I guess I should be more clear about my plan. I will polish the top 1/3 with the 3M polish and felt pads, in an attempt to replicate the process described by Sunnen. I'm doing this for two reasons: 1) the polish (either 3M or AN-30) and felt are available to everybody, and 2) it's much like honing a cylinder with stones, so everybody here should be able to do it. The middle 1/3 will remain untouched so I can get a handle on the morphology of the worn surface. The bottom 1/3 is the original factory finish because it's below the rings, so that's what we'll shoot for in the polishing step. Once the cylinder is polished, I'll cut up the cylinder so I can get it into my instrumentation. After I've examined the worn surface (middle 1/3), I'll send some of those pieces out to be cleaned and clean some others at home. If you guys have any other suggestions, let me know.

Furthermore, snowman will hone another cylinder with his silicon carbide grape hone and then send it to me.

Jack,

Do you need me to send another cylinder from this set to you?

Rondinone et al,
Great work! Although my deal for the used set of Alusils has stalled a bit, I'm still very intrigued with the progress. Rondinone, I think the 3M paste is a good alternative, being that it is readily available and presumabaly cheaper...why break the bank now? :-) I too was really encouraged about the industry standard for the surface of the bores and the very real possiblility of reconditioning a set of cylinders by merely re-establishing the surface within a comfortbale tolerance. Can't WAIT for the results. Who knows, this thread may come up in the next edition of BA's book (or Wayne's for that matter) taking a whle different position on re-using Alusils due to the great work done...

R/
Dustin

Rondinone, is it possible once you cut it up that you could send samples to William so that he can use his machine to compare cyls with the different mileage? William could you do the same? I believe the one William is using has 88K and the one you have Rondinone is 222K. I'd also be interested in knowing how the untouched finish below the ring wear surface compares. Theoretically they should be very close but it might be interesting to check. (variation in the original finishes could give us some idea of go/no go parameters) This way we would have data from two independent sources on the same samples.
Jack, do you know what knd of material the cylinder in the pics is? Thanks.

I also like the idea of trying to do it with readily avalible materials.
Remember, last summer I cleaned/polished mine with the scotch brite pad sandwiched between stones on an off the shelf 3 arm hone and the cylinder wall. It that time everything was a no-no. But I knew I had to try something for the rings to bite on.
What's the hardness of the material they use in the scotch brites anyway? It would be a hoot if it turned out to be simular.
Anyway anh911, Those P&C's are in my car that I have driven almost daily since the rebuild. Now about 3,000 miles ago.

If you want to send me something to test, I'm sure my freind Doug would be happy to do it. He may be lurking here anyway. I'm also trying to grow the audience.

Ok, so I guess that means you won't take one out and cut it up? ;)

Nope!

Is Charles still checking in? Charles, in your experience with refinishing niks how large have you successfully bored a 95mm cyl?

You guys are certifiably neurotic. Any competent pshchiatrist could probably diagnose your problem from this thread.

I love it and will check your findings regularly.

BTW, my used alusils have about 50K miles now since the rebuild and I actually do not ever need to check my oil (but I do, of course). They have about 235K miles altogether. Pretty hard working devices, considering the world regards them as useless, disappointing throwaway cylinders.

Amen, http://www.pelicanparts.com/support/smileys/pray.gif

I think the official term is alusilliosis...

Once I've had my look, I'd be happy to send the cylinder pieces out.

I just had a look through some of the scotch brite msds sheets (companies are required by law to reveal ingredients in their material safety data sheet (MSDS) so if you ever want to know the ingredients to a chemical product just look up the msds.). Some of those pads contain aluminum oxide, some contain plastic beads. Do you remember what type of scotch brite pad you used? It's possible it was abrasive enough to do the job. Certain aluminum oxides are very hard (corundum is one).

We're not neurotic, just cheap. I just bought the 3M polish and will get to work Saturday. I'll probably get a first look with the SEM on Monday.

