Tecumseh HM100 ignition coil mounts

[mowfixer]

I have a generator with a Tecumseh HM100 159409P motor. The generator was running and suddenly a loud noise and engine quit. When I removed blower housing I found the ignition coil flopping around loose. The coil is mounted to two posts that are a part of the block with two 3/4 in extensions to move coil out over the magnets. Those extensions use a 10-24 bolt and both were broken off in the block. Looking at the coil I saw damage where it had made solid contact with the flywheel causing the mounting bolts to shear.

Seems like a poor design as the weight of the coil is being held by 10-24 1/2 in long threads. I have worked on small engines for 20 years and I have never seen a failure like this.

From what I can see, one side of the coil mounting extension broke allowing one side of the coil to drop down and hit the flywheel. I checked the flywheel to see if it is properly attached to the crankshaft and checked it for runout but all looks fine. I have removed the broken bolts and ordered replacement extensions and replacement coil.

Any ideas what might have caused this? Has anyone else seen this before?

Gary (Mowfixer)

 

[Rivets]

I don’t think it a poor design, as Tecumseh used that setup for years with no real problems. The only time I saw any problems is when there was a bad post casting or a foreign object would get caught in the flywheel. See you casting looks good, I suspect something got wedge in there.

 

[StarTech]

IF they are only 1/2 long then someone have installed the wrong screws.
Screw, Torx T-15, 10-24x15/16"

 

[mowfixer]

This is the 3/4 in extension Tecumseh installs, .the threads are 1/2 and they screw into posts shown above and coil screws into extension.

 

[StarTech]

Ah I see what you are writing about. Just need a little more coffee and the picture. Most things breaking like this is from being over tightening or leaving them loose.

 

[mowfixer]

It sheared one side off, coil dropped and hit flywheel then other side sheared. Been a nightmare getting sheared bolts out as they got deformed by force so EZ outs and heat didnt work. Had to drill and tap and may still need helicoil if those posts have enough material to drill enough to insert helicoil. Guess I could get hollow spacer and machine screws

 

[StarTech]

It wont be the first time a tech had to re-engineer something. I got some HU675(625)HWT that I have to knurl the spindle shafts for proper fit and Husqvarna just keep the same design out on replacement orders. The only thing did different was to zinc plate the shafts still the same loose fit.

 

[mowfixer]

when I get the new extensions in a couple days I will see how well they thread into my tapped holes. If a little loose I will put red threadlocker on them and maybe I wont live long enough for the ignition coil to fall off again. Otherwise as you said some re engineering or maybe a visit to a welding shop to weld the holes shut and re-drill and tap again.

If Tecumseh had made those posts 3/4 in longer coil could attach directly like every other small engine. Seems they found a flywheel with magnets too far from engine and they had to adapt. 10-24 threads are a bit small to hold this heavy coil. Any vibration and I could see this failure again. Wont have all the parts until the end of the week so I can see if it will run again.

 

[indinjon]

when I get the new extensions in a couple days I will see how well they thread into my tapped holes. If a little loose I will put red threadlocker on them and maybe I wont live long enough for the ignition coil to fall off again. Otherwise as you said some re engineering or maybe a visit to a welding shop to weld the holes shut and re-drill and tap again.

If Tecumseh had made those posts 3/4 in longer coil could attach directly like every other small engine. Seems they found a flywheel with magnets too far from engine and they had to adapt. 10-24 threads are a bit small to hold this heavy coil. Any vibration and I could see this failure again. Wont have all the parts until the end of the week so I can see if it will run again.

I got the same thing but caught mine before it sheared any bolts. Vibrated itself apart the intake bolts , coil, winter carb warmer and even the carb all vibrated loose. Used red thread locker and so far so good. Now it doesn't want to start set new coil yesterday to .012 thousandths even if I spray a little engine starter, plug is good so wondering if the key sheared . Guess that will be the next thing to look at.