chasing knock/ Think i found it.

[robztheman]

What is this? one piston looks like someone machined it (#6 piston) why would someone do this to #6 only? anyone have any ideas? see the piston skirt is damaged.

 

[Scott Atk]

If you're talking about the machining on the bottom side, that is part of the balancing process. The scuffing on the skirt.... well, that's an issue for sure.

 

[pajo]

balance

Underside looks like balancing allright but it appears the your piston to wall clearance is on a high side ..

 

[spoolie]

running lean...ive done that twice...except with a boosted honda...piston looked exact same.

 

[charlief1]

In the 4th pic it almost looks like you cracked the skirt. Look at the 5 oclock position. Not the best pics and my eyes aren't great but it does look like it cracked.

 

[Chuck Leeper]

Scored skirts:
1. Dirt. Wall not clean when engine was assembled?
2. Too tite in the bore.
3. Wrist pin locking up.
4. Insufficient lube.
5. Detonation.
A. Look for pinched rings.
B. Look for "nibbled" edges at the top of the piston.
C. Plug for that cylinder looks like? [Look at all 6]
6. Leaky inj washed the wall down.

 

[robztheman]

My turbo was leaking oil. I think the cylinder was washed out from the oil /turbo leaking. I found oil on top of the power plate during disassembly. I don't know why someone would balance only one piston.All cylinder bores look ok there are some very miner marks on #6 wall(no groves).I have been chasing a slight knock since i bought my car a little over a year ago. I couldent find anything wrong plenty of fuel so it was not detonation.It was never a audible knock just a warning from caspers and scanmaster.As soon as it became Audible a week or so ago i started my tear down.I believe my turbo has been leaking for a long time maybe sense i bought my car.

Please give me some recomendations for my rebuild.
sorry I know my post is not easy reading.

 

[Chuck Leeper]

"My turbo was leaking oil. I think the cylinder was washed out from the oil /turbo leaking."
I doubt it was oil wash.. More likely that the oil, being poor in octane, created some knok.
What do the plugs look like?

"I found oil on top of the power plate during disassembly".
PCV problems?
Leaky turbo could have allowed this.

" I don't know why someone would balance only one piston".
Could be that the mfgr had done a "close match" of a set. Most aftermkt piston users have the complete engine balanced. That would likely have resulted in more machine evidence, on other pistons.
I'd start w/ a COMPLETE measurement of all components. All the way from the bores to the ring gaps, to the brg clearances, to the piston dimensions.
I'd then consult w/ the piston mfgr and see what they recommend.

 

[robztheman]

The rods are definitely balanced. Other than#6 the pistons have no material removed so i would say no balancing was done to them.There might have been a problem with #6 in the past and only it was replaced it might have been balanced by itself.All bearings looked ok but had more wear on them than i think a 8,000 mile motor should have especially seeing as i use full synthetic mobil one oil With oil changes every 6 to 8 weeks or so.I only put 3,000 miles on car in 14 months.
I am thinking that the balancing on #6 might be a problem.

 

[robztheman]

all plugs looked ok #6 had oil deposits.
I did replace the pvc valve thinking this might have been the problem.