Discolored cylinder

[pittss1c]

I pulled my engine apart for having low compression (I was told it was a high compression engine, but only had 110 PSI)
One of the things I found was the brown/tan discoloration of the cylinder between the exhaust port and the head. I have not seen this before, any clue why this would happen?

 

[yb200]

thats how far the rings go up on the cylinder

 

[little3mil]

looks pretty clean tho.

 

[pittss1c]

Not the dark area around the circumference, the two dark patches between the exhaust port and where the rings stop. Those aren't shadows, those are actually tan spots on the cylinder wall.

 

[Brute71]

i believe these spots are what he's talking about:

it looks like thats where your compression leak is. The rings arent sealing against the cylinder in those spots.

 

[J4M1E333]

^^^^^^^^^^^ i 2nd that, ring blow by i think the name is

 

[little3mil]

yep and is there feelable scratches on it? if not just get a good hone and do a leakdown test when you put it all back togather

 

[yb200]

what does the piston look like on the exhaust side

 

[xjma]

3rd (or 4th) on the ring blow-by. Get a micrometer on the cylinder, do it in a bunch of places, and if it's within spec just get it honed. If the cylinder looks good, just put new rings on. Don't bore to the next size if you don't have to!

 

[pittss1c]

I didn't feel any scratches. I just wanted to check if this was normal... I have not seen it before. I wanted to make sure there is no known cause outside of worn rings....

 

[Little-J]

it can happen, but its not the greatest thing?.. Its just carbon deposits from hot combustion gases leaking past the rings in an effort to get to the lower pressure in the exhaust port.

Get your cylinder measured to see if its out of round.


A picture of the piston would tell a great deal.

 

[pittss1c]

I'll get some better pictures of the piston tonight... but I did not see any glaring defects, and my first few measurements did not appear to point to an "out of round" condition.
Here is a pic of the top, all the other pics are of the intake side at the moment.

 

[pittss1c]

Looking at the piston, there isn't anything too abnormal in the areas where the discoloration is on the cylinder. The only difference is that there is standard brown coloring on the piston everywhere but the exhaust side. I just ordered a new forged piston/rings gaskets and bearing from vitos. I wonder if it was not broken in properly and the cylinder is glazed...