MY1978 930 engine rebuilding in process

[hannu_911]

I’m currently rebuilding the engine for my 930. The car is MY 1978 Japanese version and the build date is late 1977. Engine is matching numbers to the car.

Currently the engine is in pieces and I’m cleaning and measuring the parts. I have a couple of questions related to the cylinders and pistons I’m hoping to find the answers.
This is what I have measured from the cylinders


I assume that all the cylinders are original to this engine. Top end has been rebuild once sometime in the past. I don’t know why but the evidence I saw when I disassembled the engine points towards chain or chain tensioner failure. I found a piece of broken plastic chain rail inside the engine. Engine had also the Carrera oil fed tensioners installed when I got it.

Mahle’s Maker’s quality sign is 705M117.

I’m pretty sure that the latter number is the date code. That would be 117 -> means November 1977. That matches with the manufacturing date of the engine. The Mahle quality code on the pistons is 114M107, meaning 107 -> October 1977.

Question 1: Does anyone have any idea about what is the number on top of the M?

All of the cylinders look identical with the following exceptions

Question 2a: I wonder what do these M, M. or L… mean? Keeping in mind that all of these have been made November 1977

Part numbers are identical with the exception of the last digit, it’s either 1 or 2. Probably just a versioning number, remembering this was still very early on the 3.3 engine production. This would mean that the switch from version W1 to W2 happened during November 1977.

Question 2b: Have anyone of you seen two different last digits on your engines? I mean that would Porsche had used two different cylinder versions in one engine?


Cylinder inspection
None of the cylinders have any deep scratches or anything that would feel on the fingernail. All look and feel like they have no wear.
But there is some porosity/pitting on cylinders two, three and four. The sizes of the biggest single holes are about 1mmx0.5mm.
I wonder if these have been there from the beginning or have they been caused by some bad maintenance during the life of the engine. Too long service intervals? or very long period with no use?
Cylinder 2: One are of concern at 12:30, 22mm from the top (1mm scale on the picture)

Cylinder 3: One are of concern at 10:00, 81mm from the top

Cylinder 4: One are of concern at 12:00, 34mm from the top and one other at 10:30, 25mm from the top.


Question 3: I wonder what actions should I take with these?
1) Reuse them as such. The holes are very small and they don’t currently cause any problems. But the worry is that if they would grow bigger.
2) Replace the three with used used cylinders/pistons.
3) Re-plate the three cylinder with Nikasil. Millennium Technologies would do re-plating but that would be costly option to ship them back and forth from Finland. Does anyone know if there is a company doing that in Europe?

From the Millenium-tech web page I found this spec for the porosity.


Measurement data shows that all of the cylinders are still within specs.
Ovality is also within specs, only point to note is that the middle cylinders 2 and 5 have the ovality in different direction that the others. Maybe the thermal load has caused this.
Question 4: Have anyone seen this before?

[Catorce]

I'd be shopping for new cylinders. It's a 930, there is no reason to skimp. At the very least send them to US Chrome or Millennium, have them re-nikasiled.