Yard Machine needs Help!!

My son has a used Yard Machine 17.5HP/42" Shift on the Go lawn mower. He is having trouble with it starting and asked me to look at it. It has a Briggs & Stratton I/C motor, model 42A707, type 2238E1, code 9904225B. He said it would only start when cold, if you shut it off hot, it would not start. Today he showed up at noon, his mower won't start at all, so I loaded my mower and took it over for him to use while I looked at his. First thing I did was put the spark plug tester on the right side plug and crank it over. No fire. While cranking, I heard a hissing noise, so I checked the spark plug on the left side, some one has cross threaded a plug into it and stripped out the threads. I took my test light and started checking for power. The seat safety switch was unhooked, the 2 wires taped together with no connection between them. Not sure how it ever ran. I have power to the solenoid on incoming side, nothing going out. I took the solenoid off to have it checked at work to see if it's bad. The label on the hood says it uses Champion RC12YC plugs. It has Champion RJ19LM plugs in it. He had a RC12YC plug there that had been in it. It's a long thread plug and has the end beat up and the end of the plug is bent tight against the electrode. Is this the correct plug for this engine?
Can the threads in the head be repaired or does he need a different head? New or are there any used ones around? Looks like a long way to go on this one, but need to start with getting the spark plug hole taken care of and check out the solenoid and then go from there. Any help appreciated, thanks, Chris

for the stripped head it can be helicoiled

some of the safety switches ground the ignition out and need to be open to operate,and on some of the newer mowers it is a two sided switch to eliminate people bypassing the safety switches one side needs to be open and the other side closed to work so be carefull how you bypass stuff it could cause even more head aches

Take the head to your local auto machine shop and have them install a helicoil as been mentioned. I had one installed on my old Toro Whirlwind years ago. Don't over tighten the plugs just snug them.
Hal

Correct plugs for this eng are champion RJ12 or RJ19LM(resistor)or J19M(standard),briggs oem plugs pn 394539,492167 or 802592

Might want to try a spark plug thread chaser type tap. I had mixed results with this method.
After cleaning out the tread, try a new plug. Do not put much torque on the plug.
Helicoils work great and a lot of parts on ebay.

Used heads should be plentiful, probably cheaper than having it repaired. Might check a local repair shop or Ebay.

Be interesting to see what that long plug did when it was forced in there... Not sure what it would have hit, hopefully not a valve or valve seat!

You can get a kit for repairing the thread at either Auto Zone or Advance Auto. The kit costs about $30 and has several inserts, an oversize tap, and a swaging tool. Eliminates the need to remove the head and buy a lot of extra parts.