1945BN Mag Timing

[herne19d]

I've got a 1945 Farmall BN and when I go to set the magneto, I crank the engine to TDC cylinder 1, and set the Mag so that the rotor points to the #1 plug wire, mount the Mag with the top of it as close to the engine as possible, crank it fully around, back to TDC for #1, and then advance the Mag until the impulse spring trips.
Textbook, except that the impulse spring doesn't trip until the engine is well past TDC.
If the hand crank is at about 4 o'clock (facing the tractor) for TDC , the impulse spring doesn't trip until the crank handle is at 6 or 7 o'clock.
The impulse spring is in good shape, the mag is in good working order, points are new and set, new plugs/wires/condenser/distributor cap, all the things.
It starts with the starter but I can't crank it by hand to start it.
It also doesn't seem to have a much power as it should.
So, I'm wondering if, the last time it was rebuilt, if the timing marks on the magneto drive gears weren't lined up properly? I can't ask the guy who did it because he died about 4 months ago.
Any ideas or advice would be welcome.

 

[wore out]

I've got a 1945 Farmall BN and when I go to set the magneto, I crank the engine to TDC cylinder 1, and set the Mag so that the rotor points to the #1 plug wire, mount the Mag with the top of it as close to the engine as possible, crank it fully around, back to TDC for #1, and then advance the Mag until the impulse spring trips.
Textbook, except that the impulse spring doesn't trip until the engine is well past TDC.
If the hand crank is at about 4 o'clock (facing the tractor) for TDC , the impulse spring doesn't trip until the crank handle is at 6 or 7 o'clock.
The impulse spring is in good shape, the mag is in good working order, points are new and set, new plugs/wires/condenser/distributor cap, all the things.
It starts with the starter but I can't crank it by hand to start it.
It also doesn't seem to have a much power as it should.
So, I'm wondering if, the last time it was rebuilt, if the timing marks on the magneto drive gears weren't lined up properly? I can't ask the guy who did it because he died about 4 months ago.
Any ideas or advice would be welcome.

Apparently, the mag drive/governor is not correctly timed to the camshaft.

Gotta ask, is it an IH H4 mag, or some other mag intended for a different tractor? (Many mags will bolt up, but some will fire with the drive tangs "clocked" differently.)

 

[Janicholson]

Put put a cotton ball in the #1 plug hole. Turn it by hand until the cotton blows out. Then put a plastic straw in the hole and turn it until the straw is as far up as it will go (back and forth as needed). Now look at the timing marks, they should be very close to the TDC mark! This assures the Marks are correct. To index the mag put it close to the engine, turn it 2 revolutions (4 stroke is every other time) then turn it back away until it trips. Jim

 

[herne19d]

Apparently, the mag drive/governor is not correctly timed to the camshaft.

Gotta ask, is it an IH H4 mag, or some other mag intended for a different tractor? (Many mags will bolt up, but some will fire with the drive tangs "clocked" differently.)

It's an H4 and in good working order.

I'm thinking that the gears weren't lined up properly amen it was last rebuilt.

I just want to see if other folks agree, or if I'm way of track.

Thanks!

 

[wore out]

It's an H4 and in good working order.

I'm thinking that the gears weren't lined up properly amen it was last rebuilt.

I just want to see if other folks agree, or if I'm way of track.

Thanks!

It's not clear to me if you are talking about the mag drive/governor gears or the gears inside the mag the drive the rotor.

The ROTOR drive gears can't cause your problem, that of the impulse tripping "late", that would HAVE to be the mag drive/governor gear - camshaft timing.

If you want to check the rotor drive gears anyway, the procedure is detailed in the GSS-5035 Magneto Manual.

https://farmallcub.club/rudi/farmal...Magnetos/GSS-5035 Service Manual Magnetos.htm

 

[rustred]

I've got a 1945 Farmall BN and when I go to set the magneto, I crank the engine to TDC cylinder 1, and set the Mag so that the rotor points to the #1 plug wire, mount the Mag with the top of it as close to the engine as possible, crank it fully around, back to TDC for #1, and then advance the Mag until the impulse spring trips.
Textbook, except that the impulse spring doesn't trip until the engine is well past TDC.
If the hand crank is at about 4 o'clock (facing the tractor) for TDC , the impulse spring doesn't trip until the crank handle is at 6 or 7 o'clock.
The impulse spring is in good shape, the mag is in good working order, points are new and set, new plugs/wires/condenser/distributor cap, all the things.
It starts with the starter but I can't crank it by hand to start it.
It also doesn't seem to have a much power as it should.
So, I'm wondering if, the last time it was rebuilt, if the timing marks on the magneto drive gears weren't lined up properly? I can't ask the guy who did it because he died about 4 months ago.
Any ideas or advice would be welcome.

That is because u are not taking into account the impulse coupling. Turn the mag in reverse when lining up the rotor before mounting the mag.

 

[herne19d]

That is because u are not taking into account the impulse coupling. Turn the mag in reverse when lining up the rotor before mounting the mag.

I did that.
Like I said, I did all the things and followed the directions right out of the owners and shop manuals.
Thanks though!!

