rrrg - another magneto question.

Tried to install the magneto earlier today.

I can get the thing to fire right AT tdc, but that's with the mag already in the fully retarded position.

We did line up the dots on the governor gear/cam/gear/crank gear when putting the engine together.

This is how the tractor used to run - from the original owner - so I'm pretty sure it would run (though it used to kick back often)

So I'm thinking the mag is off somehow.

It's a Wico mag. I've include a picture of the bottom of it.

There are degree markers - and a ring with a V shaped projection (to the right of the 3750 in the picture) that trips the mag.

I'm assuming I can loosen the 4 screws and turn this ring a bit to make the mag trip later in relation to the rotor position - and solve my problem.

Seems kind of obvious - but figured I'd check before I break something.

Leave that alone. The mag fires when the points open. That changes the lag . Hard for me to explain. The last one I worked on I had to pull the governor and move the gear until I could get it to impulse at TDC. I don't know if IHC ever used a Wico mag. It is maybe from something else, but can be used if you can time it right. Good luck.

You don't say what tractor this is on, but yes you can move the ring to make the mag impulse later, thus setting it more in the center of the adjustment range to trip at TDC. What will happen is that your running timing will be advanced from where you are now. Running timing is not changed by moving the impulse trip point, so if it's correct now, it won't be after your adjustment. John T & F-I-T have posted their methods of adjusting magneto impulse timing, so check the archives.

Set the mag to fire on #1 TDC and it will work just fine You are either in time or 180 out. Does the rotor line up with the tower on the cap when it fires. Put it in a vice and turn it over watching it snap and mark the location of #1 on the body and you can see the rotor stop at that position when it fires. I fasten them in the vice hook up wires to all plugs then using my batt drill can see all plugs firing at start and running rpms

If it clicks right at TDC it's FINE. Leave it alone. running it will be slightly advanced. Look at the degree marks. What angle is it set at? I think it should be 35° if it is faster than that (ie 23° or so) moving it will cause the impulse to fire later (LAG behind) in STARTING only. Running timing will not change. If you need to change running time you are going to have to pull the drive out and move the gear a tooth or two.

I'm not so concerned with the running timing - at least at this point in time.

My main concern is that I don't have a starter, so I hand crank this thing. It ran like this from the previous owner, and I got frequent kick backs while starting.

Not the end of the world, but I was always gun shy starting it - hoping it wouldn't kick.

And even if I HAD a starter, I still don't want it kicking back.

I just want to retard it - even just one degree -for starting purposes.

Right now it's so close I just can't tell if it's slighty ahead or behind. And that's too close for comfort for me. (and I think it's exactly where it was originally)

Somebody made a good point that it sparks on the points opening. That got me thinking more. I'll research timing the mag itself a little more.

But if I were to move the governor gear back one notch - ... I can't see where that would be a bad thing. Right now that's making the most sense to me. That should in effect just move the whole magneto back a few degrees and give me the adjustment range I'm looking for.

Thank you all.

If your mag clicks when the piston is in the up position your fine,this is not rocket science

jimmy

Okay Im familiar with that Mag on a two cylinder Deere application but not so on a 4 banger or opposite direction rotation BUT I STILL BELIEVE THIS TO BE TRUE.....

1) If you loosen the 4 screws and rotate the stop plate THAT INDEED AFFECTS START/IMPULSE TIMING BUT NOTTTTTTTTTT RUN TIMING.....

2) Rotating the stop plate can indeed cause it to trip/impule sooner or later and thats how I rough in the start/impulse timing so she fires at TDC at slow cranking so she dotn kick back. Right at TCC is when you want it to snap because if before she kicks back yet if too much after she dont start as well.

3) AFTER I set the lag angle (how much start timing lags run time advance) by rotation of the stop plate, then I fine tune the start timing by rotating the mag in its mount flange THAT WAY YOU CAN GET IT RIGHT ON TDC (assuming stop plate lag angle is correct and drive gear is in time) WHEN SHE SNAPS.

4) On the Deeres those witness marks represent 5 degrees each.

5) I FIRST set the lag angle by rotation of the stop plate, if the drive cup is say a 25 degree cup then since I want the start time to lag the run time by 25 I set it accordingly (on the Deeres straight up center = 12 1/2 degrees lag so 2 1/2 more marks = 25),,,,,,,,then I insert the mag and fine tune adjust the start timing to TDC by rotating the mag in the flange

NOT familiar with IHC but if I were you Id FIRST see if you can rotate the entire mag in its flange so she snaps at TDC but if thats not possible then go in the rear and adjust the stop plate a little at a time (each mark = 5 degrees) until you can get it to snap at TDC

NO WARRANTY IM NOT AN IHC USE MAG GUY

John T headed to a Bluegrss fest so may not get back at ya

Paul, youre correct in your statement ..." Running timing is not changed by moving the impulse trip point,..."


