Reynard38

OK, lets assume the worst case scenario and I really do have an honest SAI fault (clogged ports). Lets also assume that it really is caused by the worn valve guides (my mechanic says so).
What are the best guides to use for replacement? My guy wants to use the stock Porsche part. I'd rather use something that isn't going to cause me to go through this in another 40,000 miles.
Anybody here done a top end and used a better guide?

Geoffrey

I have found that it is the valves and valve guides that are an issue. The valves are soft and get pitted on the seat which causes higher than normal leakdown numbers due to improper sealing. The valve guides have two issues, one that they are soft and wear quickly, and two, I believe they have too loose a tolerance from the factory. When the valve guide wears, the valve no longer seals in a correct circle and the valve seat wears on one edge more than the other. This is another contributing factor to the valve sealing issue. So, the result is twofold, one increased oil into the exhaust port which burns and clogs the air injection port, and two, the valves don't seal properly and power is lost.

So, the 993 heads have threee issues in my opinion - 1) Air injection ports, 2) soft valves, 3) soft valve guides with wide tolerances. To fix the issue, I use a generic aftermarket valve guide and cut and profile it to the proper size. This is the first thing I'd do. Next I would evaluate if you wanted to replace the valves or reuse the factory valves which depends on the condition and monies allocated to the project. If I were to replace the valves, I'd use some aftermarket valves which are lighter, better flowing, and have a finish on the backside to promote swirl into the chamber. Lastly, I would only use a Serdi or similar style valve machine to properly cut the valve angles into the head. Doing the old way with a stone is not nearly as accurate as with a cutter type machine.

jimbo3

IMHO, Oil consumption is more indicative of worn guides than the SAI issue. Clogged passageways may be a result of driving 20,000 miles with a bad SAI check valve.. How much oil are you using?

Mike J

It seems a popular guide is the SI guides. Have any of you experience with that manufacturer?

Cheers,

Mike

Terry Adams

At the 120K rebuild, Devek replaced my half worn OEM valve guides with an aftermarket alloy, name and brand unknown as it seemed to be some kind of trade secret. My oil use:
0-10K miles, 1qt/1K
10K-110K, 1 qt/2500,
about 1qt/2K just prior to the rebuild.
After the rebuild, I seem to be at an incredible 1qt/5K. Yes, 1qt/5K miles.

Reynard38

I had Performance Imports hook the car up to there scanner today. The codes had already been cleared, and have not yet reapeared. The scanner (Porsche) did allow the tech to trigger the SAI system and according to the scanner everything worked OK as the scanner saw the fan come on and the corresponding change in the 02 sensor voltage.
Just the same I am going to do the flush and replace BOTH valves ASAP.
My oil usage is about 1 quart/ 2000 miles.