Just why are these bolts striping out?? They make thread inserts in which you would have to drill out the holes to a larger size to install the inserts.
#4
ILENGINE
If we are talking about the tecumseh on the mower in his profile, Tecumseh had some issues like the briggs with the valve adjustments. except in the case of tecumseh would sometimes pull the starter bolts out of the block when it kicked back.
lawnguy, due respect to you...helicoils are supposed to be stronger than the base aluminum if installed per instructions. I don't use them, but a kit (I think) typically comes with a carefully sized drill matching the insert. Next (me talking) alignment is very important when drilling, but might have been difficult due to the size and bulk of the engine. If the inserts were not put in @ 90 degrees to the flats the final torqueing of the starter motor will not properly stretch the bolts and lock down the the starter. And would tend to overload one side of the insert and pull it out.
If it were mine I would measure the starter holes and see if they could be safely enlarged to a next standard size bolt/thread (coarse) .Measure safe depth into the engine holes.
Next removal of (broken ) inserts. If out ok, if not seems like you could pull them out with the bolts used. If you are careful and good with tools select a proper drill for the new bolt and drill @ 90. You can get a hand drill with a dual bubble gauge on it to hold 90 degrees, then tap. Or make or buy a drill jig that will hold the drill @ 90. Tapping must also be done @90. Don't know how valuable the mower is, but this may be a machine shop job. Or you could repeat the helicoil in a bigger size.