John Deere B Magneto

If you run into a failure, contact me for further directions. If I am in, I will respond. Here is the series called Basic Engine Timing -- assuming you have a "B" John Deere -- (PatB)
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BASIC ENGINE TIMING

1. To check valve timing when engine is assembled, first adjust tappets to 0.022 (for series A, B, & G).

2. Verify Flywheel is Installed Correctly on Crankshaft:

Deep keyway of flywheel should be placed over locating screw on shaft; OR - - - if wheel hub carries a rivet, the rivet should be engaged with cutaway spline on shaft.

3. Verify Relationship Between Crankshaft & Cam Shaft:

Turn flywheel in normal direction of rotation until exhaust valve of left cylinder is just beginning to open (tappet gap closes to 0.000), and STOP!

At this time, the flywheel mark L.H. EXHAUST OPEN should be within one inch of 3:00 o'clock!

4. Verify Relationship Between Governor Shaft and Cam Shaft:

Remove left spark plug & remove the magneto.

Hold your finger over the empty sparkplug hole & rotate flywheel in normal direction until you feel compression build up & stop.

Observe that mark L.H IMPULSE is in close proximity to 3:00, and gently move the flywheel until it is dead nuts at 3:00 -- aligns with the mark on gear cover behind the flywheel, and STOP.

[This is defined as the No. 1 cylinder @ TDC position]

With the engine in this position, the magneto drive coupling slots should be horizontal.

5. Reinstall Magneto and remaining ignition parts:

With the engine in position defined in item # 4 above, connect spark plugs to the magneto using spare ignition wires and ordinary baling wire to connect the ground side. When held in the same attitude as when mounted on the tractor, the upper terminal is the No. 1 terminal, and the lower is for No. 2.

Holding the magneto in the same attitude as when mounted on the tractor, rotate the magneto drive cup CCW until you hear a trip. One of the plugs will have fired -- make note of which one. Repeat this process until you are sure of what you are doing, and stop just as the magneto fires at No. 1 plug. DO NOT TURN THE MAGNETO FROM THIS POSITION!

Disconnect bench set up WITHOUT MOVING THE MAGNETO SHAFT, and remount magneto WITH GASKET onto the tractor. The flange alignment shouldn't be much different from the horizontal direction discussed in para 4 above. Do not tighten bolts just yet!

Once mounted, gently grasp the magneto with both hands and rotate it CW as you are standing there looking into the tractor's right side. Take the magneto in this direction as far as it will go.

Back on the other side, rotate the flywheel in its normal direction until the L.H. IMPULSE mark is at the 3:00 o'clock point, in alignment with the marker on the gear cover. Approach this point carefully, not overshooting! If you overshoot and the magneto fires, you must go around again.

Back on the right side of the tractor, begin to slooooo ooowly rotate the magneto in a CCW direction (top of magneto to the rear) until you hear the impulse "click". FREEZE. Tighten the bolts. Timing is complete. ++++

Timing a Deere is quite simple really. (1) The flywheel must be on the crankshaft "so-so". (2) The crankshaft-to-cam shaft relationship has to be sort of "right-on". (3) And then the governor which drives the magneto must be installed in a "right" relatinship to the cam shaft. and finally, (4) The magneto is "trimmed" to strike when the piston is at TDC. This is all under a heading of Basic Engine Timing. I can lead you through this I think, but when you write back with your home e-mail (I know it's dial-up -- and will keep things simple)-- when you write, include the Model and serial number of that tractor so we can zero in on things at first blow.

You are welcome to give me a call too -- if I am in the office, I will usually pick up. The number is (830) 627-0430. (PatB)

If you get confused when trying to set the magneto starting timing correctly, take a peek at page 8 of ELECT SYSTEMS over at the JD-H Site (Below). Look through the drop-downs under Articles 1. There you will find a step-by-step procedure for setting the magneto up. In the early going, however, I would recommend that you DO NOT remove the magneto. Simply loosen the two mounting bolts by about a turn (best done with an old distributor or obstruction wrench - especially for the lower one). Once loosened, you should be able to gently rotate the magneto (top toward front of tractor) to its limit. The mounting holes are slotted. Then pick up in the middle of step # 3, "Rotate the flywheel . . ."

