Out of timing

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ctm4003@bvu.net
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Joined: Tue Aug 02, 2022 5:51 pm
Zip Code: 24202

Out of timing

Postby ctm4003@bvu.net » Mon Sep 12, 2022 1:58 pm

1948 cub….I pulled distributor to work on points. I did not pay attention to rotor button. Now, tractor will not start and backfires like it’s firing mortars. I tried removing #1 plug and marking rotor button when valve closed, then rest of firing order pew google search, and it’s still out. Help!

Ctmcmurray@bvu.net
423-383-9025

Thank you,

Trevor McMurray

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Bill V in Md
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Tractors Owned: 1948 Farmall Cub
LT1045 Cub Cadet
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Location: MD, Catonsville

Re: Out of timing

Postby Bill V in Md » Mon Sep 12, 2022 3:08 pm

I am assuming your 48 Cub still has a magneto ignition. With number 1 piston at TDC and on the compression stroke (valves closed) the magneto rotor should be pointing at the number plug tower in the distributor cap. Make sure the mark on the magneto rotor lines up with the mark on the rotor pinion gear. Points should be gaped at .013. Assuming you have not loosened and moved the magneto body, it should still be in time.
Bill VanHooser
Circle of Safety

ctm4003@bvu.net
Posts: 6
Joined: Tue Aug 02, 2022 5:51 pm
Zip Code: 24202

Re: Out of timing

Postby ctm4003@bvu.net » Mon Sep 12, 2022 3:36 pm

It was converted to 12 volt, so it has coil. I pulled the distributor out of body to file on points, now it won’t start…but wants to

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Glen
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Re: Out of timing

Postby Glen » Mon Sep 12, 2022 3:57 pm

Hi,
A 1948 Cub came with a magneto, I don't know if you meant it has been changed to a Battery Ignition unit, some Cubs have been changed to them.
The Battery Ignition unit came out in 1950.

Below is a page from the 1949 Cub owner's manual telling how to time the magneto to the engine.

http://farmallcub.com/rudi_cub/www.clea ... age-32.jpg

The number 1 cylinder spark plug wire post is originally the top post on the magneto cap.
When removing spark plugs clean any dirt that might be at their bases, to keep the dirt from falling in the engine.

I file or replace the points without removing the magneto or Battery Ignition unit from the engine.

I sit beside the engine on a lawn chair, and use a good light to see in the magneto.
I put a large towel on the floor under the magneto to catch small screws I might drop.
You need a short screwdriver with a sort of wide blade, and usually an 11/32" open end wrench for the nut at the end of the point spring.
If the Cub has a rotary mower under the middle of it, instead of the chair, let the mower down to the floor, and put something on the mower to sit on.
You have to run the engine to let the mower down, so if it doesn't run, you can't let the mower down.
Maybe put blocks under the skids on each side of the mower to make it stable, and then you can put something on it to sit on.

It is not hard to time a Battery Ignition unit to the engine.
Turn the engine to number 1 cylinder TDC, like it explains how to do in paragraph 2 in the link above, use only paragraph 2.
Install the Battery Ignition unit with the rotor pointing to the number 1 spark plug wire post on the cap, which should be the upper right post, looking from the rear forward.
Usually they will run, then set the timing using a timing light.

Below are pics from TM Tractor.
The 1st pic is a magneto.
The 2nd pic is a Battery Ignition unit, there is a car style coil goes on a bracket on top of the unit, it is not there in the pic. :)
Attachments
Cub magneto 5.jpg
Cub Battery Ignition unit 4.jpg
Last edited by Glen on Mon Sep 12, 2022 4:06 pm, edited 1 time in total.

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Bill V in Md
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Posts: 1018
Joined: Sun Feb 02, 2003 6:51 pm
Zip Code: 21228
Tractors Owned: 1948 Farmall Cub
LT1045 Cub Cadet
Circle of Safety: Y
Location: MD, Catonsville

Re: Out of timing

Postby Bill V in Md » Mon Sep 12, 2022 4:04 pm

Assuming it has been changed to battery ignition, the points are gapped to .020".
Bill VanHooser
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staninlowerAL
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Re: Out of timing

Postby staninlowerAL » Mon Sep 12, 2022 8:27 pm

But if the mag is still being used with an external coil set the points at .013 and make sure the rotor and pinion marks are aligned as noted above.
USAF & Reserves, Reg ARMY, ARMY NG


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