# Tecumseh hm100 engine: no spark even with new parts



## fernando65

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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## td5771

did you set the gap between the magnets (flywheel) and the coil?


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## fernando65

td5771 said:


> 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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## bwdbrn1

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.
Ignition Parts - ELECTRONIC IGNITION MODULE NOVA II - Welcome to WNY Small Engine Experts


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## td5771

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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## fernando65

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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## HCBPH

*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.


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## fernando65

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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## bwdbrn1

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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## fernando65

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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## HCBPH

*Settings*



fernando65 said:


> 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


From the manual, page 71:
Check the air gap between the flywheel magnets and
the laminations of an externally mounted coil or
module. It should be .0125 (.317 mm) or use gauge​
part # 670297.

Page 73
Begin the procedure by replacing the points if necessary.
To do this remove the nut that secure the movable portion
of the breaker points. Remove the screw from the
stationary portion of the breaker points and the worn
breaker point assembly. Install a new breaker point
assembly and adjust the point gap. This is done by rotating
the crankshaft until the point arm is resting on the high
side of the ignition cam. Set the point gap by loosening
the screw on the movable point set and insert a feeler
gauge per specification. Adjust the point gap so that a
light drag is felt on the feeler gauge. Tighten the screw
and recheck the gap. Leave the leads unattached for the
timing procedure. Use this procedure on all standard point
ignition systems when point replacement is necessary
(diag. 21).
Install a dial indicator (Part # 670241), equipped with the
correct tip on the extender leg. Use the small tip for
engines with timing dimensions of between top dead
center (T.D.C.) and .050" (1.27 mm) before top dead
center (B.T.D.C.). Use the large tip for engines with timing
dimensions of between .051" (1.295 mm) B.T.D.C. to
.150" (3.81 mm) B.T.D.C. Make sure to secure the
extender leg in position to locate the tip directly over the
piston head. Loosen the screw on the side of the adaptor
sleeve to allow the sleeve to be turned into the threads of
the spark plug hole, not the entire dial indicator. This will
ensure the proper location of the tip. Once the adapter
sleeve is secured in the hole, tighten screw on sleeve
adaptor to prevent the dial from moving up or down, which
would give a false reading (diag. 22).
Find T.D.C. with both valves closed by rotating the
crankshaft clockwise when looking at the magneto end
of the crank, until the needle on the dial stops and
reverses direction. Where the needle stops is T.D.C.
Loosen the screw on the dial, and rotate the dial so that
zero is lined up with the needle at T.D.C. Tighten the screw
on the dial to secure it in place (diag. 23).
While watching the needle on the dial indicator, rotate
the crankshaft counterclockwise when looking at the
magneto end of the crank, .010" (.254 mm) past the
B.T.D.C. dimension. Then rotate the crankshaft clockwise
to the proper B.T.D.C. dimension, this will take out any
slack between the connecting rod and crankshaft
assembly.
Example: If the specification of .080" (2.032 mm) is the
B.T.D.C. dimension, rotate the crankshaft counterclockwise
so that the needle on the dial indicator travels
to .090" (2.286 mm) B.T.D.C. (diag. 24), then rotate the
crankshaft clockwise so that the needle travels to the
specified dimension of .080" (2.032 mm) B.T.D.C. (diag.
25).
Next, if the original breaker points are being used,
disconnect the leads from the point terminal. Reinstall
the nut & tighten. Connect one lead of a continuity light,
or ohmmeter to the point terminal and the other lead to a
good ground. Loosen the two bolts holding down the stator
and rotate the stator until the continuity light or ohmmeter
indicates a break in the circuit. Torque down the stator
bolts while maintaining the stator plate position and the
timing procedure is completed. Reconnect the leads on
the point terminal and tighten the nut making sure that
the leads do not touch the flywheel (diag. 26).
24 25
23
22
21
DIAL AT
.090"
(2.286 mm)
DIAL AT
.080"
(2.032 mm)
DIAL AT 0"
SLEEVE
SCREW
SLEEVE
DIAL SCREW
PIVOT POINTS
ARM
IGNITION
CAM
CRANKSHAFT
(continued on top of next page)
26
70
30
Before putting the dust cover back on the points box,
clean the points by sliding lint free paper back and forth
between the contacts. Manually, open the points when
removing the paper to eliminate paper fibers from​
remaining between the contact points (diag. 27).


Try seeing if there are any marks on the stator plate from where the bolts originally held it down. try moving it back to that position and see how it works. If not then do what the manual says to adjust the timing to where it should be.

I've never done this, but I keep it around in case I ever do.

Here's a thread I've been working on that includes going through that motor:
http://restorationmen.lefora.com/20...-used-snowblower-purchase-and-proceedi/#post8
Might help you out on checking or cleaning up some stuff on it.

Good luck


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## fernando65

Thanks HCBPH,

I appreciate the service manual info but most of it has to do with timing. my issue is even more primitive than timing! I cant even get spark. 

thanks for the air gap info- but that's for an external (and therefore adjustable) coil.

here are some pics i just took. as you can see, this blower is a beast. 10hp, 32" width with a unique "drift breaker" auger. My stator does have some tooth marks from the washers that go on the bolts. i did do my best to line them up. This adjustment controls the "dwell" i believe. 




i have an old ariens st824 that runs fine.. it has a tecumseh in it too.. i plan to dig into it and maybe interchange the whole magneto assembly and possibly fly wheel..


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## HCBPH

*Timing*

Whether you working on one of these:








Or this one:








or any one of these:








You have some common factors. The points open in relation to the ramps on the crankshaft and stay open based on the same ramp. The spark is initiated by the magneto in relation to the flywheel, also based on a offset of TDC.
If all the pieces and parts are in there in the right positions relating to TDC, you should have a spark.


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## td5771

you probably have by now but, before all that other work... change out the points, seems to be the only thing that hasnt been changed, i just pulled my hair out with the same issue on a tecumseh 5 hp and it was the great looking points that needed to be changed.


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## fernando65

update: i replaced the points and now have spark!! blue spark! the old points look great, and they both seem to read the same resistance (although i dont know what im doing with this meter).. sooo i put it together, and found out that the spark plug threads are totally gone.. so i could spend $45 on a helicoil or $20 on a used head (ebay) and new gasket.. i ordered the parts and will post results!


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## Pat DEwitt

im thinking that the coil or magneto has to be adjusted but don’t quite know if that is the problem or not or know how you would set it as it is under the fly wheel


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## nwcove

This thread is 6!years old.


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