Engine enigma

[Mike Attew]

So I developed a tinny knocking which sounded like something bouncing in the cylinder which now may have been ignition?
Anyway I was going to rebuild the engine in September, just brought forward as No 4 was down on compression and the rear crank seal leaked badly and hardened valve seats being fitted.
Head off, nothing untoward, engine out and stripped. Over 1/4" sludge in the sump.
Now what I can't understand nor my mate who refurbs engines.
Shells and pistons all standard, piston bores have no ridge and look really good & within 0.0005" tolerance, same with the crank journals, pistons don't look to have seen much work, main bearings also look new. Valves all look good but now the enigma, the big end shells are down to copper?

It does look as if the engine had some new bits but used the old big ends? I have never seen anything like it before.

[Mike Attew]

And the shells

[1972nail]

I did open an engine like that years ago, one from a Marina I believe. My late father in law, who was a very experienced mechanic, reckoned that the engine had been used on an excessive number of short runs where the engine oil never reached operating temperature and the poor engine would have had a lot of cold and dry start ups too.

Since then I have read somewhere that advanced engine timing can accelerate big end wear so that may have been the cause or a contributing factor too.

[Mike Attew]

I can see with short runs it may cause wear as the big ends take alot of punishment so that may be the reason. Strange cause my engine bloke and another friend who used to work with him was there and they had been doing engine work for 40 years and had never seen it?
I would have thought advanced ignition would also show at the top end.

Incidentally how do you recognise a Low or High compression engine? there are no marks on the pistons.

[1972nail]

Incidentally how do you recognise a Low or High compression engine? there are no marks on the pistons.

Both these threads are in the Member's only area, I trust you can see them.

viewtopic.php?f=289&t=16060
viewtopic.php?f=289&t=16058

[Mike Attew]

Thanks for that, I didn't find them. I think there may be a mistake at the bottom where it says
minimum compression pressure when engine hot
1159cc (9.2:1 engine) 135 ibs/in2
1256cc (7.3:1 engine) 110 ibs/in2
1256cc (8.7:1 engine) 125 ibs/in2
I think the top one should be 1256cc which is what my engine is.

[jpsmit]

Just speculating here but if the sludge were primarily thrown at the big ends (being lower on the engine) that might have caused premature wear. I similarly managed to once kill a (modern) engine by driving with a misfire which poured raw gas past the rings and ruined them.

On another forum we had a car where everything was tight yet the sump was full of sludge and we deduced that someone added some fluid (likely rad fluid or washer fluid) to the oil by mistake.

[Mike Attew]

Amazing the things you learn. Looks like I caught this engine in time.

[redfirenza]

I should think its just a case of oil starvation, it was probably like trying to suck up treacle looking at the sump contents, all the crank bearings need a good high pressure oil supply but the rest of the engine will survive on lower pressures and oil splashing around
Looks like a cheap and nasty aftermarket head gasket as well

[Mike Attew]

The oil pick up seems high in the sump and the mesh was clear , the engine also had 40 psi oil pressure hot so I didn't expect the big ends that bad but when the crank is polished the oil gallery will be checked incase of a partial blockage.