1973 911E Pistons and Cylinders

[Steam Driver]

I have a friend who has a '73 911E 2.4 that needs some help. This car is being worked on by a local shop which is quite knowledgeable, but how to approach this has them stumped. The car was originally in the shop to have the MFI pump rebuilt, but this has since led to some other stuff; we all know how that goes. This car is, by the way, the one that has been featured in a recent video that has been in eBrake, among other places. Neat, R-gruppe car. Anyway, that's the back story; here are the issues:

Issue number one: Two of the barrels have noticeable problems. One appears to have had some trash in it at some time or other that scratched the barrel quite deeply. The other barrel seems to have a rash, or chicken pox, or something, where there are noticeable pits in the surface. If my memory serves me correctly I believe these cars had chrome-plated aluminum barrels did they not? So it may be the chrome plating coming off the aluminum. Obviously a lot of things are possible in an engine this age.

Porsche themselves want $850 per P/C set; that's an individual jug and piston, not a set of six. (That would be a great price for a set of six!) What are the alternatives? It seems to me that I have read/seen that there are places that replate these barrels back to stock. Suggestions/ recommendations about this would be appreciated.

Issue number two: (And this is really odd, to me and I've seen a few trashed pistons having been in the supercharging business.) The pistons all appear and mike to be great shape, EXCEPT for one anomaly. On the piston crown, directly under where the spark plug electrode would contact it if permitted to, is a depression in the crown. These depressions could almost be a machined relief for the plug electrode, but they are not identical, nor even symmetrical, like a machined, on-purpose relief would be. and in any case I've never seen a piston for anything with such a feature.

Could the piston coming very close to the plug electrode and some ignition or flame propagation phenomenon be going on that caused that? I wouldn't think it would be physical contact; such a thing would be obvious and at the very least close the plug gap to nothing and cause a miss, if not smash the plug outright. Either thing would prompt an engine shut-down and tear-down.

Any ideas where these little depressions came from? All six pistons exhibit the same thing to differing degrees.

Any help/information/advice on any of the above will be appreciated.

[DRACO A5OG]

Pics would have been nice :-(.

Try sending P&C's to EBS, ask for DON. If cylinders can be saved, he can do it. Again as far as the piston goes, hard to tell without seeing it.

Option would be to have the Cylinders bored out, plated and honed and get new CP Carillo Pistons.

I just did this to my 3.2 that is now a 3.4 $1200 plus shipping, that is for a complete set including piston Rings and Wrist Pins.

Tell your friend to break a leg

[Steam Driver]

Yes, pictures would be good, but I'm not located in the same place he and the car are. Thanks for your information; good lead.

[Jon B]

Originally Posted by Steam Driver

I have a friend who has a '73 911E 2.4 that needs some help...

Issue number one: Two of the barrels have noticeable problems...
If my memory serves me correctly I believe these cars had chrome-plated aluminum barrels did they not? So it may be the chrome plating coming off the aluminum.

No, they had Biral cylinders, which were cast iron cylinders with aluminum cooling fins. The bores were not plated or coated.
They can be replaced with two good, used cylinders of the same height and bore dimensions. Biral 84mm cylinders were used on engines from the 1970 to 1973 model years.

[Steam Driver]

Thank you for the additional information.

[florio]

Hi, I just recently had my 72 biral cylinders (same as yours) nikasil plated to recover from being oval and a bit over-spec in places (ca .1mm). The pistons were fine and could be re-used. If you send the cylinders and pistons together, they come back fitting great. Another idea (faster and potentially cheaper) would be call Henry Schmidt for a re-plated set off the shelf. I couldn't go that route as shipping to europe is prohibitive.

Good luck,

[cmcfaul]

Carefull changing displacment. The MFI will give you fits getting it calabrated.

The pistons do not sound like stock Molley pistons. You sure you have MFI and not CIS injection? your discription sounds like a CIS piston. There are tons of used parts available. Having the jugs Nicacell coated is a nice upgrade.

CM
73 E