New Variation on Old Question

[Halm]

General topic is "What do I have, Nikasil or Alusil?" After doing some research, it seems the best test discussed is to use a magnet on the inner surface. If it shows magnetic properties, it's Nikasil.

What about checking the piston top with a bore scope? It seems to me that if the piston has a deep relief pockets for the valves, then the cylinders are Nikasil. If the piston is low domed with shallow pockets, then designed for CIS and probably Alusil.

Or were there enough 2.7 / 3.0 CIS cars made with Nikasils that this doesn't work?

[KobaltBlau]

Nikasil and Alusil 3.0s have basically the same shape piston dome. The finish is a little different on the cylinder and the piston, but you are not likely to see that on the piston due to carbon. I'm not sure if your bore scope image would be good enough to see the difference in the cylinder finish.

Hopefully you found these relevant threads on external identification, but here they are just in case:

nikasils used in 3.2 L engines?
11 fins means mahle?

There are also pictures in previous threads of nikasil and alusil cylinder walls to look at.

[KobaltBlau]

but I'm low on battery so you'll have to find them!

[Halm]

LOL Thanks Andy. What I am trying to determine is is I have RS p&c or a CIS set. That is why I was thinking of have a wrench I know take a look with a bore scope. I would think / hope the crown difference would be great enough that he could tell without tearing the engine down.

[KobaltBlau]

on a wired computer now...

Ah, OK Hal. The usual situation people are in is that they have a 3.0 or 3.2 with the CIS or DME pistons and want to know if they have nikasil cylinders.

This is not the situation you are in. I think it should be possible to tell the difference between 2.7RS pistons and 2.7CIS pistons with a bore scope. your biggest problem would be carbon build-up on the top of the pistons making it hard to see features like valve pockets. Maybe run some berryman chemtool/techron/equivalent through the engine first. Be sure you have good photos of 2.7RS and 2.7CIS pistons to compare to when you do it.

What induction does your engine have? Do you know what cams it has? If it has CIS induction it would be surprising if it had RS pistons. If it has Webers, who knows. Cams could say a lot too but only if you know what you have.

[Halm]

Andy, you nailed it. . . Webers! Great idea on the Berryman or something to help with the carbon. I'll post results in a week or so after I get it examined with a bore scope.

[KobaltBlau]

cool, definitely let us know! you don't know the cams?

[911pcars]

I don't have pics to illustrate, but Mahle RS pistons have a mild dome and valve pockets as opposed to CIS pistons which have an accentuated "wave-shaped" dome off to one side of the piston crown. You can't confuse the two even with carbon encrustment.

Sherwood

[Halm]

Cams are one of the "still to be determined" issues.

[Halm]

Thanks for the update, Sherwood.

[KobaltBlau]

well, carbon encrustment can be pretty bad, and he's going to be looking at a less than ideal image! anyway running a de-carbonizer through the engine doesn't have many disadvantages.

[Bill Verburg]

I don't have pics to illustrate, but Mahle RS pistons have a mild dome and valve pockets

here's a pic of a 2.7RS piston

Don't have one of the funky cis pistons

[Halm]

Thanks Bill. All help on this is very much welcome.

[KobaltBlau]

here's a picture of a 2.7 CIS piston I found on this board. Not shot from the perfect angle, but you get the idea. I didn't realize the asymmetrical dome was this extreme, it's more than a 3.0 piston I think:



I bet these are what you'll find in there but I hope for your sake that you see what you see in Bill's photo.

[geof33]

Andy,

Are you sure those are CIS pistons? One of the issues with CIS is the valve lift. The dome appears to be WAY too aggressive for a CIS piston. Normally, a CIS piston is very shallow. This piston could "work" with CIS, but I would question wether it was designed for CIS...

[KobaltBlau]

yes, I am absolutely sure that is a CIS piston. The dome is a very specific swirl-inducing design, see there is still crappy valve clearance because that dome isn't in the middle, and there is no relief in it. 3L CIS pistons are shallower than that one, but I do believe that is a 2.7 CIS piston. Here's the old for sale thread the shot came from:

fs;2.7 nikasil cis 911s pistons/cylinders like new

[KobaltBlau]

here's a 2.4 CIS (CIS T) piston for reference:

[KobaltBlau]

And some 8.5:1 3.0 CIS pistons (look, they have a little flat spot for valve clearance:

[KobaltBlau]

Here are some 9.3:1 3.0 CIS pistons (look, they have a bigger flat spot for valve clearance):



And here are some pistons identified by Henry Schmidt as being 2.7 8.5:1 CIS pistons:





Now, I am quite sure that this (posted above) is a CIS piston:


however, the dome looks bigger than on the pistons identified by Henry as 2.7 8.5:1 CIS. I do not know whether 2.7 CIS pistons were made in different compression ratios. The original ad with this photo claimed they were 2.7 CIS pistons, but didn't state a CR.

[Tim Walsh]

That piston does look unusual, It's got the CIS swirl to it, but if you notice it doesn't have a full skirt on it. I think that's a sign of a forged piston instead of a cast one. (the only other pistons I've seen with the half skirt are JE's and 2.2S's , both are forged)