Well, the paste does contain silicon, but I think that it is there as an abrasive rather than a silicon source. I've been pondering what sort of silicon might be in that Sunnen AN-30. Most lapping pastes use silicon carbide, but that would be too abrasive and would chew up the imbedded silicon particles. Pure silicon abrasive would would match the hardness of the imbedded particles and would not wear the particles as much as it would remove aluminum. I'd love for some wrench to send me a small sample. I could analyze it and tell everyone what's there.

For those who are interested, a material that is well known and similar to alusil (which is proprietary) is Reynolds 390 aluminum.

Hello All,

As promised, here are the pertainant pages from the workshop manual.

Allow me to clarify a bit.

It was explained to me that there are crystals embedded in the cylinder itself. Additionally, the final application of the paste applies even more crystals into the aluminum surface. The ultimate goal is to have the rings wear on the crystals as a sliding steel surface on aluminum would tear it up very quickly.

If I can get a sample of the paste, I will send you some. :D

As an off topic side note, the Boxster uses LOKASIL cylinder liners - which are 75% air by volume.

**Legal disclaimer**
These pages are copyrighted by Dr. Ing. h.c. F Porsche AG and its affiliate Porsche Cars North America. I, the poster, attest that these pages were posted here strictly for educational purposes and I make no claim of ownership of the data contained in these pages.

Document extract Porsche Factory Repair Manual 944 MY 1983 - 1987 Volume 1 Engine, Repair Group 13.
**Legal Disclaimer finished**

(that should keep it nice and legal for all concerned, damn lawyers)

AFJuvat

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Just some general observation about some of the "old school" info in some more popular literature on 911 engines. Indeed the rings on bare aluminum would chew the cyls quickly which is exactly the reason for the embedded silicon particles...being MUCH harder than the rings. Some of the documentation I have read that basically excuses Alusil as disposable insist that it is a coating, and "softer" than the rings:

"The basic rule of thumb is that Alusil piston and cylinder sets have a soft-walled clylinder and a hard piston..."

I think it's crucial to understand that the rings are still actually being machined and bedded in by the extremely hard, exposed silicon particles, and not the other way around i.e. the cylinders are machined by the rings. Also, another point missed in some of the popular literature is that the iron coating on the piston was apllied to protect the piston! Another simple analogy makes me think of an Alusil cylider surface as a piece of hardwood. If the grain (silicon particles) is raised above the surface of the wood (aluminum), it usually takes a plane (hone) to get it smooth again. Excessive sanding (like lapping) will make the grain stand out even more as it removes the softer material. Course, its been years since I even worked on a piece of wood...
R/
Dustin

Dustin,

MOST EXCELLENT analogy

PS ,

AFJuvat

Those unsupported cylinder tops look, almost, EXACTLY like the cylinders in a HONDA! Just an observation.

Well, it seems like my original question has sparked some serious discussion :) There's a hell of a lot of great info here, and despite my previous post suggesting I was going to bite the bullet and re-ring my Alusils, I've now decided against it. This is for no other reason than I've purchase a full set of good, used Nikasil cylinders with Euro spec pistons, and it was the extra potential of the the high compression pistons which threw the decision, NOT the fact I currently have Alusils. I've taken a risk buying these as I've not seen them, but the seller is a well recognised specialist who assures me they are from an 80k motor and well within spec. I guess I'll just have to wait until they arrive :rolleyes:

Now, who can tell me how to hone a set of Nikasils.....??!!

Myth Busted?
How about a concensus on the process for re-ringing 911 Alusil cylinders.
I've seen these options. I won't include what I did with scotch brite.
Don't take them apart.
Clean them only in BFPW.
Grape hone them.
Lap them with the silicon paste and felt.

If the cylinders are the same material throughout then it would be logical that they can be bored oversized. How far can they be bored out to increase displacement? (Short Stroke 3.2?) That would be from 95mm to 98mm right? That's 1.5 mm cut from the inside edge. (All the way arround.)
This seems easier and possibly cheaper than getting them plated with Nikasil. Are pistons avalible from anyone for this size?
What do these P&C sets look like that Wayne refers to in his book?

