[jonvo]

According to the service manual, when honing the block, it must be done in a manner that the silicium particles in the sleeves protrude out of the aluminum so that the rings only make contact with the silicium. This is done using a Sunnen silicium mixture.



Is this standard procedure on a lot of sleeves? And will most machine shops will know what I'm talking about if I bring it up?



I also had some confusion with the factory main bearing and rod bearing clearances for this motor. The "Tolerance and Wear limits" page (pg. 10-3) of service manual says:



Con-rod bearing/crankshaft

Radial clearance: 0.027-0.069



Crankshaft main bearing/crankshaft

Radial clearance: 0.028-0.070



However, on the "Checking Crankshaft Bearing Clearances" page (pg. 13-28a), it says:



Play of new bearings: 0.020-0.098



No bearing clearances are mentioned on the connecting rod installation page (pg. 13-35)

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[Monstrous4Banger]

The alloy our blocks use, from what im told are tricky to bore on. Not just any machine shop can do it, or will know how to do it. If it were me, Id be giving Lindsey a call, or Chris White(944enhancement.com) Not sure if RS barn does machine work, or if they outsource it. They are another great choice, and a site sponsor.

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[Cloud9...68]

Yeah, I have similar questions. I'm planning to give Lindsey a call, since, while they're not exactly close to me, they are in my same general region of the country.

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[jonvo]

Thanks guys.



Any input on bearing clearance?

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[Cloud9...68]

I'm afraid I don't have any insight into your question, and to be honest, I doubt anybody outside of an experienced builder of these engines likely can. Like Monstrous said, you should contact Mike Lindsey of Lindsey racing, or Pete or Max of RS Barn. They'll probably give you an earful about the many other nuances of these engines.

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[flash]

this piston/sleeve thing is exactly why i am getting rid of all that nonsense when i have to rebuild the engine, and going to standard sleeves with standard pistons, just like i've done forever - costs less - works great - no fuss - i'll likely use gapless rings too to keep the compression at maximum - that trick was good for about 15hp in a small block

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[jonvo]

I just sent Dave from Lindsey Racing an email. I'll let you all know what he has to say.

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[Monstrous4Banger]

Sleeves? Ive never seen any year block, sleeved in stock form. Am I missing something here? jonvo, when you say sleeve you mean the cylinders themselves right? AFAIK the cylinders are forged with the block. Dave has done machine work for me before, and does nice work. Chris White is my number one vote tho, FWIW. Might wanna drop him a line chris@944enhancement.com Hes always more than happy to talk your ear off too.

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[jonvo]

Yes, by sleeves I my the cylinder walls. I'll shoot Chris an email too.

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[tamathumper]

Definitely talk to Chris or someone with similar expertise, the Internet can't help with this one and the opinions are dangerous to follow. Just Google "Nikasil Alusil" and try to find out which one your 968 has - if you're to believe the various forum posts, you've got one or the other or they're the same thing or they're not, or... Oh, and don't use chromed rings, or do, or,...



Best to talk to somebody right up front who does it 24x7.

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[jonvo]

I got responses from both Chris at 944 enhancement and Mike from Lindsey Racing. They cleared everything up for me. Here's what they had to say.



Chris:

Welcome to the fun would of 944/968 rebuilds! Not a lot of info out there and a pretty good chunk of it is wrong.



First thing is to clear up some wording – the cylinders are not sleeves – that term is usually used for a different material (usually steel) inserted as a wear surface. The 944/968 blocks are one casting of Alusil. The final step in finishing them is not really a honing process in the traditional way, is a chemical/abrasive process that erodes the aluminum away and leaves the silicon exposed as the wear surface. Not very common and its hard to find a good shop that does this process. It takes the right felt ‘stones’ and the right chemicals. BMW and Mercedes have used a similar system so look for a shop that specialized in high end euro stuff.



The bearing clearances are pretty typical – the mains are set like most aluminum blocks and the rods are set a little tighter (no problems with aluminum expansion). Stick towards the lower end of the ‘play’ spec and you will be OK.



I would also recommend getting your bearings coated for a little extra protection. Check out Calico Coatings.



Good luck!



Chris White



944 Enhancement



Mike:

Hello Jon,



Dave asked me to answer your questions, I take care of most of the engine related questions here at LR. For starters, these engines do not have sleeves. The blocks are what is called an Alusil material, this is a silicon impregnated aluminum alloy. It required use of very specific honing tools to properly do the job, you cannot use the conventional stones like you would on a steel sleeve or cast iron block. The machine shop we use here locally uses the Sunnen equipment. I would have the cylinder bores measured by a professional with a dial bore gauge, if the cylinders are within tolerance and visually look to be in good condition, it is not necessary to hone the bores. We have simply cleaned the bores really well, oil them up and install the pistons with new rings. What ever you do, don't use one of those glaze breakers or hone stones. Those will ruin the cylinder walls and require boring to a larger size the clean them back up.



As far as the rod and main bearing clearances go, I find that most of the engines we have built come in around .002" or .05mm clearance. I personally do not like to see an engine run too tight of a clearance, you need to have a good amount of clearance to allow for good flow of the oil.

Matching oil viscosity to engine clearances is important. If all of the engine clearances were tight, at the minimum of the tolerance, then you could run a light weight oil, such as a 10w-40. I prefer to see clearances a little greater, like I said in the .002" range, this allows you to run a thicker 15-50 viscosity oil. Running too light of an oil with larger clearances will definitely lead to troubles.



Another thing to check when you build this engine is the side clearance on the connecting rods. Porsche typically runs a very tight side clearance, that is fine for normal street use, but if you intend to do autocross or drivers ed events, then you need more clearance. This will allow for more oil flow through the bearings and help to keep them cool under the constant high rpm conditions.



I hope that helps

Regards

Mike Lindsey

Lindsey Racing



I also found a thread on Pelican Parts about re-ringing Alusil cylinders. It's pretty long, but there's some good information in there.

Re-ring Alusils?

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