Valve guides, valves and carbon

From pcarworkshop

This article is on the 993 heads. I took it upon myself to take one of my heads (#1 piston is a good choice) apart to see how much wear I have on the valve guides.

Here is a picture with the valve springs/retainers removed. The smaller valve (the one on the right) is the exhaust valve, the other of course is the intake. The intake passages are covered in a light coating of varnish from the fuel but are pretty clean. The exhaust side is another story. The combustion chamber is actually pretty clean in that there is a coating of carbon but no thick buildup.

Here are the valves. You can see part of a retainer above the valves. They hold the valve springs onto the valve stem. I measured these valves, the exhaust appears to be worn beyond the limits and the intake is marginally OK. I will let the machinist take his own measurements and we will discuss it.

Here is the exhaust port close up. You can see the SAI passage entrance just right of the guide entrance. Its pretty small. Notice all the black gunk on the port walls...these walls are ceramic lined althought you would never know.

I wanted to see how clear the SAI passage was so I dropped a drill bit down the hole...it was a loose fit and it went in no problem. The hole is a straight line and perhaps it could be drilled out a little larger.

Here is the end of the drill bit poking out of the SAI outlet in the exhaust port. It would be no problem to enlarge this port at this time if I knew there was enough meat in the head.

Oka, for fun and no profit, I setup my trusty gauge to see what the wiggle would be at the head of the exhaust valve. You normally are supposed to use a new valve but I do not have them yet.

When measuring the valves you have to have the head off the seat so the exhaust valve has been pulled off the seat by 10mm or so.

So what did I find? Well the wiggle appears to be about 0.6-0.7mm at the head of the stem. If you wiggle it it definitely moves back and worth quite a bit. Its not just a little bit loose is quite loose. I am sure they can get looser but I can see how heat would have problems transferring from the valve to the head when they are in this state.

The intake is also worn but not as much as the exhaust. The seats in the heads look OK in that they to not appear to be beaten up too much but the machinist will take a look. I definitely needed valve guides althought I bet the car could have been driven quite a bit more. It all depends on the risk someone is willing to take.

Links to Rebuild Tour

1. Getting started, dropping the engine and superficial stripdown
2. Checking the default timing and Cams
3. Looking at the heads and the SAI passages
4. Valve guides, valves and carbon
5. Further Dissassembly
6. Exploring the SAI passages
7. Cleaning and getting ready to put it all together again
8. Rods and last minute checks before putting the case together
9. Sealing the case (or tomb)
10. Putting the pistons/cylinders back
11. Camshaft timing Part I
12. Camshaft timing Part II
13. Messing up a clean looking engine
14. Not quite there
15. Cranking it up