Q: I have an old Sears mower (Tecumseh engine) I have been trying to get running so I can sell it (I bought a new mower out of desparation when it died). Here's what happened when it died:

I was mowing and hit a large branch in the yard. It was big enough that it stopped the mower dead. I couldn't get it running again, so I started trying things. I changed the spark plug. No luck. Then I thought I would change the oil. The blade seemed very hard to turn while I was doing this. I also noted what looked like a small amount of metal shavings in the oil. I then flushed oil through the system a couple times, rotating the blade and working the action until the oil ran out very clean. Then I put clean oil in, and was able to get it to start. It worked fine for the next two months, then I hit another branch just like before.

So I took the same approach. I changed the oil. The blade seemed to turn fine, and no metal shavings like before. But, it would not help. I put in a new spark plug. I did the spark plug test, to see if a spark would jump the gap. I can see no spark. However, when I do this test on my new mower, which runs fine, I can never see a spark on that one either. And, when I do this test on the old mower, I can feel the pulse of electricity in my fingers as I hold the plug, and the plug is brand new. I also cleaned out the carbeurator, reset the float, and got a new bowl for it (the old one had a tiny hole in it). However, I can not get this mower to fire. I also tried the test of putting a teaspoon of gas directly in through the spark plug hole, and it will still not fire.

I guess my question is, what is my next step? What would be the likely affect of hitting a large branch that makes the mower stop dead, and then not crank? How hard is it to see a spark jump the plug gap, because I can not even see this happen on a mower that is working fine? I know the timing is somehow connected to the turning of the flywheel, and could hitting a large object knopck out the timing so the plug fires at the wrong time? How could I test for this?

A:  I would check to see if the crankshaft is bent on the bottom. Take the plug out and turn the mower up where you can see the blade turn. Pull the starter and see if the blade wobbles and the shaft. Next take the top apart and check the flywheel key. More than likely you have sheared a key.

To see the spark from the plug you need to be in a shadow to see it. If you take an old plug and make the gap about 60 or so it would also be easier to see because it has to jump farther and make a sharper and bluer spark.