Small Engines (Lawn Mowers, etc.): My Lawnmower Wont Start, crank shaft, bernzomatic torch

Question
Good Morning Michael

I have a 20 inch rotary mower - very generic (I think made by MTD, the engine is a Vantage 3.5 Tecumseh with a quick start primer.

It was becoming a hard starter - so I replaced the plug. Yesterday morning I was mowing and hit something - the engine stalled. Now despite prayers, curses and threats (to say nothing of a sore arm) it refuses to start. I put it up on my woerk bench and held it up on blocks so I could see if perhaps something had wrapped around the blade - nothing.

Next I let it cool down a bit, pulled out the spark plug and put into the cylinder a shot of starting ether. Not even a cough. There is some spark - I think! I got a slight "lick" as I accidently held the plug wire. Then I took the plug and heated it with a Bernzomatic torch. This an automotrive engineer once told me was a good way to defoul a plug - particularly in winter. No improvement

Now I have tried it again and it gets almost to the point where the engine is going to catch - but nothing.

Questions:

1. Could oil somehow have gotten into the ctylinder.

2. What is the correct setting for a plug of this type of small engine. Can anything be gained by decreasing the spark gap.

3. Could I have bent the crank shaft when it stalled?

Any help or direction would be appreciated

Dave thanking you for your time


Answer
Hi Dave,

If it quit right after striking an object, I could almost guarantee that the flywheel key is sheared.  The timing would then be off.  The flywheel is located under the recoil/cooling shroud. It is tapered and mates with the tapered crankshaft. The keyway in the flywheel and shaft
keeps it from spinning on the shaft.  A nut secures it.  The recommended way to remove a flywheel is to use a puller.  An alternative, is to tap on the crankshaft top, with a brass hammer or use the round punch on an air
hammer.   The flywheel will need to be held up and supported or upward pressure applied with 2 large prybars. (A 2 person job.) Care is needed so the flywheel doesn't crack or bend.  Also be careful to not mushroom over
the crankshaft top.  Replace the key.  Install the flywheel after cleaning the tapers and re-tighten the nut to 65 ft/lbs.
There is also the possibility of a bent or twisted crankshaft depending on the severity of the impact but usually the key just shears.  

The spark plug is gapped at .045
For more info see: http://www.tecumsehpower.com/Tecumseh.nsf/Second%20Level?OpenFrameSet&Frame=Fram...

Let me know how you make out.
Michael