JR, If you move the rear stop plate that indeed changes start/impulse timing BUT THAT HAS NOOOOOOOOOOO AFFECT ON THE RUN TIMING.. Once shes over 250 RPM the dog pawl stays tucked inside and does NOT come out so the spring never winds and theres never any wind n trip impulse going on. The run time advance is primarily a function of which drive cup is used (say a 25 advance) and the mags rotational position in the flange plus points gap and wear n tear etc.

If you install the mag back exactly in its same rotational location in the flange, the run timing will be the same EVEN IF YOU ADJUSTED THE REAR STOP PLATE TO CHANGE THE START/IMPULSE TIMING

John T

The information John T gave you is on the right track. However, some of the details (proper lag angle and how to set it) depend on what model magneto as well as the application. I don't believe you have mentioned a model id for the magneto. Most letter series IH tractors call for a 35 degree lag angle. If your timing gear marks are all in line, with the engine at TDC, the magneto drive lugs should be 35 degrees above horizontal oriented at 2 o'clock 8 o'clock. Lag angle setting in the magneto will have an effect on whether you can properly mount it.

This manual covers 3 Wico magnetos, each considerably different from the other. If yours is covered, good. Otherwise it may call for some more digging.
http://www.cleancomputes.com/Cub/Bl...s/GSS-5035 Service Manual Magnetos/index.html

again - the problem is that it's NOT fine.

It's firing too close (or aparently a split second before) TDC.

The engine DOES kick back occasionally when hand cranking.

I need to retard the mag, but it's already in the fully retarded position.

Ok - with all this good info - I may be getting somewhere.

The tractor is a 48 super A - but I believe the engine is a 50 (t in the date code).

The magneto is a Wico Model X - spec#XH-3001

I found a mag manual for lower model numbers - states the center lag angle marker is 13 degrees (close enough not to argue with what JohnT said - 12.5)

manual agrees with John T that each tic is 5 degrees.

That puts my current lag angle at 18 degrees.

If in fact the lag angle is, as you say, supposed to be up around 35 - that should certainly fix my problem.

And it looks about right to put the mag roughly where it should be so it can be adjusted back and forth a bit when mounted.

But that's a rather drastic move.

The tractor DID run fine with the mag as is. Starting was a problem because of the kickbacks.

Moving the lag angle up should solve the kickback problem - but if I'm understanding this correctly - will also advance the run advance an equal amount (assuming I turn the mag to get the snap after tdc).

I don't know what the run advance WAS to begin with - could have been way off for all I know.

But is it safe to say - if I were to set the lag angle to 35 - time the mag to fire on start say 5 degrees after tdc - that my running advance would be 30 degrees?

30 degrees sounds a bit much, no? I just have no idea what it's supposed to be on these engines.

Perhaps I'll split the difference and worry about fine tuning later.

I will dig through those pages you sent to see if I can find anything more.

Thanks again all for the help!

... too early to get excited - but I think I figured out the problem.

If each tic mark is 5 degrees - I'm thinking the orignal owner set this mag counting from the first mark as 5.

5 - 10 - 15 -

Where the pointer is now would be 35 using that method.

Might just be a coicidence, but would explain the problem.

CHANGING LAG ANGLE DOES NOTTTTTTT change run timing. Over 250 RPM the spring never winds up and trips, its out of the equation. Over 250 RPM run timing is a function mostly of the drive cup used (like a 25 cup etc),,,,,,,,the rotational position of mag in govenor,,,,,,,,,,points gap,,,,,,,,wear n tear n slop.........

