I have a 6 inch TH Marine Jackplate on a Triton TR 18 1998 model. Probably has not been adjusted ( moved up or down} in 20 years. I now have a Merc 150 HP 4/stroke on it and while it runs fairly good I thought I would tweaked it some today. It seems the threads are corroded in the adjustment nut. I can't move it up or down with a 25 inch breaker bar. I put a lot of force on it and it AIN'T moving. If I put a cheater pipe on it I am afraid I will break the adjustment bolt. Bolt appears to be 1/2 or 9/16 inch in diameter. It is single rod adjustment. I have put penetrating oil on threads hoping it will soak down into the nut. The nut is a machined piece and appears about 1 1/4 inches in diameter and about 1 1/2 inches tall. The nut is below a plate so you can't access it directly. The P. oil will take a long time if ever. I will put the P. oil on it for several days. I see no way to put heat on it safely without removing it from boat. Anybody know any good ways to free the adjustment up?
Thanks