prop turning in neutral

[Ardenfour]

Volvo MD1 = In neutral with engine running, the shaft turns. I can stop it by hand, so it's definitely out of gear. It slows as the engine warms up, but never actually stops. I can select fwd and reverse ok. Boat's on the hard so no drag from water, but still doesn't sound right. Any ideas anyone? Can't see anything relevent in the manual.

 

[puddock]

Volvo MD1 = In neutral with engine running, the shaft turns. I can stop it by hand, so it's definitely out of gear. It slows as the engine warms up, but never actually stops. I can select fwd and reverse ok. Boat's on the hard so no drag from water, but still doesn't sound right. Any ideas anyone? Can't see anything relevent in the manual.

Vibration???

 

[Ubergeekian]

Volvo MD1 = In neutral with engine running, the shaft turns. I can stop it by hand, so it's definitely out of gear. It slows as the engine warms up, but never actually stops. I can select fwd and reverse ok. Boat's on the hard so no drag from water, but still doesn't sound right. Any ideas anyone? Can't see anything relevent in the manual.

Bit of drag from oil in the gearbox. Entirely normal, nothing to worry about.

 

[Spyro]

ok thanks. Poor choice of words - I didn't mean starnge noise, just the fact it was turning didn't sound correct. Looks as though there would be enough force to move the boat, surely can't be right? What's the solution. It's new oil, after engine repairs, but did it before. Cold weather = thicker oil? Engine and box share oil I believe.

If you can stop it by hand I don't think it would move the boat.

 

[Ardenfour]

ok thanks. Poor choice of words - I didn't mean starnge noise, just the fact it was turning didn't sound correct. Looks as though there would be enough force to move the boat, surely can't be right? What's the solution. It's new oil, after engine repairs, but did it before. Cold weather = thicker oil? Engine and box share oil I believe.

 

[SAMYL]

Ubergeekian has got it right, drag from the oil and perfectly normal. Bit like creep in an automatic car at the traffic lights when you need to keep your foot on the brake.

 

[VicS]

What gear box is fitted . An RB ? (presumably not an MS, that does not share the engine oil)

Which ever they operate using cone clutches, (they do not operate like car autoboxes!).

I believe that in the RB whole drive shaft moves backwards and forward to engage one clutch or the other. If so perhaps the shaft is not moving as freely as it should is and preventing the complete disengagement of the forward clutch. Or the shifting mechanism could be getting worn.

Unfortunatey the link I have to the MD1 workshop manual no longer appears to work but there is a description of the RB gearbox in the MD1B workshop manual HERE

 

[earlybird]

I think that you should keep a close eye on it. IMHO, the output shaft should be stationary in neutral.
Cone clutch boxes, if it's that type, have a self-servo action, the transmitted torque forces the clutches into firmer engagement. Slight progression of, eg, selector wear might mean gear selection becoming hard.

 

[oldharry]

Absolutely normal, most any box does this, marine or otherwise. Often the sterngear is too tight to allow it, or grease from the greaser holds the shaft, and as long as there is no water ingress that is not a problem either. If gear engagement is normal, neutral is set correctly on the gear control, and there are no odd noises then all is well. Wear in the set up tends to make engagement less positive to the extent that eventually it does not engage drive properly.

The only exception I know to this is the old Parsons gearbox where a slipping friction band meant that it would not select neutral - but there was no way you could stop the shaft by hand when this happened!

 

[VO5]

I think it may be a charateristic of Volvo Engines and Gearboxes. The rotation is slow and can be easily arrested by hand as you say. This occurs even if the vessel is stopped, It becomes really significant if the vessel is under sail and making way through the water but that rotation is not connected to the engine running or not but due to the prop being pulled through the water and the inclination of the blades causing the rotation. You must not worry about it. It is common to most boats. If the gland packing is tight then the start up rotation is less. If the vessel is stopped where thre is no tide or current then this initial rotation stops after a few minutes of the engine in neutral. If there is tide or current and the engine is stopped, the movement of water under the keel will cause the rotation to last longer.

