DarylJ

Boring or honing doesn't matter. The very site you took that picture from states they they use that tool on alusil motors that they have repaired before coating with Nikasil.

http://www.928motorsports.com/services/uschrome.html

What they don't mention is that you need different rings and pistons, because they are not the same as those for alusil. While some have used the same ones, it's not really suggested by more conservative shops. And while you are correct that alusil is not a coating, a finished alusil bore IS plated with a layer that leaves (more) exposed silicon on the cylinder walls. This is why you can't hone/bore them without re-plating. I'm not aware of anyone who does that process (re plate alusil in the aftermarket), as Nikasil is a superior process, so people looking to rebuild a motor are typically looking for the performance gains and longer life of a Nikasil coating.

As I understand it, the process was dropped on most Porsche production cars in 1974 due to cost, not because of high-sulfur fuel damage issues (prevalent in certain BMWs). Porsche/Mahle must have sorted this problem out, as they still plate GT2/GT3/CGT buckets with Nikasil.

The only machine shops that will hone Alusil either really know what they are doing (928 Motorsports) or have no idea what they are getting into. Honing the coating off down to the Alusil is a recipe for poor compression in short order.

I'm not trying to argue with you here. A little research will show you that the major points I'm making here are well known. I just don't want to see even more bad information end up on Rennlist.

Legoland951

Sigh, I am no engine builder but they do hone alusil blocks and we do not have to replate our cylinders. The entire cylinder is made of alusil and the bore surface is hard silicon exposed after the aluminum is honed/etched away. If you have special equipment, you can hone/bore the silicon away but will have to etch/hone away the aluminum between the silicon with a special process. They "hone" to achieve what most people define as "bore out" from what I understand and the etching process DOES NOT HAVE TO BE A CHEMICAL PROCESS using acid. Oversized pistons are used afterwards in most cases due to the amount of material that needs to be honed/bored away dictated by the depth of the scratches. Here is a summary in how MS motor service hone their alusil cylinders here: http://www.ms-motor-service.com/xima...018_en_web.pdf and here is the detailed version in page 8 of the service tech manual here: http://www.bmwseven.com/Alum_engine.pdf. They use a felt pad instead of a honing stone for the last process to expose the silicon, which traditionally is done chemically.

The 928 site chooses to nikasil coat the cylinder after they hone it, but it does not have to be that way. I have known several people go through boring and etching their cylinders with absolutely no recoating or plating.

https://rennlist.com/forums/924-931-...linders-2.html post #25 is by a guy who has ringed 40 stock blocks and 30 bored/honed blocks. I find it hardly impossible.

Sorry for the hijack. I'm out.

kiesan

I have a 26k mile 1991 944S2 that I am considering having a local shop do an LS1 conversion on. I know.... insanity!

If that happens I would sell the engine and I guess all the peripheral stuff that goes with it. It has brand new everything... belts, w/p, front seals, rollers, bearings, timing chain tensioners, etc. Brand new like less than 200 miles and done this year. It runs perfectly.

What would a guy charge for something like that?

DarylJ

Sigh. You use posts on forums as evidence. I use machinists and books.

Sorry, I just don't buy it. I'm sure they guy has made it work. I'm sure he's achieved less than 2% leakdown. I'd like to see those numbers after streeting the motor for a couple of years.

Maybe you can "get away with it", but alusil bores are etched (sorry, I said plated in the previous post) after boring. I still don't know anyone who does that process. Without etching, you aren't exposing enough silicone to make the microscopically rough surface that holds oil on the walls of the cylinder, basically making that motor out of spec.

Again, all very well documented. You can choose to believe what you see on forums as fact, or you can speak with and read material from people in the business. I happen to have Holbert's Porsche down the street from me, and send my machine work to their machinist. He has a pretty good handle on these things, doing machine work for Al Holbert and all.

