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Posted by: kpfoten Nov 25 2008, 01:22 PM

I'm a relative newbie when it comes to engine rebuilding, the physics, mechanics, etc, but I'm fascinated by it all and have been reading up on how it all works...

I've done my share of valve adjustments, but the thought came to mind--why do we adjust valves? Is it a combination of heat and wear that causes them to need adjusting? Does spring fatigue have something to do with it??

Posted by: 749142 Nov 25 2008, 01:28 PM

Its a combination of heat and wear mainly, the valve stem and tappet obiously wear, but the valve wears into the valves seat, and over the period of about 3,000miles the valve and valve seat where enough to remove your clearance, or your tappet and valve stem wear faster and then theres too much clearance

Posted by: ericread Nov 25 2008, 02:13 PM

Accordint to Auto Atlanta:

"Proper valve adjustment is critical to proper engine operation. Since the 914 engine is air cooled, it operates in a much broader temperature range than a water cooled car, resulting in more extreme expansion and contraction. This movement necessitates periodic valve adjustment."


Eric Read

Posted by: kpfoten Nov 25 2008, 02:39 PM

Thanks!

I would assume that air cooled motors (even though with valves regularly adjusted) need the heads re-done sooner over time?

Posted by: Cap'n Krusty Nov 25 2008, 07:36 PM

Not particularly. BTW, spring fatigue has come up before, and it's not a possible answer, because the valve is a fixed length, the spring retainer is in a fixed location, and any tension at all will cause the valve to be fully closed at rest. Note I said "closed", not "sealed". The Cap'n

Posted by: Vacca Rabite Nov 25 2008, 08:28 PM

There is a brilliant B&W video on Youtube about VW T1 valve adjustments, and why they are important. I think it was from a VW tech school in the 60s. I'm going to go look for it, and if I can it will post it up. Its fun to watch old movies, but this one really cleared up a lot of questions for me when I first started getting curious.

Zach

Posted by: Vacca Rabite Nov 25 2008, 08:30 PM

Sorry, not B&W, but still old and good. here is part 1:
http://www.youtube.com/watch?v=EpH7VftH3_I

Here is part two:
http://www.youtube.com/watch?v=vQ9ccGXtZL0

You should watch, its good stuff.
Zach

Posted by: kpfoten Nov 25 2008, 10:05 PM

Thanks! Youtube is great for a lot of rebuild stuff. There's some guy in New Jersey that has good (Type IV Beetle?) rebuild video, and then the stuff from Costa Mesa R&D is really something else--I'm hooked on machining videos right now. I really wish I knew more about this stuff when I was younger--it may have influenced a career path...