Exhaust Port Color
 

Im replacing the stock oil return tubes on my '83 SC motor and had to take off the heat exhangers. The color of the exhaust ports:

4 are white, white, white.
2 are blackend.

This bothers me. White means lean, Blackend means rich, no?

I have new Magnacore wires and fresh plugs on this motor. The motor is low mile, 70K+. The timing was set too-far advanced for awhile a few months ago, but I've toned it down quite a bit. It starts fine, it sounds great. Some questions:

Could poorly adjusted valves cause this?
I can't test the injectors because they have metal lines. Maybe run some Techron?
Any other advise?

i really do need some advise here guys. Anyone?

Yes white means lean and black means rich. Which cylinders were showing lean and which were showing black? I guess its possible poorly adjusted valves could cause this. More air could enter and lean out the mixture. Not sure though. I would think the injectors could also cause this though too. Slightly plugged injector would not supply enough fuel also leaning out the mixture. Couldn't hurt to try some Techron.

Just some thoughts, hopefully some more will chime in.

Timothy

3 & 2 are black
the rest are white

With dramatic differences among cylinders I think some careful diagnosis is in order. Black can also mean oil.

Since it runs properly, go do some spirited highway driving with fresh oil and fuel.

First do a cylinder leak test and a cranking compression test. If there is any leak, note if it is intake valve, exhaust valve, ring, or head gasket. There are plenty of posts on this subject.

Next measure, not adjust, the valve clearance. You want to see if there is a difference between #2 and #3 compared to the other four. Inspect the rocker arms and cam surfaces with a mirror. Make sure the rocker arm shafts are properly in place.

Take a “light on a stick” past the fan and see if the #2 and #3 cylinders and heads have anything restricting the air flow. Same for the other cylinders.

If you still have the heat exchangers off the engine, rotate the engine and inspect the exhaust valve seating surfaces best you can.

Check the cap, wires, and plug connectors for high voltage arc tracks. If in doubt, replace them later – these are normal service items.

Please report what you find.

Best,
Grady

thanks grady.
sounds like lots of work :(
but what choice do I have...

Mat,

Same thing bothered me. See this thread;

http://forums.pelicanparts.com/porsche-911-technical-forum/132581-your-opinion-pic-please.html

a side question: should I replace exhaust studs if they came out when I removed the heat-exhangers?

No, this is not much effort compared to the potential alternative.

Here is Kurt V's head. You can search out his posts but he had very littile indication there was this serious of a problem. His cat was working as intended.
This is about as close to disaster as I have seen.


http://forums.pelicanparts.com/uploa...1102033455.jpg


Best,
Grady

White is pretty common with todays fuel even with a proper mixture. Really, really white probably indicates a lean condition.

Jeff

Grady, looking at that picture makes me cringe in thought of what that could have done. Yikes!

Timothy

whats all the cringing about? Its just a burned valve. Maybe Im wrong, but the only thing to fear about that valve is a loss of compression. An old subaru of mine had the same issue, ran like champ for 250K miles. Is there really need for concern?

Secondly, I think I found the cause of the problem. The blackened cylinders are not 2 & 3, they are 5 & 6. I had a small mouse nest over 6 when I bought the car (no PPI (i know, i know)) but it was really minor. Anyway, it must have toasted those valves back there. 6 is definitely the worst, 5 is not so bad, the rest are fine. I did inspect the #6 exhaust valve as best I could and I didn't see any pieces missing or fried off, so either I can't see it or the problem is with the rings and not the valve.

Chalk it up to a rookie mistake I guess. Maybe one of these days when I find time for an engine rebuild I'll get a chance to replace that stuff, but Im going to run it for now. Hell, theres probably enough room back there to do the whole thing with the motor in the car! Unless theres a threat of the car exploding into a ball of flame, Im going to keep pounding on the beotch...

Aren't those big cracks through the head of the valve on the right? That would make me cringe. Given some more time I would think the head could/would break off. And that would be a problem.

Timothy is right on!

I cringe also.

Had Kurt’s valve come apart (and this seems very close to me), at the least it would have destroyed a head and a piston. I have seen many cases where it effectively destroyed the entire engine; case, crank, some rods, all the P&Cs, oil pump, some rockers and a cam, and several heads.


I will speculate that the ring(s) on #6 (and possibly #5) were damaged from heat due to the mouse nest. What happens when a ring brakes apart and comes past the piston lands is not pretty and can become exceedingly expensive in a flash.


What are the cylinder leak numbers? Where is the leakage?


No, I don’t think the engine will explode in a ball of flame. The potential malfunction is more sudden and expensive.

Best,
Grady

see, I don't think of those as cracks as much as just burned material.

Bad compression? yes.
Leaking? yes
Catastrophic? im not convinced yet

Lots of cars burn their valves. Owners run them hot, electric fans stop working, thermostats wear out, scale builds up in the cooling system.

Maybe the wear and tear of near red-line RPMs will demand more strength from the valve head, I don't know. Is it common for valves to break off the stems?

we need to find an engine expert. John Walker maybe?

You've heard from an engine expert. You don't want to hear from your engine. The risk is catastrophic. Pony up to the bar or risk paying 10x that much later. People are trying to help you.... nobody posting has a $$ interest in your engine repair.

Im not trying to be a jerk, I just want the opinion of someone who builds 911 engines as a profession. Unless Grady runs a shop, I'll need to get a second opinion. I respect everyones opinion here.

JW seems to think that 911 valves don't get cooked as much as the guides and seals wear. I may be doing a leakdown soon...

You have..........Grady has been doing this longer than I have been alive.

Grady ran THE shop in the Denver area for 20 years doing everything from stock rebuilds to full bore race cars. I would put his opinion right up there with JW.

Right now the situation is that you don’t know if there is a problem and if there is what is it. Here is my recommendation from above:



“With dramatic differences among cylinders I think some careful diagnosis is in order. Black can also mean oil.

"Since it runs properly, go do some spirited highway driving with fresh oil and fuel.

"First do a cylinder leak test and a cranking compression test. If there is any leak, note if it is intake valve, exhaust valve, ring, or head gasket. There are plenty of posts on this subject.

"Next measure, not adjust, the valve clearance. You want to see if there is a difference between #2 and #3 compared to the other four. Inspect the rocker arms and cam surfaces with a mirror. Make sure the rocker arm shafts are properly in place.

"Take a “light on a stick” past the fan and see if the #2 and #3 cylinders and heads have anything restricting the air flow. Same for the other cylinders.

"If you still have the heat exchangers off the engine, rotate the engine and inspect the exhaust valve seating surfaces best you can.

"Check the cap, wires, and plug connectors for high voltage arc tracks. If in doubt, replace them later – these are normal service items.”


I will modify my recommendations to encourage you to do the cylinder leak test and cranking compression test first!

This may be a “tempest in a teapot” but if there is a problem, you don’t want it to turn into a much bigger one. Testing gives you the necessary information to make informed decisions, not guessing or rolling the dice.

Best,
Grady