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PRM 150 Gear box


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The PRM 150 gearbox on Dasque has had a small leak for sometime. This has now got worse - the seals to the selctor mechanism have been replaced and do not appear to be leaking. The leak is definetly at the output shaft end of the box. Despite having had a really good clean up I've not been able to track down the leak. Are the oil seals on the output shaft susceptible to leaks? What about the gaskets to the oil pump?

Can any one make any suggestions as to where the leak is from or how to track it down?

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Even if the selector "O" ring has been replaced, it's worth checking again. The PRM on Copperkins had to have it done twice: I suspect that the first time the new ring was slightly undersize.

 

Our leak from the selector was difficult to spot : apart from a smear of oil left on a finger rubbed under the selector, and a very small amount on the casing, there was little trace of a leak, although it was enough to drop the gearbox oil level enough to stop the box working in about a week.

 

Iain

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The PRM 150 gearbox on Dasque has had a small leak for sometime. This has now got worse - the seals to the selctor mechanism have been replaced and do not appear to be leaking. The leak is definetly at the output shaft end of the box. Despite having had a really good clean up I've not been able to track down the leak. Are the oil seals on the output shaft susceptible to leaks? What about the gaskets to the oil pump?

Can any one make any suggestions as to where the leak is from or how to track it down?

The simple answer is yes!

Can I first confirm (due to changes over the years with names and numbers) that this is the sort of roundish lump?

If so, they have no breather and therefore if worked hard or run in hot conditions tend to pressurise the seals! (Usually find this happens after a long river trip!)

They only have two gaskets, which rarely leak, but a number of seals, inclduing the selector, output and input shafts, any number of which can 'blow'.

Also the heat can exerbate the wear on the clutches, so if its over 5 years old, it may be worth going for a complete overhaul.

The selector shaft is easy to change seals on, albeit fiddly, worst is the input shaft, output shaft may be easy if the drive flange will come off, otherwise both of these require a complete dismantling.

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The simple answer is yes!

Can I first confirm (due to changes over the years with names and numbers) that this is the sort of roundish lump?

If so, they have no breather and therefore if worked hard or run in hot conditions tend to pressurise the seals! (Usually find this happens after a long river trip!)

They only have two gaskets, which rarely leak, but a number of seals, inclduing the selector, output and input shafts, any number of which can 'blow'.

Also the heat can exerbate the wear on the clutches, so if its over 5 years old, it may be worth going for a complete overhaul.

The selector shaft is easy to change seals on, albeit fiddly, worst is the input shaft, output shaft may be easy if the drive flange will come off, otherwise both of these require a complete dismantling.

 

Are you sure? My Delta has a very small hole in the dipstick/filler cap as did the 150 in my previous boat. So small that i would think it easy to block with debris and if blocked might pressurise and cause seals to leak.

 

Regards

Ditchdabbler

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Are you sure? My Delta has a very small hole in the dipstick/filler cap as did the 150 in my previous boat. So small that i would think it easy to block with debris and if blocked might pressurise and cause seals to leak.

 

Regards

Ditchdabbler

 

Beat me to it!

 

Richard

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Two likely places that they tend to leak from are the hydraulic pumps securing bolts, situated next to the output flange, these have small copper washers under their heads which often leak i've found as a couple of them are not in blind threaded holes but are in open holes into the oil space. Also the oil coolers banjo pipe fitting underneath the box is also always suspect as its out of sight.

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Are you sure? My Delta has a very small hole in the dipstick/filler cap as did the 150 in my previous boat. So small that i would think it easy to block with debris and if blocked might pressurise and cause seals to leak.

I think they altered the design for the Delta (as many people had already drilled a hole!)

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My PRM 150 has a small breather hole in the filler cap/dipstick. Did someone already mention that?

 

My engine & gearbox have only done about 800 hours but most of that has been on the Thames including tidal so the gearbox has worked fairly hard. When these leaks happen can they be sudden and serious or do they occur gradually? I wouldn't know about a serious leak until I'd stopped and would hate to wreck my gearbox.

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Our PRM 50 has always leaked, never have managed to trace it, mind you, regular topping up does save oil changes.

We don't change the oil because it leaks somewhere between 200 and 300ml every three days or so depending on use. The filler does have a small breather hole I will check that it is not blocked.

Will look at and do a general tighten up of bolts around the hydraulic pump - this does appear to be a possible source of the leak.

Thanks every body for comments. I'll let you know how we get on.

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Our PRM150 started leaking from the selector at about 1,000 hours. I acquired a new O ring to swap, but was advised to check the breather first. I found it was blocked and tried to clean it out, but couldn't get it cleaned out there was something solid in the hole. So I drilled it out and found some brass swarf probably from the original drilling :( While I had the drill out I drilled a second hole opposite the original. The box has not leaked since 3 - 4 years and I still have the O ring :)

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Our PRM150 started leaking from the selector at about 1,000 hours. I acquired a new O ring to swap, but was advised to check the breather first. I found it was blocked and tried to clean it out, but couldn't get it cleaned out there was something solid in the hole. So I drilled it out and found some brass swarf probably from the original drilling :( While I had the drill out I drilled a second hole opposite the original. The box has not leaked since 3 - 4 years and I still have the O ring :)

 

That's not a bad tip. I might drill a second hole in mine.

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  • 5 years later...

I have noticed yesterday when changing the oil on my PRM 260 that it was pressurized:o there were no leaks as yet and there is NO breather on my box or on the filler/dipstick nut i to will be drilling a hole in the filler/dipstick nut as previously mentioned to alleviate the pressure BEFORE it does cause some damage ;)    

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