why is number 6 piston so black

[cmcfaul]

Engine has about 10k miles on it since top end rebuild, rings and chains. Nickecill cylinders were professionally deglazed. P/C's have about 100K mi's on them.

All the pistons look basically the same except for number 6. What could cause it to be so black?

Don't see how it could be related but the oil cooler blew and spewed oil all around Number 6.

Engine is apart for pulled head studs and a broken piston (number 2). 6 new pistons are on order from JE and the case is at the machine shop. Wondering what going on with number 6.

Any thoughts appreciated.

Chris

73 911 E

[safe]

what is the condition of the valve guides and seals?

[cmcfaul]

All guides, seals and valves were all replaced 10K miles ago (two years ago)

[safe]

Originally Posted by cmcfaul

All guides, seals and valves were all replaced 10K miles ago (two years ago)

I saw that after I posted!
Still, I would check that the seals are still in place, they can slide of the guide sometimes.

[Henry Schmidt]

# 6 is pumping oil from somewhere. I would suspect a damaged piston. Perhaps damaged from detonation.

The leaking from the cylinder sealing surface is inadequate clamping force caused by cylinder head stud or case threads pulling.

[cmcfaul]

Yep, the engine is apart because of a pulled head stud. Can clearly see where it was leaking. I already ordered 6 JE pistons as number 2 was damaged due to detonation. The other 5 pistons look fine. Will check the #6 head valve seal and take a closer look at the piston.

Thanks

Chris

[Lapkritis]

What is your fuel delivery system (carbs or, mechanical fuel or EFI)? What is your crankcase ventilation system setup? What did the spark plugs look like for each cylinder? My experience is a silver edge around the outside of the dome of the piston may also indicate blow-by. I see this more on performance engines where the combustion gases strip the carbon as they escape past the rings.

How do you drive the car? If it is daily driven then the possibility of oil leaking into the combustion chamber (blue puff on startup) is less likely to contribute. Perhaps consider changing your gasoline supplier or cycling techron or seafoam into your service schedule should everything check out.

[cmcfaul]

MFI with higher compression pistons. Supposed to be 9.5 / 1 CR but the heads have been decked twice so I suspect compression is a bit higher. Running Super Unleaded pump gas and have an LM2 AFR meter installed. I know it runs lean when warming up at just off idle which is not unusual for MFI. The rest of the time it indicates 13.0 AFR.

Having the injectors checked and going to syncronize the cylinders with emphisis on richer.

top three plugs are 1-2-3
bottom are 4-5-6

just like they would be in the engine

[Lapkritis]

I would recommend an injector/differential pressure regulator service looking at those plugs. Some are running lean and some are running rich. Test and confirm all injectors/fuel output to the port are balanced; this may be the cause of your piston issue on #2 as well... full inspection of the engine would be wise. Lean heat warps and cracks so if the o2 trim is pulling the mixture up (depending on management configuration) to make it rich then some otherwise normal cylinders would over-fuel if you had weak injectors causing lean cylinders.

Edit: I would also try a colder plug once everything is right with the world.

[cmcfaul]

I switched to a colder plug and it helps. Each cylinder has it's own throttle body so easy to adjust mixture individually. But first want to make sure injectors are all working correctly then mess with individual mixture / synchronize them.

just spoke to the machine shop doing the case work....almost done:-). Said the crank was bent and he fixed it. How does that happen?

Need to find the one over bearings (.25mm) for the crank and rods...SUCKS in that they are stupidly expensive.

Chris

73 911 E

[Mr Beau]

Looks like you should have the whole system flowed. You can adjust each throttle body individually but really that's only for idle. Plugs can be colored from idling, so perhaps we're just seeing difference in idle mixtures, but given your issues it sound like something else is going on.

[HawgRyder]

Check the flow from the MFI pump for each injector.
If they are not even...then everything else you try will be in vain.
Disconnect the lines from the pump to all injectors...place the ends of the lines in separate jars or containers....turn the engine over with the starter for a number of seconds...and compare the amount of fuel in each jar.
I have seen flow charts on this site before...but can't find them right now.
But if the amount is close...at least you are eliminating one of the biggest problems.
Bob

[docrodg]

I have seen people straighten cranks... they look at it, place it in a press and put pressure on it then smack the crank with a big hammer once and presto. Needless to say this is not only an art but also not something I would do with one of these engines.

[johndaroza]

Did you replace your head studs when you rebuilt? You could be lifting the head as well ?

Any mods ? how hi of RPM do you go?

[johndaroza]

Did you replace your head studs when you rebuilt? You could be lifting the head as well ?

Any mods ? how hi of RPM do you go?

[cmcfaul]

Replacing all the head studs this time around with case savers as at least two had pulled out of the case as can be seen in the first picture. Redline is 7300 rpm's

[cmcfaul]

Number 6 piston is looser in the cylinder then the others. Hopefully a piston issue, not a cylinder issue. I will attempt to use my new / cheap micrometers to measure that cylinder vs the others.

Chris

73 911 E

[Lapkritis]

You may already know this but the piston can be a little loose near the top. It shouldn't pull a volume of oil unless the rings are toast. Have you removed the pistons from the cylinders yet? I would inspect the ring lands and also ring gap in the empty #6 cylinder to see what things were running at prior to tear down. Generally speaking the ring gap can be a little on the big side without a problem ... it's when they're too tight that you have an issue with potential cylinder wear. If this is a piston issue then you would expect to see wear on the outside of the piston relative to the neighbor pistons. The margin for JE pistons is +/- .0005" if I recall correctly and their QC is pretty good to have one get through way out of spec. Given the damage to the other piston, it is possible the piston began to erode or scuff due to lean mixture/piston overheat and may be what you are perceiving as loose. I won't ramble on much more but I would flush the piston squirt circuits and confirm they're functioning. Clogged squirters will give you fits chasing piston problems.

[cmcfaul]

Yep the squirters are on my hit list to check. They are highly suspect.

Chris

[cmcfaul]

Good news, I think. Sent my injectors to MFI Werks for testing and all tested OK except for number 6 which apparently would drip at idle. So I am hopeful that is my issue.

Injector was cleaned and run at high RPM on their machine for a while and should be good as new :-)

Chris

73 911 E