Volvo MS2B gearbox with RH prop

Jaz

Jaz

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My 5 tonne Seacracker fitted with Volvo 2002 engine & MS2B gearbox 2.3 ratio and 13 X 9 .55 Right Hand prop will do 5 knots at 2000 revs, but only 1 knot into a force 7 in a flat river mouth. The engine has had new piston rings and the valves ground in, and runs well with no black smoke but still puts out "blue haze". Just discovered from gearbox installation instructions that the control cable should move the selector forward for reverse, but mine is set up opposite way with a Right Hand prop. Will this affect power output, or cause gearbox wear, or can I carry on running in reverse for ever?
 
I am inclined to say it will cause no problems. But see HERE for an exploded diagram.

The only difference between forward and reverse is which of the two gears labelled #8 tramsmits the drive from the input shaft (also labelled #8) to the vertical shaft #23. One will turn it one way the other the opposite way. Power is then transmitted from the vertical shaft to the gear on the output shaft, # 46, by the lower gear on the vertical shaft (also labelled #46)

However others may know better.

Since there you end up with the prop-shaft rotating in the opposite direction to the engine there will be a big load on the bolts between engine and gearbox ... I think. i cant get my mind around that one.
 
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Thanks, I can see from the diagram it should run in either direction, though I wonder if the lower gear on the vertical shaft should be used for forward if it is more immersed in oil - the top gear is above dipstick level. I would need to check on the boat which gear turns in forward.
 
Wouldn't it be cheaper to get it turning with the forward gears when going forward, which most probably means getting a new lh propeller, it is a costly experiment to start having to get the gearbox cogs replaced if you need to get it repaired, i had to get a clutch cone and cog, over £850 for one part. the correct prop shouldn't cost too much..
 
Yes, it makes sense, I'm seriously considering a RH prop, maybe a bit more pitch too. Incidentally, what were the symptoms of a worn cone ? I guess yours is a different gearbox, as my interpretation of the diagram (see link on thread) is that the MS2B engages directly by cogs and doesn't have cones.
 
Jaz said:
Thanks, I can see from the diagram it should run in either direction, though I wonder if the lower gear on the vertical shaft should be used for forward if it is more immersed in oil - the top gear is above dipstick level. I would need to check on the boat which gear turns in forward.
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As Ruffles says the oil is ging to be pretty well distributed around inside the box... the top bearing of the vertical shaft would soon suffer if it was not.

yo can work out from the diagram which turns in what direction and which of the upper pair of gears will be transmitting the drive.

The input shaft is rotating clockwise viewed from the front so the uppermost gear will be rotating anticlockwise when viewed from above and the lower one clockwise.

With a RH prop fitted when going forward the output shaft will be rotating anticlockwise when viewed from the front so the gear with which it mates and the vertical shaft will be going clockwise.

That means that of the upper pair of gears it must be the lower one that is transmitting the drive.

With a LH prop it would be the uppermost gear transmitting the drive.

My only concern is what effects, if any, the fact that the input and output shaft are rotating in opposite directions will have.

Where are the Engineers when you need them?
 
i don't know if it would apply in your case.

When i got my boat the performance under engine was awful, 4.5 kts from Yanmar 2GM20. When the boat was lifted i discovered that i had the wrong handed prop and that when going forward the prop was effectivly working in reverse.

I changed the prop to a new correctly handed one, what a difference 7.5 kts easy, although astern is not as good as it was!!

As i say, i am not sure if this would apply in your case, however the correct handed prop made a massive difference, i can only assume that when the previous owner re engined he failed to change the prop. Another of the many bodges i have found as i have gone along
 
Yes, as VicS says, I could work out from the diagram that in forward gear it is the lower of the gears which is driving the output shaft. However, being a doubting soul, I just went down to my boat and checked, and VicS is vindicated - the vertical shaft rotates clockwise when viewed downward, so my concern about oil immersion is irrelevant. I wonder then, why Volvo recommend a LH propeller? Maybe Vic has a point about the rotation of engine and shaft.
Ruffles - the "installation guide" was left to me by the previous owner, but don't expect anything too technical, It's a 2 page pictorial guide covering 6 languages, with pictures of spanners & arrows to show actions. I'm not sure if I can attach anything to this thread, but I'll send you a message via the forum. Shaun - thanks for your input, I have the previous owner's invoice for the RH propellor, so I don't expect I am running a LH prop backwards.
 