SAFETY FIRST! It is best to remove both plug wires to avoid an inadvertent start when you least expect it!

Feel free to write or call (830) 627-0430 if you get confused or hung up. Have a Great & Successful weekend! (PatB)

• Restoration Site, JD-H

Your questions are telling me you do not have an operator's manual or any kind of service book for the tractor & you need to get them! Once again, I send you to the JD-H site, and under articles drop downs, look for DEERE PUBS. There you look up your tractor and see the JD publications that are for it -- also the piece tells you how to obtain them.

Now -- back to timing. When the tractor is running, TDC IS NOT the firing point, but rather -- some 25 - 35° BTDC. This is what is called Running Timing, and is a function of the magneto -- which is described in the JD-H restoration site piece entitled ELECT SYSTEMS that I referred you to earlier. I realize you are new to magneto-based systems, but if you are going to help yourself, you must do as John T tells you -- loosen the magneto so it can be rotated forward enough to have the impulse click happen when the LH Impulse mark is at 3:00 o'clock. No one on this board would try a setting like you have and expect it to work. (PatB)

• Restoration Site, JD-H

If thats NOT the case (WHEN THE FLYWHEELS LHI IS AT 3 O CLOCK), then your flywheel could be off a spline or so !!!!! !!!!! ! cuz if its on the correct crankshaft spline, when the LHI mark is lined up with the flat mark at 3 o clock, the left cylinder is at TDC

With the left plug removed perhaps you can use a piece of wire etc to observe the pistons TDC to confirm all this.

NOTE If shes firing at 3:30 thats BEFORE the piston reaches TDC so what you describe is somewhat Id expect, cuz 3:30 is before TDC so the flywheel needs to turn a tad more CCW before it reaches TDC i.e. she fires BEFORE TDC so the flywheel needs turned more before the piston reaches TDC kinda what I understand you to mean correct????? ????? ?

I still think (assuming cranks on correct spline which I think it is) you just gotta time the mag so she snaps at TDC (LHI at 3 o clock) NOT 3:30 BEFORE TDC

If you cant get enough forward CW retarded timing adjustment on the mag so she snaps at TDC (LHI at 3) then you gotta remove it n adjust the rear lag angle setting.

LOOSEN THE MAG N ROTATE IT FORWARD CW ENOUGH TO RETARD THE SPARK SO SHE SNAPS AT TDC (3:00 NOT 3:30 before TDC) MAY CURE ALL YOUR PROBLEMS If not adjust the lag angle

John T

If you loosen n rotate the mag backward CCW that advances BOTH the start n run time advance while forward CW retards them. You might adjust it there externally to set the start timing so she snaps at TDC ifffff ff its adjustable to such a position and use a timing light to determine when shes firing at once over 250 RPM. However if its not possible to externally rotate time it far enough to do that (snap at LHI at 3 o clock) you need to remove the mag and adjust the rear lag angle setting and then start over. On the rear the drive cup may or may not be labeled with 25 or 35 degrees etc or 6274 which allows for the proper lag angle setting. If its labeled 25 that means (when all new n no slop or wear) the run time advance would be approximately 25 BTDC but still dependandt upon the front external rotational timing adjustment n what wear is present ASSUMING the cam n governor gears etc are alllll ll in tiem as they should be.

Adjust the external rotational timing (CCW advance, CW retard) to get her to snap at LHI at 3 o clock if possible n see what happens. Again, if she cant be rotated far enough to do so, then its time to set the rear lag angle n check the governor gears timing while in there.

John T

To learn a bit more about how your magneto works, check in at the JD-H Restoration Site (below), and upon arrival, one-click on the Articles # 1 drop down to ELECT SYSTEMS. 'Interesting read. (PatB)

• Restoration Site, JD-H