Boat Fault Finding - Marine Gearbox Problems

First I wonder if you are removing the dip-stick, wiping it and then putting it back to get a reading. If you are just pulling it out and reading it, you may well get an artificially low reading on some boxes. If it is not that it must be a leak.

What is in the drip tray under the engine - could it be gearbox oil?

I found that I had a leak from where the drain tube to the drain pump is fitted to the gearbox. Clean the gearbox, paying special attention to the underside, and go on as normal. After a few days run your hand under the gearbox, with a bit of luck this should locate the leak. It could also be leaking from where output shaft leaves the gearbox, but the hand should find that, or from the input shaft.

The input shaft is inside the engine case, so is more difficult to find, but there should be a drain hole just in front of the gearbox, again its a hand test.

I regret that if the box is leaking it will have to come off - not difficult if it is fitted with an Aquadrive, but quiet hard if not.

A leak from the pump fitting pipe may be cured by a new length of pipe and new sealing olives - I do not think Bukh parts are required for this - use the old nuts.

A leak from the adaptor between the pipe and box might be cured by removal, very careful cleaning, a new copper/fibre/nylon washer and refitting with something like Loctite stud & bearing lock. Leave overnight before filling with oil.

Any other leak probably means you either live with it and keep topping it up each morning (as I think it uses engine oil at perhaps £5 a gallon this may be sensible at the moment) and wait for it to get a lot worse - cleaning the engine tray weekly, or sending it away for professional attention. I have the manual for my DV36 and it uses a not very common Spanish gearbox. I would rather get someone else to overhaul the box because of all the setting up and selective shims (washers) that are required. If your box is leaking badly from either end, I would suggest that you talk to TW Marine at High Peak.

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Do I understand that the old gearbox was a 1:1 and now its a 2:1 reduction.

If this is the case then the symptoms would be as described. Little wash, low speed, and high engine revs. From distant memory, I would have thought that 14X12 would be a bit large for a 1.8 with 1:1 reduction, but I have long since learnt that prop sizing is 20% fact and 80% black magic, so I leave it to the experts.

What I think is happening is that your prop is now turning only half as fast as it was with the old box, for similar engine revs, so the boat only goes a little bit more than half the speed it once did.

My advice would be to contact someone like Crowthers (Manchester area I think ) and ask them to recommend the correct prop size. They will need to know the engine power and maximum rpm, the hull design speed or waterline length, how large a prop you can swing, giving an absolute minimum of 1 inch clearance between the blade tip and hull/skeg - 2 inches is better., and a bit about the hull shape. The fact that it is a Hampton Safari may do for this. They will then recommend a prop size.

You are right, a lower pitch would not increase the power, unless you increased the diameter significantly. If I am right about the ratios, you need to increase it, however it is often a bad idea to alter the reduction ratio because the original one was probably designed in to the boat from the very start, having taken into account draft, hull design speed, engine type etc.

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I am afraid that this sounds like a "bitsa" to me.

I have never come across a Penta gearbox on anything other than a Volvo Penta engine.

Most boxes on marinised engines (like yours) are driven by a splined input shaft from the gearbox entering a drive plate that is bolted onto the flywheel, a bit like a clutch plate. I think the Penta box (but can not be 100% sure) is driven by a special adaptor bolted to the flywheel.

Some boxes do bang into gear (my ZF box on the Bukh) does, so if its always done it, is not getting worse, and there is no sign of slippage it might be normal for the box.

At least one Penta box in the early 70s used prop thrust to help it into gear, and that could bang a bit.

I fear you need to first find your local Penta agent and get them to test the box (lots and lots of cash) and then decide what to do next.

Nearly any box can be made to fit given enough time or cash for machining parts, but I suspect a repair may be the cheapest and easiest option. Especially if you can remove and replace the box.

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As the coupling on the gearbox almost certainly has a sleeve that goes into the box for an oil seal to run on, I think it highly unlikely that you will be able to get a different gearbox coupling, but if you measure the outside diameter, the diameter of the land/recess on the face of the coupling, the diameter of the holes and the distance a hole id from the centre, PRM (address of dealers in mags.) just might be able to supply you.

