I am redoing a KF3 (essentially a KE3 powerhead on a KF5 lower unit). Finished powerhead and started on
lower unit...could not get cover started using the "correct Mercury Service Tool...consulted with an
experienced friend...he warmed up gear case and applied
PB Blaster...still no go...MORE heat...still nothing doing.
Tried pipe wrench on projecting rim...no soap. Tried to
drive a little tighter then reverse...again no go.
Got out the hammer and punch and tapped around rim of gearcase over threaded area...then used hammer and punch
to work on turning cover...moved a little...installed
Mercury Service Tool and spun the cover off easily.
Using hamnmer and punch to loosen the grip of threads
is a suggestion I picked up from reading Mr. Bob Grubb's
comments sometime ago. Tuck this idea away for the day
you will need to remove a really tight waterpump cover to
replace impeller or seals. It really works.
Louis

It has worked on every motor but the KE4 LU I got up in Rocky Hill. I set that one aside when I got real frustrated. I am convinced someone put it on with Loc-Tite.