I suggest you check if it is running on BOTH cylinders. Place plug wires on losely, remove one at a time and see what happens. Engine should fall off about the same amount as each wire is removed alternately.

I suspect sticking valve or stuck valve which can be checked by removing valve cover IF engine is only running on one cylinder.

Walt Conner

By the way, have you checked the valve adjustment since you have had it? Instructions at address below, put in proper format and remind me what you want.

Walt Conner
wconner5 at verizon dot net

Thanks Walt,

I will try the spark plug wire thing.

I think the Valve adjustment info is in my Owners Manual.

If it is a stuck valve does this mean a "take apart job"? or can it be freed up with some penetrating oil.

rlargaespada

If it was due to a stuck valve (at first), the problem may have escalated from there. I hope you have time to read this carefully.
Sticking valves most commonly occur when the engine chances to stop with an intake valve open.
With the intake valve open, the resinous film (mix of engine oil & varnish from fuel) on the portion of valve stem inside the intake passage of head acts like "glue" and prevents the valve from closing when the engine camshaft rotates next time the engine is cranked.
Most times, a sticky valve actually causes no problems because the valve is not stuck "hard enough" and breaks free before other, disastrous things happen.
The "other things" that might happen include the pushrod falling out of its pocket on the rocker arm and disengaging altogether from the rocker arm.
A worse version of that scenario would be that instead of the pushrod falling completely free of the rocker arm, it gets "caught" on the edge of the rocker arm. Having gotten trapped in that position, the next upstroke of the piston results in the piston striking the open valve, which may bend the pushrod (usually does bend the pushrod), break the rocker arm, bend the valve, or all the above.

If you take off the valve cover and find a loose, disconnected pushrod, take the pushrod and roll it across a smooth surface (kitchen counter top smooth) to see if you can detect any "wobble" which means the pushrod is bent.
If you are fortunate enough the pushrod is still ok, you can very carefully reinstall the pushrod using your fingers to depress the valve so you can get the pushrod back into its pocket.

IF.......this turns out to be the case, you must immediately begin doing things differently in regard to your fueling and other maintenance.

Fueling the tractor: From this point on, you need to add Marvel Mystery Oil (or equivalent lube) in the recommended volume to the fuel container used for fueling the tractor.
Also, add gasoline stabilizer in the recommended amount to the container.
If you fuel other engines from the container, those engines will benefit too.

I don't know how often you are changing the engine lube oil currently, but with 9 acres of ground, and an admittedly vigorous workout, you probably should change the oil more often.

But, find out if the problem is actually valve/pushrod related and post back.
Check your e-mail for a PM.

Thanks Mownie, that is exactly what I found as I removed the valve cover. one pushrod had fallen out! It goes back in, but I'll have to check it again to see if it is still straight.
By the way, somehow my post was not on here this morning, so I put up another, very similar! Now both are on here for the same problem! Strange.

I can push on all the springs except the one that the pushrod fell out from. Actually, on that one valve the rocker arm was loose. Would this be caused by not adjusting valve clearance like I should? If this valve is stuck can it be freed up? Or do I need to start a disassembly job here.

I would be hesitant to try to start it again even if I tighten down the rocker arm and did a valve adjustment. By any chance would this valve on which I can not push the spring down be in a position (on the cam) that it won't budge or just plain stuck?

Thanks for the Marvel Mystery Oil tip, etc.

I don't actually mow 9 acres. about six acres are overgrown fields and meadows...probably do about 3 all together and not all at one time, but that machine has gotten a work out and never gave me a problem until now.

Are you saying that the adjuster screw and jam nut were loose?
That has occurred but is usually not the case.
The valve which you can not press down, does this valve spring appear to be "shorter" than the spring on the other valve? You may have to turn the engine by hand (spark plugs removed) using the grass screen on top of the engine to allow the other valve to close before comparing heights of the 2 springs. (valve is close when it is all the way UP and there is clearance between valve and rocker arm)

If the affected valve spring appears to be shorter than its neighbor, the valve has probably been struck by the rising piston as described in my first post. The valve may have bent which is now preventing the valve from seating, and making it hard to push down also.

You are correct in NOT STARTING this engine until the issue is identified and resolved.
The Vanguard series engines are pretty dependable, but nothing is bullet-proof.
Check the height of the valve springs before going further.

This did not happen because the valves were not adjusted, but..........if you HAD done the recommended annual valve adjustment, you might have precluded the adjuster screw and jam nut from loosening as it did.

Thanks Mownie...

Did as you described above and found the spring does appear a tiny bit shorter when "seated" after I turn the engine around. I can easily push in all the springs except this particular one gives a sticky resistance each time. I am supposing this means a new valve and valve jobs???

At least a new valve if the valve is bent.
After you get the head off and the valve out of the head, chuck the valve into a drill and slowly rotate the valve while holding the drill absolutely stationary (or use a drill press if available).
Look at the valve from the side (looking at edge of valve), and from the end (looking at valve face) while it spins. If you see any wobble at all, replace the valve.
If the piston has struck the valve, it may (or not) have sustained damage too. A small mark or indentation in the top of the piston is not a cause for concern.
A "worst case" scenario would be that the valve head broke off and buried itself in the piston, but if that had happened, your opening post would have read something like "was mowing along and suddenly my engine began making a loud knocking sound".

If you see only a small mark on the piston, get a new valve, oil up the stem and see how the new valve slides up and down in the guide.
If the new valve feels nice and free, put the thing back together and proceed with a valve adjustment.
Be certain to install new oil seals on the intake valve guids.

Thank you Mownie!

I'll soon get to work on this. Actually, the only noise I ever heard was a slight metal ring every now and then which I think may have been the pushrod laying there behind the Valve cover. The engine sounded nice and smooth, just low rpm. I can move the spring, but it gives a "stuck" feeling just before I push it in.
I'll write back on here with my findings.