Valve Adjustment Observations

[Worksmart]

After owning my '66 for about 15 years, I decided it was time to adjust the valves amongst other maintenance items. For the first 11 or so years it just plowed snow a few times a year. The last 4 years it has been worked a bit harder at our farm doing field work for our little veggie operation. The tractor has run flawlessly as long as I've owned it. Other than rebuilding the carb years ago and some new spark plugs last year, I've subscribed to it ain't broke so don't mess with it. Now it's time to mess with it.

I had never done this task before and found it to be pretty easy. I only had to move the choke rod and governor to carb rod out of the way to get at the valves. Everything looked good and was very clean when I got the tappet cover off. I observed the following starting clearances prior to adjusting all to .015:

1 .011
2 .010
3 .009
4 .011
5 .011
6 .009
7 .011
8 .010

Is there anything to be gleaned from these measurements other than pretty consistent across the board? Valve seat wear or ? Will I really notice much difference in performance? Just trying to understand the theory why more clearance will be better. Should I expect a change in the engine sound when I start it up with the additional clearance?

Thanks
Chuck

[indy61]

I doubt you will notice any difference. I didn't when I adjusted mine but I did not check clearance beforehand. The only improvement I could notice was when I replaced sparkplugs and when I installed a Pertronix ignition.

[Boss Hog]

It will run better under a hard pull Remember the wise words of Art , when they are tapping they are not burning
More lash is better than not enough
Boss

[Worksmart]

That's the word I was looking for Boss! Lash. In all my years working on muscular Mopars, I always had hydraulic lifters to take up the lash. Never worked with adjustable valve trains. It's coming back to me now. I was thinking about lift, duration and cam profile. Trying to figure out how more clearance i.e. lash from my starting point(s), would make this engine run better. It just does because the cam profile of this engine is designed to work well with .015 or so lash.

Found this when I went off on a "lash" search:

Valve Lash or Valve Clearance is the gap between the Rocker Arms and the valve tappet. This clearance must be tightly controlled. If it is too little, the valves may not seat properly. If it is too much, you create valve train noise, and excess load on the valves and valve train components.

As the picture shows below, valve lash basically cuts off the lower portion of the cam profile. This lower section is where the cam profile is designed to gently open and close the valve. If you have too much valve lash, you eliminate the more "gentle" sections and are basically "slamming" the valve open and closed.

Because of manufacturing tolerances, engine wear, and because different parts of the valve train and engine "grow" as the engine heats up, this clearance can change and must be set correctly. Camshafts are ground assuming a certain amount of valve lash. If you change it, you risk changing the performance and durability of what the cam grinder designed into their lobes. http://performancetrends.com/Definitions/Valve-Lash.htm

Thanks for the word of the day.
Chuck