First of all, I am by no means an expert, but I did manage to adjust my valves and live to tell about the experience.
A couple of things you'll want on hand before you start this adventure:
(2) 1/2" open end wrenches (having one being a thinner helps)
(1) 9/16" closed end wrench (for the manafold nuts)
(2) 251233R2 (Manifold Gaskets)
(1) 251371R1 (valve tappet cover)
(1) 251235R1 (carburetor gasket)
a can of PB Blaster or Kroil
a set of feeler gauges (.013 - .016 at least)*** for earlier engines 0.013" is the correct gap (1600 rpm engines) So you would use 0.012, 0.013 & 0.014 for you gauges instead.
some sort of scraper
and lastly a 7/8" deepset socket or wrench to remove sparkplugs.
Here are the steps I followed:
1) Drain gas from tank and remove hood.
2) Spray the following items with Kroil (or the like) - 4 nuts on exhaust manafold, 2 bolts on valve cover, 2 bolts from carb to manafold. If you have underslung exhaust, get the exhaust clamp too.
3) For best success, let that sit overnight and start again fresh in morning.
4) Remove the carb & fuel line first. Curse excess gas that magically appears. This includes choke rod and governor rod.
5) Carefully remove manifold. Curse the IH engineer that put those two center nuts so close to the manifold tubes.
6) Now the object of your desire is getting close, remove the two bolts that keep the valve cover on. Struggle with the cover to remove it as in my case the hydraulic tubes made it a challenge, basically the cover in my case would only go up and to the left towards the manifold.
7) Finally the valves. Spray them down with Kroil and let sit. This is a good time to call the spouse over and have them panic at the mess you're created. At this point I covered the valves with rags and scrapped off the hold gaskets (both manifold and valve cover) Keep the junk out of the engine if at all possible.
At this point I rolled the engine (by turning the fan towards me by hand) and watched the valves go up and down so I kinda got an idea of what was going on with my engine. I let the kroil sit overnight as I didn't want to break anything.
9) Remove spark plug #1 & #4 (#1 is closest to radiator).
10) Put thumb over spark plug #1 and turn engine by hand until you feel air pressure on your thumb, looking at the crankshaft pulley (locate the notch or notches) I have a factory distributor, so I have two notches. Line up the TDC (top dead center) with the pointer. At this point do a sanity check - by watching the valves go up and down before, you should now see that valves # 1, 2, 3 & 5 should look closed (meaning the tappet is in the lowest spot of it's travel)
11) Try to put a feeler gauge between the tappet adjusting screw and the valve. If your experience is anything like mine, they were really really tight and had no detectable clearance. Starting with valve one, put two 1/2" wrenches, one on the tappet (it has a flatten face where the wrench fits) and the other on the adjusting screw (looks like a nut to me). By tightening the screw, the tappet basically become shorter and you get clearance. The trick is to be able to insert a (0.015" gauge) and have it rub (meaning some resistnace) when you slide it between the valve bottom and the adjusting screw. This will take some practice as it is mostly a two handed job. I then use a (0.014" and 0.016 gauge) to double check my work. The 0.014" should feel easy to insert and the 0.016" should be really tight.
12) repeat for valves 2, 3 & 5.
13) Now with your finger on spark plug hole #4, turn engine until you feel pressure just like step #10.
14) Once you find TDC, you should have following valves closed (4,6,7, 8 ).
15) repeat step #11 for them.
16) reinstall everything removed in reverse order, make sure you set the correct adjustment to your governor rod as the carb never seems to go back in the same place it came from.
17) check for fuel leaks and enjoy the new sound of your tractor.
I'm the 3rd owner of my loboy and from the age and condition of the valve cover gasket and the tightness of my valves, I'd guess they haven't been adjusted in quite some time. Correct Valve lash seems to be important for low end engines to give them more "grunt."
Good luck! Like I said, I'm no expert on this subject, so if you have any suggestions for making this more complete or accurate, please let me know - Lance