Can the block be honed?
05-21-2013, 05:07 PM
#31
Because I've been out of town for a funeral and replied on my smart phone, that's why. That said, anyone competent enough to be removing material from the cylinders should have understood my response in full. I didn't have time to do other people's research for them. FWIW, I was actually working on a degree in Materials Engineering with a specialty in metallurgy when the 968 was still in production, which is really how I know the difference. Pretty cool to see how etching makes all the grains and features and stuff visible under a microscope after it has been polished and etched.
FWIW, I'm not competent enough to be removing material from the bores, either. I'm not trying to be snarky, but see cruise's response, and you'll see why it is important to understand the difference. People who don't understand the process may think they can just take a ball hone, and fire away. This is an abrasive step, and will remove the aluminum and the silicon. The only way to selectively remove one element from an alloy is with chemistry. Abrasion will remove the entirety of one surface.
FWIW, I'm not competent enough to be removing material from the bores, either. I'm not trying to be snarky, but see cruise's response, and you'll see why it is important to understand the difference. People who don't understand the process may think they can just take a ball hone, and fire away. This is an abrasive step, and will remove the aluminum and the silicon. The only way to selectively remove one element from an alloy is with chemistry. Abrasion will remove the entirety of one surface.
Here I am propagating even other bad info, even though I have done it to my engines and have the pieces now to do it in my garage (past, felt pads, sunnen tool).
I did not know that it was an etch, and I was wrong in stating what I did. When you say that physical removal from an alloy is never going to leave one thing there and another is taken away, I did not think of it that way.
Even official documentation states that it "wears the aluminum away" leaving the "silicon to stand out", etc.
I thought it saw silicon paste because it would affect the AL and not the Silicon. Well, it does, but you state that its a chemical event.
05-21-2013, 05:32 PM
#32
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I had my 86 944 turbo block coated in Nikasil a little while ago. I did so becasue I wanted to retain the stock displacement instead of boring out the cylinder walls and having to buy new pistons. I took Chris White's advice and sent my block to Millenium Technologies for the job. It cost about $1300 said and done, but they also machined my deck, re-weld a chipped boss on the side of the block, and had to deal with the fuss of taking my head studs out. The block looks absolutely beautiful. I will post a thread soon with pictures of the entire rebuild process if anyone is interested.
05-21-2013, 06:20 PM
#34
Yes pics please 
I had my 86 944 turbo block coated in Nikasil a little while ago. I did so becasue I wanted to retain the stock displacement instead of boring out the cylinder walls and having to buy new pistons. I took Chris White's advice and sent my block to Millenium Technologies for the job. It cost about $1300 said and done, but they also machined my deck, re-weld a chipped boss on the side of the block, and had to deal with the fuss of taking my head studs out. The block looks absolutely beautiful. I will post a thread soon with pictures of the entire rebuild process if anyone is interested.
OK it's chemical but the way the paste is applied is mechanically on the rotating pads
05-21-2013, 07:08 PM
#36
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The stock 944 turbo rings are compatible. Nikasil is not fussy about rings. <---words from Chris White himself. I'm about to throw my entire rebuild thread up tonight, so you will be able to see pictures soon.
05-21-2013, 07:14 PM
#37
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Kwenak, I just noticed your location, haha! I'm from Georgia, but I'm actually living in Columbus, IN right now for the rest of the summer. I'm working over at the Cummins Technical Center downtown. You'll have to show me your car sometime!
05-22-2013, 12:53 AM
#38
Race Car
When sanding/polishing/mechanically removing material, there is a hard material and a soft material. the hard material removes the soft material. If the silicon is harder than the material used to remove the aluminum, it would remove that material, making it unable to remove the aluminum. Doesn't matter which one moves or is stationary - a mill and a lathe work in opposite ways, but the soft material is always the ones that is removed. The only way you can finish the bore is by chemically removing the aluminum.
