Riceman

Pulled the heads on my L92 427 build and noticed a few things. One, the burn pattern is strange, not symmetric between sides and pistons. Some say it's normal, I'd never seen it but I'm no major league engine builder.

Second, the cylinder wall clearance. It wasn't as noticable when it was new/when I got it because it was all shiny and didn't contrast much. Now you can clearly see the clearnance. Is this normal? This was built by a reputable shop. I didn't order it with any crazy specs or tolerances, this is just what I got.

(reason heads came off: compression and head gaskets. Stock L92 head gaskets were shipped to me to use, so I used them. After some research it looks like the bore on those isn't large enough to support my 4.080 bore. Upon pulling them it's easy to see some burning and carbon buildup on the fire-ring/edge. Don't want them in the cylinders now do we?)

REEFAR

BUILD IT LOOSE WOOT NASCAR!

Tireburninls1

I appreciate that you wanted to get a picture of your piston sitting in the middle of a huge coffee can so we could see the detail clearly but please get a pic with them installed in the block so we can see what the clearance actually is.

Forged pistons intentionally have a lot of taper so unfortunately it's impossible to see how much clearance you actually have from the top. Clearance is measured in the skirt area.

sj24

iTrader: (1)

The top of the piston is much smaller then the skirt to allow for greater expansion caused by the combustion heat. The gap you see is normal.

bandit1

iTrader: (12)

Ur fine boss when I built my 427 it too has a bit of gap when you look at it from that vantage point especially when you use forged pistons they expand as the car warms up. Its there so the piston doesnt acually cause problems after it expands to its proper place.

racer7088

The pistons in your picture look normal. There is always a lot more room around the crown or top of the piston than at the skirt. The rings do not reach the top of the bore so you will always have the carbon at the top of the bore since nothing touches that area at the top. The top of the piston is always smaller to let gas down to activate the top rings and to allow for more expansion when hot.

racer7088

With flat top pistons and 427 inches hopefully your chambers are big enough to make for the right compression. From just looking at your pictures here on the internet though your stuff looks pretty normal so far.

Riceman

chambers are supposed to be around 67cc, I'm going to have the heads gone through to make sure as I'm not sold that both were milled. Static should've been around 11.5:1 depending on the installed deck height of the piston, not sure on that. Counting on a -.005"

Thanks for the replies guys, now I don't feel as bad

Riceman

About the carbon, I was just referring to the pattern on the piston not so much the top of the bore. It's not etched into the piston/the piston is fine, but the pattern was just strange to look at. My stock LS2 didn't look like that which was my basis for comparison.

racer7088

That sounds about right for your compression too if all ealse is normal. You look good.

Riceman

something someone else mentioned... the scoring on the walls. The up-down marks, look to be piston scuffing or similar. What the heck? What did I do wrong?

racer7088

You will always see tiny scatches up and down the bore from small pieces of grit etc. Use a very good air filter and assemble any piston and engine under the cleanest possible conditions but no matter what you will have a few of these on every engine you tear down. It's pretty much normal again basically from the little I can see.

Riceman

Most of the scratches can only be seen not felt, but in probably 2 cylinders you can feel them with the fingernail. I took as much care as possible to keep clean during install and am using vararam ('06 vette this thing goes in) air assembly.

racecar

If you are seeing scratches on the cylinder walls, it could be from all of that carbon flaking off. Are you running rich, or just ******* it around on the street too much. Maybe you just need to get out and get the pedal down more often !!
The burn pattern does look normal. I have never seen one that looked 100% like I expected to see.