What would cause this combustion pattern?
What would cause this combustion pattern? Engine is a rebuilt LS1 (block, but mostly LS6 parts) with about 1400 miles on it. There was a bit of oil consumption from a broken PCV tube inside the LS6 valley cover.
For some reason #3 has this weird combustion pattern. The bowl area has carbon, but the rest of the chamber doesn't. The piston looks the same - it has carbon in the same shape with a clean area toward the top that mates up with the head.
You can see #1 below it doesn't look the same (and neither do the others).
The heads and block were both surfaced before I put the engine together, and I was using the GM MLS gaskets.
So any ideas why that one looks that way?
For some reason #3 has this weird combustion pattern. The bowl area has carbon, but the rest of the chamber doesn't. The piston looks the same - it has carbon in the same shape with a clean area toward the top that mates up with the head.
You can see #1 below it doesn't look the same (and neither do the others).
The heads and block were both surfaced before I put the engine together, and I was using the GM MLS gaskets.
So any ideas why that one looks that way?
Last edited by Lothar34; Jan 19, 2011 at 01:26 AM.
Rod bearing? hah.
Looks like its possible that you were getting water/coolant into the cylinder on that side. Usually when you do it will "steam clean" the area where its coming in. You can almost see a line where it might have been entering the cylinder.
Looks like its possible that you were getting water/coolant into the cylinder on that side. Usually when you do it will "steam clean" the area where its coming in. You can almost see a line where it might have been entering the cylinder.
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This was it when I got it back from the machine shop.
Could definitely be a spun bearing...but to be that bad and have that severe contact, I would have expected it to have made some serious noise!
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Largest Stocking Distributor of LS-x Engines / CHECK OUT OUR NEW WEBSITE!
COMP - FAST - PACESETTER - DIAMOND RACING - EAGLE SPECIALTY PRODUCTS - CALLIES - COMETIC GASKETS
RAM CLUTCHES - MOSER ENGINEERING - KOOK'S HEADERS - ARP - GM BOLTS AND GASKETS - MSD - NGK
POWERBOND - ASP - AND MORE!
It started making a loud ticking Friday night when I was coming back from RPR. At first I thought it was an exhaust leak or a stuck lifter. The ticking wasn't loud enough that I could hear it over the cutouts. It was rpm-dependent and sounded a little quieter when I gave it gas, and then a little louder if I let it decel in gear with no gas.
That and I knew I was getting too much oil in the intake was why we pulled the heads and stuff off.
So there was a loud noise BUT when I checked with the stethoscope, it was coming from #7, not #3.
There are some really small scratches on the head around #3. I thought they were shallow enough that the gasket would fill them in, but it's possible that there still was some coolant getting by. I will see if I can measure them tonight, but I don't think they were big enough to catch a fingernail.
As disco posted, I have ARP rod bolts on there. When the engine was rebuilt, it was built with new rings, new cam bearings, new service-grade rod bearings (at +.002") and new service-grade main bearings. The main studs are GM.
That and I knew I was getting too much oil in the intake was why we pulled the heads and stuff off.
So there was a loud noise BUT when I checked with the stethoscope, it was coming from #7, not #3.
There are some really small scratches on the head around #3. I thought they were shallow enough that the gasket would fill them in, but it's possible that there still was some coolant getting by. I will see if I can measure them tonight, but I don't think they were big enough to catch a fingernail.
As disco posted, I have ARP rod bolts on there. When the engine was rebuilt, it was built with new rings, new cam bearings, new service-grade rod bearings (at +.002") and new service-grade main bearings. The main studs are GM.
Last edited by Lothar34; Jan 21, 2011 at 05:08 PM.
OK upon closer inspection, that little concentric ring groove pattern on the top of the piston is also on the head.
Unfortunately the guy at the machine shop who I dealt with is on vacation so I'll have to wait for him to get back to see what can be done.
I reused the old rods. Is it possible that #3 broke AROUND the rod bolt?
Unfortunately the guy at the machine shop who I dealt with is on vacation so I'll have to wait for him to get back to see what can be done.
I reused the old rods. Is it possible that #3 broke AROUND the rod bolt?
