2.4 911S pistons

[Neil '67 911S]

I believe that the standard Mahle 2.4 911S piston is 84P11. I also believe that the first oversize is 84P11+. What is the ID for the second oversize?

Is there any significance to 84P11+ with a W2 underneath these numbers?

Thanks!

[tom1394racing]

Neil

I don't think "+" designation is for the oversize pistons. I have seen this designation on many standard size pistons.

The oversize pistons should be marked "KD 1" for first oversize and "KD 2" for second oversize

[Neil '67 911S]

Tom,

Thanks for the reply.

Tom F and I figured out that it was the second among the three sizes in the standard 84 mm group as shown in the little spec book. Standard 0 cylinder diameter is 84.00-84.91 mm diam; standard 1 is 84.01-84.02 mm (what I had) and standard 2 is 84.02-84.03 mm.

Cheers!

[tom1394racing]

Neil

I wonder if that is correct.

I think the size group was stamped on the piston crown after machining and gaging. The piston crowns have the 0, 1 and 2 markings stamped on the machined surface.

The "+" designation underneath the piston was put in during the forging or casting process before final machining.

I have wondered what the "+" marking actually does mean. I may be able to check your assumption regarding the relation of the "+" marking to the size group by looking through my piston collection.

[kllr901]

Take a look at this document, it should help explain the markings you see.

Ron

http://www.motorenteile.mahle.com:80...n_markings.pdf

[tom1394racing]

Here's an example

The pics show (3) Mahle 90L58+ pistons. These are 2.7 8.5 CR Nikasil pistons.

The crowns show the size group markings "0", "1" and "2" clearly stamped.

Note the 90L58+ forged markings are the same for all (3) pistons.

I would love to know what the "+" marking does mean.