[jonvo]

I bought a 968 motor with about 190k miles to put into my 944. Previous owner said the motor ran great, didn't burn oil, and had consistent compression in all 4 cylinders. I have all the paper work showing that the head was rebuilt at 160k. I want to put in new rod bearings/belts/rollers/water pump before doing the conversion, but my question is if I should re ring it? I have been reading a bunch of mixed opinions on re-honing alusil bores. Some say you can do it, some say you can't, some say it's a gamble, and some say if the bores look ok, you can re ring it without a problem.



The options I'm deciding on are to:

1. leave the rings and just do the rod bearings/belts/rollers/water pump

2. re ring without honing if the bores are in spec and visually in good shape

3. freshen up the bores with scotchbrite pads and the Sunnen silicuim mixture



What should I do?

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[Monstrous4Banger]

You should re-ring it, and send it off to a machine shop familiar with our alloy. If your cylinders are flawless, shouldnt be a need to mess with it. Id contact Chris White personally. www.944enhancement.com

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[jonvo]

Thanks, I've emailed both Chris from 944enhancement and Mike from Lindsey racing. It seems like they both say that it is ok to reuse the bores if they are in good condition. Are Goetze rings ok for alusil bores? In other words, are they chrome plated like the OEM rings?



and is all this talk about "you cant rebuild alusil bores" an old train of thought? It looks like this book by Wayne Dempsey says rebuilding alusil motors is never reliable.

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[Monstrous4Banger]

IIRC Goetze makes a compatible ring, Id clarify with Chris or Mike though.



As far as rebuilding old blocks, I have 15k miles on my rebuilt 944s2 block. The cylinders were flawless, and didnt need to be touched though. You can bore on them, but it requires a process most shops dont know how to do. This is why you should leave this stuff to the experts. This isnt something to do in your garage. At the very least find a reputable machine shop in CA, that can do alusil. IIRC it requires a chemical process.

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[Cloud9...68]

You need to take the block to a reputable machine shop, and have them measured the diameter of the bores at top, center, and bottom using a specific tool (I think it's called an align bore gauge). This will tell you if any honing is needed. As a point of reference, at 116K miles, my bores showed close to zero wear, so Mike Lindsey told me that honing (let alone boring) is not necessary. The machinist I went to told me alusil engines like ours are designed to go a million miles. When you think about it, what is alusil, but a ceramic, and ceramics are some of the hardest substances on earth.

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[Monstrous4Banger]

[quote name='Cloud9...68' timestamp='1303006844' post='108521']

The machinist I went to told me alusil engines like ours are designed to go a million miles. When you think about it, what is alusil, but a ceramic, and ceramics are some of the hardest substances on earth.

[/quote]



Yes, as an alloy with a composition of 17% silicone polymer, would technically be ceramic. Silicon is a really cool metalloid. Not only very hard, but heat, and wear resistant.



Interesting wiki entry:

Alusil as a hypereutectic aluminium-silicon alloy (AlSi17Cu4Mg or A390) contains approximately 78% aluminium and 17% silicon.[sup][1][/sup][sup][2][/sup] This alloy was created in 1927 by Schweizer & Fehrenbach[sup][3][/sup] of Baden-Baden Germany and further developed by Kolbenschmidt.[sup][2][/sup]



The Alusil aluminium alloy is commonly used to make linerless aluminium alloy engine blocks.[sup][4][/sup] 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.

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[tamathumper]

contains approximately 78% aluminium and 17% silicon

The other 5% must be unobtanium?

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[Monstrous4Banger]

Actually copper, and magnesium. AlSi17Cu4Mg Which wouldnt be metalloids (semimetals), but alkaline earth metals.

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