Allis B timing

Howdy folks,

Working on a 1940 Allis B hand-cranker. I
can't seem to get the little feller to start.
The tractor has had the engine totally rebuilt,
it has a rebuilt carburetor (which I have also
taken apart and checked to see if any jets are
plugged) and a "re-re-rebuilt" magneto. The
plugs and wires are all new too. When I crank
it over in any configuration of choke and
throttle I might get a pop out of it or a hit
once in a great while but it won't start and
run. I had it running a couple days ago and
didn't change anything with the tractor except
cleaning out the suction end on the oil line
down in the pan.

Now, when I timed the tractor I followed the
old operators manual and brought the mag up to
where it sparks on number one plug. I then
bring number one cylinder up on compression and
on over till I see the "center" in the timing
window. Then I put the mag on. The
interesting thing is that when I leave number
one plug out of the tractor but still hooked up
to the wire and crank the engine around until
the plug sparks, the "center"is not in the
window when it does. Is it possible that my
magneto guy didn't time it correctly? I am an
idiot when it comes to mags. I appreciate any
help you can give. God bless!

--old fashioned farmer

It sounds to me that either the magneto is not properly timed to the engine or the magneto itself is improperly timed internally, assuming a Fairbanks Morse FMJ4B3 magneto. See my page on how to time the B <a href="http://rodnh.byethost12.com/acb/magtiming/magtiming.htm">here</a>.

Send me an e-mail and I can then in turn send you the manual on that mag. There are 2 common mags used on that tractor and I have manual for both

Thanks Old and Rod,

I got brave and took the mag apart this evening. The fella that worked on it had the metal gear tooth with a white mark pointed right at the mark for counter-clockwise mags. Well, this one happens to be a clockwise turner. Both of those points had little dobs of white paint. I assume the previous mechanic had marked it. Anyway, after putting it together with the marks corrected I found that I had no spark on any wires. Hmmm. I took it apart again and looked a little closer. I finally noticed a tooth on the metal gear that looked like it had been filed back just slightly. It looked different from all the rest,including the painted one. I realigned it with that tooth pointing at the "c" for clockwise rotation and reassembled it. Testing it in the vice with a spark plug connected, I am getting more consistent and hotter spark than it ever did have. Whew! I was glad to see that. Hopefully she will fire right up now that it is all timed right. Thanks again for the help.

--old fashioned farmer

If I were to show up at your place to check it out the first thing I would do is to pull the magneto and check to make sure the governor drive slot for the magneto was horizontal when the center line was centered in the inspection hole on the compression stroke.

This is if you can not rotate the magneto one way or the other within the bottom slot on the magneto to get it on center.

If you bring it up on the compression stroke slowly you need to have the center showing at the instant it snaps. If you get a spark at the snap and you do not see the center in the hole it will not be in the magneto. You can not adjust the impulse snap in the magneto. That would be a gear timing problem. The magneto drive slot must be horizontal at TDC on number one cylinder.

If you have the cylinder at TDC and your installing the mag so it is getting ready to wind up and fire, the mag still has maybe 20 degrees to go till it fires. You bring the #1 cylinder starting up toward TDC and install the mag "getting ready" to fire #1... then roll the motor over and see if you are at TDC when it fires.. If its a few degrees off, you loosen and push the mag inward or pull outward to get the last few degrees........ If your 90 degrees off, then you slid the mag in when the Crank was not close enough to TDC..... read Dicks post.