2.4 with 5R and 7R cases

[mydmolly]

I was just looking over a 911 and noticed the cases on the motor are different. One side a 5R and the other 7R. Is this a common thing to see? The story is the motor was rebuilt and Balanced/Blueprinted.

Any comments on this . . . doesn't look right to my untrained eye.

Tom

[RTincher]

There was an earlier thread on this around December 2005...the consensus was that Porsche would occassionally mix case halves when they were upgrading case designs in order to use up the existing stock. So you could find a 3R/4R engine, a 4R/5R, or a 5R/7R (there was no 6R).

The original case on my 12/72 build date 1973E is a 7R/7R, and it has not been apart. I have not been able to confirm definitively when Porsche stopped using the 5R cases - most people think it was in the early spring of '73.

What is the build date on the car (on the driver's door jamb sticker?

[mydmolly]

My build dat is 12/72. Was there any major difference between the 5R/7R cases? I'm guessing they were certainly compatible . . . of course matching cases would be "best" but does it really matter?

Thanks for the reply . . .

Tom

[RTincher]

The 7R cases are much preferred due to additional reinforcement webbing that reduces the case flexing and resultant oil leaks and internal wear. However, for a relatively unstressed engine (moderate RPM, moderate compression, less than 210 operating oil temps) it shouldn't make that much difference.

[kenikh]

I have seen some 1R/2R case combos, so the 5R/7R mating doesn't seem too odd.

[Steve@Rennsport]

I've never seen a 5R/7R from the factory.

Every 2.4 I've looked at over the past 30 years has been either a 4R/5R or 7R (both sides) case.

Just for grins, I would carefully inspect the case # and the type # as those are stamped on each side of the case, respectively, to see if the numbers jive with each other. That will validate whether these were matched at Porsche or during a subsequent repair.

[fryardds]

Steve,

When my RS case returned from C.E. (machine shop) the mechanic showed me a stamped 2 digit # on each case halve that match to confirm the case halves match. This was different than the type # and I seem to remember they are stamped on the bottom of the case along the seam. Is that correct?

[Steve@Rennsport]

Hi Brian:

Hmmm,..I'm going to go have a look,..

[berettafan]

OT but what did the 3R cases hold? i was told early 2.4?

[RTincher]

I defer to Steve's experienced opinion here....