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Farmall & IHC Tractors Discussion Forum
Show Parts for Model:

Re: H-4 MAGNETO PAWL SPRINGS

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Kelly MT

05-14-2013 20:22:41
216.14.236.72



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I'm working on a H4 right now that doesn't have any pawl springs. I found an old magneto manual that said early h4s had springs and later ones had counter weighted pawls. I have a query over on Red Power checking that out. I found the pawls were worn and very loose. I'll tighten them up with some machinist washers and see what happens.




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Patrick HMD

05-14-2013 21:52:29
75.9.216.217



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to Kelly MT, 05-14-2013 20:22:41  
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The mag without the springs rattles a lot when I pick it up and shake it a little. Sounds like a couple of marbles rattling around inside. Not a very comforting sound to say the least. I'm just wondering what do those pawls do. Why are they there for. This dumb A would sure like to know.

Patrick

'49M



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John B.

05-15-2013 19:50:35
50.40.115.126



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to Patrick HMD, 05-14-2013 21:52:29  
The pawls hold the rotor inside the mag from turning while the impulse spring winds up while the engine is being cranked over or when the engine rpm is very low. As the impulse spring winds up and builds tension the pawls eventually let go and the rotor spins at a high speed momentarily to get hot spark so the engine starts easier when cranking by hand. This is the noise you hear when you crank the engine over to start it. It's a distinct sound...

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Patrick HMD

05-16-2013 03:14:46
75.0.231.143



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to John B., 05-15-2013 19:50:35  
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John B.- The mag is not mounted on the tractor yet. The rattling noise I was talking about are the pawls pivoting on the posts unrestricted without springs. That's the way it came. (no springs)

The blue ribbon service manual states (page 54) that the early mags did not have the small springs (that are directly under the pawls). just the pawls. It goes on further to say that the later mags did have the small springs along with counterweights added to the pawls. Like I said before, this mag has no springs but the pawls do have counterweights attached. So I'm still not sure if this setup will work.

Now I have another mag that does (did have, lost one) have the small springs and counterweights, and does not rattle when I pick it up and shake it. The pawls stay put and don't rattle. The distinct sound you're talking about, is that caused by the pawls?
One more questions about those small springs. When the springs are properly mounted and under tension, will they push the pawls out or tuck them in?

TIA

Patrick

'49M

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John B.

05-16-2013 16:15:03
50.40.115.126



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to Patrick HMD, 05-16-2013 03:14:46  
The springs tuck them out so they engage at a low rpm. As the mag speeds up the counter weights bring the pawls in against spring pressure. If you turn the mag over by hand in the direction it is used it will turn a 1/4 turn and the pawls should engage and then the impulse spring will start to wind up, you will feel this tension build the more you turn it. Then all of a sudden the pawls let go and the impulse spring unwinds and spins the armature in the mag at a faster RPM to create a good hot spark while hand cranking the engine. The impulse spring is located behind the mag drive coupling. It's actually called "Impulse Coupling".

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Patrick HMD

05-16-2013 17:36:24
75.0.232.183



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to John B., 05-16-2013 16:15:03  
So John, all this stuff about the pawls that we have been discussing about is really for the benifit of someone who is hand crank starting the tractor. So if I'm just going to be using the electric starter, then all this shouldn't be all that critical, right? Or am I wrong?

Patrick

'49M



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hoof print

05-15-2013 10:07:51
173.219.54.222



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to Patrick HMD, 05-14-2013 21:52:29  
the pawls retard the timing when starting the motor. They rotate inwards away from the stop after the engine climbs above a certain RPM. They do not contiuously operate, they move out of the way.



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Kelly MT

05-15-2013 12:24:40
216.14.236.72



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to hoof print, 05-15-2013 10:07:51  
So HP when the book says 120 to 150 RPM cut out speed this is when they pull in?



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Hoof Print

05-15-2013 16:02:10
166.137.156.31



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 Re: H-4 MAGNETO PAWL SPRINGS in reply to Kelly MT, 05-15-2013 12:24:40  
Yes, that is correct.



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