Help ID P's & C's - new tear down

[Dan Morton]

I recently purchased a '68 911 which was running very rough and had lots of oil leaks. I just tore it down and was surprised to find 90mm mahle cylinders with what I believe are Mahle pistons but need help ID'ing them.

The engine had all head studs very loose and one broken head ring. Compression test after torquing the heads resulted in 200 with 5 of the cyl's and 175 with the cyl with the broken ring. The cylinders had a small spacer and there has been work down the case to allow for the larger pistons (ground down around where the piston skirts could hit the case).

The engine is in very nice shape fortunately. It has the original heads though. Seems as though the valve sizes would not be optimal for a 90mm setup.

Thoughts?

[tom1394racing]

These appear to be high compression MFI/Carb pistons. I'd guess there are the 10.5 RS style piston.

If these are Mahle, there will be a part number forged into the bottom of the dome that will tell us exactly what pistons these are.

The number will be hard to read but should be something like "90PXX".

[kenikh]

Tom, you'd know better than I, but at first blush, they looked like 9.5:1 to me.

[jpnovak]

I bet that would be a fun motor in a SWB car. Is it a 2.5 or 2.7?

They look like the higher compression pistons to me. The area of the valve pocket is quite large indicating a higher compression.

[Dan Morton]

not sure what the configuration is. It's the original 2.0 engine case with these unknown P's&C's.

Tom, the only number I can see forged inside the pistons are "4/50/5" The number is not on the dome itself but just off-center and is forged into it.
Also, in looking at the top of the piston where it has the 102 and the letter "M" and 026 - does this indicate Mahle? It seems to match the M used in the Mahle logo...??

The cam numbers are 901.105.139.0R
Heads 901.104.303.1R
Conn Rods 901.103.101.0R
Bearings - 901.132.00, 916.137.00, 901.131.00

Any thoughts on these numbers?

Jamie, how is Austin these days? If I remember correctly we had the twin targas. I'm now in Houston.

-Dan

[Dan Morton]

Found this on the Mahle site


"Identification Marks

These markings guarantee Quality MAHLE Pistons (on top of piston):

* Maker's quality sign
* Piston diameter in mm
Measured across the greatest skirt diameter (at the bottom of the skirt, perpendicular to the pin axis). On small pistons, mostly, only the measurement group and the nominal diameter are marked. Further information concerning the diameter as well as the fitting clearance are quoted on the package.
* Standard or oversize dimensions in inches
On pistons for engines with cylinder dimensions in inches: "Std." or for example, ".020" for oversizes, in addition to the greatest piston diameter.
* Fitting clearance in mm
Equivalent to the difference in diameter between the cylinder bore and the piston skirt at a temperature of 20'C (68'F).
* Installation direction
The direction of installation in the form of a crankshaft flywheel symbol or an arrow showing the direction with respect to the control side of the engine. The marking "vorn", "Front" or "Abluft" (exhaust air) or a cast-in notch also indicates the installation direction, which must be considered not only because of an asymmetrical crown shape but also on account of the offsetting of the gudgeon hole for noise reasons.
* Additional markings if necessary, e.g. A = Exhaust, E = Intake, 1 = Cylinder 1, Z 2/3 = Cylinders 2 and 3."

Notice the small marking in the pic looks like the top marking on my pistons