Legoland951

Did you read the other links? Why don't you quote them? They make it very clear that they don't chemically etch the cylinder to expose the silicon but rather use a felt strip to "hone" the cylinders. If you question the validity of the manuals, do a search on Kolbenschmidt and you will know their history, which is distributed by MS motor service, which has locations in multiple countries both based in Germany. Here is a little background by KS:

"Kolbenschmidt is a leading global supplier of gasoline pistons with 21 percent of the global piston market. Metaldyne is the world’s largest supplier of powder metal forged connecting rods, manufacturing nearly 40 million per year." Per link: http://www.kspg-ag.de/index.php?fid=1770&lang=3

The manual I cited is by KS, which is an abbrivation for kolbenschmidt. Read here as they are the manufacturer of the Porsche Cayenne V8 engines: http://www.kspg-ag.de/pdfdoc/kspg_pr...rsche_v8_e.pdf and yes they bore and "hone" them too as shown in section 4 of manual: "This meant that the mechanical uncovering of the silicon crystals in a final HONING step was developed to commercial maturity with an optimised cycle time for ALUSIL as well." They manufacture the engines by honing.

They also manufacture these other alusil engine blocks: "The following are current engine block customers with KS Aluminum-Technologie AG: 4.0L V-8 (Jaguar), 4.0L V-8 Supercharged (Jaguar), 3.6L V-8 (BMW 735i), 4.4L V-8 (BMW 745i), 6.0L V-12 (BMW 760i), 6.0L W-12 (VW & Audi), 4.0L W-8 (VW), 2.5L R5 TDI (VW), 5.0L V-10 TDI Biturbo (VW Phaeton/Touareg), 4.5L V8 (Porsche Cayenne), 4.5L V.8 Turbo (Porsche Cayenne), 3.4L Boxer 6-cyl. (Porsche 911 Cabriolet & 911 Carrera Coupe), 1.4L inline 4 (A-Class), 1.6L inline-4, (A-Class), 1.9L inline 4 (A-Class) 1.6L Diesel (A-Class), 1.9L Diesel (A-Class). They also supply for the Volvo S60 and S80 as well as the BWM 5-series. Applying this technology, to the VW "W" series engines was particularly challenging." The link for the rest is here: http://findarticles.com/p/articles/m.../ai_109505538/

This article http://www.mmsonline.com/articles/ne...der-bores.aspx written by Tim Meara (senior honing technician for Sunnen Products Company) makes it as simple and thorough as it gets. Summary: "A major advance came in 1971 when GM used Reynolds A390 aluminum alloy in the linerless Vega block (one of the first alusil engines). A390 is a hypereutectic alloy saturated with silicon, such that silicon particles are dispersed throughout the alloy similar to chocolate chips in cookies.... On the rebuilder's side, Sunnen developed a GM-certified method for restoring a factory-quality surface for the Vega engine. Damaged bores were honed oversize using conventional abrasives, followed by an exposure step using a special lapping paste and felt honing pads. The process could be used with hand-held portable tools or honing machines, and it produced excellent results and was ideal for occasional users. That process has since evolved, thanks to metal-bond diamond abrasives, and today there is a new honing option for OEMs or production rebuilders, as well as the low-volume rebuilder. It should also be noted that rebuilders have the option to use a replacement, press-fit hypereutectic aluminum cylinder liner available from Kolbenschmidt if a cylinder is damaged beyond the point where it can be repaired by over-boring or honing. The honing process described here will work with this replacement liner, too."

I think Kolbenschmidt Pierburg knows more about alusil and engines and pistons than all of rennlist put together and then some. Heck, they may even have manufactured Al Hobart's engine blocks. Originally I was just going to know what I know and walk away from this by playing ignorant so I didn't have to pull up all the documentation but I agreed with your statement about having misinformation. Just because someone doesn't know something doesn't mean it does not exist.

Too bad I am not getting paid for this...

pjburges

I was under the impression new rings in an old bore just wouldnt seat.....but I dont know squat about Alusil or Nickasil or what to expect from a Porsche engine anways...im an SBC guy when it comes to engine rebuilds.

Voith

Great video on this procedure:

http://www.youtube.com/watch?v=-ek5qv8Nmg0

Voith

New rings in old bore are WAY better than old rings in old bore.