# Would an armature-magneto just suddenly stop working?



## shelzmike (Oct 15, 2008)

I have an older (80's model) B&S 11HP. Not sure of actual model number, but all the parts and repair info are in the 252707 manual. 

Anyway, it is fairly old, but is in pretty decent shape - in fact, when I use it still starts up on first try and runs pretty darn good. Until today...

I was right smack dab in the middle of mowing the front yard and the engine just died - no sputtering, just died..I know that the carbs are fine, so instincively I knew it was probably something electrical (for some reason, all my motorized things have electrical problems - motorcycle and the family van!). Anyway, I pulled the plug and checked the spark by grounding it to the engine and got nothing. The terminal cable end seemed a little loose, so I tightened it up with some needle nose pliers and got nothing still. The spark plug was new as of last year and looked fine. Just to rule out the easily fixable things, I got another one. When I put it in and tried to start it still nothing..so I pulled it back out and tested the spark against the engine again. I was not getting a spark, but I wiggled the cable and suddenly got some spark, it was not the strongest ever - was white and a little weak. I put the plug back in and it worked! However, only for about 10 more minutes, then the same thing happened. 

But this time, wiggling did not work. Now, my question is, would the amature simply just stop working like this? I can work on cars and can work on motorcycles, but these small engines are a little new to me. I understand the principals of most of it, but some of the electrical is a bit trickey for me (for instance, not sure what it is, but there is a bolt on the front of the engine(outside) that is grounded to the frame, but if it is not bolted to the engine, it will not even turn over.)

Basically, what I did was took the amature off and cleaned it and the flywheel with some steel wool as it was a bit dirty and had some buildup on it. I put it back on and still am getting no spark at all. The engine is turning over just fine though. (Electric start by the way, in case you haven't figured that out!). 

Finally, the amature is basically touching the flywheel - is there supposed to be some sort of gap here?

I do have a multimeter and know how to use IT, but not sure how to test my mower with it. 

Besides the amature, what else could be causing this problem? Thanks in advance for any help!

Mike


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## k2skier (Sep 30, 2008)

The only test is to remove the "shorting wire" from the coil, the small black wire that connects to the spade terminal, from the coil. Crank the engine over with the shorting wire remove, about .012 (business cards work great to set this) coil to flywheel air gap and it should have spark, if not, replace the coil. If the problem is in the high tension lead, plug wire, then it will still need to be replaced as the wire is not serviceable on B&S coils.


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## shelzmike (Oct 15, 2008)

Thanks for the reply. Turns out it was the armature-magneto-coil. Luckily the local shop had one in stock. Now my lawn is mowed and the mower hasn't been better (except for a slight surge at idle which I am still trying to figure out!).

Mike


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