PRM 150 Gearbox - Sump Plug Seal

[Withywindle]

I need to get some sump plug seals for my PRM 150 Gearbox which was first commissioned in 2005. 
 

I downloaded the workshop manual from PRM which specifies an M16 Dowty Bonded Seal (part number PRM 0191716) as you’d expect the genuine PRM seals are expensive when I see generic M16 Dowty Bonded Seals are widely available elsewhere at a fraction of the price. 
 

Before I bite the bullet and buy the genuine PRM seals I was wondering whether other owners have used generic seals without any issues? If so, any recommendations for good quality aftermarket seals?

[Bee]

Don't worry. Its a washer. I doubt if PRM make their own, they will be a bought in part. Well done for trying to fit decent parts but over the years i have done countless oil changes on cars using either the old washer or something else that was in the shed and never had a problem.

[Tony Brooks]

I don't think I have ever used a "genuine" Dowty washer. Always from a selection box, that is in both automotive and marine workshops.

 

One should be careful to ensure the "rubber" part is compatible with oil so i would try a bearing supplier or engineer's supplier rather than Ebay/Amazon.

 

Make sure that the hexagon on the plug has not been burred, so the seal can not seat on it. Also check the face on the box, although that is less likely to be a problem.

Edited September 19, 2022 by Tony Brooks

[blackrose]

I can't actually remember seeing a separate sealing washer on my PRM 150 sump plug. I must have done at least 5 or 6 oil changes. Could mine be stuck to the underside of the gearbox so I only see the metal plug when I take it out?

[Tracy D'arth]

Buy 2, the fill plug/dipstick is the same size. If you are ever faced with a leaking drain plug, swap them over.

[Withywindle]

18 minutes ago, Tracy D'arth said:

Buy 2, the fill plug/dipstick is the same size. If you are ever faced with a leaking drain plug, swap them over.

That’s interesting. The dipstick washer on my gearbox is copper not a Dowty bonded seal. Perhaps I’ve got the wrong part number. 🤔

[Bee]

2 minutes ago, Withywindle said:

That’s interesting. The dipstick washer on my gearbox is copper not a Dowty bonded seal. Perhaps I’ve got the wrong part number. 🤔

I think mine is copper too. Having worked in factories this sort of thing happens when Fred in the stores forgets to order something in time.

[Tony Brooks]

In theory a Dowty asher should be more lone lived than copper because the copper work hardens, but I suppose the rubber in a Dowty might degrade. As far as the filler is concerned I doubt it matters which you fit, it only has to stand up to oil splash, not have oil laying on top of it.

[Withywindle]

5 minutes ago, Tony Brooks said:

In theory a Dowty asher should be more lone lived than copper because the copper work hardens, but I suppose the rubber in a Dowty might degrade. As far as the filler is concerned I doubt it matters which you fit, it only has to stand up to oil splash, not have oil laying on top of it.

Yes I thought the dipstick one wouldn’t be critical as an oil tight seal. Perhaps PRM fitted it for that reason and because it would be more durable in day to day use? I’ve just checked the parts list and a 1/2 BSP Bonded Washer is listed as the dipstick seal. Out of interest, here is the list and diagram I’ve been referring to…

[Tracy D'arth]

Drain washer  is M16 and dipstick is 1/2" BSP, never knew that. Thank you. Ignore my suggestion then, they are different sizes.

[Withywindle]

4 hours ago, Tracy D'arth said:

Drain washer  is M16 and dipstick is 1/2" BSP, never knew that. Thank you. Ignore my suggestion then, they are different sizes.

Well I think ‘Bee’ might be right. Who knows, PRM might have substituted copper crush washers for a while if there was a problem with supply of the bonded type.
 

I’ve only come across bonded sealing washers once before - the sump washers on a Toyota Yaris my daughter once had, they were extortionate from the main dealer too! Anyway, in this case I’m about to buy some M16 bonded washers from Simply Bearings at £3.99 for five. It was going to cost getting on for £10 for one genuine PRM washer once I’d added on the carriage. I’ll leave the copper one under the dipstick alone I think. 😊

[robtheplod]

As this now seems sorted can i hop in here?.... if changing the oil in the PRM 150 i know lots use pumps in the dipstick hole, is this purely due to accessibility of the sump plug or in case of problems with it and it leaking?  doing mine shortly....  

[Tracy D'arth]

Its an access thing. If you can get to the plug its better to drain and get the muck and metal shards out. The plug has a magnet on later boxes.

With a decent washer it won't leak.

Folk forget which way is undo when its upside down!

[Tony Brooks]

1 minute ago, robtheplod said:

As this now seems sorted can i hop in here?.... if changing the oil in the PRM 150 i know lots use pumps in the dipstick hole, is this purely due to accessibility of the sump plug or in case of problems with it and it leaking?  doing mine shortly....  

