JOHN DEERE 41 H HAND START

[Anonymous-0]

DID OR IS THERE A JD 41 H THAT NO MATTER WHAT YOU DO JUST WONT START? IT WILL POP ONCE WITH THE GAS VALVE CLOSED AND CHOKE AMD NO THROTTLE.

PULL IT AND IT RUNS JUST FINE.

 

[Mike M]

Once in awhile you come accross those.

Check the mag for a correct impulse snap and for good spark would be a starting place.

 

[PBrowning]

I’d sure be suspect of the magneto! Do some checks for a nice, 1/4-inch long blue spark jump as you hear the magneto impulse click. When you pull-start a magneto tractor, the impulse isn't in play -- it jumps out at about 250 RPM -- engine idle speed on the H is around 600 RPM. I list these numbers only to give you and idea. What I am thinking -- your magneto has a mechanical issue involving the impulse spring, weak or partially broken.

For some basic theory on your magneto, go to the JD-H Restoration Site (below). Whence there, scan across to ARTICLES 1. From the drop-downs, select ELECT SYSTEMS. (PatB)
Restoration Site, JD H

 

[John T]

The start/impulse timing on those mag equipped hand start tractors is pretty CRITICAL. If timed too fast the flywheel can kick back butttttttt if too slowwwwww shes hard to start. The Mag needs to SNAP at near dead TDC which is when the flywheels Left Hand Impulse (LHI) timing mark is even with a flat mark on the tractors side located at 3 o clock. If you loosen the mag in its mount and rotate it forward CW it retards timing (start and run) while backwards CCW advances it. Get it to SNAP right at TDC n see if she starts then. NOTE on the rear of the mag the Lag Angle is adjustable which affects start/impulse timing ONLY while rotation of the mag in the governor flange mount would affect BOTH start n run timing.

If the impulse spring wind n trip assemby is good n strong n works correct the Mag should produce a loud sharp SNAP but if its a faint dull clunk it may be a weak impulse spring which yields a weak starting spark (hard to start). If theres NO snap at all theres an impulse or spring problem causing no spark at hand cranking while it can still run fine if pull started

You need a strong visible blue spark when the mag snaps for good hand starts but if its a thin wimpy yellow its weak n hard to start. Main causes of weak sparks are the points are burned or mis adjusted, if the spring is good n she snaps good n loud but the spark is still weak, Id be replacing the points n condensor UNLESS the points are good but only gray oxide coated in which case dragging a dollar bill ect between the surfaces may cure the problem.

Check for loud sharp SNAP,,,,,,,,check for start/impulse timing right at TDC,,,,,,,,check and clean n gap or replace the points,,,,,,,

TRY A FRESH SET OF SPARK PLUGS !!!!!!!!

NOTE this is for ignition problems n doesnt address carb or carb settings or choking which is also critical !!!!!!!!!!!

John T

 

[Anonymous-0]

As others have said, check out the magneto. What you describe (won't start but runs fine) is common behavior if the magneto is weak. Magnetos are at their worst when cranking. To a certain extent, the faster they go the better they work and at cranking speed they're simply at their worst. Is the nature of the beast.

 

[PBrowning]

I do not agree. In fact, a magneto is a pair of ignition systems, one for cranking speeds and the other for running speeds.

It is the "nature of the beast" to give a nice, hot, blue quarter-inch-long arc at cranking speeds; needed just as much when starting as when running; maybe even more so for some of who seem unable to learn how to start our tractors!

Read on to learn how the “starting ignition system” works, and I think you will come away with an appreciation that the magneto is indeed quite a piece of work; also super reliable. It must be fully understood that for adequate starting ignition fire, the spring-loaded impulse system must be up to par. The impulse mechanism is the heart of starting ignition timing! See below, an Excerpt from the John Deere Model “H” Restoration Guide -- PatB

THE IMPULSE MECHANISM

A device called an “impulse mechanism” is part of the drive coupling mechanism in every WICO C and XH magneto. The action of the impulse mechanism can be envisioned as follows:

