49 Cub magneto impulse timing

[Shot (MI)]

There is a thread for J4 rotor timing that may help if you can find it.

Thanks, I'll look for that thread too.
My rotor is gear driven. I checked and double checked it while I was trying to get the mag right.
I'm aligning the dot on the gear with the rib on the back of the rotor opposite the metal part.
Hopefully I have that right.

[Jim Becker]

Messing with the rotor timing (rotor mesh with pinion inside magneto) will have no effect on your problem and cause other problems.

If your mag drive slots are not in the right position when the pulley timing mark is at TDC, the problem is somewhere between the pulley and the drive slots. Specifically either:
1) The gears are not properly timed (installed with marks not in line).
2) The pulley is out of position on the crankshaft (installed without key or key/pulley/crank damaged).

Tell which it is by checking actual piston TDC vs. TDC mark on pulley. To accurately find TDC. Remove #1 spark plug. Insert something (screwdriver or whatever) into the cylinder so the piston will bump it on the way up. Slowly rotate the crankshaft forward until the piston bumps the stop. Put a temporary mark on the pulley at the pointer. Slowly rotate the crankshaft backwards until the piston bumps the stop. Put a second temporary mark on the pulley at the pointer. TDC is half way between the two temporary marks. This process is easier if you have a helper to hold the tool in the plug hole.

Case 1: If the gears are so far off you can't get it in time, it probably hasn't been in time. If this is the only Cub you have experience with, maybe it seemed like it was running fine but really it wasn't. The fix is to remove the governor and remesh the gears to get the drive slots in place.

Case 2: Get a temporary TDC mark on the pulley and use it to time the ignition. Long term, you want to find out why the pulley is out of position and fix it (pull, inspect, repair, reinstall in right position).

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

The drive slot will be in this position anytime a piston is at TDC (2 times per engine revolution). The mark on your pulley will line up for piston 1 TDC and for piston 4 TDC. If your pulley has 2 marks, it is normally the second one that passes the pointer. I say normally because you never know what has happened in the past, such as a second notch being filed in the wrong place, woodruff key in crank pulley partly sheared, etc.

[Shot (MI)]

The drive slot will be in this position anytime a piston is at TDC (2 times per engine revolution). The mark on your pulley will line up for piston 1 TDC and for piston 4 TDC. If your pulley has 2 marks, it is normally the second one that passes the pointer. I say normally because you never know what has happened in the past, such as a second notch being filed in the wrong place, woodruff key in crank pulley partly sheared, etc.

Thanks John, I'm sure I read that 2 and 8 o'clock position reference somewhere before.
And if mine looked like yours, it would match my magneto when the mag points to #1 but it doesn't.
I verified with a wire that when my #1 piston is at TDC it matches the mark on the pulley.
However my mag drive is closer to 3 and 9 o'clock. Here's a picture of it.

[k hutchins]

I still think you'ld be ok with that positioning. Install the mag keeping the top as close to the block as possible.
Crank it by hand to the next TDC then slowly pull the coil away from the block until it trips.
Keep in mind the mag has to be fully assembled. What I learned the hard way was that even having the cap off seems to mess up the timing.
Good luck.

[k hutchins]

Just watched a video on timing a cub magneto produced by mike from Wisconsin.
I believe it was titled How to time a magneto equiped cub....film at 11:00

Hopefully it will help. It did show and they emphasized the slots being at 2 & 8.

[Shot (MI)]

Just watched a video on timing a cub magneto produced by mike from Wisconsin.
I believe it was titled How to time a magneto equiped cub....film at 11:00

Hopefully it will help. It did show and they emphasized the slots being at 2 & 8.

I found that video, that's exactly what I'm trying to do.
Looks like I may have to pull the governor and mess up my new paint.

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

You may be able to get it run with the lugs in the position you show, but it will not run right. I ran into that with my 49. It had been overhauled by a sloppy mechanic and rather than pull the governor and fix the problem he told the owner the mag was bad and sold him a distributor. I discovered the problem when I tried to convert it back to a magneto.

[Mag Man]

Sitting here sore as heck from my back procedure yesterday . But I only loosened my gov when I had to fix mine did not have to take it all the way apart if that helps. I have dist and live hyd. and good pain meds LOL

[k hutchins]

Heal fast and feel better soon Mag Man
Shot could really use your wisdom.

[k hutchins]

https://googleads.g.doubleclick.net/acl ... 6t%3D44758

Hopefully this works
here is the video thread

[k hutchins]

http://www.farmallcub.com/phpBB2/viewto ... 54&t=44758
Incase that link doesn't work, here is the one Mike from Wi posted on another thread.

[Shot (MI)]

http://www.farmallcub.com/phpBB2/viewtopic.php?f=54&t=44758
Incase that link doesn't work, here is the one Mike from Wi posted on another thread.

Thanks for the link, that looks to be the same procedure I was following.

I believe I have it fixed, thanks to all of you.
I took the governor loose and moved it forward just enough to clear the gears.
Then turned it one tooth counterclockwise (from the mag drive end)
Now it lines up with the ears at 2 and 8 like in the video as well as John and Magman's pics.
My magneto slipped right in when turned backwards to #1 after doing that.

One turn around on the crank, turned the mag away from the block until it tripped and snugged it down.
One more turn around to TDC on compression stroke and it tripped just as it passed TDC. Perfect!
It also tripped at the half-way point as in that video, so that made me feel I had it too.

I put some gas in it and decided to try to start it for the first time in over five years.
The engine fired almost instantly but wouldn't stay running.

Ok, timing is very close, probably have a fuel problem.
The carb was full of mud dobbers nests after all these years before re-assembly.
So I had already cleaned and rebuilt it. I figured maybe I missed something in there.

I choked it some more to see if it got better or worse. It got worse.
Still fires, but now with smoke out of the exhaust.
Yep, definitely flooded.

Decided to wait until tomorrow and try it again.
I put the battery charger on the battery for the night.
While doing that I realized the #1 spark plug was still laying on the bench.
I guess in my excitement of getting the timing right I forgot to put it back in.
I'll try to start it again after work tomorrow. LOL

[k hutchins]

Great news, glad if I was some help.
yea leave a plug out can definitely be detrimental to smooth running.
Best of luck with the restart.

[Shot (MI)]

Great news, glad if I was some help.
yea leave a plug out can definitely be detrimental to smooth running.
Best of luck with the restart.

You guys are too kind. Someone should have given me flack over that faux pas!
After setting overnight the tractor did start and run.

It fires quickly and easily but it does take a few tries before it stays running.
Then it runs a bit rough. Not timing rough, sticky valve rough.
I've hear that many times before and since this tractor has sat for so long I'm not surprised.
That's an easily fixable problem a lot of the time so I'll get after that.

I'm waiting on one last part then I'll take it for a test drive.
When I have it outside I'll take some pictures of it and post them.

Thanks again for all the help!