I have a 4.2L 1991 F150 that intermittently has a bendix to flywheel mis-engagement. The flywheel teeth and the bendix teeth look good. It has always done this. The bendix acts like it does notmesh with the flywheel teeth and makes a bad grinding noise. Most of the time when theigintion switch is turned off and thekey isreturned to the start position, the starter will engage normally. I've read a lot of complaints on other websites from others who have the same problem with various models/engines. The starter on this engine is not like the old Ford starters, it is smaller and the bendix does not stick out at the flywheel end of the starter housing like the older ones. Is this a common problem and did Ford have a service fix for it?

 

I've never seen this issue, and as a mechanic I have seen a lot of these trucks. The problem I have seen most though is the starter motors going bad and making a very harsh grinding noise upon power engagement. Remeber you don't own a Chevy it does not need to be shimmed LOL. What you could also look for is any metallic particles caught around starter housing from grinding.. I would break down and replace the starter, and worry about other problem if it reoccurs instantly with new starter.