Otherwise I fear its changing the coupling on the shaft. If its a fairly modern one it is likely to have some form of clamping device. If its older (and you are lucky) it will be on a taper with a nut hidden in the end of the coupling, or if you are unlucky it may be shrunk on - in which case a hydraulic puller may be required to shift it.

If its one of the later two types any half decent engineering shop should be able to make you one up, otherwise start by asking PRM for suppliers of suitable couplings and also try any engineers/millwrights suppliers.

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I am not familiar with a gearbox called an MD, unless it is the designation of a Volvo box. If so and Volvo-Penta agent should be able to obtain spares for you.

You description of how the box sounds tells me what you have inside it. In ahead gear, all the "guts" revolve as a single unit,
hence no noise. In reverse the drive goes through (probably) two or three parallel gear trains, each consisting of two gears (one double), plus the input and output gear. This explains the noise, and with this type of box is not unusual.

In general terms, the lubrication of the reverse gear trains is not usually adequate the ensure prolonged, reliable running in reverse gear - using it as ahead. The risk is yours, but I would not do it, marine gearboxes are expensive!

By far the easiest way of solving this problem is to fit the opposite handed prop, so from your description you need to swap your right hand one for a left hand one. In any case, a change of engine often indicates a change of propeller to obtain optimum performance - talk to Norris of Isleworth, Steel developments of Merton (I think) or Crowthers - possible Manchester. They should be able to advise on the correct prop size, matching engine to boat. Some suppliers will give an allowance against the old prop.

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The two main problems with what you propose are:-

1. The rudder will normally stop the prop moving back by more than about 3 inches or so. This means you have to also remove the rudder. Just make sure that if you have to drop the whole rudder and stock (the shaft) that you block the "hole", if required, to stop the boat sinking.

2. You have to remove the shaft coupling from the shaft, and depending upon he fixing method this can be difficult.

You will need to loosen or even remove the sterngland packing, because the shaft is probably worn to a smaller diameter under the packing.

Do not try it unless you can stand on the bottom whilst drawing the shaft - it will be unwieldy and heavy, and will not pass through the weedhatch.

I do not think you will need a rope, the assembly is too big, with too many bits sticking out to lose if you drop it. In any case you will have to take the shaft/prop assembly ashore to remove the old prop, I think you will need a strong vice and lots of padding to prevent the vice jaws "bruising" shaft where the outboard bearing runs (exactly where you need to grip it, to give the most rigid "hold".

A tapered wooden plug is all that's needed to stop the very considerable leak when you draw the shaft - fit it by use of the mooring hammer ;-) Make sure you have an assistant, so one of you can drive the plug, whilst the other is handling the shaft and prop. Just make sure you have a bilge pump. It might be an idea to have two plugs, so if the inside one does not "hold", whack one in the outboard end of the tube.

To remove the prop from the shaft you need a very good puller (I have yet to find one) or a couple of good blowlamps, a sledge hammer, and a lump hammer. Undo the nut, heat the prop boss with the blowlamps until its as hot as you can get it. Place sledge hammer tight against one side of the boss and hold it tight. Whack the other side of the boss. Eventually the taper should just "pop" free - ha ha.

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I think you have an outdrive which is also known as a Zdrive. I suspect bad wear somewhere or a maladjusted gear cable or control.

If you can get at the inside of the box your control lever is fitted to, you will find two internal levers and two cables, the lower lever is for the gears. Make sure all screws and bolts are tight, and that the nipple fixing the cable to the lever is not worn through by the lever. Lubricate this point.

Follow the cable to the lever that fixes it at the other end and make sure there is no wear or play, but I rather suspect it would be inside the leg.

Make sure that both the levers on both ends of the cable are in the neutral position and then adjust the cable length to suit.

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I have no direct experience of the Yanmar gearbox, but I will try to answer in general terms.

