1939 John Deere H mag issues.

[Ratrod]

I have a 1939 John Deere H it starts very hard. Usually I can’t get it to start without towing it. I’ve heard some discussion versus the C versus the X mag and I’m wondering if I can put an X mag in it without any issues. Any information or advice is greatly appreciated. Thank you.

 

[Mike(NEOhio)]

An X will drop right in but before you invest in a mag make sure there are no other issues causing the hard starting. Is the mag putting out a good spark and timed correctly? Plug wires crossed, points clean, is the impulse coupling working, plugs? Then it could be fuel issues. All are commonly overlooked problems, especially with JDs.

 

[DaveBN]

How is the compression on this engine? Low compression will cause hard starting.
Dave

 

[Ratrod]

Just completely rebuilt the top end. New pistons and rings. New valves cylinders were honed New gasket set. Carb was completely rebuilt. It seems to run ok when I get it started. But seems to have to be towed to started. Mag is original and was rebuilt about 15 years ago. Points are clean and adjusted correctly.

 

[Loosehandle]

I have a 1939 John Deere H it starts very hard. Usually I can’t get it to start without towing it. I’ve heard some discussion versus the C versus the X mag and I’m wondering if I can put an X mag in it without any issues. Any information or advice is greatly appreciated. Thank you.

I had this problem with my H, turned out to be cracked block around center stud seeping coolant into cylinder. Was able to be fixed, it had a wico X on it when I got it.

 

[Ratrod]

I just rebuilt the top end and new valves and all new gaskets. The cooling system is solid. It doesn’t leak. Thank you for the suggestion and insight.

 

[NoDakInMN]

If it starts by pulling but not when sitting, I would first check the impulse to make sure it is working. If you are unaware, the impulse spring, when tripped, caused the mag to spin at a higher RPM than what the mag is normally turning at during starting. It drops out once the RPM is high enough to create adequate spark. So when pull starting, the mag probably is spinning fast enough not to need the impulse. When starting the engine normally, you should hear and audible click when the impulse release trips.

 

[Ratrod]

The mag clicks and sounds normal but rarely starts it. If I tow it about 25’ it starts right up.

 

[DaveBN]

I would still do a compression check. Maybe your rings aren't seated yet from a fresh rebuild. Have you worked it HARD since the rebuild, if not you need to. Also check valve lash. Lastly have the mag checked and or rebuilt.
Dave

 

[BobTx]

Back in the late 1980's, my Dad had an old John Deere A with the exact same symptoms. It turned out to be an intake manifold gasket. It might be worth a check. Bob TX

 

[KL in Wi]

Not a JD but. same issue. My Oliver 70 acted the same way. Electric start. While cranking once in a while it would fire once then quit. If you messed with it long enough, sometimes 15 tries or more it would finally start maybe. I could hear the impulse working. If i would pull it ten feet, it was running and running perfectly. Had the mag tested. At low rpms it would occasionally fire once or twice then miss a few times and fire again. Once it got to about 200 rpm it would fire perfect. It was a bad coil. replaced the coil and it starts great.

 

[Ratrod]

Thanks. The hardest this tractor ever works is pulling a backhoe tire around my snowmobile trails or skidding some small trees out of the yard. It lives inside my heated garage and is a family heirloom lol. I will check the compression again and try to get it working a bit harder than normal for a bit.

Not a JD but. same issue. My Oliver 70 acted the same way. Electric start. While cranking once in a while it would fire once then quit. If you messed with it long enough, sometimes 15 tries or more it would finally start maybe. I could hear the impulse working. If i would pull it ten feet, it was running and running perfectly. Had the mag tested. At low rpms it would occasionally fire once or twice then miss a few times and fire again. Once it got to about 200 rpm it would fire perfect. It was a bad coil. replaced the coil and it starts great.

thanks. That sounds exactly like my situation. I’m going to have the mag tested later in the week