Porsche 944 2.5L Machine Work

Does anyone know what the cylinder honing process for the Alusil cylinders is called?

Here's the scenario:

The Problem: 86 944, non turbo, lost oil pressure and broke #2 connecting rod. I bought it this way.

What I did: Installed used crank (had it polished), used rods (had them re-sized), new main & rod bearings. I had these parts from a previous project. I was told, by my machine shop, not to hone the cylinders and to reuse the original pistons and rings. Against my better judgment, I did exactly that.

Now, naturally, the engine smokes like a train. It has great oil pressure, but smokes terribly. I'm going to take it all apart again and have the cylinder walls honed, then install new rings.

My usual machine shop doesn't know how to hone the Alusil cylinders. I do know it can be done, though. So...

Does anyone know what the cylinder honing process for the Alusil cylinders is called?

You're sure it's coming from the cylinders?

I'm pretty sure you're not supposed to hone them if the bore is not damaged as it will remove the Alusil coating. I'm a bit surprised that your machine shop didn't suggest new rings, though.

It surprised me too. They said that the rings & Alusil 'wear in' together & that honing and/or new rings would make it smoke.

And, no, I'm not 100% sure that it's smoking because of the cylinders, but since that's the only part of the rebuild that I "hacked", I think it's the most probable source of the smoking problem.

you really only want to "deglaze" a Nikasil lined bore. flex hones work well, and give you a bit of cross hatch. look carefully for any chips in the coating, find or create any(watch the edges,) and the bores will need to be relined, so thats very bad.. but a good scuff up a new set of rings after that and you should be golden...

In reply to 924guy:

I emailed Bruce Anderson of Excellence magazine about this, and he told me that the 944 doesn't use Nikasil lined bores, but rather, Alusil. I was under impression that 944s used the Nikasil. Either way, he said to hone the cylinders but he doesn't remember the name of the process. Hence, this thread.

Do you know what Alusil is? Do you know the difference between it and Nikasil? I have to admit that I don't. Unfortunately, neither does my usual machine shop. If I can't find the answer, I will probably do what you suggest and just give the bores a good scuff up, then install new rings. Keep your fingers crossed for me that it doesn't smoke when I get it all back together.

M030 wrote: Do you know what Alusil is? Do you know the difference between it and Nikasil?

http://en.wikipedia.org/wiki/Alusil

http://en.wikipedia.org/wiki/Nikasil

I know of a machine shop in Marlboro MA that can take care of your block if you don't mind traveling a little. PM me if you want the info.

If I understand it correctly you need special tooling for you machines to bore the blocks (I am not sure about honing). The tools have a different cutting angle so as not to "grab" the metal when it is cutting it. After the machine work they then wash the surfaces down with an acid to slightly etch away a little bit of the aluminum leaving the silicon exposed. The pistons actually bare against the now exposed silicon particles that are sticking out of the aluminum as do the rings. This is one reason why newly rebuilt 944 motors will usually smoke when first run and will slowly get better as the sides of the cylinder walls have to seal up a bit as well as the rings have to seat. This process is much slower. You may want to try different oil. I seem to remember me of the porsche motor builders I know telling me this.

Read this thread over on Pelican parts forum. http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/487924-project-924-s-engine-replacement.html It has a lot of really good details on how to hone and what to use. Basically don't touch it with a stone, cover the stones with felt and use a witches brew made from fluffy owl dung and blood from a virgin birth or something like that as the lubrication..

Thank you all for the information.

In reply to dean1484:

I would really like the name/info for the machine shop in Marlboro. I have a friend who lives in Hudson, MA, and I think I can make the logistics work somehow...

M030 wrote: In reply to 924guy: ...Do you know what Alusil is? Do you know the difference between it and Nikasil? I have to admit that I don't. Unfortunately, neither does my usual machine shop. If I can't find the answer, I will probably do what you suggest and just give the bores a good scuff up, then install new rings. Keep your fingers crossed for me that it doesn't smoke when I get it all back together.

IMO alusil and nikisil should be treated the same way, light scuff with a cross hatch pattern... im no expert, not even close, one version was used on 911's, the other on 944/928, dont remember which was which and ive always put them in the same category. I do know if you damage the coating your screwed... one of the many reasons i went back to a good old iron block 2.0 engine, much harder to destroy it, but still possible :)

dean1484 wrote: I know of a machine shop in Marlboro MA that can take care of your block if you don't mind traveling a little. PM me if you want the info.

Sorry to bump this old thread but I could really use this contact info for the machine shop. I think I sent you a PM.