A cone clutch consists of a male and female cone. One cone (often the male) is fitted with some form of "friction" material. This can be similar to car brake linings, but suitable for use in oil, or bronze or cast iron. These are usually of sintered construction (powder is put into a mould and subject heat and pressure to partialy "reform" it). If your gearbox is more than 30 years old I would suspect it to have "brake" lining, and newer boxes are likely to use sintered material - but this is a very general comment.

You will have one half of the clutch splined to the gearbox shaft and the other half fitted to the gear. When the clutch is engaged it locks the gear to the shaft.

I always would prefer to use a propper manual, but have found that most marine stuff is not difficult to strip, once you have it on the bench and can inspect it. I regret I have no further contact details or links. I suspect tha if you posted on uk.rec.waterways, or uk.rec.boats.power you would get the info you require.

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I hold no data for old engines, but from memory 52 bhp. Max revs - not sure, but suspect about 3000. Try giving Calcutt Boats a ring and asking them if they can remember - otherwise ask Newage transmissions for a lead, their predecessor company marinised them or AMC. Beware of taking the automotive data, because the data may well be derated for continuous marine use.

For the gearbox, you need the number (I am not sure that the plate did not also give the reduction ratio), but the plate may well have fallen off. If this is the case you need to hire/borrow a stroboscopic revcounter - one where you put a white mark on the shaft/pulley, and in subdued light a strobe is shone onto the mark, either you will get a direct reading of RPM, or you adjust a knob until the mark is stationary. Do this for the propshaft & on the engine front pulley and calculate the ratio. If you have a number, look at magazine adds for someone who specialises in them - I think Newage might have taken them on.

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As far as I am concerned a shear pin and a "safety pin" are one and the same thing - although I thought a safety pin was something rather different ;-)

I hope you have some form of weed hatch on the bow thruster tube or the motor is mounted on a housing at right angles to the main tube, that is high enough to allow the assembly to be withdrawn without flooding the boat, but you can never tell with boat builders/fitters.

If you can get at the prop in the tube (making sure all possible power is isolated) try and turn the prop both ways by hand. If it feels as if you are turning gears and the motor there is no reason why it should not work, but I suspect it will turn very easily. This shows the pin or something has sheared. If the pin has not sheared you may have stripped teeth on a gear, sheared a key, torn rubber drive bush, or broken a shaft. I think the whole motor assembly should lift out of its own "well" with the boat in the water, if not I am afraid that at least the front must be clear of the water.

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There's only about 3mm take-up left on the compression sleeve. I tweak it up a quarter-turn, and the dripping stops fine. But then after only a couple of days cruising the water is dripping in as a slow stream rather than slow single drips, and I get to turning down the greaser anything up to 4 turns to stop it. Most of the grease then finds its way back past the sleeve and into the boat and gets flung about by the prop shaft. Should I just keep tweaking up the sleeve nuts until there's no more adjustment at a quarter-turn a time?

Or is it really time I grasped the nettle and repacked the gland??

This is typical of what to expect when the gland packing is on its last legs - it probably now resembles chewed up string.

You need to repack it. Make sure you have a bilge pump hand when you try though.

Turn the greaser down hard (to try to seal the inboard bearing). If you have any "Sylglass" you could reach through the weedhatch and pack it behind the prop to seal the outboard bearing. This would only be appropriate with very badly worn bearings and you must remove it afterwards.

Undo whatever you do up to tighten the gland. You should them be able to withdraw a sleeve so you can measure the gap between the outer part of the stern tube and the shaft. Expect a leak of of some kind during this operation.

Put it all back & tighten to stop any leak. Go to a chandlers & get some new packing.

Repeat the above, but use a long screw, pin nosed pliers, other pokey things to remove the old packing - the leak will get worse.

I should tell you to cut a series of packing rings with a 45 degree cut and push these down the hole with the joints spread about the circumference, but the ends usually end up like chewed string.

Wind the packing around the shaft and work out if shaft rotation in ahead will tend to force water up the spiral, into the boat, or back down.

