Magneto timing on 51 B

ndgregor

Member
Hello. I recently exchanged my old WICO C I was having some trouble with for a rebuilt WICO C. Now I am trying to install and time it. Can someone let me know if I am doing this correctly?

My first step is to stick a wire into the top plug hole and run it to a place 1/8" or so from the mag frame. I turn the coupler until the impulse snaps and I get a good blue spark.

On the tractor side, I remove the valve cover to watch the valves and watch the LH cylinder intake valve open and close confirming I am now at a compression stroke. I roll the flywheel forward until the LH IMPULSE mark on the flywheel lines up with the line on the tractor frame. At this point, the coupler on the governor is horizontal. I install the magneto and finger tighten the cap screws. I then rotate the magneto forward (towards the front of the tractor) as far as possible.

I now go back to the flywheel and rotate one complete revolution, and again line up the LH IMPLUSE mark on flywheel with the line on the tractor frame. As soon as I get to this point however, the mag impulse trips. I thought the last step was to rotate the mag rearward slowly until the impulse trips? Is something wrong with this procedure? It doesn't seem to want to start following this procedure. New plugs and cables and correct cables running to each cylinder.
 
Great question, here's how I do it.

I "rough in install" time it with mag first set forward retarded,,,,,,,,,slowlyyyyyyyy bringing the left piston to TDC (Flywheels LHI at 3 o clock flat mark) and stop, and then slowlyyyyyyyyy turn mag backwards CCW advance until it snaps/impulses BUT THEN I FINE TUNE IT PER THE BELOW. Actually however, you can have the flywheel BEFORE TDC (LHI before 3 o clock flat mark) in order to get mags coupler installed into the govenor shaft female open slot,,,,,,,,,, then you can install the mag in a retarded forward CW position,,,,,,,then slowly bring the flywheel to TDC (LHI at 3 o clock flat mark) and stop,,,,,,,,,,,then slowly rotate the mag backwards CCW to advance it and STOP when the impulse snaps. THAT GETS YOU IN THE BALLPARK THEN DO THE BELOW

Sounds like you're well aware rotating the mag backwards CCW advances timing while forward CW retards. I first adjust the lag angle and then install the mag and for best starting it needs to snap/impulse right when the left piston crosses TDC (LHI on Flywheel at the 3 o clock flat mark on tractors side) on the compression power stroke. Once roughed in per the above, I watch the flywheel, rotate it slowlyyyyyyyyyyy, and then adjust the mag in the governor until it snaps/impulses right at TDC (LHI at 3 o clock). If it snaps AFTER that (late) rotate the mag backwards CCW, if it snaps BEFORE (early) rotate the mag forward CW. Very carefully and slowly a tad at a time rotate the mag until it snaps/impulses right when LHI on flywheel passes 3 o clock flat mark. It starts best at TDC, if it fires late its harder to start but if it fires early the flywheel can kick back.

Mine start best when I can advance the start/impulse as far as possible advanced right up to TDC just so shes not too fast where the flywheel kicks back.

Mine hand start best when impulse snaps right at TDC,,,,,,,,,,,with throttle at idle,,,,,,,,,, don't over choke and flood,,,,,,,,,,, then I bring left piston to TDC on its exhaust stroke where its ready to go down and suck in fuel,,,,,,,,,,,then give it a good spin to suck in fuel (dont dilly dally so the gas stays in vapor state) ,,,,,,,,then roll it over on compression and it should start.

That's my method and what works best for me, others may use different methods which works best on their tractor, no two are alike so no warranty what I do works on your tractor BUT STILL THE IMPULE NEEDS TO OCCUR RIGHT AT TDC

John T
 
Thank you very much for the information and reply. I will try modifying per your procedure. It sounds like what I have done so far though is correct. If I am having trouble starting, only occasionally getting a pop would you guess the mag is too advanced or too retarded? Based on what you said it sounds like if anything it is too retarded? I even went ahead and shot some starting fluid into the cylinders then replaced the plugs and all I got was one small pop. Everything from the magneto to the plugs is new, and the carb has been thoroughly cleaned. It HAS to be a timing issue then right?
 
When you rotate the flywheel the mag should trip at LH impulse. You can hear it. Is it possible you got the timing off 180 degrees? Ron Mn
 
I can hear it going off, it seems to be right at LH IMPULSE. If I did have it 180 off, I could just swap the plug wires right? I am almost certain this is not the case though but I will check.
 
