Question on timing

[Don McCombs]

Photo courtesy TM Tractor Parts

In this photo, you can see the shaft that the rotor attaches to. On this shaft the is a square area, with the corners rounded. Each of these rounded areas is a cam or lobe. On the moveable part of the points assembly is a brown L-shaped block of plastic or bakelite. This rubbing block rides on the square part of the shaft. When the rubbing block reaches each of the rounded corners (cam/lobe) the points gap is at it's maximum opening. This maximum opening is where you want to measure the gap with a feeler gauge. You adjust the gap by moving the part with the screw. It takes a lot of trial and error.

[jdeere86]

Hey Glen - merry xmas - the cub has a magneto. The way you describe setting the points makes it much more clear…thank you. I believe I must have lost the timing of the rotor to the magneto as I cranked it a few times with the cover off.

[jdeere86]

Merry xmas Don! Thank you for the photos and explanation.

[Glen]

Hi,
Merry Christmas.

Too bad you turned the engine, it can only be turned a small amount with the cover with the rotor off, you have to keep track of where the D shaped hole, and the D shaped shaft are turned.

You will need to find TDC to put the cover with the rotor on in the right position.

Below is a page from the 1950 Cub owner's manual, telling how to find TDC for the engine.
Paragraph 2 tells how. Use only paragraph 2 at this time.

http://farmallcub.com/rudi_cub/www.clea ... e%2032.jpg

After turning the engine to TDC, turn the rotor to number 1 cylinder's position on the distributor cap, and put the cover on the magneto.
Number 1 is originally at the top ignition wire hole on the cap, the posts go clockwise around the cap, 1, 3, 4, 2.
If you haven't disturbed the magneto mounting bolts, it should run, if there is spark.

If the impulse trips, or snaps, when you align the mark on the front pulley with the pointer, the rotor may not be in exactly the straight up position when you put the cover on. I think they have said on here it would be more clockwise, or past number 1 slightly.

I don't know if you have greased the rotor gears, it is easy while the cover is off.
Remove the 2 screws holding the cover at the rotor, and remove the cover.
Clean out the old grease, check the condition of the gear teeth, and put in some new grease, on the gear teeth.
There are timing marks on the rotor and it's drive gear, they should be aligned, you could check them.

Below is a picture of under the cover, and the timing marks.
If you don't want to grease the gears, it will probably work anyway.