Should I be able to turn the prop when the engine is in gear?

[Ruffles]

I was cleaning and anti-fouling the prop yesterday. I noticed that I could turn it one way but not the other even though the gearbox is in gear.

Is this normal? Or does it indicate that the selector needs adjusting?

 

[mikecontessa26]

mine does that...

 

[Ruffles]

[ QUOTE ]
mine does that...

[/ QUOTE ]
That's reassuring.

Seems odd though. It's a mechanical gearbox with crown gears. I can't see why it would behave like that.

 

[mikecontessa26]

ah don't think mine has a gearbox...

 

[earlybird]

[quote}
Seems odd though. It's a mechanical gearbox with crown gears. I can't see why it would behave like that.

[/ QUOTE ]
I'm not sure what you mean here by crown gears, but in many gear-box designs, the drive is transmitted through friction clutches which have a self-servo action to increase the engagement pressure with the applied torque, hence it will slip one way but not the other.

 

[Ruffles]

It's a VP MS2A-D. From the parts diagram it seems to have 2 crown gears which are alternately engaged. Not sure there's a clutch involved.

 

[spannerman]

Its normal on all Volvo mechanical gearboxes, shaft and drive as they all use the same type of shift mechanism.

 

[earlybird]

I'm not familiar with your VP box. I'm thinking of boxes such as the Hurth, Yanmar etc. which have parallel input and output shafts, and helical tooth gears. In these there are plate or cone cluches sliding on helically splined shafts. These connect the gear to the shaft. Both forward and reverse sets of gears are in constant mesh but only one set is transmitting torque. The splines exert end load to force the clutch into engagement.
NB My definition of a crown gear is part of a bevel gear set, with shafts at right angles, do you mean this? This would apply to, eg, a saildrive

 

[Ruffles]

[ QUOTE ]
Its normal on all Volvo mechanical gearboxes, shaft and drive as they all use the same type of shift mechanism.

[/ QUOTE ]
Thanks. I guess that's why you engage reverse rather that forward to stop the shaft spinning.

 

[Ruffles]

[ QUOTE ]
NB My definition of a crown gear is part of a bevel gear set, with shafts at right angles, do you mean this? This would apply to, eg, a saildrive

[/ QUOTE ]
Yes. THE VP gearboxes use two crown gears.
See here.

 

[earlybird]

Agreed, it's totally different from any gearbox I've ever owned. It looks like an old-fashioned crash gearbox with the difference of bevel gears. Bet you could make a fair old crunch if you're too hasty!
Having said that, engaging reverse to stop the shaft spinning is the same as the Hurth box

 

[Ruffles]

Actually, if you engage reverse too hastily it doesn't engage at all!