If its too fast you will soon find out because the flywheel will kick back. If to slow hard to start. Its gotta SNAP right when flywheels LHI passes the flat mark at 3 o clock. Like greenmech said it can be 180 out but in that case it may pop n bang n kick back something awful.

John T
 
Do you have the flywheel cover off? Steel frame letter series tractors from 1948 to the end of production in 1952 are usually timed with the cover on. The insert in the middle of the flywheel cover is removed. There is a center punched dot on the flywheel hub. TDC is obtained when this dot is aligned with a vertical slash on the flywheel cover at the 6 o'clock position. It is not necessary to remove the valve cover to determine whether the no. 1 piston is on compression or exhaust stroke. The letter series and first numbered series ignition systems are governor driven and fire on BOTH compression and exhaust strokes. If your magneto is firing too soon, you will need to loosen the little screws inside the back of the magneto and adjust the impulse stops to make the magneto fire later. When the flywheel side piston is at TDC, the first prong of the forked rotor should be pointing at the top lug on the magneto cap. Is it?
 
Forget what I said about the forked rotor as I was thinking you had a Wico X instead of a Wico C. The rest of my comments still apply. I would think a 1951 tractor would have the improved X magneto.
 
I removed the flywheel cover bolts and shifted it to the side so that I could see the letters and marks on the flywheel edge. I did not know that you could do it through removing the middle of the flywheel cover. Both the magneto and carb on this tractor are not original, and I have no idea how it ended up with a WICO C and a DLTX 107U carb.

Is there anyway to tell (other than comparing when you hear the snap of the mag to the position of the center punch/vertical slash) whether the mag is firing too early or too late? This is a freshly exchanged mag so I am inclined to believe the impulse stops SHOULD be set correctly. I previously timed the older WICO C mag myself and was successful. It baffles me that I can spray starting fluid into each cylinder crank it with a freshly rebuilt mag, new copper core plug wires and new Autolite 3116 plugs and I only occasionally get a pop. The only possible way I can think of that happening is the timing isn't right?
 
You were doing ok. Here is what you may not be aware of. The magneto turns at crankshaft speed not cam speed. And it fires LH at impulse mark and the RH 180deg later both at compression and between exh and intake. If mag is tripping too soon, impulse trip thingie may not be in right place. If at LH imp mark the slots are true horizontal, then gears are timed correctly. Had one that was a tooth off and still ran.
 
When I line up the LH IMPULSE mark on flywheel with slash on the tractor frame, the coupler coming out of the governor IS horizontal that I did check. So it sounds like governor is set up and geared properly, which makes sense since it ran just fine a few months ago.

What would be the impulse trip thingie that may not be in the right place? Is there a way to confirm the mag is tripping too soon? Maybe I should try to intentionally retard the timing by rotating the entire magneto forward?
 
Since it is not starting for me, would it be fair to assume it is too slow/retarded? Should I try rotating the magneto rearward/counter-clockwise and see what happens?
 
You ask " Is there a way to confirm the mag is tripping too soon?"

YES if it trips BEFORE the Flywheels LHI passes the 3 o clock flat mark THATS TRIPPING TOO SOON

You state "Maybe I should try to intentionally retard the timing by rotating the entire magneto forward?"

You retard or advance it by turning it in the governor UNTIL it trips at TDC IE when flywheels LHI passes the flat 3 o clock mark.

John T
 
The thingie.. Looking at the mag coupling end, holding the mag as on tractor, turn mag in direction of normal rotation and you should see the lock bar for lack of better name, flop out and try to stop mag shaft from rotating. Where that occurs in the 360 deg of the rotation sets the relationship of trip to where the engine rotation is. If you have the old mag look at it and see if the stop is in same location. I think it is usually about 7oclock. When you say you got replacement mag, the stop could have not been set. I have a C mag at shop I can check later. There are 4 screws the hold the ring in place. Maybe some one else will have more info as how to set that trip point. I'm going from experience here, have never seen info on how to exactly set it. I think originally that was done on a test machine to get the degrees correct.
 
You ask "Is there anyway to tell (other than comparing when you hear the snap of the mag to the position of the center punch/vertical slash) whether the mag is firing too early or too late?

