Hello out there......I understand why valves need to be set so that the engine runs its best, but why do they go out of adjustment? On my 914 I think the manual says adjust valves every 3-6 thousand miles, but I think 911 engines only need an adjustment every 30,000 miles or so. I used to do my own valves on my Norton Commando which was a piece of cake, but on the 914 I typically have an expert do them so that my car will run at its peak. Would love to hear what is actually going on in the engine that keeps me wondering "are my valves out of adjustment?" Thank you very much/
gg

Probably is more appropriate to say:
"check valve adjustment every 3-6 thousand miles. Adjust if necessary."

I routinely 'Check' the valve adjustment on my engine, but rarely do I need to adjust a valve.

If you can adjust valves on a Norton Commando - you can adjust valves on a 914. Fellow Commando lover here! Unfortunately my Copper Cafe Commando project hasn't progressed much in the last 7 years for a variety of reasons; my current 914 project being but just one of them.

Click to view attachment

As to why valves would need adjusting its related to wear and mechanical fatigue.

1) Valve face to valve seat recession.

2) Valve stems tend to stretch over time from inertia and spring loads acting upon them.

3) The end of the valve stem can become slightly concave over a long period of time due to scuffing wear between the valve adjuster and the valve stem. This is very hard to detect since a simple feeler gauge won't measure the wear to the bottom of the concave surface. Luckily this takes a lot of miles to occur and by then there are usually other serious problems that point towards the need for a rebuild.

4) Cam wear over time

5) Lifter wear over time

6) Push road wear over time (minimal but it is occurring)

7) Rocker arm to push rod pocket wear over time

I recommend keeping records of your valve adjustments over time.

A valve that is repeatedly becoming tighter over time may be showing signs of the valve stem stretching. This warning can be a precursor to impending valve failure at worst. Better to see it coming than to wait for the valve head to separate and destroy the engine. At best, the valve seats are recessing and it's probably time for a top end refresh.

30k on a 911 motor can’t be accurate

I do the valves on my 914/6 racecar every race. Probably 2-4 hours. Maybe 250 miles of hard use

I adjusted my valves after 500 miles on a full rebuild. Now, I check/adjust them once a year (about 8,000) miles. They normally don't need much tweaking.

I would'nt leave valve setting on my 911 for that long,the buggers are worth too much to risk it,my understanding is 10K miles which seems reasonable.
I traveled 14,000 kms around Australia during a hot summer in my 72 bus and keep checking the valves and generally found some reason to adjust one or more settings,not sure if the T4 would require less checking.
Loose or tight valves cause a number of problems,wear,overheating and loss of power to name a few,very important they are kept up to scratch.