Calling all petrol engine combustion gurus (M102 based qu)

[Stretch]

G'day Folks,

Due to a slight mishap that I'd rather forget I've got my engine in bits.

I was wondering what has caused the amazing rock hard coke-like build up of crud in this engine.

I think it is probably due to a life of just going to the shops but just in case I thought I'd ask you guys if you think there might be a fuel problem too.

The pistons are pretty grotty =>



(Oil on piston is actually ATF - I'm soaking the muck off)

Oil scraper ring is also pretty clogged up - holes / slots in the ring are totally full of rock hard gunk



But the cylinder bores are still in good condition

[oldsinner111]

looks like sugar in the gas tank by a enemy

[Stretch]

The top end of the engine seems to have suffered from oil ingress via the inlet =>



^^^ cylinders #1 and #2



^^^ #3 and #4

So here's a picture of the combustion chamber recesses in the head



And the valves



Inlet valves looking quite clean actually despite evidence of crank case breather oil being sucked through.

But the exhaust valves - yuk!

[Stretch]

Originally Posted by oldsinner111

looks like sugar in the gas tank by a enemy

Are you sure? Most forum members can't reach me here!

[Stretch]

Seriously though - fuel problem as well as a crank case breather gunk related problem?

Or just crank case breather a life of short trips problem?

[oldsinner111]

oh yes looks like it was sucking oil.

[Mike D]

I think you called it. Low maintenance, cheap oil and short trips. The engine gunk doesn't look bad, about what you'd expect.

[Stretch]

Originally Posted by Mike D

I think you called it. Low maintenance, cheap oil and short trips. The engine gunk doesn't look bad, about what you'd expect.

Thanks Mike - really? That amount of gunk normal for about 100,000 miles?

[duxthe1]

I wouldn't call that abnormal. Looks about average. In fact the head is a little above average. If you note the area of clean aluminum around the intake valve, in the chamber, tells me that it has been burning a decent grade gasoline.

[Mike D]

Normal on a properly maintained car? No. On a car using cheap oil, short trips, etc, yup, pretty common.

There used to be an oil (and it"s probably still around) by the trade name of "Pennz-oil". When it was used in a car which only went on short trips, it would build up a waxy residue. I have personally seen it so thick inside the valve covers it actually restricted the return flow of oil into the sump. Once a week drive on the highway kept it flowing but short trips, forget it.

I don't see much wear on the bores. How were the measurements? Out of taper?

[Stretch]

I haven't got a bore micrometer yet. (In the post)


Thanks for the condition opinions - it is interesting to hear what everyone thinks - I just haven't seen enough of them to form an opinion. (I hope I don't get to see any more actually!)

[nandgopal]

coming from India, I have see that stale gas causes such deposits. Gas sitting idle in a tank allows the volatile portions to evoparate but on deposits such gunk in the cylinder head. I have seem premature failure of engine due to build up of such deposits. I would suggest that unless you propose use up the gas do'nt let it sit idle in your tank for over 30 days.