Which piston ring style is correct?

[Noahs944]

So I bought a "basket case" of 944 & 944S parts. I'm in the process of trying to sort out the 16V components so that I can have a complete running S engine to install into my '88 non turbo car. The problem is someone has been in the engine before. And I don't trust any of their work.

The piston compression rings that came out of the 16 V are have a square cut edge (non beveled on the outside) and the top and bottom of the compression ring is a dull grey, with no stamping or etching of brand or orientation.

What bothers me is the condition of the cylinder bores. The finish is kind of pitted and I don't know if it's from storage (I doubt it) or dirt or carbon (there are signs of carbon on the oil control rings) or dirts, or lastly pre-detonation (cheap gas)?

What I want to be sure of is that these rings are correct for the application.


This is the first 944 that I have fully disassembled, and all I have to compare it to are the other 16V pistons that I got also. But they look to have a cast compression ring (black finish up & down, chrome on outside, "TOP" markings & a bevel on the top outer edge of rings.

Why the two different styles? Which is correct?

Thanks for your time.
Ideas?

[Backyardbodyman]

I wouldn't worry about the rings,probably aftermarket if you think someone's been in there. From what you described about the condition of the cylinders you should have the block checked, bored and honed with new pistons and rings. Even if the cylinders are good and can just be honed and you use the old pistons you still need new rings.

[Pauld_94S2]

You don't "hone" Alusil cylinders.

It is a special procedure to conditon the cylinder walls.

Search on this forum for details.

[Backyardbodyman]

Ya,what do you do then. I just had my block bored and honed. The proper(special)bits or whatever you want to call them were used to bore and special pads were used on a sunnen hone machine to bring out the silicone in the cylinder walls.

[Pauld_94S2]

The comment was made to alert Noahs944 between using a conventional hone process versus using the special sunnen hone with pads and the paste used to polish and expose the silicon carbide embedded in the aluminum matrix.

Clearly you know the difference. Possibly Noahs944, or another reader might have seen "have the block checked, bored and honed" they been mislead.

No offense intended. Your other comments are correct.

[toyotagt]

Originally Posted by Pauld_94S2

You don't "hone" Alusil cylinders.

It is a special procedure to conditon the cylinder walls.

Search on this forum for details.

So what do you think conditioning the cylinder walls is? It's called HONNING!

[Backyardbodyman]

No worries,it's all good. No offense was taken. I know what you mean. You still hear stories about shops making a mess out of someone's block. Cheers

[Bradical]

I'd take the block to a machinist for a second opinion, but unless you are looking to match numbers I'd blueprint and keep the crank and other components and scrap the block. You could get a short block for much cheaper than having a block machined, with new pistons.

[TibetanT]

First, the 944 cylinders are usually Alusil so they would use the chrome-edged rings.
Second, if you plan on getting the bore redone, it must be done with sleeves which means you had better send that to a shop that has done Porsche 944 work.

You might try contacting Ian in Florida about another block, or a reconditioned block since I believe he sells those.

However, with that said, a micrometer which measures the inside bore would give you a better answer to whether the block is within Porsche specifications.

Do you have the Porsche Factory manuals for the 944? There is a section which gives you the Porsche specifications and the limits for (out-of-spec) the pistons and the cylinder walls.

If you do not have the Porsche Factory manuals and plan on doing this work, let me know via PM your mailing address. I can then send you the information I have.

Hope this helps, and good luck to you!

[Noahs944]

Thank you everyone for the GREAT answers. I do have most of the factory manuals on line THANK YOU), except for #5.

I had measured the bores and I thing the late block would need to be oversized. Curious to know how oversize we can cut the late (87) block. Is 4mm too big?

The clean block on the right measured in spec (to me) and I dropped that one off to the engine shop that has done excellent head work for me in the past. They were very comfortable/knowledgable with Alusil. A breath of relief.