 

[herne19d]

Put put a cotton ball in the #1 plug hole. Turn it by hand until the cotton blows out. Then put a plastic straw in the hole and turn it until the straw is as far up as it will go (back and forth as needed). Now look at the timing marks, they should be very close to the TDC mark! This assures the Marks are correct. To index the mag put it close to the engine, turn it 2 revolutions (4 stroke is every other time) then turn it back away until it trips. Jim

Yuppers, did that. That's what the problem is, turning it away and it doesn't Trip. I turned it as fast is it goes, to the end of the bracket.
To get it to Trip, I actually have to crank the engine well past TDC.

Thanks!

 

[Janicholson]

Make a mark on the housing on the cap mount flange at exactly the point that the rotor is located when the impulse snaps. (likely requires a helper). that should be TDC! if not adjust it so it happens at TDC. There are timing marks on the rotor gears to align if they are not. Jim

 

[Dave BN]

I would like to know how the small gear under the rotor is set. It is marked R and L. Should be set to R. Which way does your rotor turn? If your sitting on the seat does the rotor turn clockwise or counter clockwise?
Has this engine run since the magneto was rebuilt?
Dave

 

[wore out]

I would like to know how the small gear under the rotor is set. It is marked R and L. Should be set to R. Which way does your rotor turn? If your sitting on the seat does the rotor turn clockwise or counter clockwise?
Has this engine run since the magneto was rebuilt?
Dave

From the O.P's first post (Post #1)... "It starts with the starter but I can't crank it by hand to start it. It also doesn't seem to have a much power as it should."

It's obvious the mag drive gear timing is "late", NO amount of twiddling with the ROTOR drive gears is going to affect the late timing.

 

[560Dennis]

I don’t use that method any more . I use the vacuum gage connector to adjust your idle screw to carburetor highest vacuum, , at low idle ,rotating magneto to highest vacuum . Mark the locat , go to high idle , mark it , split the difference and lock it down there.

 

[Janicholson]

I would like to know how the small gear under the rotor is set. It is marked R and L. Should be set to R. Which way does your rotor turn? If your sitting on the seat does the rotor turn clockwise or counter clockwise?
Has this engine run since the magneto was rebuilt?
Dave

R Jim

 

[Geo-TH,In]

I'm not looking forward to replacing the points and condenser on my 1950 Farmall C Mag, because I've never worked on a Mag.
I'm planning on putting the #1 piston on TDC with both valves closed. Make sure the rotor is pointing to the #1 spark plug, then use a sharpie to mark on the mag and engine to show where the mag was mounted. Then after I get it running I'll use a timing light to see how close the timing is.
I'm sure it is not all that simple.

 

[wore out]

I'm not looking forward to replacing the points and condenser on my 1950 Farmall C Mag, because I've never worked on a Mag.
I'm planning on putting the #1 piston on TDC with both valves closed. Make sure the rotor is pointing to the #1 spark plug, then use a sharpie to mark on the mag and engine to show where the mag was mounted. Then after I get it running I'll use a timing light to see how close the timing is.
I'm sure it is not all that simple.

George, if you don' already have it, print out (at least the pages that pertain to your mag) from the Official Blue Ribbon Magneto Manual I linked in Post #5.

 

[wore out]

I don’t use that method any more . I use the vacuum gage connector to adjust your idle screw to carburetor highest vacuum, , at low idle ,rotating magneto to highest vacuum . Mark the locat , go to high idle , mark it , split the difference and lock it down there.

560, for a tractor used for it's intended purpose I don't understand why anyone would want to muck around with the mag timing once it is "static timed" to fire @ (or just SLIGHTLY after) TDC?

I you just HAVE to, it would still be a good idea to verify that the timing hasn't been advanced "ahead" of the TDC mark, which can result in broken arms or broken starter nose cones.

You already know that, but a "newbie" finding this thread may NOT.

 

[herne19d]

Thanks for all the advice!
I pulled the radiator off, took the governor off and, lo and behold, there are no timing marks on the mag gear or the intermediate gear. I wiped then off and looked with a flashlight, nothing there.
So, I took the mag off, pulled the drive gear out and then turned it and reassembled everything, over and over, until the mag tripped at TDC.
Then I locked the bolts down and but the whole thing back together.
It started and ran, at lot easier & smoother.
I haven't tried to hand crank it yet, but it started.
Win, Win!!

Thanks again for the advice!!

 

[used red MN]

I'm planning on putting the #1 piston on TDC with both valves closed.

George, are you planning to set the valves during this magneto work? If not no need to determine if the valves are closed or not. If your tractor is in running condition when you pull the mag,
when you position the rotor to point at the terminal for the number 1 spark plug wire the valves with be closed.

 

[wore out]

George, are you planning to set the valves during this magneto work? If not no need to determine if the valves are closed or not. If your tractor is in running condition when you pull the mag,
when you position the rotor to point at the terminal for the number 1 spark plug wire the valves with be closed.

There's really no need to pull the mag on one of those engines to replace the breaker points, so long as the condenser hasn't failed and needs to be replaced.

 

[herne19d]

I would like to know how the small gear under the rotor is set. It is marked R and L. Should be set to R. Which way does your rotor turn? If your sitting on the seat does the rotor turn clockwise or counter clockwise?
Has this engine run since the magneto was rebuilt?
Dave

Sitting in the seat, the rotor turns clockwise.
Yes, it has run since I rebuilt it.
The problem is that it only starts with the starter and the impulse spring released very late.
I've gotten to where the impulse spring releases at exactly TDC, and I haven't tried it by hand yet.
Having time to work on things in the spring is tough.