Low compression on built motor tore up the cylinder walls

[Rotormike]

Just finish building my speed 6 engine a few months ago. Once the motor was broken in I proceeded to get it tuned. Everything was going well. Compression was 150 across the board. Changed the oil and it looked good as well. Right around 1000miles I noticed when starting the car cold I could hear it crank unevenly. I ran a comp test and it came out 1-168, 2-110, 3-135, 4-172. Car still seemed to run find but had lots of blow by. Just pulled the head and found this. Pistons look perfect but the cylinder wall are all screwed up, ive never seen this before. I have no idea what caused this. Any ideas?


Recently I noticed that

 

[L337TurboZ]

Yeah piston slap. Improperly measured, machined, and incorrect piston size.

Was everything measured before machining? With either a gauge or T gauges? Did you properly set ring gap? Piston installed in the correct orientation?

Not bashing you just trying to get all the information. That doesn't look good at all. Did you select lower compression pistons because 150 psi after initial setup seems low.

 

[Cfoldone]

This was a 88mm rebore, new pistons / rings / rods. Manley Pistons clearance is 0.003 mine measured at 0.0031. Ran 400 miles. Was a screw up by me with oil control rings. So pulled apart and deglazed and all new rings. Correctly sized oil control rings this time and returned normal. Compared to yours I see in your cylinders scratches on piston pin sides of bore ...
I find that unusual. That's normally only very long 100k+ wear. Piston rock on the rod pin ends means rocking like complete piston movement which would sound like very loose piston clearance.
Can you show us more pictures of pistons especially all around the sides? Bore is the hard metal surface, piston will leave more damage to look at.

 

[Rotormike]

It was indeed a 88mm over bore. Running new cpe mag 2 pistons and eagal rods. I will go grab some pictures. The damage being on the pin side caught me off gaurd too. Also both cylinder 2 and 3 have the damages in the same area.

Pictures of cylinder 3 piston

 

[L337TurboZ]

In the picture of the wrist pin bore for Cyl 3 piston, is that the circlip or oil residue? If it's the circlip then it looks jacked up and bent

 

[Cfoldone]

Seeing the lathe machining still on piston lands just below oil control ring @ pin ends of piston. Yep looks new. So I'm only guessing now....on tuner doing tune..a generally known person on here? Could a ton of knock cause this? The top of bore area where compression rings move into tdc that shows combustion blacking suggests large blow by or never seating. Now was a after effect? Or principal starting cause? The at rebuild start compression value (150) seems low. On my builds I see around 165-180. But then I mostly use only leak down tests, a better gauge of rings/bores/head gasket/valve faces health. May the forums knowledge base give answers.
I can say with buying gaskets and seals ..
BUY NOW... Apparently national parts stocks are still trying to catch up to demands

 

[Rotormike]

Freektune was the tuner. Also i always logged and monitored KR on the coob when doing pulls for tune logs. Time to tear it all apart and see about sleeving the block.

 

[L337TurboZ]

You haven't really answered some of the questions asked regarding measurements, the wrist pin clip etc.

 

[Rotormike]

The pictures of the wrist pin are showing oil residue and the pins a securely lock down with the c clips. Just finished putting a stock short block in while I sort this mess out.