Merc ProXs problem

Today I ran my boat about 1 mile from the ramp and lost rpm so I shut down and motor was shaking violently then died. I trolled back to ramp and saw metal( looked like cast aluminum) in the exhaust port by prop. Gear shift wouldn't go into forward until I too the prop off to look at lower unit oil. ( which was ok). Any ideas on where to start as far as a diagnosis would be helpful.

Pull the plugs and look for melted aluminuim spots on them. Sounds like a piston let loose but I hope it's something else.

Hate to hear this...look into cold seize.

I'm afraid this might not end well.
As mentioned, pull the plugs, activate the kill switch and see if it will crank, and if so what it sounds like.
With the plugs out you should be able bump the starter incrementally until you can see each piston top with a flashlight.

Drop the lower unit off first. See if it runs alright then. It will not hurt it to run for a few seconds just to check. If motor still sounds bad you have powerhead problems. How long did you let the motor warm up before you took off?

Just got home to tools to do some checking. Motor ran for several minutes before I ran. Outside temp was upper fortys water temp 55.

I say lower unit as mentioned above.

I pulled the plugs. The #6 plug was damaged and had melted metal on it. So I guess I dropped a piston. What are y'alls suggestions going forward?

not good news, sorry man... even if you're able ta diy its gonna be expensive when its fixed tha right way!

Take the engine to a reputable engine builder that will give you a warranty. The cost to rebuild is going to run close to 4000. Thats a lot of coin to spend on the motor and not have at least a year warranty. Or you could talk to Mercury about a remann.

I am in the process of rigging a new Pro xs 250

Sounds like it cold seized those 3 litres are famous for that this time of year. Piston swells faster than the block because of trash in the thermostats,gets # 6 everytime.

where you located I'm in McKinney I can rebuild motor you I have a shop

Sounds like a similar situation I've heard about with a 200 Merc. Different model, but long story short reed valve chipped off and got sucked into the piston and made a terrible rattling noise. This was a mid 80's 200 black max engine but the reed valves are paper thin and once they develop cracks it's easy for them to get sucked into the engine when the piston comes off and explosion.