1948 John Deere magneto timing

[trocken10]

I had my magneto rebuilt, and now I am trying to get it timed up correctly.

I have spark, compression, and it is not firing on any ether.

I have seen videos of the magneto timing, seems straight forward, but on my 1948 A, I am not seeing the timing identifier on the flywheel. The flywheel is pretty pitted, so it s hard to make out any factory markings.

 

[rustred]

get the plugs out and turn it till number one piston is at tdc on the compression stroke then look for the mark if its there , if not no big
deal. top dead centre is when u rock the flywheel back and forth slightly and the piston dont move. get the centre of movement and good to
go. and make a mark on flywheel.

 

[trocken10]

(quoted from post at 19:17:16 11/22/23) get the plugs out and turn it till number one piston is at tdc on the compression stroke then look for the mark if its there , if not no big
deal. top dead centre is when u rock the flywheel back and forth slightly and the piston dont move. get the centre of movement and good to
go. and make a mark on flywheel.

Rustred, thanks! I did that, and marked the flywheel.

I then reinstalled the magneto, turned the flywheel, and then aligned the magneto, so it pops when it hits the mark on the flywheel.

I shot some ether into it, and still cannot get it to fire. Anything else to check?

 

[rustred]

Make sure it is on the compression stroke by pushing air
out the plug hole. U might be on the tdc on exhaust
stroke. Plus hold the plug so u can see it the instant it
fires. Then check your timing mark if your correctly on it.

 

[greenmech]

Could you have the mag 180 degrees off? Ron MN

 

[Mike(NEOhio)]

Did you check the position of the magneto drive coupling before you put the mag back on. The slots should be horizontal. Then you have to have the
mag rotor ready to fire the top terminal for #1 (left) when you put it back on. Don't tough the flywheel. Rotate the mag forward some then rotate it
backward slowly until the impluse trips and tighten it.

 

[trocken10]

(quoted from post at 20:05:02 11/22/23) Make sure it is on the compression stroke by pushing air
out the plug hole. U might be on the tdc on exhaust
stroke. Plus hold the plug so u can see it the instant it
fires. Then check your timing mark if your correctly on it.

Will check that tomorrow!

 

[trocken10]

How would I know if it s 180 off?

 

[trocken10]

Fellow Buckeye!

Yes, it was horizontal.

I will check mage impulse again tomorrow. Was throwing me off, doesn t seem to click as loud, when magneto is off the tractor.

I was trying to move it, so it would be close to impulse when I put it back on the horizontal aligned, tractor side. Set it all the way forward, and then slowly tilted it back but didn t hear it impulse. Just went back to flywheel and it seemed to impulse where I had marked it, with piston TDC. Going to check that TDC again tomorrow too, to make sure I didn t have it marked at the exhaust TDC.

 

[rustred]

As I said u could be on the exhaust stroke. That is 180
out. The piston is at tdc but no compression because the
valves are not closed. Either back the flywheel up then
turn it forward with a paper towel in the plug hole. If it
blows out ur on compression. If it dont ur 180 out. Plus
make sure the mag rotor is pointing to number one
cylinder also. Its very easy to do.

 

[KL in Wi]

Don't know what model JD you're working on but, I have a 27 D. The mag on mine fires every time the pistons are at TDC. That's on compression and exhaust. If I shoot gas in the petcocks and it doesn't fire on compression, it can sometimes fire on exhaust wit a 4 ft flame and a bang loud enough to rattle the shed. Take a spark plug out and put the plug wire on then, lay it on the block. See if you have spark at the plug and if it is firing in time.

 

[Mark-Ia]

Just switch the wires in the cap and see if it will fire. That would show 180 degrees out of time. It won't hurt to run it like that. Ideally, the top hole should go to the #1 piston(left-side).

 

[620 John]

Another thing to watch for is when the magneto is installed make sure the drive cup does not bottom out against the drive cog before the magneto case tightens up against the governor housing. Good way to see if this happens is take the gasket out for the magneto and with the cog and drive cup horizontal the magneto will rock back and forth vertically and the magneto case will not sit flat against the governor housing. If this is the case you might get by with adding another gasket or two between the magneto and governor. Hope this makes sense.

 

[Mike(NEOhio)]

Does your mag have a two-contact rotor. Some Wico used them. I happen to have the mag off my H yesterday, I'd forgotten about that. Also with JDs
the mag or distributor runs at crankshaft speed, not camshaft, so TDC on either stroke works.

 

[trocken10]

(quoted from post at 22:38:32 11/22/23) As I said u could be on the exhaust stroke. That is 180
out. The piston is at tdc but no compression because the
valves are not closed. Either back the flywheel up then
turn it forward with a paper towel in the plug hole. If it
blows out ur on compression. If it dont ur 180 out. Plus
make sure the mag rotor is pointing to number one
cylinder also. Its very easy to do.

Checked it, it is impulsing at TDC on compression stroke.

You mentioned may rotor pointing to number one cylinder. How do I confirm that, appears when I remove the cap the rotor can be installed only one way.

 

[trocken10]

Yes two contact rotor.

 

[trocken10]

Tried switching wires, no change.

Running 55-60 psi on each cylinder.

New rings, pistons, and had the head re-machined, and installed new valve springs.

 

[trocken10]

(quoted from post at 22:38:32 11/22/23) As I said u could be on the exhaust stroke. That is 180
out. The piston is at tdc but no compression because the
valves are not closed. Either back the flywheel up then
turn it forward with a paper towel in the plug hole. If it
blows out ur on compression. If it dont ur 180 out. Plus
make sure the mag rotor is pointing to number one
cylinder also. It s very easy to do.

Got the mag rotor pointing to #1, figured out what you meant there!

 

[NoDakInMN]

Let's recap.

You have compression on each side.
You have impulse tripping at TDC on the left hand (flywheel) side.

Ok, have you visibly observed the spark plug firing when the impulse trips? If so, what color is the spark? It should be blue. Sometimes it is hard to see in the daylight, so try to find a way to shade the plug so you can observe it. If isn't a good blue spark, you have a weak spark, possibly due to many things, among them failing condenser, corroded points, corroded contacts on the cap, weak impulse spring and so on. You are using a solid metal core plug wire, right? Mags require solid metal core wires.

If all that checks out, access the inlet side of the carb and shoot in a little starting fluid while moving the left hand cylinder through the intake stroke and then run it through compression and see if it fires. We are just trying to see if it will fire, not start the engine, and it should if you have compression and spark at TDC on the compression stroke. You may need to do it a couple times. If it still doesn't fire. then obviously something is still wrong with either spark or compression. Possibly the spark plug as some have been known to spark outside of the engine but not when under compression.

 

[Rich'sToys]

(quoted from post at 12:33:31 11/24/23)

(quoted from post at 22:38:32 11/22/23) As I said u could be on the exhaust stroke. That is 180
out. The piston is at tdc but no compression because the
valves are not closed. Either back the flywheel up then
turn it forward with a paper towel in the plug hole. If it
blows out ur on compression. If it dont ur 180 out. Plus
make sure the mag rotor is pointing to number one
cylinder also. Its very easy to do.

Checked it, it is impulsing at TDC on compression stroke.

You mentioned may rotor pointing to number one cylinder. How do I confirm that, appears when I remove the cap the rotor can be installed only one way.

You should be able to hold the cap in position and eyeball which terminal the rotor is pointed at.