YES it needs to snap right when the left piston is at TDC, not before not after. TDC can be determined by Flywheel on earlier tractors (has LHI mark) or on later by removing the center of the flywheel cover

This is a freshly exchanged mag so I am inclined to believe the impulse stops SHOULD be set correctly.

NOT NECESSARILY the lag angle is adjusted to match whichever drive cup is used. If its a 25 degree cup the lag angle needs set to 25.

John T
 
YES you need to try timing the mag CCW to advance or CW to retard UNTIL IT SNAPS AT TDC

John T
 
You keep asking how to tell if it snaps too early or to late or if it needs adjusted. So here is info that should help and answer alllllllllllll your questions below:


IT NEEDS ADJUSTED SO IT SNAPS AT LEFT PISTONS TDC

CCW ADVANCES SPARK CW RETARDS

THE LAG ANGLE NEEDS SET TO MATCH WHICHEVER DRIVE CUP IS USED. If its a 25 degree cup the lag angle needs set at 25

Rotation of entire mag in governor changes BOTH start impulse time plus run timing

Adjustment of lag angle in rear ONLY affects start impulse timing NOT run timing

John T
 
You ask "What would be the impulse trip thingie that may not be in the right place?"

On the rear of the mag is where you loosen 4 screws and adjust the lag angle. It needs to be set to match whatever drive cup is used. If a 25 cup (very common) set the lag angle to 25 degrees.

Adjusting the lag angle ONLY affects start impulse timing

Rotating mag in governor affects BOTH start impulse and run timing

See my very top post above

John T
 
Tom, you state " I would think a 1951 tractor would have the improved X magneto. "

It can operate with a Wico C or a Wico X or a Fairbanks Morse Magneto, they all fit and work on that tractor.

Hope this helps

Best wishes n God Bless

John T
 
You ask if there is another way to know when the impulse snaps rather than listening to it. Yes, remove the flywheel side sparkplug wire from the plug and hold it about a quarter inch from metal. With the flywheel piston at TDC rotate the mag all the way forward. Now rotate the mag CCW and you should not only hear the impulse snap but also see a spark. This method sets timing as well as makes sure the rotor is pointing at the flywheel cylinder.
 
Tom, when you state "With the flywheel piston at TDC rotate the mag all the way forward"

FYI That may or may not work because unfortunately if you turn the flywheel piston to TDC there's a darn good chance the impulse WILL ALREADY TRIP subject to the mags timing.

A better way to do what you're suggesting is to stop the flywheel BEFORE the flywheel piston is at TDC,,,,,,,,then rotate the mag forward CW to retard the spark BEFORE it trips the impulse,,,,,,,,,then turn the flywheel so the piston is at TDC,,,,,,,,,,then slowly rotate the mag CCW to advance it and if its anywhere near right timing you will hear the loud SNAP and get the spark as you talked about. Its easier to hear the loud sharp SNAP then see a small spark lol

Again you should retard the mag FIRST before turning the Flywheel to TDC as you suggested because otherwise it may well SNAP already.

Hope this helps, post back any questions best wishes and God Bless. I hope youre doing well and welcome back

John T
 
FWIW here was my late friend Duane Larsons method of mag timing. He was a retired Nuclear Physicist and I a retired Electrical Engineer and we did it slightly different but arrived at the same conclusion. My method below is what I taught when I gave Wico Mag Seminars at Two Cylinder Expo and Gathering of the Green Seminar Workshops.


Magneto Timing ? How to Do It
Duane C. Larson
May 2009

Proper timing of a magneto is essential to good operation of the engine. The following
two processes provide information on how to determine the proper mounting of any magneto on
a Deere tractor, and once it is mounted, how to fine-tune the timing. Note that Wico C and XH
series magnetos allow independent adjustment of the impulse (or starting) timing; neither
Fairbanks Morse or Edison Splitdorf magnetos have this option. Further information and
pictures can be found by scrolling down to 2008 GOG Magneto Workshop on the home page of
this web site (www.jd2cylservice.com). Also note that the #1 cylinder is on the flywheel side
and the #2 cylinder is on the pulley side.

