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Join Date: Nov 2007
Location: Chandler, Arizona
Unfortunately, since you worked on it first, then took it to the shop, you have no way to prove there wasn't something wrong with it beyond what you told them. The ONLY way a plug can get smashed is if got hit by the piston, and the only way that can happen is if the plug is too long. The collision likely damaged the piston, possibly even the rod. Unfortunately I don't have an answer for you. I always recommend keeping your vehicles away from shops, but I am also a professional auto/equipment mechanic with 34 years experience. I realize not everybody has that. If you intend to rebuild it, or tear it down and see what the problem is, I highly recommend Roach's series of videos. They are WAY better than a manual, though you will need one of those too.
I am a motorcyclist, NOT a biker.
1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike