Picked up some 317s for a future turbo project. Seller didn't originally point out the marking of two of the combustion chambers..looks like a plug or valve came apart in there. It was a pretty good deal still so I grabbed them thinking it's just a mill.. Well that kinda kills my whole lower compression plan.

So opinions please? How "bad" is this, does it need to be fixed?

Thanks!

Chris

 

I'd just smooth the marks a bit and use them. Its not going to amount to anything.

 

Run them. Smooth out any nicks so there's no high spots, and they'll be good to go.

 

Those are from detonation. I bet the tops of the pistons that those heads were sitting above look even worse!

Fortunately, those are perfectly fine to run. Let me guess, that's cylinders 5 & 7 down the drivers side?

 

Thanks guys! That makes me feel a bit better. I didn't see them on the engine/vehicle but you are probably right on the cylinders.

I haven't played with boost much(one factory blown vehicle) and am diving in a little blind. Surprised to hear detonation can cause that much physical damage to a head without actual physical bits of something banging around in the chamber!

 

I'm gonna' have to respectfully disagree...looks like something was in those two cyl's...



Can't be...if that head was on the drivers side they would be at the front, #'s 1-3. If the passenger side, #'s 6-8...


I agree I would also run them, although I would really take a close look at the exhaust seats...the one on the left looks pretty beat...

 

I disagree too, that wasn't from detonation. Something did a little dance in thoses cylinders.

 

Thanks for the additional input. I am probably headed for a light port and valve job on these anyway so hopefully the seats will clean up. $140 with some stock valves in fair shape.. Figured I at least wasn't wasting my money.

Gotta love Craigslist. EVERYTHING is in great shape until you get there. Last year I went looking for a set of axles for a CJ. Went right before dark so working by flashlight. The lady tells me 10 minutes in that I'm digging these axles out of a gigantic ANT PILE.

Picked up a complete 4.8 for $200 last weekend..drive 45 mins to get it and the guy suggests he and I just pick it up and put it in the back of my truck. SMH.

 

I don't know about that. I have seen multiple LS motors with the #7 piston and area around the combustion chamber look identical to that. The last one that looked like that, I actually cut apart the fuel rail with a pipe cutter and it was full of junk. (This is on the returnless fuel rails).

The #7 intake runner is also the furthest back runner on the LS motors if my memory serves me correctly.

This piston also had the same indents just above the compression ring.


If you look closely at the area of the head that is sealed in the head gasket/combustion space (to the right where the oil looks disturbed) you can see 1 or 2 single indents.




Maybe... I am wrong but I am going to have to insist that I am right based off my personal experiences. If something was banging around in the combustion area between the head and crown of the piston, I'd imagine their would be more damage present to the head (I was always under the impression hypereutectic piston were stronger than normal aluminum?) and it wouldn't have worked it's way past the crown to the side of the piston (above the compression ring land).
I am rather seriously over estimating how violent cylinder detonation can be or the two of you are underestimating it.

 

I believe you that number 5 and 7 can run hot. I've lost number 7 piston myself but I've never seen sharp looking detonation marks like that and I've had a ALOT of engines apart over the last 45+ years. In the LS engines it destroys the top edge of the piston ring land area 1st, can't miss it.

 

Interesting. I've never seen marks like the ones pictured other than in LS motors. I always assumed it was detonation causing the damage.

 

I agree.

 

I've been at this less than RockinWs6...(only 35 years) and again very respectfully your picture is NOT detonation...there was foreign material in your cylinder...

And again, his picture cannot be #7cyl...it has to be #1-3 or #6-8.

 

damn chris is you were closer i'd run my tig over the nicks until they flowed out and you wolnt need maybe a .010" clean up cut

 

I'd sand those marks with some 800 grit sand paper just to knock the sharp edges off and forget about it. You could also use a razor blade on edge and knock them down carefully. In a mild street engine even if you didn't smooth those marks you'll never know they were there. Those marks are going to be covered with carbon in a few miles anyway.

 

I've seen this twice on the #7 cylinder now.

 

The rear cylinders are prone to anything that gets into the intake going into those rear cylinders. Its also the same reason they run hot because they run leaner than the rest because air tends to ram into the back of the intake. Trust me on this that is not from detonation, damage from detonation is broken melted nasty fubar. It doesn't look anything like the hammered nicks you show. Do a search on detonation and you'll find plenty of pictures of broken melted pistons and rings. Imagine a giant 2500 degree plus hammer that acts like a hammer and a torch, that detonation. When it happens parts overheat and break. The 1st signs you would see on a piston would be melted edges, broken rings and ring lands. Extreme cases its will melt the tops of the pistons too. Never any marks like you show, those are without doubt hammer marks from something that ventured into the intake and got blown into the rear of the intake then down into a cylinder. Doesn't take much either, pistons come dam close to the cylinder heads when the engine is cold.

These engines will knock terrible cold from carbon on the tops of the pistons hitting the cylinder heads. This is why you hear PISTON SLAP PISTON SLAP my LS has piston slap. Its nothing more than cold carbon knock. But shhhh no one wants to hear that PISTON SLAP IS BULL PUCKY round here. LMAO

 

Thank you guys for the input. I will just knock down the high spots and lightly sand. Use these for milder build. Found a better set of 317s for higher boost later.

Doug, I wish. I am picturing a Craigslist ad: "Drinking buddy needed. Must have Tig and know how to use it."

WS6, seems like it's been a while since I've seen a good piston slap knock down drag out smackdown debate around here. Maybe we're due!

 

i found out how to fix the piston slap in my daily
before i start the truck, i turn the stereo up

 

don't get me started on piston slap..........it gets me revved up