993 cylinder removal for orings - OK to separate P&C?
 

Hey folks. So I have my heads off and out for a rebuild (due to heavy pitting on exhaust valves and bad sealing confirmed by leak-down testing). I thought that since I have one of those complete gasket sets I may as well pull the pistons and replace the o-rings at the base of the cylinders. Note that the engine is pretty low miles (only 50K), so I assume the piston rings are in good shape. I'm only where I'm at now because I had the engine out anyway for some basic maintenance type stuff and then did the leak down, and then pulled a head and examined a valve, and ... so it goes...

I've never done aircooled P&Cs before, but I've read and watched it and know I can handle it ... but I have a question:

It seems to me that it'd be easier to pull the cylinder off - leaving the piston attached to the rod and not having to deal with the circlips and then just use the Hazet ring compressor tool to put the piston back in the cylinder. I've seen Kurt from Klassic Automotive do this with the pistons on the engine, and he explains how the rings should be positioned before putting the piston into the cylinder, how they should be oiled, etc.

Is there any downside or risk to doing this vs removing the circlip and keeping the P&C together? Removing / reinstalling the circlip seems like much more of a PITA than just compressing the rings with the piston on the engine. Leaving the piston attached also allows me to do one at a time vs having to remove a cylinder and leave it off to give me access to the circlip on the next cylinder. Having a chance to look over the rings, and possibly re-position them also seems worthwhile.

Thanks!

I don’t like to break down P&C’s if possible. Remove as a unit. I’m right handed so I pull back cylinder remove outside snap ring first on #3 & #4, use a small slide hammer I’ve modified a little, and remove pins enough to get unit off. Then 2&5, then 1&6. Install in reverse order. I build engines the same way, all pins face the same direction. Just the way I do it. Also the way I replace the lower head studs when in question. ?do u have old type Deliver head studs, now would be the time to replace them.

It's always a good idea to inspect every part before installing it. Low mileage is relative to driving habits.
The 993 has a horrible rod length to stroke ratio which means excessive side loading on the pistons. Combine that with a very short piston skirt and excessive wear is not uncommon.
You should always check ring land clearance and ring gaps. New Goetze ring packs are relatively inexpensive on the after market.
I stay away from the Mahle Brazilian version in favor of the German Goetze rings.

On a side note: I've taken apart engines that were factory built that had broken rings installed.

When i redid mine a couple of years ago the main issue was the undersized green base gaskets supplied w/ the Victor Reinz

be sure to use the correct round black ones from Wrightwood Racing

Thanks for the tip Bill, when you say “undersized” do you mean undersized because you had larger diameter bore-in cylinders, or undersized because they weren’t thick enough?

No, the 3.8 is different, but I rebuilt my stock 3.6 a couple of years ago, the Victor Reinz kit had some green slightly undersize cylinder base gaskets. They leaked so the engine was torn down again, and the base gaskets replaced w/ the Wrightwoods

Ug, that sucks - sorry to hear. I did some searching based on your comments and found others who had mentioned a size difference as well. I couldn't find the Wrightwoods sold outside of a complete gasket kit, but it looks from posts I found that the black "Genuine Porsche" ones are the thinker ones.

Cheers!