When you have it wound so the water would be forced back, simply push and twist the packing down the hole - pushing with something as required - until about 3 to 6mm from top of hole.

Refit the sleeve and nut and tighten until just about dripping.

Run the boat in ahead and reverse for a while to settle the packing and then tighten until it drips about once every 30 to 60 seconds (or do as I do and tighten until the drips just stop).

Run boat again and check that you can the gland is not so hot it burns your hand - if so slacken a little.

Over the next few cruises check every evening to make sure the packing has not packed down and requires readjusting.

If the above does not solve the problem, which I think it will, then you have a worn inner bearing, shaft out of alignment or possible both. Engines do drop on their mounts over time.

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Make sure the shaft is not out of alignment - the engine may have sunk on its mounts. The "hole" the shaft goes into should be round, not egg shaped, with the shaft dead central in it. The gland should not get hot enough to burn your hand when running, if it does the gland is either overtight (which yours is not) or the shaft is badly out of alignment.

If the shaft is correctly aligned then the first thing to do is to try tightening the gland (probably two nuts, one on each side of the shaft) so the drips just stop (it should drip once every 30 to 60 seconds, but you have already found the problem of that). Only if the gland is within about 1/4 inch of fully tightened should you consider repacking it. Instruction on website above.

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As the coupling on the gearbox almost certainly has a sleeve that goes into the box for an oil seal to run on, I think it highly unlikely that you will be able to get a different gearbox coupling, but if you measure the outside diameter, the diameter of the land/recess on the face of the coupling, the diameter of the holes and the distance a hole id from the centre, PRM (address of dealers in mags.) just might be able to supply you.

Otherwise I fear its changing the coupling on the shaft. If its a fairly modern one it is likely to have some form of clamping device. If its older (and you are lucky) it will be on a taper with a nut hidden in the end of the coupling, or if you are unlucky it may be shrunk on - in which case a hydraulic puller may be required to shift it.

If its one of the later two types any half decent engineering shop should be able to make you one up, otherwise start by asking PRM for suppliers of suitable couplings and also try any engineers/millwrights suppliers.

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If your box is the mechanical "B type" box then there are adjustments for the ahead clutch toggles and the reverse gear brake band. These are under a rectangular cover, on top of the box, held down by 4 x 1/2" AF screws (as I recall). I regret that I can not describe how to do it here - its simple enough to do, but would take hundreds of words.

The other thing is that the ahead drum on theses boxes have long through bolts. These snap, and stop gear engagement.

If I am right about the box, I seem to recall that it has a solid drive adaptor from the centre of the flywheel, rather than a "flexible" drive plate. If so, you may well need to get the flywheel drilled and tapped to accept a drive plate. You would then need an adaptor plate to fit between the new gearbox and the flywheel housing. These might be available from the gearbox supplier, or they might supply a drawing so you could get one made up by a jobbing machine shop.

Nearly any box would do the job, but I would go for a PRM from choice - if they put up with hire fleets they put up with anything!

back to questions

I am not familiar with a gearbox called an MD, unless it is the designation of a Volvo box. If so and Volvo-Penta agent should be able to obtain spares for you.

You description of how the box sounds tells me what you have inside it. In ahead gear, all the "guts" revolve as a single unit,
hence no noise. In reverse the drive goes through (probably) two or three parallel gear trains, each consisting of two gears (one double), plus the input and output gear. This explains the noise, and with this type of box is not unusual.

In general terms, the lubrication of the reverse gear trains is not usually adequate the ensure prolonged, reliable running in reverse gear - using it as ahead. The risk is yours, but I would not do it, marine gearboxes are expensive!

By far the easiest way of solving this problem is to fit the opposite handed prop, so from your description you need to swap your right hand one for a left hand one. In any case, a change of engine often indicates a change of propeller to obtain optimum performance - talk to Norris of Isleworth, Steel developments of Merton (I think) or Crowthers - possible Manchester. They should be able to advise on the correct prop size, matching engine to boat. Some suppliers will give an allowance against the old prop.

back to questions

The two main problems with what you propose are:-

1. The rudder will normally stop the prop moving back by more than about 3 inches or so. This means you have to also remove the rudder. Just make sure that if you have to drop the whole rudder and stock (the shaft) that you block the "hole", if required, to stop the boat sinking.

