I've just finished a valve adjustment on my car. I found that a couple of valves were spot on. Several needed to be snugged up a bit. A couple needed to be tightened.

So, what does that mean (snugged, tigtened)?

If I look at the adjusting screw slot head as a clock's minute hand then "snugged" was a minute, or two, and "tightened" was maybe five minutes travel.

Anyone know what the pitch is on the adjusting screw? And, what one full turn represents in travel?

Also, what is the expected result of an adjustment; if any? Generally too loose? Generally too tight? Generally no change?

I understand that the valves and seat can wear causing the valves to get tight, which is bad because there is then no seating of the valve, no heat transfer, and leakage.

But, what causes the valves to get loose? Do the adjusting screws back out? Were they not well adjusted before?

Finally, I found this useful post from JasonAndreas describing a method of setting the valve:

I didn't use this method this time, as I discovered it after I was done, so I'm likely still a bit loose, but surely not much.

Anyone know what a "loose" or "tight" gap would be? If the adjustment is 0.1mm then is 0.11mm loose? And, with regard to my previous question, is that one minute's turn of the screw? Just how precise is this process?

Thanks,
Dave

 

I put thumb on the box end of the wrench, and pinky finger about where it wants to fall naturally. I put most of what I can do with my wrist, and avoid using arm strength. That is about 15 ft-lb. It won't loosen, and you won't damage the threads.I have found it worth the trouble it get it just right. The car simply runs better if all the valves are spot-on the clearance. I don't think the adjusting screws back out if they are snugged properly. Mine are generally still OK or a little tight/close - probably seat wear. If the clearance increases, the cam or the rocker are wearing, or the previous adjustment was off (probably the latter).

I use or cross-check with a dial indicator which has 0.01 mm (0.00039") resolution. At 0.11 mm you are out by 10% - quite a bit in my opinion, but probably close enough for most shop mechanics. I can read the thichness of the tick mark on the dial, and that is about a micron - 0.001 mm. Do I get that close? Sometimes, but if it get to within 0.003 mm, I am quite happy to leave it there.

 

I've done this a ton, and in my findings have never found a tighter valve - they might get a bit looser, but I've never found one to "tighten up" or decrease the gap. My 65 911 required valve lash adjustment every 3000 miles - thank goodness the interval is longer on the newer cars given how much crap is removed to get there!

Jason's description is perfect regarding the feeler gauge drag - I like that description.

 

Garrett, How often do you adjust your valves? Also, Track vs Street? Just curious. I know the factory calls for every 20k km (12,500 miles).

 

The valve adjuster is a 1mm thread pitch.

 

So a tenth of a turn gets to the 0.1mm gap!

 

I too just did my valves. Not an easy job to IMO, with the motor in the car.
Not sure when it was done previously.

Not going to disagree with anything written above, but almost every one was slightly tight for my liking. If I tried to use the method above, I found that I could not re-insert the gauge once removed. That, to me means too tight. My technique was (using the small feeler tool) was to adjust to where the tool had enough resistance that it would stay in place on it's own, but could be removed and re-inserted into the gap.
An extra .001 as insurance to not burn a valve is worth the trade off in extra lift...
My 2 cents.