Haans249

iTrader: (24)

Alright, had to tear down the engine, noticed this on the heads and pistons on only ONE side of the motor. I checked all of my clearances and they are within spec, so the only thing I can think of is that this is detonation that caused this marring on the pistons and heads. But, also, I've never had any knock retard show up during logging, so I'm not exactly sure whats going on here.

I was running 51 thou gaskets, and the pistons were out the hole between 8 thou and 14 thou which leaves me with over 35 thou clearance...

What could this be?

Adrian.

gametech

iTrader: (1)

Edit-- disregard my previous comment. I finally looked at the pics on a good monitor.

9000th01ss

iTrader: (10)

Looks more like dirt or something got in there. Detonation is going to show more on the thin areas like around the valve reliefs.
Are you sure you had .037 piston to cyl head clearance?
Why did you take it apart?

Old Geezer

iTrader: (3)

Plug readings??
Looks like erosion from detonation, in the quench area.[Highest cyl pressure]
The area at the edge of the piston is thin, due to the top ring being close.
If all cyls one 1 side are this way, I'd be looking at fueling on that side.

http://cochise.uia.net/pkelley2/sparkplugreading.html

Haans249

iTrader: (24)

Your eyes MUST be deceiving you, because the part that I'm referring to is clean lol. It is that crescent moon shape on the quench part of the chamber, and along the top portion of the piston.

Haans249

iTrader: (24)

I was running 51 thou gaskets. I checked and double checked the compression heights of the pistons on both sides. It was all ~40 thou on both sides. Double checked the gaskets as well, both the same thickness.

Haans249

iTrader: (24)

Upon first inspection of the plugs they looked alright, I think some of the plugs showed a little bit of black speckling. I think its also a fueling issue as well since it is all on just one side of the motor. Its just really weird that the knock sensors didn't pick up any detonation, so maybe it was a relatively small amount of detonation. Looks like I'll be getting some aftermarket fuel rails.

stevieturbo

It does look like detonation to a degree. That also looks like a nasty scrape on the head face.

Haans249

iTrader: (24)

I agree, the heads are at a machine shop as we speak to get all cleaned up, and get the decks refreshed, and swap out for new springs and seals.

Old Geezer

iTrader: (3)

the pistons need to come out, and have the ring lands checked, to be SURE the ring lands are not caved in.

Haans249

iTrader: (24)

I really can't take out the pistons, its not beyond my abilities, but I can't have my car down that long. There is no way the ring lands are caved in, the bores are PERFECT with not a single mark, and no evidence of the rings butting. It doesn't appear that the pre-ignition was anything major, just a slight amount over time, not even enough to be heard, nor enough for the knock sensors to even pick up. I looked closer at my plugs as well, and there really wasn't any sign on the plugs, i think one of the plugs had just a VERY SLIGHT amount on the porcelain, like a few speckles, no aluminum or anything like that. I'll get pictures posted up of the plugs from side where these marks have come from.
The forged pistons looked to hold up pretty well, as the marks on the pistons really aren't too bad, now if they were discolored from extreme heat, I would be much more worried, but they look OK.

stevieturbo

I would say chances are, the pistons are OK....

But I'll also add, It is impossible to tell if they are ok, simply by looking from above.

Haans249

iTrader: (24)

I completely agree, but if there was any real signs of damage on the ringlands, I would be all over it, but, there isn't any excess rock in the pistons, there are no marks what so ever on the bores, no signs of butting rings, no excess oil usage when the vehicle was running. If there was excess wear in the bores, or excessive oil usage, discoloration of the pistons or ANYTHING, it would be likely some sort of damage, but there just isn't, luckly. But, as you and OldGeezer said, the pistons really do need to come out, but its just not going to be able to happen in my case

The thought of the pistons actually kissing the heads is still floating around in the back of my head, but I don't see how that could be happening either lol.

One thing I did notice, is that on my LS7 fuel rail, there were three small dents made into the top of the crossover to make for clearance for a strut tower brace that was installed...I didn't know this! This further leads me to believe that it was an uneven fueling issue since it is on the pass side, opposite of where the flow comes from, and opposite those dents in the crossover.

I'm installing billet fuel rails, and upgrading to TR6 plugs as extra insurance. Bah!

XtraCajunSS

iTrader: (2)

Adrian,

That looks like classic piston to head contact. I hate to tell you this, but I have seen it more than once. Are you sure of your deck height? have you checked it with the piston at verified TDC and with the piston rocked back and forth?

BTW, the stud left priority mail today...

Thanks,
Shane

stevieturbo

In July last year, after a meth related incident, I lifted the heads. I drove home easy, and pulled the engine out, and removed the heads.
Yes, I could see ring damage from above, but the pistons looked 100% fine, no marks anywhere.

Wasnt I shocked to find that all 8 pistons had fractured ( not detonation related though )

Dont think for one second you can tell the condition of a piston, simply from looking at the crown. It is impossible.

And if it is doable to remove the pistons without a shitload of work, I really would be doing it. I know I'll never take that risk again.

Haans249

iTrader: (24)

****, thats what I've been fearing... I have double checked my deck height. Setting the piston flush to the block, and then using a dial indicator it showed that the pistons came out the hole between .008-.014. Infact, the pistons on the other side were out the hole on average higher than this side, and there was no piston-head contact on that side...
On the other hand, I will have to double check my deck height with the piston rock, which I did not do. Piston rock I did check at around .020 on both sides. I also measured gasket thickness and they were both consistant. Is it possible that the head on that side was torqued down too much? I was running cometic 51 thou gaskets.

stevieturbo

lol...no.

Haans249

iTrader: (24)

haha, I didn't think so either, was a stupid idea that one of my friends kept arguing with me about.

So, I re-checked the clearance....pistons out of the hole, including rock leave me with 20thou clearance (quench) on the pass side (where the pistons are making contact), and 26thou on the drivers side, pistons out the hole 31thou (25thou on the drivers-side)...so, definitely not enough clearance...

How would I correct for this? I cannot pull the pistons to replace them with new ones, what I initially thought was to have the machine shop machine out 15thou from the top of the chamber, and 10 thou on the other head (since the other side has 25thou clearance) to get me to an even ~35thou on both sides... Btw, I'm not talking about decking the heads, but to have them work only in the quench area of the chambers. What about running a thicker head-gasket? Are there 67 thou thick gaskets for an LS7 setup?

Please advice!
Thanks!
Adrian

stevieturbo

I think Cometic can make gaskets in any thickness. A thicker gasket would be the easiest solution by far.

Haans249

iTrader: (24)

How thick of a gasket can you run before it is not safe anymore? Would running a 67thou gasket be alright? Given the measurements that I posted, what thickness would you recommend?

Thanks,
Adrian