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Gearbox PRM120 Output shaft oil leak


adagio

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I have a small leak on the output shaft of my PRM120 gearbox when the gearbox is working suggesting it is caused by an increase in the oil pressure whilst working. Replacment seals are easily available so my question is can I replace them myself, what are the pitfalls, if any, and if so do I require specialist tools? I service my own engine and have experience in both petrol & diesel engines etc., so quite confident if pointed in the right direction. Thank you.

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There should be no oil pressure in the gearbox, there is an open breather on the top. Unless it is blocked?

To replace the seal will involve removing the output drive flange, the nut is very tight and needs to be tight on reassembly. Torque figures - ask PRM.

 

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Thank you for your reply, appreciated. Prior to the change of oil at the last service I've always had slight signs on oil around the breather after a days run (4-5hrs). Spoke to PRM and they suggested I changed the breather for a new one which I did but the problem didn't go away.I spoke to PRM and all they could offer was keep the oil level low in the box at about the bottom mark, (I usually fill to the mid point between marks). Since the service this has stopped to be replaced by a slight leak on the output shaft, hence my remark about pressure. I am happy to replace the seals but what is the best way hold the flange to undo the nut?

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8 minutes ago, adagio said:

Thank you for your reply, appreciated. Prior to the change of oil at the last service I've always had slight signs on oil around the breather after a days run (4-5hrs). Spoke to PRM and they suggested I changed the breather for a new one which I did but the problem didn't go away.I spoke to PRM and all they could offer was keep the oil level low in the box at about the bottom mark, (I usually fill to the mid point between marks). Since the service this has stopped to be replaced by a slight leak on the output shaft, hence my remark about pressure. I am happy to replace the seals but what is the best way hold the flange to undo the nut?

A substantial steel bar with 2 holes to span 2 holes in the flange and 2 high tensile bolts and nuts, tight, and let the end of the bar rest on the hull. Do not use the bolts from the coupling, the bolts you use will likely be scrap after.

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Assuming it to be a 4-hole flange.

You need a stout bar with two pins, or bolts, sized and spaced to fit into two adjacent holes in the flange.  Arrange  the flange holes  N-S and E-W then turn it anti clockwise through 45 degrees  so there are two holes at the top, horizontal .  Insert the bar pins into a suitable pair of holes so that when you turn the output nut with a socket spanner you can keep the bar still.  Sometimes you can arrange things so that a part of the boat holds the bar, pins and flange still.

Tracy beat Me to it

 

N

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16 hours ago, adagio said:

Thank you for your reply, appreciated. Prior to the change of oil at the last service I've always had slight signs on oil around the breather after a days run (4-5hrs). Spoke to PRM and they suggested I changed the breather for a new one which I did but the problem didn't go away.I spoke to PRM and all they could offer was keep the oil level low in the box at about the bottom mark, (I usually fill to the mid point between marks). Since the service this has stopped to be replaced by a slight leak on the output shaft, hence my remark about pressure. I am happy to replace the seals but what is the best way hold the flange to undo the nut?

How are you measuring the oil level? PRM say that the dipstick should be screwed down to measure, although I find it easier to loosely replace, and then treat the bottom of the dip stick as low level and the low level mark as high. 

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  • 4 weeks later...
On 16/08/2021 at 20:00, Tracy D'arth said:

A substantial steel bar with 2 holes to span 2 holes in the flange and 2 high tensile bolts and nuts, tight, and let the end of the bar rest on the hull. Do not use the bolts from the coupling, the bolts you use will likely be scrap after.

I needed to speak to PRM today to find out the size of the locking nut on the output shaft, I have every socket up to 28mm. Sods law I needed a 30mm! Whilst talking to the guy I said what is the best way to hold the shaft to undo the locking nut? He asked if the gearbox was still on the engine, which I confirmed it was, to which he said no problem. Start the engine, engage forward drive to get the prop to turn, and then turn off the engine. I did this and then just undid the locking nut no problem at all!

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