Mercruiser 260 lower end wasn't supported in tow, now it knocks when u run eng

78 Formula Thunderbird w Mercruiser 260 engine/inboard v-8 and outdrive. I recently trailered the boat around the block (somewhat bumpy road) without having strpps to support the outdrive unit while in the upright position. When I tried to start the engine (outdrive unit lowered and water attached) the outdrive makes a loud knocking noise as if the prop was banging against the ground. The propisn't hitting the ground as the unit is in nutural and also clears the ground. Is there a problem with towing the outdrive without strapping it? Whats the likely resdult of this knocking? Seems like it placed to much pressure on something and I need some advice?
Thanks

Re: Mercruiser 260 lower end wasn't supported in tow, now it knocks when u run eng

There will be much smarter people than me come along with advice, so be patient. I do, however, want to add that I've trailered boats without strapping the outdrive with no problems afterward. When you say "bumpy" are you actually meaning, "Huge 3' deep potholes and I was driving about 80mph"? If not, then it might be time to share just a little more info like; How did the boat perform prior to your towing around the block? Was there any noise before? When you say knocking, try and be a smidgeon more descriptive if you can like; where's the noise coming from? Can you relate it to any other common noise? How loud is it? Etc. etc. You should also update your information as to where you are currently located, etc. in the event someone is close by that is willing to help you.

Just trying to help you along with getting the correct answers and more swiftly. Best of luck.

Re: Mercruiser 260 lower end wasn't supported in tow, now it knocks when u run eng

Did ya lower the drive after the bumpy ride?........ or did ya leave it in the up trailer position and start the boat.......if the latter is the case then you are hearing the U-Joints grinding (knocking) saying please put the outdrive down to straighten me out.