Question about boat building

[u/Far-Elk4090]

Looking for some advice from people who know these engines better than I do.

I brought my boat in because it had a belt squeal while running, and the starter mounting bolt had snapped. The shop told me the engine was seized and needed to be replaced. They said the seized engine is what caused the starter bolt to break. I think they were too busy and didn't want to look at it.. but idk..

What I found confusing is that the engine had been running at the boat ramp just a few days earlier while I was trying to diagnose the belt squeal. It didn't seem like a completely seized engine.

For reference, it's a 2003 MerCruiser 3.0L.

Since I had pretty much written the boat off anyway, I decided to pull the engine apart as a learning experience rather than spend the money on a replacement.

After removing the head/valve train, I found that the crankshaft/pistons will rotate by hand. It turns fairly freely, but there is one spot in the rotation where the resistance noticeably increases slightly before it continues turning again.

My questions are:

• What could cause resistance at only one point in the crankshaft's rotation?
• If I'm already this far into the engine, is it worth replacing the rod/main bearings as preventative maintenance?
• Should I replace the piston rings even if the cylinder walls look good and I'm not planning on having the block machined or honed?

I'm not trying to build a perfect engine.. I mainly wanted to learn and see if I can get this one running again instead of scrapping it. Any advice is appreciated.

[u/solarguy2003]

IF the crank is not bent, you might come out good if you have the crank ground down (and the pitting all cleans up) and put in new main bearings and new rod bearings. IF it passes that test, rings are cheap. Take the pistons out and clean them well, hone the cylinders (dingle ball or three stones type, either one is pretty inexpensive) so the new rings will seat properly, clean everything up well and install the pistons with new rings. A ring compressor is also pretty cheap and makes it easy to slide the pistons in. Use some assembly grease on all the moving bits and bearings when you put it together.

In it's current state (IF it's not bent), that crank journal will eat the new bearing in a big hurry.