PRM 500 Gearbox leaking oil

[steve.sharratt]

Hi All,

 

I seem to have sprung a leak out of the rear of my gearbox.  It is noticeable at the bracket that holds the prop shaft with oil dripping out of the split that allows the prop shaft to be clamped tight.  I have checked the bolts etc and they are tight with no evidence of movement at all.  My assumption is that it is the rear seal of the box that is leaking and oil is escaping through the bracket? 

 

I am on the K&A at Hungerford.  Does anyone know of a local engineer with PRM expertise? If not, if I maintain the oil levels is it safe to continue on? The long weekend is closing fast…

 

Cheers

Steve

Edited May 31, 2022 by steve.sharratt

[Tracy D'arth]

Keep topping it up, it will be fine. If you lose too much and the level gets low you will lose drive before any serious damage is done. Its hard to stress a PRM500 on an inland boat!

[steve.sharratt]

5 hours ago, Tracy D'arth said:

Keep topping it up, it will be fine. If you lose too much and the level gets low you will lose drive before any serious damage is done. Its hard to stress a PRM500 on an inland boat!

I have considered that but it seems to be a substantial leak. I am catching the oil in a container atm to see how bad it is and expect an oil delivery tomorrow so will give it a go.

[Steve56]

It sounds as if the oil is leaking along the output shaft and through the inside of the output coupling. Therefore not the output oil seal leaking. If I remember correcty when the output coupling is removed there is an o-ring on the shaft which stops the oil. Also when fitting the coupling it pays to put a little flange sealant on the flat washer that fits below the retaining nut. It may also pay to check that this coupling nut has not worked loose. I have come across this a number of times. It doesn't take much for an oil leak to start. If you take this apart it will pay to fit a replacement lock nut and ensure the correct torque setting.

[john.k]

I think I see a Speedi-Sleeve on the coupling.....point about sleeves,any groove in the coupling must be filled with epoxy before the sleeve is pushed on.......if the groove is left unfilled,heat buildup will melt the plastic seal.

[steve.sharratt]

3 hours ago, Steve56 said:

It sounds as if the oil is leaking along the output shaft and through the inside of the output coupling. Therefore not the output oil seal leaking. If I remember correcty when the output coupling is removed there is an o-ring on the shaft which stops the oil. Also when fitting the coupling it pays to put a little flange sealant on the flat washer that fits below the retaining nut. It may also pay to check that this coupling nut has not worked loose. I have come across this a number of times. It doesn't take much for an oil leak to start. If you take this apart it will pay to fit a replacement lock nut and ensure the correct torque setting.

That sounds logical and fits what I am seeing.  I will take a look this morning to see if I can access it but I suspect I don’t have the tools on board to remove the bolts. 

[Steve56]

Here is the relevant page from the parts manual. You can see the o-ring under the coupling. The only thing I did get wrong is the fact that the coupling securing nut is castellated and held in place with a split pin. It must just be the smaller boxes that have a nylon.

[Tracy D'arth]

6 hours ago, Steve56 said:

It sounds as if the oil is leaking along the output shaft and through the inside of the output coupling. Therefore not the output oil seal leaking. If I remember correcty when the output coupling is removed there is an o-ring on the shaft which stops the oil. Also when fitting the coupling it pays to put a little flange sealant on the flat washer that fits below the retaining nut. It may also pay to check that this coupling nut has not worked loose. I have come across this a number of times. It doesn't take much for an oil leak to start. If you take this apart it will pay to fit a replacement lock nut and ensure the correct torque setting.

Good spot, I think you could well be right on the money.  Is the coupling in any way loose?

[steve.sharratt]

The coupling is tight and there is no indication of movement (there is still paint across the joints). I put a socket on as few of the nuts and they weren’t moving.  I don’t think I have a tool with sufficient leverage to undo the bolts.  It could be a loose locking nut as Steve56 says.  The challenge is getting to it.  I have contacted a local marine engineer and am waiting for a call back. 

 

I noticed that the prop shaft does not reach all the way back past the ‘cut’ (as in the picture) and that is where the oil is coming from. When I rotated the shaft and the cut was at 12 and 6 the oil poured out. I placed a bowl under and it slowed after about 100-200ml so the oil was pooling in this gap but it has stopped dripping overnight. I assume when she starts spinning again and the oil warms…. I think I dropped from the top line of the dipstick to the bottom line in a 3hr run.  I am waiting for an oil delivery to top up and will check again.

 

[steve.sharratt]

Realised that I didn’t update this one.  Turns out I had sheared the output shaft bolt clean off.  I contacted Marcus from Marcus Marine and we were initially hopeful that the output shaft bolt had fallen off but it wasn’t to be. We suspect it had been broken for some time and had been held in place by the paint on the prop shaft! Marcus was brilliant and rebuilt the gearbox and added a damper coupling to the output side (only had a damper on the engine side.  Anyway, good news is that it has performed perfectly since.

 

I would highly recommend Marcus if you run into problems.  He is Reading based, but gets around.