What Does a Burnt Piston Look Like

I pulled my intake and heads today to determine where the oil smoke is coming from. After removing my DS header, the #5 cylinder was black & wet. After removing the head, both rear pistons had a orange ring around the outer perimeter of the piston. I have never seen this before. All of the valves on the DS were black with carbon, but the PS head valves were mostly off white. I am assuming that problems with the CFI could be causing this, but what is up with the orange ring on the pistions.

Help

A burned piston will have a really ugly hole down the side or thru the top (dome). I suspect that your orange ring may be from too much side clearance on the rings and allowing those rings to twist in the groove and then the loss of seal.

Did you do a leakdown test or compression test?

If everything is running correctly, the valves should be an off white color. Any goo can be from the guides (too sloppy) the valve guide seals being hard, or just the residue from poor combustion.

TimAT said:

A burned piston will have a really ugly hole down the side or thru the top (dome). I suspect that your orange ring may be from too much side clearance on the rings and allowing those rings to twist in the groove and then the loss of seal.

Did you do a leakdown test or compression test?

If everything is running correctly, the valves should be an off white color. Any goo can be from the guides (too sloppy) the valve guide seals being hard, or just the residue from poor combustion.

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I did a compression check. The #5 & 7 cylinders were the lowest @ 165 & 170. This was with the motor cold. It looks like the PS of the motor might be ok by your description. I looked at the head gasket on the DS & didn't see any problems. The heads are loaded and ready to go to the machine shop. Hopefully it's just one of the valve seal boots leaking. Both heads will be torn down for inspection before anything else takes place.

Now I need to find the underlying problem with the IAC motors. I am starting to study how the neutral safety switch & VSS work together to see if that might be the problem. If the IAC motors are controlled by these ckts, thats where I need to be looking. Are VSS ckts still available for purchase?

This is starting to get deep.:bomb::cussing:

Thanks for the help!

The VSS "used" to be in the back of the speedo. There was a 2-sided blade that rotated with the speedo cable. One end was white and was picked up by the VSS. As far as the VSS and neutral safety switch, I don't remember. The IAC should be controlled by the ECM either on base programming (open loop) or real time(closed loop) thru the O2 sensor.

Here are some pics of the engines. Does anyone have a clue what would cause the orange color. It only did this on the 2 rear cylinders.

Dirtbuster1 said:

Here are some pics of the engines. Does anyone have a clue what would cause the orange color. It only did this on the 2 rear cylinders.

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That almost looks like some water/coolant got in there.(Rust)

Here's a pic of one of my LS5 pistons. They are all pretty much the same under the soot...some darker and some lighter. I suspect if you clean the piston off that you will see that the top is all brownish orange.

The car burned oil at a pretty good pace. I also burned a mixture of 110 race and 93 unleaded. It has also seen it's share of cleaners which obviously didn't do shit to clean anything (seafoam, lucas top end).

Never leaked coolant as far as I could tell.

I was thinking mine were like this because of a weak ignition system not burning the oil/gas mixture combined with a rich carb..my plugs always were pig rich.

As you can see on the top of the piston to the left, I wiped a bit of it off with a rag. My guess is that they might clean up.

SmokinBBC said:

Here's a pic of one of my LS5 pistons. They are all pretty much the same under the soot...some darker and some lighter. I suspect if you clean the piston off that you will see that the top is all brownish orange.

The car burned oil at a pretty good pace. I also burned a mixture of 110 race and 93 unleaded. It has also seen it's share of cleaners which obviously didn't do shit to clean anything (seafoam, lucas top end).

Never leaked coolant as far as I could tell.

I was thinking mine were like this because of a weak ignition system not burning the oil/gas mixture combined with a rich carb..my plugs always were pig rich.

As you can see on the top of the piston to the left, I wiped a bit of it off with a rag. My guess is that they might clean up.

Click to expand...

Yep. That be varnish allright. His others looked different to me.

:withstupid: looks like alot of oil varnish to me.



Sorry Jeff there is no I Agree smiley :harhar:

Thanks for the reply's.
You were all right. It was definently a varnish buildup. I just wanted to throw this out to see if anyone else had experienced this. After about an 2 hours of some good elbow grease and some cleaning agent, I removed it all. The pistons look like new again, with the exception of some minor detonation on the #7 piston. I feel better about not having to go into the bottom of the engine.

I think the discoloration around the outside could have been some coolant leakage, or were the oil was leaking through the heads on some of the cylinders. The detergents in the oil might have loosened up the carbon. I should here from the machine shop later on the problems found with the heads.