If the drive cup is a 35 then FIRST set the lag angle (how much start timing lags run timing) to 35 degrees that way it will fire at TDC at cranking which is 35 slower then run timing DUH

The fine tune the start timing to TDC by movign govenor in flange

HOWEVER MOVING MAG IN GOVENOR DOES AFFECT RUN ANDDDDDDDDDDDDDDDDDDD START TIMING

The middle straight up is 12 1/2 degrees of lag angle and each mark = 5 degrees soooooooooo for a 35 angle move the stop plate 4 1/2 notches. 12 1/2 + 5 + 5 + 5 + 5 + 2 1/2 = 35

UNLESS A 6274 DRIVE CUP IS USED then straight up = 2 1/2 not 12 1/2

SET LAG ANGLE TO MATCH DRIVE CUP,,,,,,,,,,,,,,,,, FINE TUNE MAG IN GOVENOR SO START TIMING IS TDC


This is for Wico XH series Mags used on Deeres
BUT I THINK ITS RIGHT FOR YOURS ALSO

John T

CHANGING LAG ANGLE DOES NOTTTTTTT change run timing. Over 250 RPM the spring never winds up and trips, its out of the equation. Over 250 RPM run timing is a function mostly of the drive cup used (like a 25 cup etc),,,,,,,,the rotational position of mag in govenor,,,,,,,,,,points gap,,,,,,,,wear n tear n slop.........

If the drive cup is a 35 then FIRST set the lag angle (how much start timing lags run timing) to 35 degrees that way it will fire at TDC at cranking which is 35 slower then run timing DUH

The fine tune the start timing to TDC by movign govenor in flange

HOWEVER MOVING MAG IN GOVENOR DOES AFFECT RUN ANDDDDDDDDDDDDDDDDDDD START TIMING

The middle straight up is 12 1/2 degrees of lag angle and each mark = 5 degrees soooooooooo for a 35 angle move the stop plate 4 1/2 notches. 12 1/2 + 5 + 5 + 5 + 5 + 2 1/2 = 35

UNLESS A 6274 DRIVE CUP IS USED then straight up = 2 1/2 not 12 1/2

SET LAG ANGLE TO MATCH DRIVE CUP,,,,,,,,,,,,,,,,, FINE TUNE MAG IN GOVENOR SO START TIMING IS TDC


This is for Wico XH series Mags used on Deeres
BUT I THINK ITS RIGHT FOR YOURS ALSO

John T

PS

That mag can be used for CW or CCW rotation and for Deeres they rotate CCW facing the rear (view from your picture) and therefore on a Deere the stop plate is rotated 4 1/2 to the LEFT buttttttttt for CW facing rear rotation mag use it would be 4 1/2 to the RIGHT

If the mag turns same direction as on a Deere for a 35 lag angle its set 4 1/2 to left but if your mag turns other direction its 4 1/2 to right of center as lookign at rear of mag

IM LEAVING NOW FOR THE NORMAN STATION BLUEGRASS FESTIVAL so I wont be able to provide more feedback so hope my three posts below help???

I gave Seminar Workshops on Wico X Mags at JD Two Cylinder Expos (CCW facign rear) but I have no idea which way yours turns SO NO WARRANTY but I believe the above is still true

Post back Sunday evening and let me know what happened please

John T

Right - I got that changing the lag angle doesn't affect run timing by itself.

But by changing the lag angle in a way that allows me to move the whole mag forward before it snaps, I've also advanced the run timing.

Which I think is fine.

My assumption was that if I gave it a lag angle of 35 degrees - I set it to snap 5 degrees after tdc - the run advance must be 30 (give or take)... no?

Hope you enjoy the show.

I bit the bullet and advanced the lag angle to the full 35 degrees.

I just put the mag on the tractor - and it at least "feels" right.

I can't try starting it till I get a few more parts done.

The mag now sits where I would expect it to. It's roughly in the middle of the swing angle. I've got it snapping a few degrees past tdc.

So I'm thinking this was probably the right thing to do - of course I won't know till I try running it - but for now I'm happy.

Thanks once again to all that helped - I will follow up in a few days when I actually try firing it up.

(quoted from post at 15:15:18 05/17/12)But by changing the lag angle in a way that allows me to move the whole mag forward before it snaps, I've also advanced the run timing.
. . .
My assumption was that if I gave it a lag angle of 35 degrees - I set it to snap 5 degrees after tdc - the run advance must be 30 (give or take)... no?

Click to expand...

Exactly.

I think you will be OK with what you have done. (Unless you crossed some plug wires . ) Having the mag set for too little lag angle then making it up by setting too much advance would give the exact symptoms you describe -- runs OK but kicks back when starting.

I wouldn't go much after TDC on timing the impulse click. Much after and it won't start as well as when set closer. I'd try to stay within a degree or 2 after, just making sure it is never before.

Thanks - now that I've got it working better over all, I will try to bring it in a bit closer to TDC.

I'll start a new post when I actually try starting it (hopefully this weekend).