My turn with valve adjustment query!

[cab83_750]

After having found out about how much (over $800.00) it would cost for a tune up, I knew that self-study was a prerequisite to owning a daily-driver 911.

So I have done at leat 4 valve adjustments (successfully if I may add). And Yes, I am forever grateful to everybody and the tech article.

Just one questions; in my last valve adjustments about 4 weeks ago, I noticed that the exhaust valves are ALL tight. The upper valves all seem to be within spec.

Has anyone experience this? It seems strange to me that all bottom ones are super tight. Any causes (other than heat)?

[Doug Zielke]

Tight Exhaust Valves = Burnt Exhaust Valves

[cab83_750]

Originally posted by Doug Zielke:
Tight Exhaust Valves = Burnt Exhaust Valves

Doug,

Now I just confused myself. Specifically, tight means that there was still gap but definitely requiring adjustment (only one exhaust was within spec).

Now, as far as your response, are you saying that I have 'burnt' ones. Or are you trying to say that tigthness WILL result to burning.

BTW, the car runs perfectly! I do the adjustments/checking between every 10-11K miles!

[Doug Zielke]

Originally posted by cab83_750:
[B] Or are you trying to say that tigthness WILL result to burning.

B/B]

That's exactly what I meant.



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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website
"If it ain't broke...we'll help you fix it 'til it is!"

[cab83_750]

Thank God!

And I thought you were telling me that I HAVE burnt valves!

Thanks for the clarification. Now I can log off and sleep tight (or should I say loose).

[Pillow]

Be careful of the root cause of the tightening valves. Are the heads getting too hot? Was the car completely cold when doing the adjustment?

A normal valve adjustment will envolve tightening the valves and not loosening them... Hopefully that made sense. The valves should wear the gap wider instead of closer.

IF the heads are getting too hot the exhaust valves can be "stretching" from the heat and they will eventually snap the valve heads off... Maybe the engine is running lean or is it pinging?

IF the motor was not 100% cold then that is probably the problem.

For good measure it might not hurt to do a compression check on it just to make sure the exhaust valves are on the money...



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Adrian Pillow
1979 911 SC
1966 VW Microbus
PCA - Peachstate Region

[Jdub]

Pillow:

I don't know if I get it...the gap would tighten by default from spec. because the valve is seating further into the valve seat, thus valve moves towards adjuster resulting in less clearance, right?

Of course, I guess if there is alot of carbon building up on the valve seat and valve itself then you would see a larger clearance between valve stem and adjuster, but I'd hope we're all doing regular Techron runs to get rid of this stuff.

Jw

[Superman]

Valves need to rest on the 'seat' in order to release their heat into the heads. This is what cools valve heads. Yes, valves that are adjusted too tight have less time to release the heat.

Valves that get too tight, are probably wearing down the seats.

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'83 SC

[Pillow]

Superman brings up a good point about the seat pounding into the head, but I always thought that this was very minimal wear compared to the valve and adjuster mushrooming...?

The adjuster itself will wear down/in and also the valve tip will mushroom from the impacts. Also as the camshaft and rockers wear down the valve adjuster clearance will widen.

About two months ago I was tearing down a type 4 motor and found a head destroyed by the valve seat literally tearing throught the back of the head... Valve did not snap! I took off the spring and retainer and pulled the valve out and then the seat just fell out on the floor... Never seen that happen before.



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Adrian Pillow
1979 911 SC
1966 VW Microbus
PCA - Peachstate Region