VISUALIZE -- Imagine a special electric clock with a sweep second hand, but with another identical hand on the same shaft. However, this redundant second hand is able to spin freely on the shaft and is not geared to the clock drive. Now, suppose this loose hand is tied to the sweep hand with a torsion spring (such as a clock spring). Accordingly, the loose hand moves along with the rotation of the driven hand, and so they both spin together around the clock face. Now let’s add another detail. Suppose a little catch or dog of some type is added to our clock that grabs and stops only the loose second hand as it (and the driven hand) passes the 12 o’clock mark. So now, the movement of the loose hand is arrested at 12 o’clock, but the driven hand continues to rotate. As this happens, the spring connecting the two hands starts to stretch. Next, imagine the catch holding the loose hand being tripped open as the driven hand passes the 3 o’clock mark. Once freed, the loose hand instantly jumps ahead and catches up (with a bang) to the driven hand, just like a mousetrap snapping closed. Then, both hands rotate in unison back around to the 12 o’clock position where the exact same process repeats.

TRANSITION -- The above example shows approximately how an impulse mechanism works. In reality, as the engine is rolled over during cranking, the magneto tags along in lockstep, driven by the governor shaft through the drive cup at the same slow speed—until it encounters a “catch”. (In the magneto, this means a little arm called the impulse pawl catches on the stationary impulse stop.) Then, the magneto drive cup continues to rotate for another 60 degrees or so while the magneto armature remains motionless. After being held stationary, the armature is suddenly released because a tab on the revolving drive cup (which is keyed to the engine rotation) sweeps past and trips the impulse pawl. The coiled drive spring inside the impulse mechanism causes the armature to instantly jump ahead and catch up to the drive cup, just as the engine reaches TDC (Top Dead Center). The snapping sound heard in a healthy impulse mechanism during cranking is the result of the spring-loaded armature in the magneto bumping into a rotation stop when the armature catches up with the drive cup.

If spun faster than about 250 RPM, the impulse mechanism doesn’t engage. Influenced by a delicate balance between gravity and centrifugal force, the impulse pawls retract at running speeds and allow the magneto to rotate continuously, and in direct synchronization with the engine.

"CATCH & SLINGSHOT RELEASE" -- The impulse mechanism performs two vital functions:

First, the “catch and slingshot release” design causes the armature to spin fast enough to generate sufficient energy to create a spark, even though the engine may be rotating very slowly. WICO Magnetos are incapable of generating spark at cranking speeds. The impulse mechanism spins the armature really fast through a brief, short 60 degree angle, and that’s enough to develop a spark.

Second, the impulse mechanism automatically retards the spark timing to coincide with the piston arriving at TDC for ease in starting. The magneto ignition run timing is typically 30 degrees BTC (Before Top Center), but is a function of the particular magneto drive cup chosen. Without the spark retarding effect created by the impulse mechanism, engines would kick back during starting attempts, because they would fire well before the crankshaft arrived at TDC.

AUTOMATIC SWITCH IN TIMING -- The magneto is timed 30 degrees in advance of the engine TDC. That is, if the impulse mechanism was inoperative and you slowly rotated the engine and watched the points, you would discover the points opened (which would cause spark at a plug) when the crankshaft was approximately 30 degrees BTC. Now, imagine the impulse is working properly. As the engine is slowly rotated, the impulse stops armature rotation at about 60 degrees BTC. As the crankshaft reaches TDC, the impulse suddenly releases the armature, and it immediately spins and causes a spark—that coincides with crankshaft arrival at TDC. When the engine starts and magneto speed passes approximately 250 RPM (Ref. FSB 159-S, 1-16-48), centrifugal force prevents the impulse from engaging anymore, and everything putts along perfectly, with the ignition timing locked in at the run timing determined by the magneto drive cup which is typically 30 degrees BTC. ++++
Restoration Site, JD H

 

[John T]

Pat, GOOD INFORMATION, its true, of course, the faster a mag (same as a generator) turns the more spark energy it produces. As far as the start/impulse spark energy, thats again a function of the RPM, but if I recall correctly a good strong spring can yield an impulse RPM of like over 500 RPM (and higher, depends on spring strength) which results in as much spark energy as if the tractor were running at 500 RPM sooooooooo the start/impulse spark of a good mag is sufficient to produce a plenty good enough spark to start a tractor. Although several things can affect starting performance, its still true if a tractor pull starts n runs fine but is a bear to hand start, I'd still place a weak or non working spring/impulse assembly as one of my prime suspects right up there with its start/impulse timing which is also critical

Fun discussion

John T