I have just replaced a cambelt and waterpump on a 2009 1.6 focus s. Straight forward enough. ..bottom pulley bolt was tight but snap on gun rattled the bolt off eventually. Timing engine with the locking kit as a weird setup with the floating crank. ..put back together and rattle gunned the bottom pulley back on with a new bolt....started and ran perfectly. ....until I revved it. ...pulley went loose and bent exhaust valve or valve s....head off tomorrow. ...is this a common thing as many a cambelt changed on several makes and models but the bottom pulley makes no sense on the zetec. ....🤔

 

I've never had a crank pulley come loose. I've also always used a Impact gun to tighten the bolts. I know they do 2 lengths of crank pulley bolts for some of these cars, did u match up the length of the old bolt with the new bolt?