How to set timing for BN?

I don't know of any timing marks on my Farmall bn gas tractor with horizontal distributor. Nor do I know what the timing should be set to. I do have a Sun Tune up kit with timing light and tach/dwell meter that I've used on my classic cars that have timing tabs.

Help appreciated.
I recently changed out the distributor amid chasing an intermittent spark gremlin. It is not impossible that it may be a tooth off. I tried really hard to install the new one in the exact orientation of the old one. Since I did it, the idle hasn't been as smooth as it used to be, and there is a a stumble when applying the throttle that didn't used to be there or as least was not prominent.

Under the tractor at the rear of the engine is the flywheel housing. In the very bottom of that housing is a viewing hole. There
is a mark on the flywheel that is TDC. I use this method of finding it. I put my thumb over the #1 spark plug hole ( all plugs
out). I hand move the engine (ignition off, using the fan, or pushing it in 4th gear) when air begins to be pushed out, I stop. I
place a plastic straw in the sparkplug hole and continue turning gently while watching the straw. As it slows its moving up to
just barely, I make a mark on the straw. I continue turning till it begins to go down. I turn it till it is at the same mark as
on the way up. I then make a new mark half way between them on the straw and turn it backwards till that line is aligned. This
is really close to TDC and if you now look at the flywheel through the hole you will be looking at the spot where the mark should
be. Clean and clean till it shows up. Move the engine till it is aligned (centered). Mark it with paint, or chisel a little
deeper and fill with paint.
Now you have the static timing mark where it belongs on compression.
Put a plain old test light or volt meter on the distributor side terminal. Turn on the ignition (plugs still out) The timing will
be perfect when rotating the distributor body toward the engine block and the light just flickers on. This is the opening moment
of the points, and is correct timing. Lock it down. Jim

You can also just remove a spark plug and shine a bright flashlight into the hole and visualize the piston.

On my Super A I can turn the engine over with the fan belt, but on the SMTA, no dice. (I think Grandpa was running something a little better than stock pistons) I had to jack up the rear wheel and use 5th gear to turn the engine.

I also pull the rocker/valve cover because there are two TDC where the piston reaches the top of the stroke in the 4 cycles, and only one of them is appropriate to set the timing. At the "proper TDC" the valves are stationary on both sides of the top of stroke. On the "wrong" TDC" the intake and exhaust valves are in motion on each side of the top of the stroke.

If you choose the wrong one you will either have no starting/running or some crazy event like firing when the intake is open causing a massive backfire.

The timing marks for that engine is on the flywheel and are hard to see. Originaly that engine came with a Magneto and it fired on TDC thenwhen the engine startrd it went to around 33 deg. Now with the dist your best bet would be to remove #1 plug and look in the hole and watch when the piston is at the top on combustion then check rotor to see if its pointed at the tower where the wire goes to #1.Then start engine and by sound you can rotate the dist till engine sounds good. That dist will advance around 25 or so degs advance. You can remove the flywheel cover and check the marks with the pointer there for TDC but remember they are hard to see but cleaning the flywheel they can be seen. You could chalk the mark on the flywheel and then use a timing lite. I have had many of those engine over the yrs and those that have been converted to a dist i just timed by listening to the engine.

The TDC mark is in line with a bolt that holds the pressure plate on.

If you ever hand crank the engine, set it to TDC!! Nasty results happen with a kickback. Jim

Initial Distributor Timing

1. Have the distributor ready to install - with the points gapped.

2. Position Cylinder #1 at TDC (Top Dead Center) after the Compression Cycle.

An easy way to do this is to remove all the spark plugs except for Cylinder #1. Crank the engine, and when you feel the Compression Cycle, remove the spark plug from Cylinder #1. Insert a wire into the spark plug hole and crank the engine until the piston is at the top.

3. Install the cap on the distributor, and mark the location of the Cylinder #1 tower on the distributor.

If the distributor is painted black, or if you don't want to mark on the side of the distributor, use a piece of masking tape and place a mark on it.

4. Remove the cap from the distributor, and install the rotor. Position the rotor just past (clockwise) the mark for Cylinder #1.

5. Install the distributor on the tractor, keeping the rotor in the same location. (The #1 Cylinder is typically on the top right of the distributor, but that is not really important).

6. Install the distributor clamps, and tighten them only slightly.

7. Connect a test light to the battery hot side (or connect an ohm meter to ground). Connect the other end of the test light (or ohm meter) to the terminal on the side of the distributor. The test light should not go on (or the ohm meter should show an open circuit).

8. Slowly rotate the distributor to the left (counter-clockwise) until the test light comes on (or the ohm meter shows zero ohms).

9. Tighten the clamps on the distributor.

The distributor is now timed - at least well enough that the engine should start. With the engine running, you can do the "fine tuning" on the timing.