2. You have to remove the shaft coupling from the shaft, and depending upon he fixing method this can be difficult.

You will need to loosen or even remove the sterngland packing, because the shaft is probably worn to a smaller diameter under the packing.

Do not try it unless you can stand on the bottom whilst drawing the shaft - it will be unwieldy and heavy, and will not pass through the weedhatch.

I do not think you will need a rope, the assembly is too big, with too many bits sticking out to lose if you drop it. In any case you will have to take the shaft/prop assembly ashore to remove the old prop, I think you will need a strong vice and lots of padding to prevent the vice jaws "bruising" shaft where the outboard bearing runs (exactly where you need to grip it, to give the most rigid "hold".

A tapered wooden plug is all that's needed to stop the very considerable leak when you draw the shaft - fit it by use of the mooring hammer ;-) Make sure you have an assistant, so one of you can drive the plug, whilst the other is handling the shaft and prop. Just make sure you have a bilge pump. It might be an idea to have two plugs, so if the inside one does not "hold", whack one in the outboard end of the tube.

To remove the prop from the shaft you need a very good puller (I have yet to find one) or a couple of good blowlamps, a sledge hammer, and a lump hammer. Undo the nut, heat the prop boss with the blowlamps until its as hot as you can get it. Place sledge hammer tight against one side of the boss and hold it tight. Whack the other side of the boss. Eventually the taper should just "pop" free - ha ha.

back to questions

I think you have an outdrive which is also known as a Zdrive. I suspect bad wear somewhere or a maladjusted gear cable or control.

If you can get at the inside of the box your control lever is fitted to, you will find two internal levers and two cables, the lower lever is for the gears. Make sure all screws and bolts are tight, and that the nipple fixing the cable to the lever is not worn through by the lever. Lubricate this point.

Follow the cable to the lever that fixes it at the other end and make sure there is no wear or play, but I rather suspect it would be inside the leg.

Make sure that both the levers on both ends of the cable are in the neutral position and then adjust the cable length to suit.

back to questions

I have no direct experience of the Yanmar gearbox, but I will try to answer in general terms.

A cone clutch consists of a male and female cone. One cone (often the male) is fitted with some form of "friction" material. This can be similar to car brake linings, but suitable for use in oil, or bronze or cast iron. These are usually of sintered construction (powder is put into a mould and subject heat and pressure to partialy "reform" it). If your gearbox is more than 30 years old I would suspect it to have "brake" lining, and newer boxes are likely to use sintered material - but this is a very general comment.

You will have one half of the clutch splined to the gearbox shaft and the other half fitted to the gear. When the clutch is engaged it locks the gear to the shaft.

I always would prefer to use a proper manual, but have found that most marine stuff is not difficult to strip, once you have it on the bench and can inspect it. I regret I have no further contact details or links. I suspect that if you posted on uk.rec.waterways, or uk.rec.boats.power you would get the info you require.

back to questions

I hold no data for old engines, but from memory 52 bhp. Max revs - not sure, but suspect about 3000. Try giving Calcutt Boats a ring and asking them if they can remember - otherwise ask Newage transmissions for a lead, their predecessor company marinised them or AMC. Beware of taking the automotive data, because the data may well be derated for continuous marine use.

For the gearbox, you need the number (I am not sure that the plate did not also give the reduction ratio), but the plate may well have fallen off. If this is the case you need to hire/borrow a stroboscopic revcounter - one where you put a white mark on the shaft/pulley, and in subdued light a strobe is shone onto the mark, either you will get a direct reading of RPM, or you adjust a knob until the mark is stationary. Do this for the propshaft & on the engine front pulley and calculate the ratio. If you have a number, look at magazine adds for someone who specialises in them - I think Newage might have taken them on.

back to questions