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Allis B Ignition problems

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Bob

06-18-2003 20:02:07

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I have a 1939 Allis B that I use to mow with. The other day, while mowing it just quit and I could not get it started. Starting with the basics I determined that the plugs were not getting a spark. I disassembled the Magneto and found that the gear that drives the rotor was stripped because the bushing on the Mag cap had failed. I bought a new cap, gear and rotor put it on and it ran good, but was hesitating under load. Thought the timing was just a little off so I adjusted. Unfortunately when I tightened up the Magneto I broke the lower flange. Went to the slavage yard and got another Mag. Changed the condensor and plugs from the previous unit. Lined up the fire line on the fly wheel and lined up the magneto to the motor, keeping the rotor on the emboss. I can no longer get the tractor to start. I checked for a spark and am getting one. Any ideas? Need my mower back soon!

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Duey (IA)

06-20-2003 21:11:38

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Re: Allis B Ignition problems in reply to Bob, 06-18-2003 20:02:07

Bob, Timing a mag. (FMJ)
1. If you have taken the Mag. apart, the internal gears need to be timed. (Set points at .020)
2. Remove the large cap and line the C mark on the fiber gear with the marked tooth on the steel gear. Tip- turn the engine backwards to get the steel gear tooth to stop straight up and position the C mark on the fiber gear straight down. This times the rotor to the points. It is pretty simple in theory. Like all four cycles, the piston comes to TDC (top dead center) twice for every time the magneto or distributor rotor goes around. ("B"&"C")The left side of the engine has a hole in the bell housing where you can see the timing mark on the flywheel. ("WD" &" WD45" The timing mark is found by looking under the flywheel housing for a small hole possibly covered by a small plate held with two wing bolts. The FIRE mark and the TDC mark are located on the flywheel through this hole. Use a little light colored paint to make seeing them much easier). 3. Take out the #1 spark plug, and put your thumb over the hole while hand cranking the engine(best to have all the plug wires off while doing this so the tractor doesn't try to fire) , the cylinder will force air past your finger on the compression stroke. (The other FIRE is the exhaust stroke and has the exhaust valves open so no air will come out of the plug hole).
4. When you feel the air coming past your thumb, look for the FIRE mark on the flywheel. When this mark is centered in the hole, the rotor on the mag should be just lower than the #1 lug on the mag. Looking at it as a clock, #1 lug should be near 10:00. Just before the lug is a plastic stud called the timing stud. Perfect timing is when the rotor points to the timing stud while the FIRE mark on the flywheel is centered in the hole. 5. If your rotor points to 5:00 your mag is 180 degrees off and needs to be removed and the coupling turned till you achieve 10:00. If it is not right on the timing stud, you can loosen the mag and rotate it until it is. 6. Put it all back together and time your spark plug wires 1-2-4-3 clockwise on the magneto cap.

Remember if the rotor is aligned with the timing lug when the fire mark is in the window, you got it right. If it's not quite aligned when the fire mark is in the hole, then you rotate the mag clockwise or counter clockwise until it is. Remember Perfect timing is when the rotor points to the timing stud while the FIRE mark on the flywheel is centered in the hole.

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Rod (NH)

06-19-2003 09:20:13

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Re: Allis B Ignition problems in reply to Bob, 06-18-2003 20:02:07

Hi Bob,

Another thought: Were you careful in meshing the rotor pinion and drive gear with the proper marked teeth when you replaced the magneto end cap? If these teeth are not properly meshed (it's not particularly easy), you will be out-of-time.

Rod

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dave of southwest michiga

06-19-2003 03:56:10

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Re: Allis B Ignition problems in reply to Bob, 06-18-2003 20:02:07

Bob, Did you check to be certain that when the firing mark was visible that the engine was on compression on #1 cylinder? You have to rotate the engine with spark plugs removed until you feel the compression building in #1, then align your firing marks. Also, make sure that the magneto is read to fire #1. Hope this helps.

Dave

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Bob

06-19-2003 05:05:20

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Re: Re: Allis B Ignition problems in reply to dave of southwest michiga, 06-19-2003 03:56:10

Dave,

Thanks for the input. I made sure that #1 cylinder was under compression and that the fire mark was aligned. I am at wits end. The motor wants to start, it will fire, but not start. I bump started it, but it ran rough and would not idle. While started I tried to adjust timing with no luck.

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dave of southwest michiga

06-19-2003 20:04:54

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Re: Re: Re: Allis B Ignition problems in reply to Bob, 06-19-2003 05:05:20

Bob, Dick has some good thoughts. Another comes to mind too after reading your follow-up. Are you sure you haven't got a spark plug wire crossed? I'm not positive of the firing order for a B (I have a C), but it's easy to cross a wire, which could allow you to start it, but it would run rough and adjusting the magneto would do little to improve the situation.

I'll sleep some more on it. When was the last time it was running ok?

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Dick L Probly Timing

06-19-2003 09:17:04

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Re: Re: Re: Allis B Ignition problems in reply to Bob, 06-19-2003 05:05:20

A little trick if you do not have a timing light.
Take number one plug wire off and position it to spark to ground where you can see it while turning the crank. Crank very slowly and watch for a spark. When it sparks look into the inspection hole and you need to see the Top Dead Center Line. Reset your magneto untill you are very close. You can put the tractor in third gear and rock the wheel to see how far you are off.

A little post note, Forget about the fire line unless you are using a timing light. When timed not running to the top dead center line, the advance built into the magneto will cause the fire line to show under the timing light.

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