I had an exhaust side push rode break on me while riding my T140 last year. I didn't realize was was happening at first... the bike would start but something was clearly wrong when it was running. Because the exhaust valve would no longer open all the pressure from the left cylinder was being pushed out through the intake valve and the carb. I knew something was wrong so I didn't attempt to ride the bike home. As soon as I got it back to my garage, I took off the inspection covers and slowly kicked the engine over. When my front left tappet didn't move at all I knew the push rod broke (plus I could look in there with a flashlight and see there was a missing push rod.) I was kinda relieved because that's not a crazy hard thing to fix. And it didn't do any damage other than gouge the rocker box a little. Could have been worse.