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Re: [T3] Valve Adjustment Questions


On 8 Jun 2003 at 19:51, Chris J Valade wrote:

>         I was adjusting my valves today for the first time, and all went well
> with #1, but then when I rotated the engine as Muir says to (i.e. 180 degrees
> from TDC#1) I noticed that the two valves for #2 were offset, so I turned the
> engine clockwise until both were even, which was about an inch (on the
> crankshaft) off of where it should be according to Muir. 

The firing order is 1 4 3 2, so if you started with #1 and then turned the 
crank 180 deg CW, the next valve to adjust would be #4, not #2. If you want to 
adjust the valves in the order 1 2 3 4, you have to start with #1 and turn the 
crank CCW 180 deg between each one.  

>         Could someone explain why there needs to be a gap, and why its size
> matters?  I like to know the hows and whys for curiosity's sake, so I'm not
> just doing as told, and because it makes figuring out what is wrong, what to
> do, etc. easier. 

The point of this exercise is to set up the valve train so that, as the engine 
runs and warms up, there is never a time when the valves don't close all the 
way. Zero clearance would provide this if nothing else changed, but the various 
parts of the engine warm up at different rates.  

According to Berg, as the engine warms up, the valve clearances close up at 
first, and then open back up, approximately to the cold settings, once the 
engine is fully warmed up.  

The main thing we want to avoid is any situation where the clearances become 
negative, as this would mean that the valves would not be allowed to close 
completely. This has 3 consequences, all negative.  

1) The loss of compression would severely hurn engine power.  

2) Exhaust gasses escaping around the edge of the exhaust valve would overheat 
those edges and burn the valve.  

3) Most of the valve cooling comes from the valve sitting against the head for 
about 1/2 the engine cycle. If it can't touch the head it won't cool, and it 
will burn.  

-- 
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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