 

[Norman_E]

Sounds like a worn selector to me. My Yanmar gearbox did the same, and the cause was a worn selector quadrant.

 

[Ardenfour]

Mmmm, conflicting opinions... There is no packing in the stern gland, so the shaft is very free to turn. Fwd and reverse selection is positive. Don't know what box is fitted, other than it's old and original. Difficult to estimate, but I guess when I first start the engine and give it some revs the prop spins at around 400rpm, slows as it warms up. I can still stop the shaft from cold.

 

[VicS]

Don't know what box is fitted, other than it's old and original.

Rather relevant to the question though!

Different gearboxes function in different ways so no point in comparing the behaviour of this one with different makes or even later Volvo gear boxes.

As far as I can deduce from original Vovlo literature this gear box is one that operates with two cone clutches. Whether or not it is the RB I am not sure ... I think it is though.

One of the claims in the old literature is that:

"in the neutral position there is no friction to result in a slow turn over of the propeller shaft."

I'd suspect that there is now some wear in the selector and that the forward cone clutch is not fully disengaging. I doubt if it is now practical to do anything about it other than keeping an eye on things.

 

[lenseman]

Volvo MD1 = In neutral with engine running, the shaft turns. I can stop it by hand, so it's definitely out of gear.

I don't think you have mentioned whether it rotates in a going forward rotation or a reverse rotation?

If you have disengaged from a forward direction, I presume it continues in this direction but easily held by hand?

If you have disengaged from a reverse direction, does the shaft rotate still in reverse or does it change back to a forward rotation?

This test might give you a better understandning of how the engine thrust is getting through to the shaft?

 

[VicS]

Success.

I tried again and I have located the full workshop manual for the MD1
It contains a description of the Gear box, an RB as I thought, and details for dismantling reassembly and adjusting.

All yours now ... All you have to do is locate any spares you may need

http://privateer26.org/pdf/Volvo_MD1-D1-MD2-D2.pdf

Make a note of it. Better still, save it or even better print it.

 

[earlybird]

Just had a look at the link given by VicS. As far as I can tell , (from page 30), initial engagement of the cone clutches is accomplished by sliding the output shaft fore and aft. The text says "the cones are then retained in engagement by propellor pressure".
If so, with the boat out of the water, there is no prop. thrust forcing the cones together, hence the ease in stopping the shaft by hand. The situation when afloat will be rather different. I don't think that the "hand-brake" will be anything like as effective.

 

[Ardenfour]

Thanks for link. Have to check rotation after reverse

 

[Ubergeekian]

Just had a look at the link given by VicS. As far as I can tell , (from page 30), initial engagement of the cone clutches is accomplished by sliding the output shaft fore and aft. The text says "the cones are then retained in engagement by propellor pressure".
If so, with the boat out of the water, there is no prop. thrust forcing the cones together, hence the ease in stopping the shaft by hand. The situation when afloat will be rather different. I don't think that the "hand-brake" will be anything like as effective.

If the prop can be stopped by hand on land there is practically no torque being applied to it. That means it will generated practically no thrust in the water, which means practically no forces on the cones.

I really don't think this is worth worrying terribly much about. Unless there is a physical brake to stop the shaft turning in neutral, oil drag is always going to rotate the output one way or another. Which way depends, I imagine, on which cone gap is closer.

 

[VicS]

That means it will generated practically no thrust in the water, which means practically no forces on the cones.

It may depend on how much drag there is on the clutch. If it is sufficient to generate a bit of thrust that will tend to make the clutch engage more positively. If there isn't no problem.

 

[Ubergeekian]

It may depend on how much drag there is on the clutch. If it is sufficient to generate a bit of thrust that will tend to make the clutch engage more positively. If there isn't no problem.

Indeed, but my point is that if it's generating so little torque that it can be stopped by hand, there won't be much resulting thrust.