# Help! Need engine help for ignition troubleshooting on chipper-shredder



## NuclearNick (May 23, 2020)

Good morning,

I'm having ignition troubles with a Craftsman chipper-shredder that I bought used earlier this year. I had it completely torn down earlier this year, replaced all chipper blades and got it up and running. Ran several trailer loads of sticks through it a few months ago, so it was working like a champ. Went to start it up about a week ago, and no spark. Fuel was feeding fine, but it never attempted to fire. Changed spark plugs, no luck. Took covers off, checked gap between flywheel and coil, it was very close to nominal (0.012 versus nominal of 0.0125). There was a lot of corrosion buildup on the flywheel, so based on advice from another user I sanded the corrosion off the permanent magnet to clean it up, check gaps again, no spark. Disconnected kill switch line from coil (in case it was grounded), no spark. Ordered and received a brand new ignition coil, and another new spark plug. Replaced coil & plug again, and regapped to 0.0125”, still no spark.

The engine is a Sears/Techumseh 143.988001 running on a Craftsman 8.0 hp chipper-shredder, model 147.775802.

I'm running out of ideas. Can anyone think of what might be stopping my ignition system from creating spark? Would love to get this thing working again (my brush piles are getting out of hand).

Thanks,
Nick


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## frank_ (May 23, 2020)

safety/isolator switch maybe ?


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## NuclearNick (May 23, 2020)

Thanks for the response Frank. I don't think so - I think the ignition system on this thing is super-simple. Photo attached - there aren't any electronics between the coil and the plug. But perhaps I'm missing something obvious (I hope)?


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## frank_ (May 23, 2020)

should spark with that spade connector disconnected eh nick
i think those need to spin pretty fast to generate a spark, have you tried an electric drill ?
failing that, an ohm test on the coil windings maybe ?


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## NuclearNick (May 23, 2020)

I have been testing with the pull rope (took cover off for this photo). So it's spinning plenty fast. I just don't see a spark at the plug visually.

Would be easy enough to measure resistance across the coil windings, but I have no idea what "normal" is.

How about the magnet? It seems pretty strong to me, but is there any way to figure out if it's producing enough of a field to generate voltage in the coil? This thing is pretty old...


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## frank_ (May 23, 2020)

the numbers i use are 0.4 to 2 ohms on the primary
and 6k to 15k ohms on the secondary
and 1 to 6 k ohms on the ht lead
a magnet that feels pretty strong should work fine eh
and the coil looks mounted the right way round according to google pics


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## NuclearNick (May 23, 2020)

frank_ said:


> the numbers i use are 0.4 to 2 ohms on the primary
> and 6k to 15k ohms on the secondary
> and 1 to 6 k ohms on the ht lead
> a magnet that feels pretty strong should work fine eh
> and the coil looks mounted the right way round according to google pics



thx. The coil is sealed, so is it possible to measure all of these without tearing it apart?

I wonder about rotational speed. This thing doesn’t have a starter so it’s just me pulling. I’m giving it a good rip, and I was able to start it a few months ago with no trouble. But there’s no clutch. Cutting wheel etc is all shaft mounted. It’s a beast to pull start.


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## frank_ (May 23, 2020)

yes across the spade terminal and earth for the primary
and cap to earth for secondary (+ ht lead)
and spike the ht lead down near the coil with a sewing pin for ht lead only


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## TRTermite (May 23, 2020)

Does the motor use POINTS and CONDENSER for ignition?? I have had the points push rod (Don't know the proper terminology) hang up and keep the point s open... a bit of lube or a Nova ign. module maybe?


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## ray benson (May 23, 2020)

Engine should be a Tecumseh HM80-155587S
Magnet strength check - out of the service manual -
Check the flywheel magnets for the proper strength using this rough test. Hold a screwdriver at the extreme end of the handle with the blade down, move the blade to within 3/4 inch (19.05 mm) of the magnets. If the screwdriver blade is attracted to the magnets, the magnetic strength is satisfactory


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## NuclearNick (May 23, 2020)

Thanks Ray. I read that too, and I’m really hoping that’s not it. Mine does attract the screwdriver, but not really at 3/4”. Sounds like the only way to replace the magnet is to get a replacement flywheel which probably makes this thing a throw away...


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## NuclearNick (May 24, 2020)

OK @frank_ , I took some measurements using the engine frame as ground:

No resistance / connected to ground: spark plug threads, armature of ignition coil (laminated bars)
Infinite resistance: spark plug center electrode, spade terminal sticking up out of coil
Armature to plug wire cap - about 2K (this is open on my old coil)
Spade terminal to plug wire cap - about 250K (this is about 5K on my old coil)

I have no idea what all of that should mean to me, frankly (I'm not a very good electrician). But if my armature is connected to ground, and is only 2K to the plug wire cap, wouldn't any developed voltage just go to ground through a 2K resistor? In the old coil (which wasn't working) the armature and the plug wire cap were not connected at all. 

I bought this thing from Amazon, but not from OEM. I wonder if it's possible that I got a bad coil. But I'm a little lost as to why neither my new nor old coil develops a spark.

For @TRTermite , no points, etc. Just a sealed ignition coil.


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## frank_ (May 24, 2020)

this guy had about 2 ohms on the primary, and about 10k ohms on the secondary nick
testing from the plug cap includes the lead/cap resistance too eh
i,ve had loads of chinese parts without problems, but had 2 duff chinese coils tho


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## NuclearNick (May 24, 2020)

Measures primary and secondary resistance as shown in the video:

Old coil: primary 250 ohm, secondary 4.2 kohm
New coil: primary 5.6 Mohm, secondary 2.0 kohm

I have no idea what nominal is (the Tecumseh tech manual for the engine nor the Sears manual for the chipper say). But it seems clear to me that the primary coil on my new part is basically an open circuit and will never work. Surfed the web, and now that Tecumseh has been sold off so many times it appears that no technical info is available for these parts without going through a dealer. Any ideas for figuring out what coil resistance should be without a vendor to ask?

Ordering an OEM part now, will keep my fingers crossed for better luck.


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## NuclearNick (May 31, 2020)

Thanks for all the advice. Ordered an OEM ignition coil. Resistance across primary and secondary are identical to original rusty part (I'm returning the piece of junk Chinese coil from Amazon). Replaced, regapped, now I have a spark - clearly evident when pulling the cord. But the engine still isn't firing. I can smell fuel. Checked the choke butterfly - it strokes smoothly. Checked the fuel butterfly attached to the governor - it also rotates smoothly. Pulled off fuel line to carb and it's getting fuel. Pulled carb off intake and there is fuel inside, no obvious signs of buildup / debris.

Any other ideas on what could be causing this engine to not fire? It was running a few months ago. Next step I supposed is to tear down the carb and look for problems (or just order a new one and swap...) My wife tells me it's time to buy a real machine, but just based on principal I have a hard time giving up on an old machine that could still work. I'm just running out of ideas and getting tired of fighting this old machine.

Would appreciate any wisdom from the great mechanics on this forum.

@frank_ 
@TRTermite 
@ray benson


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## frank_ (May 31, 2020)

if its sparking and does,nt run with a drop of fuel on the air filter then i would be checking the flywheel keyway/timing nick,
then on to the valve clearances


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