When i got my boat the performance under engine was awful, 4.5 kts from Yanmar 2GM20
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Maybe your Yanmar box does not have the same gear ratio in ahead as it does in astern.

As you can see from the diagrams no difference with the Volvo one!

I would be interesting to check but I am sure there is world somewhere away from this computer ;)
 
you might have to find the serial no of your gearbox, and visit/ring the dealers and ask what type of gearbox you have, and find out which type of prop is required, you will need to start your engine (in nuetral),(presuming your out of the water, easier if your in the water as you can see which way the shaft is turning) and find out which way the engine turns (if you dont know already or are sure).
Ask them if you can see the manual for installation of control linkage to the gearbox.

It might be the only way your going to know which is the correct way the control linkage is connected up, and which way the gearbox is supposed to turn in forward gear. it could be ampedextrouse for all we know.. and not make to much difference.

Maybe find out wether someone else has the same setup as you and maybe some pics might help.
although a simple solution maybe at hand, we seem to be bogged down with not totally knowing the characteristics of this gearbox, once we know that then the solution if any will become clear.


I noticed that also 'counter clockwise and clockwise propellers', could be a clue..
 
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Is that the page which says "Choice of counter-clockwise or clockwise propellers"?
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Yes.

Presumably that means if there is a choice for the same engine and gearbox it can be happily run with RH prop or a LH prop.

I did not notice that I must learn to read the writing as well as the pictures ;)
 
it can be happily run with RH prop or a LH prop.

Thanks to the excellent Volvo diagrams supplied by Colvic987 I can now rest assured that the MS2B gearbox can run with either RH or LH propellors, as Vic had already worked out. I already have the info about engine rotation and the precise model of MS2B and the cutaway diagrams exactly match my gearbox. Problem was, the simple pictorial installation instructions did not mention choice of propellor. I mentioned that I didn't think clutch slip was a problem as this gearbox does not have cones. I was slightly wrong as I can see from the cutaway diagrams that the clutch cone is used to select either the upper or lower gear. I think I am still right in saying that the drive is not transmitted through the cone ( as in some other marine gearboxes) and so I don't think it would be possible to lose power through clutch slip: the bevel gear is either engaged or not. Also, Colvic's diagram of the MS2B dates from 1989, and the same gearbox being used on the older "MD" engine range, in this case the MD22 (59HP) : that gives me some confidence in the strength of the gearbox for my 2002BT engine at 18HP.
I can now concentrate on ensuring the prop size is correct and getting rid of the "blue haze" ( might be valve guides)! Thanks to all who have contributed.
 
I am still also a bit uncertain about the way the cone clutches work.

I think you will find that the two bevel gears on the vertical shaft are constantly in mesh with the gear on the input shaft, but are free to rotate on the shaft ( well they have to be since they'd be turning in opposite directions).

The cone clutch assembly is splined onto the shaft, it slides up or down to engage with one or other of the gears, thus turning the shaft in the same direction as the gear with which it is engaged.

Its just like an outboard engine gear shift stood on end except that outboards use dog clutches rather than cone clutches ( maybe big ones use cones .. I only know about small ones)

Ignore the first sentence ..just thinking while typing has sussed it out.
 
Going back to your original problem, you basically have the wrong prop - whether it be LH or RH. Propcalc gives a 15*12 3 blade and a 16*12 2 blade. You are unable to make progress against the wind because the prop is too small. Suggest you go to a prop supplier for a recommendation and get a new prop.
 
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