Crankshaft has a very tight spot

[Captain Golla]

Mechanic was checking the valave clearances on my Volvo MD2030 and discovered a very tight spot whilst hand cranking over the engine.... took the head off to check top stuff... still tight...
so here's a quiz for the gurus:
Is it main bearings failing
bent crankshaft
or what??? and what could be the cause? I recently bought the boat and have no idea how the previous owner used/abused her....
Whats the best/worse case scenario?
Thanks, I am just trying to sleep tonight

[MYTraveler]

Presuming that the bores were all checked, my guess would be that something is bent (could be a rod, camshaft or crankshaft). If camshaft, the tight spot should be once in two full revolutions, conversely, if every revolution rule out camshaft and all lifters and valve stems.
Probably not a bearing or bearing surface.

[model 10]

I would make sure it's not anything with the transmission etc then I would check the oil filter for metal. Accessories on the engine, cam drive, fuel pump etc.
If a crank or rod were bent enough to be felt, same for a bearing, it would have blown up long ago. Or maybe it was just a few minutes from blowing up. Whole bunch of stuff to check and you already have the head off. You are on your way

[DougR]

I second what Guy has said...

If your 2030 is an early version it was equipped with an MS2 transmission or because it is a Bavaria, perhaps it has a 120S saildrive. Both of these used a cone clutch shift mechanism where the cone was moved up and down by a shift shoe which rode in an eccentric groove. Part of the assembly procedure of the transmission was to shim this shift shoe so that there was a high drag spot as the shoe ran past the eccentric. Normally this drag wasn't enough that you could feel it with a wrench on the crankshaft, but if something is amiss in the drive, perhaps the drag has increased. You can eliminate this as a possibility by loosening the two bolts on the shift mechanism on the side of the gear case and sliding the shifter out.

If this doesn't help, or you have a different transmission, then it's back to the ideas already mentioned.
Good luck,
DougR

[Captain Golla]

Thanks everyone. Engine is being removed. I should have an answer soon I hope. Unfortunately I am not at the yard.

[Captain Golla]

As it turned out the head was not OK. Cracked across the valves. Signs of sea water damage in cylinder. Plus tight spot on crank. Plus Plus.
Obviously the previous owner did what he did.

Decided to pull the pin and get a new engine. Old engine was a 2005 Volvo MD2030. New one is a 2015 Volvo D1-30F. Being installed now.