Trick for removing stuck lower units ( worked for me! )

I cannot take credit for this idea. I read it on the Internet somewhere and can't find it now for the life of me so I thought I would post it here in case someone had the same problem.
I carried my boat to a recommended local mechanic to have the impellers changed on my twin 2001 Mercury 250 EFIs. At just under 400 hours both water pumps were going strong. Problem is , The lower units had never been off in 19 years of salt water use.( I know, I'm an idiot. I knew it would be difficult. Thought the mechanic might know some tricks I didn't ) Two days later the mechanic called me and said "sorry, I tried, but these lower units are not coming off. When one of the impellers goes out, these engines are done." Not ready to give up I found this trick online: loosen all of the lower unit bolts approximately 1/8 of an inch.( mine were the big Nylok nuts, so there was no danger of the lower units falling off ) put the boat in the water and run it for about 20 minutes going from on plane to idle a few times. At idle shift from forward and back to reverse several times. When I returned to my dock, both lower units had separated. With the boat back on the trailer and all bolts, nuts removed I shook the starboard lower unit once and it almost fell on my feet. The port came off just as easy. Changed both impellers and reassembled with grease/anti-seize compound. I've learned my lesson!
Hope this can help someone else. Saved my rear!

One way I've done it is loosen bolts like you did then get up on the fin and bounce on it. Learned that at Mercury works every time

With my luck, I would've broke the fins off!

That's an interesting tip. I hope I don't wind up in that predicament. The 1/8 inch thing makes sense as it would probably not be enough to separate shafts and gears , but would remove mount tension and the motor torque does the rest. Nice !

But what did water pressure do with a 1/8" separation?

Did not seem to bother anything and the motors are 3 feet from the transom on a Gil bracket.

Larry- I've heard of this being done in a test tank, or with the boat on the trailer for "severe corrosion inhibiting the gearcase from being removed".

NEVER have I heard of someone intentionally running an engine on the water this way.

The idea of running a boat around on the water with gearcase hardware loose is simply NOT SAFE.

Operating an engine on the water with improperly secured and torqued gearcase mounting hardware could result in severe injury (or even death).