Piston problems - JE?

[vichang4]

87 911 turbo - 50,000 miles
Over-boost caused broken top ring on pistons 2, 3, & 6. While inspecting the pistons the oil rings on these three pistons were stuck inside the ring groves. I had to use a small screwdriver to pry the ring out. I tried to install an oil ring from one of the other cylinders, but it would not fit in the ring grove without significant force. All other dimensions were fine. The cylinders all check out OK.

Are these three pistons junk?
Can the ring grove be repaired?
Can I replace just the pistons?
Is JE pistons an option?

How can this ring grove colapse?

Victor Toce
87 930

[Steve@Rennsport]

Victor:

You are a victim of detonation and what you see is the results of that phenomenon. This is the root cause and you MUST fix this first.

Too much boost, insufficient octane, and lean mixtures all cause detonation and I'd need a lot more information about your motor and fuel to help you here.

Those pistons are certainly now throwaways and I'd guess that the others will show similar damage if inspected VERY carefully. JE's are OK in these applications but must be setup and fitted properly to work. Excessive deck height and head land clearance will also trigger detonation.

Bottom LIne: You should replace all 6 pistons, pins and rings.

[vichang4]

Steve,
The detonation was caused by a faultly wastegate diaphram. The boost ran up to 1.2 to 1.3 before the overboost protection switch kicked in. This was a slow failure so the boost gradually increased over time until I realized what was happening. The diaphram has been replaced.

Is it possible to replace all six pistons with Mahle?
or do I have to buy the piston/cylinder set.

I asked about JE because I know you can buy just the pistons.

[Steve@Rennsport]

Victor:

Mahle does not sell pistons separately, only in sets with cylinders.

IMHO, thats the best choice for street Turbos.