911SC Piston Advice

[TheClassicCurve]

Hi Guys

This place is a wealth of knowledge, I can't however, seem to find an answer for my problem...

I've had to drop the engine on my newly purchased 81 911SC project to replace the exhaust side 5 broken dilivar studs. (With the aid of Wayne's excellent book)

As I'm an idiot come weekend hobbyist I've managed to damage the bottom of two (yes two) pistons near the rods. They got caught on the case despite Wayne advising 'never use any force when turning your crankshaft....any resistance, investigate before applying force.' DOH!!

This was a budget fix, I was hoping to replace the studs with steel, replace the gaskets/hardware, give a thorough clean and button her back up. Will the pistons need replacing? Or will I get away with it as it isn't near the combustion area? How essential are these 'lips/fins' and what is their purpose? I've noticed that a lot of replacement pistons (for example here on pelican) don't have these 'fins' could I break the other sides and sand them even perhaps? Could they be welded back on?
The lips I'm talking about can be seen here protruding from the bottom of the piston circumference.


The majority of my funds went on the car, so this has put a big dampener on my project, as I was shocked enough to see the broken studs. I was promised it had had a top end.

The good news is I've managed to remove the studs with a torch, PB Blaster and a stud remover tool (bar one flush, waiting on drill bits) without any real dramas.

Any advice much appreciated

Thanks!!

[VFR750]

Contact Tom134racing.

He might have some replacement pistons.

The bottom of the portions of skirt are part of the piston that keeps it from tipping too much. Breaking of a portion may not be terrible, but it is not clear how much added motion will occur.

I would have thought that would be really hard to do. But I understand how it could happen in a moment of “enthusiasm”. Happens to everyone

Did you find the missing pieces?

The other concern is the remaining edge of the skirt could be sticking out a little and drag on the cylinder wall. That would be a mess on restart.

[Trackrash]

Used pistons should be readily available for this motor. In fact I have a set of the 78-79 pistons gathering dust. Too bad these won't work for you.

Please post a shot of your damaged piston AND a good shot of your cylinder. There are two types of P&C that were used that year.

[tom1394racing]

Looks like a KS 9.3 CR piston. I have replacements. PM me for details.

[Walt Fricke]

Used replacements ought not to be expensive. If you lived in Colorado I'd give you a whole set. I replaced the Ps and Cs with Mahle Nikasils some years ago. The cylinders got Nikasiled for a race motor. The KS pistons sit in a box, peacefully aging. I'm sure others have had the same experience, and didn't think it worth while to try to sell the used ones.

[TheClassicCurve]

Thanks Guys,

good to hear that there are plenty of these pistons floating about, I was convinced it would be an expensive fix. Will they simply slip in the place of the old ones or will they need machining? Sounds as though they definitely need replacing then.

I'll get a good shot of them later when I'm near the motor to confirm what type I have.

[TheClassicCurve]

Hi guys below is cylinder and (damaged) piston #2. Have I got KS pistons? Thanks

[jamesjedi]

See link:



Nikasil and Alusil

[tom1394racing]

Those are the 9.3 CR Mahle Nikasil pistons.

I can provide replacements.