3.0 cylinder question

[outsider347]

My car is 79 911 3.0
engine all apart

How can I find out if I have Nikisil or Alusils cyl

[ed mayo]

Nikasil will have a somewhat shiney finish and some trace of hone marks, alusil has no hone marks and is a dull gray finish. Also only Kolbenschmidt made alusil, look for their 'KS' logo in the casting.

[outsider347]

Tks Ed
Mahle is cast on the side, so safe to assume that mine are nikasil?

[Flat6pac]

Yes. You will have 11 cooling fins.
Bruce

[Mark Henry]

If you put a magnet to nikasil you get a very slight... and I mean slight magnetic pull.
Alusil nothing, nada.

[outsider347]

Thanks Gents for your quick responses
Yep.. 11 fins, & slight mag pull

Couple more questions if I may.
79 911, 3.0 69k miles, disassembly because of broken studs

Had cylinder's checked & honed by "Porsche machinist" Said that everything checked out...more on this below.

I went to check new rings for gap....017" (I converted from mm to inch) no taper
Checking Wayne's book for correct ring gap spec .0059-.011
Oh-OOO!
1. maybe the new Gotzee rings are bad
2. Cylinders..... hope not

This is a stock build , no intention to track the car

Your suggestions appreciated

[Eagledriver]

Yup, new rings suck. I ended up using old rings last time I redid my Mahle set.

-Andy

[Ollies930]

Do not have my 911 bible in front of me, but .004"-.005" per inch of bore is usually the minimum spec for most piston rings. That may be a misprint in Wayne's book or he is specifying per in bore. At 95mm=3.74", multiplied by .004=.015" absolute minimum. Double check with someone else, but if you run your rings too tight, you will destroy the bores and the piston ring lands. When there is not enough room for the rings to expand, their ends but up against each other and start pushing outward against the bores. This creates a lot of drag and pushes too hard against the bores and while the rings are dragging in the bores, the pistons have a hard time pushing them up and down, which wears the ring lands.

[Ollies930]

I stand corrected! Just found factory spec for 95mm bore. New .008"-.016", worn out at .031". Must be that the aluminum cylinders are expected to grow enough to take up the slack so you can run them tighter than conventional wisdom dictates.

[motogman]

Not to far off track but.... Is there a difference in ring gap for Alusil bores vrs Nikasil?

I suspect the early cast iron were quite different.

[mikedsilva]

Originally Posted by outsider347

Thanks Gents for your quick responses
Yep.. 11 fins, & slight mag pull

Couple more questions if I may.
79 911, 3.0 69k miles, disassembly because of broken studs

Had cylinder's checked & honed by "Porsche machinist" Said that everything checked out...more on this below.

I went to check new rings for gap....017" (I converted from mm to inch) no taper
Checking Wayne's book for correct ring gap spec .0059-.011
Oh-OOO!
1. maybe the new Gotzee rings are bad
2. Cylinders..... hope not

This is a stock build , no intention to track the car

Your suggestions appreciated

My understanding is that the spec of 6 - 11 thou would be for a perfect 95mm cylinder..
But we/you are putting new rings into a used/worn cylinder.. still within spec, but worn. Instead of being 95.00mm diameter it might be 95.05 or 95.06 etc.. According to the book by Wayne Dempsey, the ring gaps should be between 0.15mm (6 thou) to 0.3mm (12 thou) but the limit is up to 0.8mm (about 31 thou) I think if your gaps are somewhere around 17 thou you are fine.
As others have said, too small a gap is much worse than too big a gap. (ask me how I know)