Shaft very difficult to turn

[SimonA]

I've got a single (small) diesel on a shaft, the engine sits on rubber mounts and the shaft doesn't have a flexible mount. The shaft runs through a PSS and then a shaft log which is just a bronze tube, then a cutlass bearing in the shaft bracket.

The shaft is very difficult to turn by hand. I have no vibration or noise. My engine mounts have just been replaced and the mechanic said the alignment is OK. So what would cause the shaft to be so tight?

 

[vas]

are you in the water or on the hard?

 

[SimonA]

In the water.

 

[vas]

there goes the easy answer that you have to do that in the water...
I wonder with PSS seal pressing the shaft against the g/b, how did the mechanic check/aligned the shaft?
the idea is you undo the shaft/gb coupling, pull the shaft back a bit and measure distances and regulate mounts accordingly.
did he do anything like that, or simply carefully removed each mount one at a time getting them in the same position?
and why did you replace the mounts in the first place? where they soaked in diesel and disformed, cracked rubber or?

 

[SimonA]

I've no idea how he checked but I presume with the shaft disconnected and measuring the gap all around. Mounts replaced as one had broken, they are a strange design with a rubber inner which had become detached.

 

[Portofino]

What is the problem if the boat works ?
Does the motor and sterngear behave as it should .
TBH I have never attempted to turn them in the boat from the engine room while it’s in the water .
I do turn them from the outside ( med warm water snorkel) occasionally when cleaning them , the props .
One s arguably a bit stiffer than t other but nothing 2500 NM of torque from a 13 L diesel can’t handle and the load / fuel burn / EGT s are identical at given rpms when running .

 

[kashurst]

Take the coupling bolts out, push the shaft back a few mm and see if you can turn it then.

 

[kashurst]

What is the problem if the boat works ?
Does the motor and sterngear behave as it should .
TBH I have never attempted to turn them in the boat from the engine room while it’s in the water .
I do turn them from the outside ( med warm water snorkel) occasionally when cleaning them , the props .
One s arguably a bit stiffer than t other but nothing 2500 NM of torque from a 13 L diesel can’t handle and the load / fuel burn / EGT s are identical at given rpms when running .

If the alignment is off making the shaft hard to turn, it will put extra load into the shaft bearings and the gearbox bearings. The shaft seal could also overheat.

 

[vas]

for the record, I can turn the 45mm shafts on both engines with the boat in the water and all coupled up. Stbrd is slightly harder than port though, haven't really bothered me as I can still turn them by hand

K., PSS wont make live v.easy as bellows are compressed forcing shaft to the gb

 

[Portofino]

If the alignment is off making the shaft hard to turn, it will put extra load into the shaft bearings and the gearbox bearings. The shaft seal could also overheat.

We are told “ the mechanic said the alignment is ok “

Aside new mounts fitted will inevitably bed in .Ie the whole lump will move down with time and vibration by the time the engineers opened his car door for his journey home . A year later you guess is as good as mine on the deviation from settlement.
It might tossing a coin actually loosen or indeed tighten .It will move there is no doubt .

@ the Op what’s the engine and the mechanics credentials FWIW .

 

[kashurst]

We are told “ the mechanic said the alignment is ok “

I have been told a lot of things by marine mechanics. I could turn 50mm shafts with a 550 Hp D9 on the end by hand. A small engines shaft should be easy. The alignment may be spot on - but something isn't right.
It's easy enough to check, might save a lot of expense 6 months later.