IMHO:
clean'em in BFPW and use the felt/silicon paste routine to renew the finish. Of course, after you have first measured to be sure they are in spec.

All the docs from KS and Sunnin say that overbore is possible but those are re: 944. I would like to know for sure. If you can take these out to 98MM and fit new coated pistons... :eek:

Perhaps Charles N can step in here and help us out.

Charles can you overbore a nikasil liner to 98mm?

That's the rub...where to buy coated pistons? Truly, I think the process of boring, and conditioning just like the 944 cylinders is possible if enough meat is left on the cylinders...plus the side benefit would be that the boring would bring it back to round spec! I think most of the the info regarding Alusil cyls is derived from old school techniques that did not consider the procedure outlined for cars like the 944...okay, maybe thats a stretch, but i still have not heard WHY IT CAN'T BE DONE. I'm working a deal righ tnow to buy a used (and presumably in-spec) set of Alusils and am willing to make them into an experimental set (assuming of course oversize pistons can be found). I think I would ask Rondinone (very nicely) to do a anaylisis of the bore prior to boring. Afterward, I'd like to do a before and after comparison to see if indeed the bores look "fresh". I know, hard to do when nobody really knows what they look like from the factory, but at least it eliminate the presence of galling as a variable. Rondinone...would you like to offer a little insight as to what can be determined from this type of analysis. If bigger pistons cannot be sourced, I'll just freshen them up with the silicon paste and felt pads and submit them for analysis.....?

R/
Dustin

Here is what I use for 911 with alusils:

1. Clean cylinder completely.
2. Measure cylinder
2a In spec - continue
2b Out of spec - discard
3. Crosshatch pattern visible?
3a. Yes - Continue
3b. No - LIGHTLY Hone with grape hone and pleanty of oil
4. Clean and measure piston
5. Apply new rings


Alusil cylinders should be a dul (not very reflective) grey with a faint crosshatch pattern visable and smooth as glass to the touch.

AFJuvat

AFJuvat,
VERY interesting! May I ask...how many sets do you think you have done in this manner, and what is the overall success rate. Please know, I'm not trying to be a wise-ass but from all the experts that poo-poo the idea, its refreshing to hear guys like you and Jack are having success using basically the same procedure...i.e. the grape hone. Also, probably not know, but how much longer do you suppose they'll last after freshened up in this manner....100,000 miles? less?

R/
Dustin

I sometimes wonder how much of the bad rap of alusil is due to the Vega.

Konish you're absolutely right about how alusil wears. It get's even more interesting, as the worn-off ring material, some broken silicon and aluminum form a compacted debris layer on the cylinder wall surface, which then buffers the rings and slows down wear of both the ring and cylinder surfaces. I just found this last week in a paper I dug up. The key to reringing may be to remove that compacted layer, which could be another explanation for what happened in the BFPW (my first thought was that the cleaner could have etched back some aluminum). A simple silicon paste lapping, or even beating it up with the grape hone may also do the trick. My personal choice would be to be gentle and go with the BFPW or paste, but that's just me.

I'd be happy to look at your cylinder, but I'm not sure what I can do without breaking it up into pieces. My electron microscope can't take something as big as a cylinder, and neither can my diffractometer. I was kind of hoping that someone would send me one that couldn't be reused so there would be no loss in breaking it up. I could do several polishing, cleaning or etching experiments and see what changes.

Anyway, to answer your question I can look at the cylinder surface with an electron microscope that can also identify individual elements. So we can identify the silicon particles, and probably see ring material and aluminum debris. The real useful info will be the texture, as that's what affects the ring wear. We could send some chips to John Walker if he's interested and have them cleaned in the BFPW, then look at the texture again.

I also have something called a profilometer that can profile a surface to less than a micron. I might be able to get the arm of the profilometer into an intact cylinder, and while that won't give us any pretty pictures it will give us a very good measurement of surface texture before and after treatment. Let me look at the instrument tomorrow and I'll get back to you.

