Calling all petrol engine combustion gurus (M102 based qu)
 

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 =>

http://www.peachparts.com/shopforum/...1&d=1378043929

(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

http://www.peachparts.com/shopforum/...1&d=1378043946

But the cylinder bores are still in good condition

http://www.peachparts.com/shopforum/...1&d=1378044083

http://www.peachparts.com/shopforum/...1&d=1378044094

looks like sugar in the gas tank by a enemy

Continued due to attachment limit...
 

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

http://www.peachparts.com/shopforum/...1&d=1378044202

^^^ cylinders #1 and #2

http://www.peachparts.com/shopforum/...1&d=1378044211

^^^ #3 and #4

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

http://www.peachparts.com/shopforum/...1&d=1378044275

And the valves

http://www.peachparts.com/shopforum/...1&d=1378044351

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

But the exhaust valves - yuk!

http://www.peachparts.com/shopforum/...1&d=1378044444

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

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?

oh yes looks like it was sucking oil.

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?

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.

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?

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.