I have a Craftsman push mower with what appears to be stripped threads where the spark plug inserts into the block. The model number is 917.378410, serial number 013101M 002501, 6..75 HP, Eager-1. The spark plug is a Champion RJ19LM4. The spark plug does not tighten and will fall out during operation. Any ideas?

go to a small engine repair shop and get them to order a new head, it should be under 25$. the spark plug has nothing to do with the head. now as a quik fix use red high strength thread locker to hold it in if it will screw in. if you do get a new head it ain't but a few bolts to take off and slap it on. always feel the plug in by hand. if at first its hard to fit try by rotating it a little at a time until it goes in by hand then tighten it with a spark plug wrench. this goes the same for the head bolts. if you can't do it by yourself get the repair shop to do it. use autolite plugs!!!!!!!!!!!

try to find an old lawn mower junk yard and snap up a head for a buck or you can put a heli-coil in it to replace the threads

take it back to Sears and get it replaced they may upgrade you!
they had a bad run of the eager-1 engines where they had bad head(s),or they had a cracked block.......and that model number is a current number as of last year.so they may have that mower in stock.........i use to work for Sears as the preventive maintenance technician(PMT)............i came across alot of these mowers with that engine returned for this problem and the block problem....... :roll:

I had the same problem with an older Ford escort with a magnesium head. My soultion was a spark plug chaser I picked up in an autoparts store. The sparkplug screws into the chaser and then by using the plug wrench, I re-inserted the plug/chaser into the head. You have to take it slow and use a little threading oil. It's the same principle as re-tapping, but you might only have one shot at it. If the plug opening is cracked, you're better off getting a new head. Don't forget to take the plug with you to the parts store. Good luck!

be carefull taking the bolt out by the exaust valve i have seen some of them break off pretty easy just my 2 cents :thumbsup

My thought is replace the head. The cost is fairly low and the time spent trying to repair yor old one does not make repair a good deal.

i usualy just tap it out and get a thread insert from a local hardware store, they are only like 25 cents not 25 dollars for an entire new head and it takes only a minute or two