged fully.

K2-K6:
Forgot to add,  yes I'd clean out the bodge in water jacket.

Reasoning that it can't run like that,  all things considered, and if there is a problem subsequently it would then show up if you run it with the components you've got there already.

Lobo:
Thanks Nige...

Yep, the scoring (piston & sleeve) are exactly adjacent to where the putty / nil cooling was. I’m still at a loss why the bodge... common sense shouts ‘crack’ in the casting - except I just can’t detect any. Muddying it all is the boss (versus straight hole) and tapped thread.
(I pondered, ‘temp sensor?’ - but there’s no corresponding hole in the cylinder head)

I gingerly tried to extricate the lower / easier ring this morn, and after an hour of coaxing it had it slightly proud of the piston - but then snapped. Tbh, it was nowhere free; and even now a 10mm bit remains ‘welded’ in the groove.
And that was the easier ring...

So - I’m up for at least 1 new piston & rings. Decision time. Do I buy a standard piston and bung it all back, or rebore and go with 2x +1 size pistons?

The localised scoring is significant, ie easily felt with a finger nail. How this translates to severity / reliable idle - I don’t know. All the engine needs to do is push a 10’ tinny about the local waters for a couple of hrs a month; if the consensus is “she’ll be right” then I’ll be totally happy to just bung in a replacement piston and rings.

Water jacket and all galleries all now cleaned thoroughly of build-up; cholesterol levels down to zero.

Appreciate the help - thanks,
Simon

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