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Farmall & IHC Tractors Discussion Forum

H4 Magneto Timing - Once and for all

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Ken Christopherson

02-15-2017 12:13:53

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Ok guys.. I know I should have this figured out by now, but after getting the timing of the mag 180 off on the 1947 M, and doing the same exact thing on the 1942 H (prior to the issue I just had).. I have to ask before I put this mag back on the H to fire it (I did get it running by the way for a short 15 minutes - see attached video)....

What position should the rotor be pointing to be ready to fire on #1. I have enclosed pictures of how I had it set up the last time I installed it, and it was 180 out. I had the impulse set to begin to reload the spring with the rotor pointing at the #1 terminal as you see in the photo.

Thing is, the mag seems to fire on #1 with every-other impulse trip when I have it clamped in my vice, but when I do this on the kitchen table, it only fires every 4th trip.. And I think this is what is [possibly] throwing me off. Check out the photos and let me know what you think. First photo is of the impulse coupling at the beginning of spring preload. Second photo is of the rotor pointing to #1 prior to tripping it to fire. This should be right, according to my brain! Bolt it on at #1 TDC... Should be good to go (I swear I try this every time, LOL). I must be doing something to mess this up, somehow.

Thanks for the help, and hopefully tomorrow or Friday when I get to reinstalling it, it will be for the last time, and I'll have mastered these H4's.

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gene bender

02-15-2017 17:32:37

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 Re: H4 Magneto Timing - Once and for all in reply to Ken Christopherson, 02-15-2017 12:13:53  
I put the cap on and make a mark on the body where #1 tower on the cap is then turn the mag when the rotor stops it should point at that mark and with #1 piston on compression at the top you will be in time like you say if the piston is at the top of exhaust it will stop at the same place thats why you need to be sure #1 is on the compression stroke mite need the valve cover off to make sure both valves are closed.

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02-15-2017 15:35:04

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 Re: H4 Magneto Timing - Once and for all in reply to Ken Christopherson, 02-15-2017 12:13:53  
You talk of lining up the timing mark with the pointer. This is correct. However, you must be on COMPRESSION stroke. Take the number one plug out and put your finger in the sparkplug hole while someone slowly cranks the engine. When you feel compression pressure, stop turning when the FIRST of the double marks aligns with the pointer. If you don't do this you have a 50% chance of being on the EXHAUST stroke when the marks align. If you don't like this method, take the valve cover off and check that the valves on number one cylinder are closed and loose when the marks align. Most like the first method as it is less invasive.

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Ken Christopherson

02-15-2017 15:50:17

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 Re: H4 Magneto Timing - Once and for all in reply to erskine2017, 02-15-2017 15:35:04  
Good point!

Also forgot to mention - when I adjusted the valves (prior to reinstalling the valve cover), I did put #1 to TDC compression. I prefer to do it with the valve cover off, that way I can see things working.

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pete 23

02-15-2017 14:13:38

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 Re: H4 Magneto Timing - Once and for all in reply to Ken Christopherson, 02-15-2017 12:13:53  
Every one is making this installation of a magneto too complicated. Make sure the H 4 magneto is properly timed internally, then turn the mag OPPOSITE direction of rotation. If you go a little too far just go around again until rotor is near number one. With engine positioned at top dead center, Install it and then check timing as it must trip NEVER before top dead center and better slightly after. I always try to time to 5 degrees (second mark) to be safe and for better running engine in most cases. If you try to install by turning in direction of rotation, you are partially winding the impulse spring and it will not hold that positon. Simple, easy and correct. If you cannot get it to make it trip (provided the impulse is working properly) at or slightly after top dead center, you are off a cog or more on the drive gear, not the magneto it's self.

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Ken Christopherson

02-15-2017 14:32:08

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 Re: H4 Magneto Timing - Once and for all in reply to pete 23, 02-15-2017 14:13:38  
I'm not trying to over complicate it... It seems that's what is happening though! LOL. These are the steps I usually follow when I install the mag:
1) Set the motor to TDC, first timing mark aligned with the pointer on the timing gear cover.
2) Set up the mag to fire on #1. 3) Prior to bolting the magneto on, because of the issue you described of the mag drive angle and the position of the impulse coupling on the mag not matching - I roll the engine back enough to align the impulse coupling and magneto drive. Bolt up the mag (fully retarded position, snug).
4) Roll the engine back forward and realign the timing marks on pulley and timing cover pointer.
5) Rotate mag (advance) until the magneto trips. Tighten.
The mag was just professionally rebuilt, so everything as far as internal timing SHOULD be set up correctly.
This may be over complicating the procedure...

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Used red mn

02-16-2017 19:40:56

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 Re: H4 Magneto Timing - Once and for all in reply to Ken Christopherson, 02-15-2017 14:32:08  
I do see a possible flaw in your step No.1, however this should not cause you to be 180 degrees out. You say you set the engine to TDC --"first timing mark aligned to the pointer" So if by first you mean the first mark that aligns during normal engine rotation this is not TDC but rather some X number of degrees advanced or the #1 piston is still traveling up. Now my disclaimer here is that I am way more familiar with automotive configurations that mostly have one pulley notch and a degree scale on a tab. (80s vintage and earlier) So I am basing my information on the post of Steve- IN in the attached 2003 archived YT post. If I am understanding your explanation correctly you could be stopping the crank at 30 plus degrees before top dead center. Hope this helps.

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Ken Christopherson

02-16-2017 23:41:24

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 Re: H4 Magneto Timing - Once and for all in reply to Used red mn, 02-16-2017 19:40:56  

Thanks for the link. I read through it and more of that applies to distributor ignition, but timing them is generally the same. Essentially, I get the engine set up to be on TDC of compression stroke, then set the mag up to fire on #1. I rotate the motor backwards then enough to align the cog on the impulse coupling with magneto drive. Install mag, fully retarded and loose. Then crank the engine back forward to TDC (First of the double timing marks). Then I rotate the mag until the impulse trips and tighten it down at that position.

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John M

02-15-2017 13:28:30

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 Re: H4 Magneto Timing - Once and for all in reply to Ken Christopherson, 02-15-2017 12:13:53  
Looks right to me. You do know #1 is the front cylinder right? You made a comment in one of your videos that you had the #1 wire on the #4 post.(Or something to that effect)

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Ken Christopherson

02-15-2017 14:02:34

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 Re: H4 Magneto Timing - Once and for all in reply to John M, 02-15-2017 13:28:30  
Yup. I know #1 is front. Firing order 1-3-4-2. Looking at the bag of the magneto, wire on top right should be #1, then below is 3, then left is 4, then top left is 2.

I think in the video I may have been referring to having the magneto 180 out, and troubleshooting by flipping plug wires around in order to figure out what I had done wrong. Once I figured out that I had #1 on the cap to #4, I knew I was 180 out of time on the magneto. I don't know how that happened, though.. I set them up to trip at #1, take off the cap and make sure the rotor is pointing to #1.. And somehow I still get it 180 out.

We'll see what happens here tomorrow or Friday!

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