Rering or salvage?

[James Renfroe]

Wayne,

I from every Alusil description I read, It is stated that the Alusil pistons are iron plated and that is the combination that works with the Alusil cylinder bores. After examining many KS pistons, I know this to be the case. This is not the case with Mahle pistons which are not plated, as far as I can tell. If this is correct, how does Mahle run aluminum on aluminum without suffering from the typical accelerated alum on alum wear?

Thanks!

[Superman]

Read the "Re-Ringing Alusils" thread on this Engine Rebuild Forum before you do this. I re-ringed mine, no problem. They were washed within an inch of their lives. All the glaze was gone. Their finish was a dull grey. I used a teensy bit of motor oil on the cylinder wall, just the tiniest bit. I used 30w non-detergent oil for break-in. And I spanked it hard right from the start. At startup, the timing light was hooked up, etc. fire, quick tune, and DRIVE (decel/accel/decel/accel/decel, etc).

[911pcars]

"....how does Mahle run aluminum on aluminum without suffering from the typical accelerated alum on alum wear?"

James,
Not an engineer so I can't give you the full metallurgical explanations, but Nikasil is a metal coating that's applied to the aluminum cylinders during manufacture, so that is the wear surface. Ideally, there's a thin film of lubricating oil separating the metal-to-metal contact surfaces. Thus the only significant friction should be between the piston rings and the cylinder wall.

Sherwood

[Wayne 962]

Originally posted by 911pcars
James,
Not an engineer so I can't give you the full metallurgical explanations, but Nikasil is a metal coating that's applied to the aluminum cylinders during manufacture, so that is the wear surface. Ideally, there's a thin film of lubricating oil separating the metal-to-metal contact surfaces. Thus the only significant friction should be between the piston rings and the cylinder wall.

Sherwood

True, but Alusil's are slightly different. I don't know enough about the manufacturing process to give out too much info here. The basic principle is that Nikasil is a hard cylinder wall with a soft piston, and Alusil is a softer cylinder wall with a harder piston.

I'm not sure how Mahle made their Alusil pistons - it's a good question...

-Wayne

[911pcars]

The Alusil process, still used in current p-cars, bimmers and mbents btw, uses a high percentage of silicon in the aluminum mix. During manufacturing, an acidic solution etches away aluminum and exposes hard silica; this is the long-wearing surface. The iron coating on the matching pistons acts as a buffer to prevent scoring the aluminum piston. Remember, everything is covered in lube oil.

Thus, I think the equation might go like this; Nikasil is a hard cylinder wall with a soft piston and Alusil is a harder cylinder wall with a softer piston.

Sherwood

[Rondinone]

I'm with 911pcars on this one. I know it's common, but in my opinion the hard/soft analogy is not quite correct. Both nikasil and alusil are based on hard particles in or on the cylinder wall. In the case of alusil, the particles are pure silicon dispersed throughout the aluminum casting. For nikasil, the particles are silicon carbide and they are bound to the aluminum surface with electroplated nickel. The hardness for both silicon and silicon carbide is much higher than the metal rings, which is one reason both types of cylinder last so long.

I like Alusil because it's elegant from a manufacturing perspective. Elemental silicon is soluble in molten aluminum. The melt is injected into a cast and cooled. The particles don't nucleate until the casting cools sufficiently to decrease the solubility of the silicon, which causes the particles to crash out in the casting. It's like metallic rock candy.

Honda also uses an adaptation of alusil that's licenced from KS.

[James Renfroe]

An interesting observation that I have made on the Mahle alusil cylinders is that I have yet to find a cylinder that has warn a detectable ring grove in any of these Mahle cylinders! of the 20 or so that I have take a close look at. Conversly, 2 out of three of the KS cylinders I have looked at have a noticable ring grove at the top of the cylinder. This may have to do with the hard iron plated pistons they use. Another observation that I have noted with the Mahle Alusil cylinders, is that there also seems to be a visible build up ring matterial buildup on these Mahle which is much less visible on the KS cylinders.

This leads me to believe that somehow Mahle has figured our a way to make there Alusil cylinders very hard. My guess is that Mahle users a special allow in their Alusil pistons that makes them resistance to the embedded silicon in there cylinders.

Based on my sizeable inventory of both Mahle Nikasil and Alusil p/c sets, Mahle produced many more Alusil p/c sets than is claimed in the recent Porsche literature.

Mahle representatives insist that if it is Mahle, it is Nikasil. this is simply not true because I have many examples of the Mahle Alusil sets with are Totally non-magnetic! I also have some Nikasil cylinder that a totally warn out but still magnet at the cylinder base.

So what is Mahle aluminum to aluminum secret?

[KobaltBlau]

I noticed that kstylianos' cylinder wall pictures in this thread were not showing up, so I found their correct links:

Alusil:


Nikasil:


Be careful though, Shuie recently posted pictures of (uncleaned) Nikasil that showed a cylinder wall that was quite gray. If you have your cylinders out, just do the magnet test. a plain flexible refrigerator magnet will cling quite lightly to nikasil, a stronger magnet might be more helpful.