Also, by getting to the edge of the cylinder where the piston doesn't wear, we could probably get a real good indication of what the factory finish looks like, and could compare that to what comes out of the BFPW or the lapping.

That car had more problems than just the alusil block! :-) My grandfathers Vega ate fuel pumps like they were going out of style. Rondinone...interesting, I'll have to keep you informed...

R/
Dustin

THe PAIN, I had totally put, out of my mind, the 72 Vega I bought, new, in 1971. The PAIN. Varped BLOCK, not heads, rusted thru fenders, in 8 MONTHS!!, to many other things, the PAIN.

Steel cylinder inserts solved the block problem.

All cylindres have areas that are not worn, both above the rings and below. If there is no ridge there is no wear. That simple.

If you pick the bottom of the cylinder, there is no action going on there, none. The bottoms should look just like when they left the factory. No deposits, nothing from rings, nothing from wear.

This should be a good referance to compare the rest of the cylinder to.

Rondinone, any thoughts on the composition and application of the piston coatings?

I was just reviewing another thread and it is possible to bore the niks out to 98mm, so assuming (i know, i know) ~ the same overall cylinder wall thickness the KS cyls could be bored out as well. Unless there's some requirement from the difference of material such that the alusil needs a thicker wall...

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this thread just passed Wayne's sticky for views!!!

I just posted a WTB add in the classifieds so we can send it to Rondinone for testing. See if we get any bites.

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/142639-wtb-single-used-alusil-cylinder.html

Rondinone,

Shoot me an email with your shipping address and I will send a very used alusil for your experiments. jstgermaine@stgassociates.com

I read the thread about boaring out 95mm to get 98 mm 3.2 short stroke.
It's long.
The problem with SC cylinders is the grove for the head gasket/ring.
The Mahle 3.2 short stroke set do not have the grove and they were originally 95mm castings that were bored to 98mm but the tops were left flat. One of the machine shops was concerned that if you bored out the cylinder with the grove there would not be enough meat left for strength. The solution I picked up was to find a used set of 84 up Carerra cylinders (95mm without the grove) and bore them to 98mm.
I'm not sure there has been any discussion here about Carerra cylinders. The thread was somewhat old so they were still only talking about Nikasil cylinders. Were any of the carerra cylinders made with Alusil. As stated above we would still need to get pistons.
Is there a next size up that is readily avalible with the SC sized wrist pins? I know the pistons were sorted in various size groups. Did KS ever produce oversize pistons? If so this would solve the problem for cylinders that are worn beyond specifications (If there are any.)

Rondineone, since you know about this stuff: My neighbor is one of the head guys at a biotech company. When I had my engine apart and was measuring my P&C's he made me an offer to measure them using sone sort of x-ray or ultrasound equiptment that was able to scan the part and measure to a millionth of a nat's ass. I didn't take him up on his offer for two reasons: I was afraid of what I might find out. (My measurements with the dial bore gauge were good enough for me. Second I didn't want to mess up his lab with my dirty parts. I believe they have some machining equiptment as well, I doubt a boring machine.
Can you identify the equiptment I am describing? Would this equiptment potentially help in this saga?

Re: Vega

I did read that poor compression on alusil cylinders could be fixed by adding bon-ami/comet type abrasive cleaner through the spark plug.

Should be good for a laugh if anyone wants to try....

As far as I know, the pistons are plated with pure iron. I have no idea if new ones are available, or if a modern piston manufacturer produces any. Plating a piston should be trivial however. All you need are a few nails, some muriatic acid (HCl) from home depot, and a battery! OK, let's not try that.

William, you're neighbor might be talking about an X-ray 3d coordinate measuring system. Optek makes one. It might be useful if the resolution is high enough. Maybe you should ask for some details about what this thing can do. I'm interested.

I sent Jerry my address, so we can get cracking on this thing. Let's all thank Jerry. clap clap clap