Smoking Tractor

I picked up a late model H that starts easily with a hand crank and runs great but smokes. It smokes more when you rev it up and then back it off. I will read the plugs tomorrow and run a compression check. I might put air pressure in the spark plug hole and listen at the intake and exhaust for air flow.
Any ideas as to what is most likely the problem? Any ideas on what I could check out? I am wondering if a head valve job will fix it.

Guessing the valves. To test whether it's the valves or rings, do a compression check and then put a teaspoon of motor oil in each cylinder and do another compression check. If the compression comes up considerably it's the rings, if it doesn't come up it's the valves.

If it smokes like a wet camp fire when slowing down in fifth gear, it is likely valve stem wear, and no valve seals. (It probably never had any, they were not stock) I would do the compression check, and if it is above 90, and within 10% on all cylinders, I would put valve seals on it.
Remove the valve cover.
Remove the rocker assembly (leave the pushrods in place down their holes)
Place a 3/4" deep socket over each valve retainer and tap it modestly with a hammer to loosen the keepers (do not hit too hard, or the keepers will come out. This just unseats them to make removal easy)

Use a piece of cotton rope, snaked into the cylinder through the spark plug hole, to hold up the valves in each cylinder, as the springs are taken off. About 2-1/2 feet of 1/4" rope will do.
When all but 6" of rope is in the cylinder, ----HAND---- turn the engine till the rope is tight into the combustion chamber
Use a lever type valve spring compressor to depress the valve springs and remove the keepers.
Put on the umbrella (or Perfect circle type BEST) seals on the stem, then put the spring back on.
Re assemble the valve train, (make sure the rope is out), and set the valves (to cold spec) .020" I think.
The seals allow proper oil to get to the stem, and not excess oil. This prevents high vacuum conditions from pulling oil into the cylinders past the guides. Good luck, JimN

Thanks for the detailed instructions for installing valve seals.
I put air pressure in each cylinder and they all held good with just a little noise heard at the crankcase. I put air pressure on each cyl with the intake taped shut and the intake valve open and there was a pretty good whistle of air in each heard at the crankcase. Compression measured 120 in each cyl.
I concluded it is the intake valve guides leaking oil. Your idea to replace the seals sounds pretty good. Maybe I should remove the head and replace the guides and or valves. Not sure what to do. I am surprised that worn valve stems or guides would cause so much smoke though! But I really think the rings and valves are sealing ok.

Here are my thoughts - if the smoke isn't choking you while operating the tractor, isn't burning excessive oil, and it isn't fouling the plugs - I'd just run it as it is.