First Process: Mount Magneto on Tractor
? Remove spark plugs from both sides
? Rotate flywheel so #1 piston is at top dead center (TDC) on compression stroke
o Feel air rushing out the plug hole when coming up on compression stroke
o Magneto drive slot should be horizontal at TDC
? Hold magneto in a vise in the same orientation as on tractor
o Connect plug wires from magneto to spark plugs ? ground spark plug cases to vise
o Rotate drive cup with wrench until spark occurs at plugs
o Drive cup lugs will be ~ horizontal when spark occurs
? Not all magnetos provide a spark every impulse
o Rotate enough times until you KNOW which plug fires first, followed by spark at
second plug 1/2 turn later
o Rotate until spark occurs at first plug, and stop
o Put magneto on tractor without rotating drive cup
􀂃 Be sure to use a gasket between the magneto and governor case
? Install spark plugs and plug wires ? wire that sparked at first plug to #1, second to #2
Second Process: Setting Running and Impulse (Starting) Timing
? Measure circumference of flywheel
o About 66? for unstyled Model A
? Calculate distances for different timing advances
o Distance = circumference ? deg adv/360
􀂃 Example for early A
? D(25?) = 66 ? 25/360 = 4.583? ~ 4 19/32?
? D(30?) = 66 ? 30/360 = 5.500? = 5 1/2?
? D(35?) = 66 ? 35/360 = 6.417? ~ 6 13/32?
? D(40?) = 66 ? 40/360 = 7.333? ~ 7 11/32?
? Measure off and chalk these distances CCW starting at the flywheel LH Impulse mark
? Locate a timing light and battery to run it
o Hook spark sensor to #1 plug wire
? Start tractor, being careful not to obliterate chalk marks on flywheel
? 2009 Duane C. Larson and Nancy M. Larson Page 2 of 2
? With the timing light in the plane of the flywheel center and mark on transmission case, see
which flywheel chalk mark lines up with case mark
o RPM does not matter
? Get about ?10? change by rotating magneto
o If the 35? mark lines up and you want 30? timing, rotate magneto forward
􀂃 Forward retards spark, back advances spark
? After running time is correct, set start timing for Wico C and XH magnetos
o Stop engine, remove timing light, mark position of magneto on governor case so it can
be replaced accurately
o Rotate flywheel, note where impulse occurs relative to LH Impulse mark
o Adjust Impulse Stop Ring for spark at TDC (or 1?-3? ATDC)
􀂃 If magneto impulses after LH Impulse has passed mark, impulse stop ring will be
rotated CW
􀂃 Remove magneto, loosen four screws holding impulse stop ring, rotate stop ring,
tighten screws
􀂃 Each cast-in mark in case near top of stop ring is 5?
o Replace magneto, lining up with mark, check impulse time, if not correct, redo last steps
? Now both running and starting timing are set to proper values.
? If rotation of magneto does not provide desired run timing
o Change drive cup, or
o Lift governor box, rotate governor drive gear 1 tooth
􀂃 Backward ? spark occurs 12-15 deg later (retard spark)
􀂃 Forward ? spark occurs earlier (advance spark)
? If timing light shows spark jumping in time
o Loose distributor rotor
o Worn bushings
o Loose point pivot pin

John T
 
While those older magnetos will fit and work, the 1951 B only came from the factory with the Wico X Magneto, the Wico XB Distributor or the Delco Distributor.
 
Yo Tom 43 or Barack or Erskine or whomever.

But he said he had a Wico C !!

So that's the Mag were trying to help him get timed, NOT a Wico X Magneto, NOT a Wico XB Distributor, NOT a Delco Distributor. His Wico C magneto will fit and work as well as a Wico X Magneto or a Wico AP Magneto or a Faribanks Morse Magneto or a Delco or Wico XB Distributor.

Hope this helps you, post back any questions and I'll be glad to help

Best wishes, God Bless you and again welcome back

John T
 
Twice now you've said 'slash on tractor frame'. Wrong thing to say and I don't know why you keep doing that.

Timing mark is a raised, embossed line pressed into a sheet metal transmission gear cover under the left brake and driver's platform. At the three O'clock position if the flywheel were the face of a clock.

Not that I'm a psychic wizard or anything but I can't help thinking your flywheel is on the wrong crankshaft spline?
 
I wanted to thank everyone for their help and assistance. I went ahead and took the magneto off and started the procedure many of you have outlined. I advanced it a tick from what I thought was snapping directly at LH IMPULSE and it started and ran! Sorry for some repetitive questions on my part, and I certainly appreciate all of your help.
 

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