1950 8N Tapping sound

We have a 1950 8N front mount 6v with a tapping sound coming from the #4 or #3 cylinder area. The engine was professionally rebuilt about 7 or 8 years ago. I was thinking maybe it was a valve issue so I bought a compression tester and checked compression. I'm getting 90#, 90#, 90#, 90# which appears to be normal, so maybe not a valve problem. The tractor has no problem developing enough power for the mower up hills and governor seems very responsive and oil pressure is always about 35 pounds when running, just this annoying tapping sound that sounds almost like a valve lash that too loose. The only thing I did notice when changing the spark plugs was slightly more carbon on the #4 plug, which is the area where the sound is coming from. I'm assuming that valve lash on this engine is adjustable - are any special tools required to do this? Thanks!
 

Welcome to the forum - Glad to have you.

I would start off adjusting the valves - You will find the tappet wrenches [b:613dbcf1fc]HERE[/b:613dbcf1fc].

The FO-4 service manual covers the procedure in more detail but here's a general overview.

[b:613dbcf1fc]Tappet Adjustment Procedures[/b:613dbcf1fc]

1. Find top dead center on the compression stroke cylinder #1, both valves will be fully retracted. Slip a feeler gauge between the lifter and valve stem.

2. Adjust the clearance using the Johnson tappet tools. Insert the tang into a hole in the lifter and hook the other end over the adjoining valve. An 1/8th of a turn is several thousandths.

Intake clearance is .010-.012 and exhaust is .014.-016.

3. Once Cylinder 1 is complete, rotate the crank clockwise 1/4 turn until Cylinder #2 reaches top and repeat. Do this for cylinders 4 and 3 (firing order). When done, rotate the crank a complete revolution and repeat the procedure. This time the valves may still be off but will be closer than the first time.

4. When complete rotate the crank a complete revolution and check again. Keep doing this until everything settles in and the valves no longer need adjusting. Usually by the 3rd time everything is settling in. Properly adjusted, the valves are very quiet.

It's only hard the first time - Good luck and post back if you need further guidance.
 
My 8N had a ticking noise near back cylinder when under load.

Turned out to be the manifold gasket was eaten out at the lower rear corner on #4 cylinder. New gaskets cleared the noise
 
Tappet wrenches ordered. I really appreciate your help! This tractor was my grandfathers who used it a lot on the farm when I was a kid (lot's of memories) and more recently by my dad, who only used it to mow with.
 
I ordered new manifold and valve cover gaskets as well so I have at least a couple of the possible tapping sound problems covered. Thanks!
 
(quoted from post at 10:00:24 07/16/18) I ordered new manifold and valve cover gaskets as well so I have at least a couple of the possible tapping sound problems covered. Thanks!
When you clean off the block, inspect it real good at the #4 cylinder position. It has been known to erode away.
 
since the cam turns at half the crank speed, shouldn't the post below be half turns instead of quarter turns since it is a four cylinder engine
 
Steve,The exhaust manifold is probably leaking around #4 exhaust port.Check the block @ #4 for bad pitting.
 
Adjust your valves when you have the manifold off, much easier.

My n was tappity tappity when I got it. I too had to replace the manifold, so brought the valve tools.
 
(quoted from post at 07:43:42 07/16/18) My 8N had a ticking noise near back cylinder when under load.

Turned out to be the manifold gasket was eaten out at the lower rear corner on #4 cylinder. New gaskets cleared the noise

I had the exact same ticking sound that also turned out to be a manifold leak.

stevh1155...When the engine is idling hold your fingers in that area. I could actually feel the puffing from the leak on mine.

New gasket and new manifold fixed it right up. You may not need a new manifold, I didn't want to chance it with my old one.
 

Thanks to all for very solid and helpful advice! I'm driving back down to my dad's again this weekend (hopefully the parts will get here by then) and I'll post back what I find. Thanks!
 
Well, I got the manifold off with no problem and looking at cyl #4, I can see a welding bead that was ground off on the upper left side of the exhaust port, but looks like it's okay now-not leaking. Removed the valve covers and right away I see about 1/4" clearance on the#3 exhaust valve....I'm guessing that was the tapper! The adjusting nut seems way too loose on that one (the others all have some resistance). Can the threads be peened slightly to keep it from getting too loose and way out of clearance, or maybe some locktite threadlocker? Thanks!
 
Got everything back together, valves adjusted and it runs much quieter now. I ended up peening the threads slightly on the #3 cylinder intake valve adjuster threads & that did the trick. I appreciate all the help and advice!
 

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