Tolerance on 0.010" valve clearance

[richard]

Everyone knows the 911 valves should be set to 0.010" (0.4mm). But what is the allowable tolerance on this? Is it + or - 0.001" or 0.002"? Is it - 0, +0.001?

[Ted Myrus]

I would think that .001 would be close enough.

I know you P&G valve gapper and dial indicator guys will cringe, but there are go/no go feeler gauges available. I have a set from Snap-on. For example, a feeler gauge's range may be .013 (0.33 mm) to .015 (0.38 mm). The gauge is actually stepped.

[Steve Grosekemper]

Not for 911's.
The valve adjustment is very critical, and takes a special tool. If it doesn't feel perfect, adjust it. Then when you are done, run through them again and amaze yourself as to how many need to be redone. A really nice 911 valve adjustment takes pracitce.

[richard]

Here's the reason for the original question: I use a dial guage. I also temporarily put an extra nut on the adjusting screw to give a better surface for the dial guage. Just moving the rocker arm left to right moves the guage about 0.001". The thread pitch on the adjusting screw is really not fine enough to get the accuracy you suggest without lots and lots of trial and error.

[Steve Grosekemper]

0.001". is fine. Press the rocker down against the rocker shaft and that will help eliminate the variance.

Put a feeler gauge through it so you can see what .4mm really feels like.

[richard]

For those who are interested: I've improved my technique. I wasnt putting the guage on the adjustment screw itself because of the slot in the middle. I was coming off the lock nut. But I discovered that there is a significant difference between coming off the lock nut at 12 oclock vs at 6 oclock. The adjustment screw is about 30 mm from the center of the rocker arm shaft. At 12 oclock it is about 33 mm from the center. At 6 oclock it is about 27mm. So to get 0.010mm at the adjustment screw you need about 10% less or 0.009 at 6 oclock and 0.011mm at 12 oclock. I finally said screw this and went to the hardware store and got a 8mm nut and 8mm cap head screw. I put the nut on the adjusting screw then screw in the bolt. This gives a good flat surface right above the center of the valve.
And you are right-going back I do find many of the settings which I was sure were dead nuts have changed. Dont know why.

[Ted Myrus]

I'm for hydraulic lifters with zero lash.

[Dan Chambers]

I'm for hydraulic lifters with zero lash.

Perfect reason (one of many) to drive a 944.