05-22-2013, 01:47 AM
#39
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I think anybody interested in this thread should read the link below. I am posting from my phone so can't insert the link, but will try to copy and paste. Please don't confuse Nikasil with Alusil. Nikasil is a coating and Alusil is a type metal alloy containing approximately 78% aluminum and 17 % silicon, and please don't confuse silicon with silicone! Silicon is extremely hard, think silicon carbide cutting tools. It is also quite brittle. In Alusil the silicon is literally imbedded in the grain structure of the aluminum. Think pebbles embedded in concrete at a microscopic level. If you etch away a small amount of aluminum it will leave the silicon "pebbles" as a raised surface for the rings to ride on. Thus the need for the proper rings! This will also mean that the surface is truly no longer smooth and has "veins" in between the silicon particles. This actually aids in lubrication, as the oil is retained in the microscopic veins/arteries. Very smart engineers developed this technology such a Harry. BTW as always if I have incorrectly stated something please feel free to correct me Harry. Here is the must read link:
http://www.aera.org/engine-professional/nikasil®-and-alusil/
http://www.aera.org/engine-professional/nikasil®-and-alusil/
Last edited by URG8RB8; 05-22-2013 at 02:55 AM.
05-22-2013, 02:04 AM
#40
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What most people don't know and lightly touched upon in the article is the fact the 1971 Chevy Vega was the first production vehicle to use a hyper-eutectic Alusil cylinder bore. The car got a very bad name due to situations like we are discussing now 40 years later! Imagine dropping your block off in the early 70's with this kind of technology required! No good ole boy shop would have known how to properly prepare this block for new positions. The Vega was truly way ahead of its time and quite the engineering marvel!
05-22-2013, 02:56 AM
#41
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Note I previously posted an incorrect composition which I have corrected.
Alusil as a hypereutectic aluminium-silicon alloy (Al17Si4CuMg or A390) contains approximately 78% aluminium and 17% silicon.[1][2] This alloy was created in 1927 by Schweizer & Fehrenbach[3] of Baden-Baden Germany and further developed by Kolbenschmidt.[2]
The Alusil aluminium alloy is commonly used to make linerless aluminium alloy engine blocks.[4] Alusil, when etched, will expose a very hard silicon precipitate. The silicon surface is porous enough to hold oil, and is an excellent bearing surface. BMW switched from Nikasil-coated cylinder walls to Alusil in 1996 to eliminate the corrosion problems caused through the use of petrol/gasoline containing sulfur.
Alusil as a hypereutectic aluminium-silicon alloy (Al17Si4CuMg or A390) contains approximately 78% aluminium and 17% silicon.[1][2] This alloy was created in 1927 by Schweizer & Fehrenbach[3] of Baden-Baden Germany and further developed by Kolbenschmidt.[2]
The Alusil aluminium alloy is commonly used to make linerless aluminium alloy engine blocks.[4] Alusil, when etched, will expose a very hard silicon precipitate. The silicon surface is porous enough to hold oil, and is an excellent bearing surface. BMW switched from Nikasil-coated cylinder walls to Alusil in 1996 to eliminate the corrosion problems caused through the use of petrol/gasoline containing sulfur.
05-22-2013, 09:22 AM
#42
Drifting
No. Abrasion does not discriminate. It removes all of the material from a surface. Boring is abrasion. The use of the pads is in all likelihood to control the rate and depth of etching.
When sanding/polishing/mechanically removing material, there is a hard material and a soft material. the hard material removes the soft material. If the silicon is harder than the material used to remove the aluminum, it would remove that material, making it unable to remove the aluminum. Doesn't matter which one moves or is stationary - a mill and a lathe work in opposite ways, but the soft material is always the ones that is removed. The only way you can finish the bore is by chemically removing the aluminum.
When sanding/polishing/mechanically removing material, there is a hard material and a soft material. the hard material removes the soft material. If the silicon is harder than the material used to remove the aluminum, it would remove that material, making it unable to remove the aluminum. Doesn't matter which one moves or is stationary - a mill and a lathe work in opposite ways, but the soft material is always the ones that is removed. The only way you can finish the bore is by chemically removing the aluminum.