Basic rule of thumb I like to stick by, as far as overboring cylinders, that the maximum that i'm comfortable doing is such that you are left with >= 1.5mm thick skirts. Some might say that's too thin, but as long as you're not doing anything too radical, or even a turbo, you're fine. We've had customers go as far as having 1mm thick skirts-- scary stuff, get the cylinders cryo'ed first. I would never try doing this with a stock cylinder, as the casting alloy mahle used had a yield strength of 36-42k psi, where our alloy we CNC specs out at 55-59k psi, and we do quality control checks with every batch from Alcoa. Having a better aluminum goes a long way.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

If that 3M polish is a white paste, it is aluminum oxide. If so it is almost as hard as diamond and will even polish carbide tools. Only a diamond tool can be used to machine a solid piece of aluminum oxide, a very common substrate material for microwave thick and thin film circuits. Its also the material used in the vane type Air flow meters for the circuit board which contains the potentiometer. This type of circuit board is called a thick film board. Thick film refers to the thickness of the film depostited on the circuit board. A thin film is relatively thin and is usually etched off to produce a circuit as opposed to depositing a film to produce a circuit. In any case the alumina substrate is VERY stable at extreem temperatures, and immune to almost any sort of chemical attack, extreemly stable mechanically, in other words an almost ideal media to attach a circuit to that won't change under exteem conditions.

In its paste form, alumina oxide is almost a perfact sandpaper material. It is harder than most anything else, it is inert, it is non conductive. Thats about all I know about it. Except that the dielectirc constant is about 9.8 to 10.25 and the loss tangent is 0.001 and the coeffecient of expansion is about 6.5ppm per deg C about the same as Kovar,, and the change in dielectiic constant is about -90ppm per degree C. PS if you use my numbers for anything please double check them as they are off the top of my head and I have not used them in over 6 years.

Yes, see private e mail for address.:)

I just talked to my bro-in law and (without having a piston to confirm) he believes the ferrous coating is done with the anodizing process. He gave me the name of a shop to call monday and confirm, but thinks it's not a problem to apply to any pistons. Some considerations of the finished dimensions are necessary due to the thickness applied but it's doable. :D

I posted a WTB ad in the classifieds to try and find a spare set of cyls to bore out and use on my '89.

I'll send it out on Monday. Look for it around Thursday.

I called the US KS rep this afternoon and she is going to forward some questions to the field engineer in Germany but I need the OEM Porsche part number for the Alusils... Anyone have it or can look it up?

Nevermind I got it, Thanks

OK, here are some results.

First I set up a polisher using the Turtlewax cloth and a regular engine hone. The fabric was folded over and stapled in place in such a way as to allow the stone to flex as usual:

http://forums.pelicanparts.com/uploa...1074555812.jpg

Here's the polish also:

http://forums.pelicanparts.com/uploa...1074555843.jpg

I masked off the lower 2/3 of the cylinder:

http://forums.pelicanparts.com/uploa...1074555880.jpg

I polished the cylinder at about 100-150 rpm, one stroke per second or so. After 2 minutes there was significant metal on the hone:

http://forums.pelicanparts.com/uploa...1074555940.jpg

I wiped the cylinder clean, and examined it, and then decided to polish it for another 3 minutes. The cloths were considerable more dark afterward.

Then I cleaned the cylinder, wrapped it up in duct tape and stuffed a rag into it. I broke it up with a sledge hammer. Then it was time for SEM!

This is the factory finish at about 1000x:

http://forums.pelicanparts.com/uploa...1074556357.jpg

Sorry for the blur, the instrument was off and still wasn't completely warmed up. The islands are silicon particles (identified by elemental analysis). The relief is evident. According to my profilometer, the relief is a couple of microns.

Here is the worn area of the cylinder:

http://forums.pelicanparts.com/uploa...1074556536.jpg

That scratch is 20 microns across, and is easily visible to the eye.

Note how each particle has an area of wear underneath it. I'm not sure how to explain that. Here's a zoom:

http://forums.pelicanparts.com/uploa...1074556723.jpg

Those real bright objects are pieces of ring imbedded in the cylinder wall. The darker circular objects are pieces of silicon.

Here's another area:


http://forums.pelicanparts.com/uploa...1074556865.jpg

The dark island at the top left is a worn silicon particle. The mud-crack area in the center is aluminum. The debris to the right of that is a mix of silicon and ring material.