What Type of Cylinders does a 911SC / 1983 USA

[porschedude996]

Hello, did Porsche use multiple types of cylinders for SC's?

[Trackrash]

Yes. either Mahles which are nikasil plated, or by Kolbenschmidt (KS) which are unplated Alusil. Mahles have 11 fins, and Alusils 10 fins.

[porschedude996]

Ok, I know i’m opening an old can of worms. I checked and mine are 10 fin. So that makes them Aulsil. There is no ring ridge and the bore surface has a strange almost clear anodized look to it. Not what i’ve ever seen. I see posts that say don’t even take the pistons out of the cylinder, to they can be reringed. Unfortunately I did not perform a leak down test, nor a compression test. I could do a top of the bore and a bottom of the bore leak down test on one bank since the rockers are removed. That would give me a general idea of the next steps. in addition I have cover plates on the ports, so I would be testing the rings only.

A penny for your thoughts.

[porschedude996]

I just performed a leak down test on one bank and they were 82/100, 90/100, 85/100 with the pistons at the bottom of the stroke. I then did the test at the top of the stroke and came up with the same. I did hear leakage around the spring seats. I have sealed cover plates on the heads and the leakage was on the intakes. Sounds like the valves are not sealing properly. With a cylinder head rebuild the numbers should come up dramatically.

[safe]

Originally Posted by porschedude996

Ok, I know i’m opening an old can of worms. I checked and mine are 10 fin. So that makes them Aulsil. There is no ring ridge and the bore surface has a strange almost clear anodized look to it. Not what i’ve ever seen. I see posts that say don’t even take the pistons out of the cylinder, to they can be reringed. Unfortunately I did not perform a leak down test, nor a compression test. I could do a top of the bore and a bottom of the bore leak down test on one bank since the rockers are removed. That would give me a general idea of the next steps. in addition I have cover plates on the ports, so I would be testing the rings only.

A penny for your thoughts.

the best test is with a magnet since the nicasil is slightly magnetic and alusil is not.

[safe]

Originally Posted by porschedude996

I just performed a leak down test on one bank and they were 82/100, 90/100, 85/100 with the pistons at the bottom of the stroke. I then did the test at the top of the stroke and came up with the same. I did hear leakage around the spring seats. I have sealed cover plates on the heads and the leakage was on the intakes. Sounds like the valves are not sealing properly. With a cylinder head rebuild the numbers should come up dramatically.

Are you sure you were at tdc for each cylinder?

[Jeff Alton]

Sounds like BDC....

[porschedude996]

Originally Posted by safe

Are you sure you were at tdc for each cylinder?

Ah, bottom of the stroke would be BDC. I tested both top and bottom.

[safe]

Originally Posted by porschedude996

Ah, bottom of the stroke would be BDC. I tested both top and bottom.

You need to be at TDC top of the stroke on compression, otherwise the valves are open...

[porschedude996]

Originally Posted by safe

You need to be at TDC top of the stroke on compression, otherwise the valves are open...

Thank you for that, but I know that the valves would be open if the engine was fully assembled. At the point of my writing my question here, I was already committed to a full disassembly but wanted the data point.

I had my cams out and cam towers removed. All the valves were closed. I first performed the test at bottom of stroke (BDC) because I didn’t have the front pulley on to control the movement of the crankshaft when air was applied during the test. After that I installed the pulley to control the crankshaft from spinning. I did re-perform the test at TDC. I thought it might be a good comparison to see the difference across both ends of the cylinder. Maybe see some ring gap closure, thus diminishing the leak-down losses. Maybe account for differences because of bore taper.

In another post I was talking about the conditions found in my engine and the tests performed. Some of it bled here. My question here was only to find out about 1983 911SC Cylinder types.