There is a ring about 1 to 1.5 mm around most of the outer circumference of the piston that is a different color from the rest of the piston crown. There is a corresponding ring on the head gasket surface that also shows about a 1 to 1.5mm ring that may be due to very light contact being made with the piston. This ring is not due to temperature but some type of mechanical contact.
Piston crown color is due to variation in piston crown temperature. Take your calipers and measure the outside diameter of the squish band where it intersects the head gasket surface. Now measure the inside diameter of this thin ring on the top of the piston and see if they have the same dimension.
The piston looks like it is hitting something. It may be the head gasket hanging out into the bore or the piston is hitting the head.
You may be experiencing multiple problems.
1. Wrong head gasket, one that was not made for a big bore.r
2. Head gasket rivets in the wrong place
3. A head not machined for a big bore.
4. A very loose rod and or main bearings.
# 4 is not likely because a lower end that loose would be spewing bearing fragments and your piston crown does not show any evidence of this problem.
Jerry I saw that little 2mm lighter color ring around the edge of the piston. It couldn't have hit that gasket, since the gasket was 69mm, the same as the bore. The ring on the head and gasket are from the pressed "V" ring in that gasket I think. You are right though about the head chamber not opened up for 69mm bore, though. When I measured it, I think it was at about 67mm where the chamber stops and the sealing surface starts. But that seems like it would only overlap the bore about 1 mm. That is how this top end was run when I got it (I know that doesn't make it right though). I don't think the piston could hit the ridge on the head, considering the piston edge is well below the deck at TDC, and add to that a 1.6mm head gasket. I don't know though, I seem to have issues with this stuff I don't expect all the time.
So, this whole top end is drving me crazy. I don't like the thought of the piston hitting anything. So, help me out here guys:
1. Is there a shop I could send my other head into, that would true it, cut it for 69mm, and adjust the dome/squish for about 95 octane, and maybe cut it for o-rings?
a. I am a little apprehensive about o-rings on this cylinder, due to the way the sleeve fits...I would expect coolant to seep up through head bolts with out a gasket sealing around each water passage.
2. If I use a gasket, I am running out of options for this 69mm bore......I tried two of the cometic/wiesco fiber ones with the metal ring, and both leaked coolant a little with this cylinder.
3. I could find a place like dem3500 suggested, to send in my other top end, for boring, truing, head cutting, etc., but then I am also buying another piston, and will be up in the hundreds of dollars.
4. Man, if I had $640 I would just buy an ESR 310 kit and be done with it. Are there any other lower priced bolt on top halfs out there?
*sigh* Now I don't even want to ride it, and risk bottom end damage, for fear of it not being right.
