Tecumseh hm100 engine: no spark even with new parts - Snowblower Forum : Snow Blower Forums
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post #1 of 17 Old 01-26-2012, 07:52 AM Thread Starter
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Tecumseh hm100 engine: no spark even with new parts

Hi all, so glad to have found thus forum!

I've got a craftsman with am hm100 in it ( I know, wrong forum but it's got a Tecumseh and I have engine probs.. This forum gets more traffic than craftsman). It must be close to 30 years old now, given to me as is- wouldn't start. So long story short: no spark at wire end.. Changed out internal ignition coil and condenser.. Points are good looking, checked continuity with meter. I removed all auxiliary wiring from magneto.. I only get a tiny spark when touching ground. The magnets on he fly wheel look great. Very little rust on the layered laminated part that coils and points attach to. No one can help Please help solve the mystery!
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post #2 of 17 Old 01-26-2012, 10:25 AM
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did you set the gap between the magnets (flywheel) and the coil?
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post #3 of 17 Old 01-26-2012, 05:40 PM Thread Starter
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Quote:
Originally Posted by td5771 View Post
did you set the gap between the magnets (flywheel) and the coil?
Because this is an internal coil (not accessible because it is hidden behind flywheel, it is not adjustable. Thanks for the suggestion!
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post #4 of 17 Old 01-26-2012, 06:27 PM
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Darned electrical stuff! Hate it when you think you got it fixed.

What do you mean by auxiliary wiring? I'm trying to learn something here myself because ignition problems puzzle me to no end too.

The magnets have a good strong pull? I think I read somewhere about holding a screw driver up near them and seeing if they pull the screw driver toward them.

I know you said you replaced everything, but I've used this to replace the points and condenser on a couple of small engines, and it has worked well. This is also the best price I've found for it.
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post #5 of 17 Old 01-26-2012, 06:36 PM
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sorry, i thought they were adjustable, must be confusing my engines. check plunger that pushes points up and down, replace points (i have had some i swear were perfect but they werent)

check spark plug connector, some of the older plug wires had only a sharp piece of metal piercing the rubber insulator of the wire to make the connection between the wire and the spark plug connector.

insure you , or the previous owner, had the right flywheel key. some are offset, i just had one that appeared to be just a hair offset, but it wasnt broken, turns out it was damaged but hadnt sheared off. needed a new straight key. it was off enough to throw the magnets out of whack.

if previous owner had a problem with the magnets, maybe glued back on in the wrong spot?


just some ideas
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post #6 of 17 Old 01-26-2012, 08:19 PM Thread Starter
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the magnets have never been removed. i followed the service manual procedure for testing magnet strength- yes you hold a screwdriver up to them.

the flywheel key looks good to me- but i dont think that would prevent spark anyway. the previous owner never dug into the engine.

the spark plug wire is brand new because i replaced the coil. it doesnt have a rubber boot on it yet- just the metal loop on the end.



thanks for the ideas.. i think i will replace the points, but i would be really surprised if it helps.
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post #7 of 17 Old 01-26-2012, 10:48 PM
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Spark issues

When you changed out the magneto coil, did you remove or change the stator plate (the thing that holds the points)? Does this engine have the ability to run a light etc or not?
If it runs a light, it should look like this:

and the flywheel would look like this:

If you changed the magneto coil without removing the stator plate, you should be ok. If you removed it then you likely have timing issues. Take a look at the Tecumseh manual, starting on page 68. You will have to check the airgap on the magneto, timing of the points and points settings. You want to avoid (IMO) steel feeler gauges when setting flywheel magnet airgaps because it can affect the adjustments, use brass ones if you can (I bought some at Sears a few years ago).

I've seen weak spark due to a bad condensor, sheared flywheel key, improper points gap, damaged flywheel magnets, even a bad sparkplug.

Pictures of your engine internals along with indication of what you've replaced and adjusted would be helpful.

Last edited by HCBPH; 01-26-2012 at 10:51 PM.
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post #8 of 17 Old 01-27-2012, 12:59 AM Thread Starter
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Thanks for the great post! I will get pics up tomorrow. I believe what u have there is almost identical to what I'm dealing with. Yes I removed the stator to replace the coil and condenser. It seems to me that the air gap is not adjustable.. There are two bolts that hold the stator to the engine, the holes these go into are oblong but the assembly must rotate on the crank shaft which keeps it from moving off center. Right? I remember there being a round impression at the mating point on the back of the stator which recieves the engines complimentary figure surrounding the crank shaft. Is the coil off center- which would make it rise or fall as I turn the stator slightly on it's axis? Yes the unit has a headlight, this is what I meant when I said I removed the auxiliary wiring. I just took it out of the equation to simplify my problem.
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post #9 of 17 Old 01-27-2012, 08:47 AM
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You're right about the air gap. There isn't any changing it like you could if the coil was on the outside of the flywheel. The elongated holes would be to allow for changes in timing. That is, when the lobe on the crankshaft opens the points.

Putting new points in, since you have replaced the other key components would make sense. Plus, for the price of a new flywheel key, it wouldn't hurt to throw a new one of those in too.
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post #10 of 17 Old 01-27-2012, 11:05 AM Thread Starter
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is it ok if i were to build the stator up to a smaller gap? the gap seems very large, we measured it to .040 all the way around. i was thinking i could build it up with some solder.. but maybe that would effect the laminations
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