Lining up gears on a J-4 type magneto

[pfj]

Yesterday I took off the rotor on what I believe to be a J-4 type magneto for my Cub Tractor so that we could check and clean the points. When putting the rotor back it was necessary to line up a couple of gears - parts number 5 and 39 on the parts diagram I have. I noticed marks on both the rotor and the gear and lined these up so they were pointing at each other. Was this correct?

I never removed the magneto and I believe the rotor ended up being pointed more-or-less where it was when I took off the distributor cap.

Any help appreciated.
Thanks

[John *.?-!.* cub owner]

There is a mark that looks like a mold mark on the rear of the rotor, line it up with the mark on the pinion gear.

[pfj]

Thanks. I believe that is what I have done, so I am going to invest in some new plugs and see if I can get this tractor running.

[pfj]

So, a follow-up question/problem.... With the magneto and rotor properly timed, the problem with the kill switch sorted, and new plugs installed the motor started easily and ran well. I went back the next day and it wouldn't start. It would pop and not catch; once and a while it would catch and run for 5 seconds. This behaviour is very similar to how the motor was behaving before it sat for a year and we ended up with old gas in the tank and it wouldn't run at all. (the old gas has been cleaned out and sediment in the carburetor cleaned out) I am wondering if there is a "usual" problem that I should look for - carburetor need cleaning/rebuild; wrong plugs; ?

[staninlowerAL]

Assuming you did not change anything between the time it ran and later would not run, my guess is you have a fuel delivery problem. You can remove the drain plug on the carb and catch a pint or more in a container. It should run a full 1/8 inch stream until the fuel runs out or you replace the plug. If not, backtrack the fuel flow until you find the restriction. Look for:
1. debris in the filter screen inside the carb fuel inlet point,
2. sediment/rust, etc in the fuel valve screen at the tank and inside the nipple where the valve screws into the tank,
3. sticking float or needle valve,
4. correct float height adjustment.
Once there is a flow at the drain plug, check the main and idle jet for restriction. Good Luck

[John *.?-!.* cub owner]

go to your local auto parts store and get one of these. You can use it with a spark plug wire directly off the coil, or just connect it to a plug wire to verify spark going directly to each spark plug. You need a minimum of 3/16 inch of spark to run the engine.


Image courtesy of Autozone

[Papa's Cub]

John, what is that instrument called. I'd like to add one of those to my tool box. Thanks, Tom.

[Hengy]

How much play is there in your rotor? It should not move but a couple degrees at most. If there is excessive slop in the rotor, it can run great one time and misfire others. Most of the time the little pinion drive that drives the rotor will get "star shaped" instead of nice and rounded and causes the slop in the rotor. While you are in there, it is a good idea to replace both items (even though a bit "spendy")...

Mike

[John *.?-!.* cub owner]

I always just called it a spark tester. Here is a link to one on Autozone, but most any auto parts store either has or can get one.
http://www.autozone.com/autozone/access ... 10257_0_0_

[pfj]

pinion 2.jpg (97.86 KiB) Viewed 334 times

With respect to the pinion gear, I would say the teeth are certainly sharper than those on the rotor. I assume swapping the pinion gear out is fairly straight forward? Any suggestions as to where I can get one, and should I get a new rotor while I am at it?

rotor 2.jpg (112.15 KiB) Viewed 334 times

With respect to the comment about cleaning the fuel, I will have a go at that again next time I can get at the tractor (not for a couple of weeks unfortunately).

BTW - I have to thank John again for all his help with this project so far.

[Don McCombs]

Pinion and rotor are both available from TM Tractor Parts at the link below.

[John *.?-!.* cub owner]

The pinion gear just pulls out. there is a flat spot on the shaft so it can only be installed in one position. The new one will be what looks like a white plastic. For lubrication, use high temperature grease such as wheel bearing grease that is used with disk brakes.

[Hengy]

Yup. That pinion will definitely cause your rotor to jump time! Replacing is very straightforward. It is a pull off affair as others have said.

Good luck!

Mike

[Rick Spivey]

With respect to the pinion gear, I would say the teeth are certainly sharper than those on the rotor. I assume swapping the pinion gear out is fairly straight forward? Any suggestions as to where I can get one, and should I get a new rotor while I am at it?

I probably would NOT replace that rotor, as the teeth look barely worn at all. I have rebuilt quite a few magnetos, and fortunately, the pinion is almost always the weak link. I replace numerous pinions, but very few rotors.