Bought a USB endoscope/boroscope to check my piston tops for carbon buildup.
Instead I found marks on my rear piston and cylinder wall. The piston mark looks like the valve is hitting, in the first picture. The second pic the cylinder wall has a similar shape mark. The front cylinder & piston have no marks. It's hard to tell which way the camera is pointing.
So I'm wondering if a ring broke, or somehow the cylinder wall failed.
I did a 95" build about 9k miles ago bike runs ok. Has run hotter then when it was a 88" especially the rear cylinder, which is normal. The mpg is low, 26-28 mpg average. Did a compression check recently, 200 psi CCP.

 

Another picture showing both marks clearer.



Might be reflection

 

Looks like you didn't have enough valve to piston clearance. The relief should of been laid back some.

 

Are you sure your timing is on? That mileage is awful, and if it is a clearance issue and only in one cylinder, then that's where I'd start.

 

You may be correct. I have a S&S VFI system on my bike. I constantly have to do a front and rear fuel map merge. Getting a rear cylinder map maxed out code.
I had shop press the cams in the plate, I thought I had lined up the primary cam (front) chain timing marks correctly.

 

Think you should pull that rear head for a closer inspection and check your cam installation.

 

I'm planning to do that, making a parts list. I'll post when I tear it down.

 

Larger valve in conjuction with a re-surfaced head can do that, along with a large(r) TDC lift cam.
Play-Doh is what we use here to check the clearence to insure that does not occur prior to full assembly.
Scott

 

I'll do that, I had asked the machinist and a local indy about claying the pistons. I was told that with .510 lift cam's and flat top pistions that there would be no clearance issues. What I can't figure is why the front piston didn't have signs of interference. I do have larger intake valves, .030 head gaskets.
I have partially tore down the motor. Cam's timing marks were lined up, adjustable pushrod were same length, by eyeball measurement.
I'll have the heads cleaned up, and checked at a shop. See if the valves are damaged. Check springs. Have them check for bent pushrods.
Can I use the same pistons with larger valve relief cuts? New rings, and hone the cylinders. Could a stuck lifter cause an interference problem?

 

A few more
Front piston





Rear piston