 

I was on a PRM course and they said that it was difficult or impossible to suck all the oil out.  It can be difficult to get a pipe in from the dipstick hole worked around a "shelf" in the box.

[robtheplod]

1 minute ago, Tracy D'arth said:

Its an access thing. If you can get to the plug its better to drain and get the muck and metal shards out. The plug has a magnet on later boxes.

With a decent washer it won't leak.

Folk forget which way is undo when its upside down!

Thanks Tracy & Alan!!

Edited September 21, 2022 by robtheplod

[Withywindle]

Confession time here. My first gearbox oil change on my boat was by sucking out the oil via the dipstick hole and I noticed the oil quantity I removed was nowhere near the amount it should have been. So I decided I needed to do the job properly next time, hence this post about sealing washers. 

[robtheplod]

second really quick question... when doing your engine its supposed to be warm... does the same apply to the PRM?  cant see how this warms that much?? 

[Tracy D'arth]

If you are draining, cold is fine, just give it time.

[cuthound]

14 hours ago, Tony Brooks said:

 

I was on a PRM course and they said that it was difficult or impossible to suck all the oil out.  It can be difficult to get a pipe in from the dipstick hole worked around a "shelf" in the box.

 

One way to partially get around that is to suck out as much oil as possible, refill with clean oil, take the boat for a short trip (to mix the old and new oil) and then suck out the oil and refill with clean oil again. 

 

It won't get all of the old oil out, but will dilute somewhat the oil originally left in with clean oil.

[Tacet]

23 minutes ago, cuthound said:

 

One way to partially get around that is to suck out as much oil as possible, refill with clean oil, take the boat for a short trip (to mix the old and new oil) and then suck out the oil and refill with clean oil again. 

 

It won't get all of the old oil out, but will dilute somewhat the oil originally left in with clean oil.

Or, to put another way, change half the oil twice as often.

[cuthound]

18 minutes ago, Tacet said:

Or, to put another way, change half the oil twice as often.

 

Not really. If we assume say 10% of the 1.4 litres (0.14 litres )cannot be pumped out, refilling with clean oil, running the gearbox to mix the oil, then pumping out again will mean that the oil left behind is 10% old oil and 90% new oil, so only 1% or 0.014 litres of old oil is left behind.

 

However no amount of dilution will remove any metal particles stuck to the drain plug magnet.

Edited September 22, 2022 by cuthound
Clarification

[Tacet]

1 minute ago, cuthound said:

 

Not really. If we assume say 10% of the 1.4 litres (0.14 litres )cannot be pumped out, refilling with clean oil, running the gearbox to mix the oil, then pumping out again will mean that the oil left behind is 10% old oil and 90% new oil, so only 1% or 0.014 litres of old oil is left behind.

 

 If you did the second oil change mid term, you would achieve exactly the same and the oil would be fresher from that time till the subsequent change

 

[cuthound]

39 minutes ago, Tacet said:

 

 If you did the second oil change mid term, you would achieve exactly the same and the oil would be fresher from that time till the subsequent change

 

 

Yes, I agree however the oil change intervals for the PRM 150 is every 500 hours (used to be 750 hours) or annually, whichever comes first.

 

Depending on how many hours per year you do, (I read somewhere that average engine hours is around 200) then changing twice annually for many boaters will only result in slightly fresher oil.

 

I suspect the oil requires changing at this interval because of water contamination from condensation rather than contamination from other sources.

[Tracy D'arth]

58 minutes ago, cuthound said:

 

Yes, I agree however the oil change intervals for the PRM 150 is every 500 hours (used to be 750 hours) or annually, whichever comes first.

 

Depending on how many hours per year you do, (I read somewhere that average engine hours is around 200) then changing twice annually for many boaters will only result in slightly fresher oil.

 

I suspect the oil requires changing at this interval because of water contamination from condensation rather than contamination from other sources.

My used gearbox oil, providing it looks OK, goes into the engine. There will be no steel bits in it, the magnetic plug sees to that. The filter will sort anything else out.

Protect the planet, recycle whenever possible.

[Tacet]

4 hours ago, cuthound said:

 

Yes, I agree however the oil change intervals for the PRM 150 is every 500 hours (used to be 750 hours) or annually, whichever comes first.

 

Depending on how many hours per year you do, (I read somewhere that average engine hours is around 200) then changing twice annually for many boaters will only result in slightly fresher oil.

 

I suspect the oil requires changing at this interval because of water contamination from condensation rather than contamination from other sources.

So, changing the oil after an hour or so, as suggested by you, does seem premature.

 

The PRM 150 manual says to change the oil at intervals corresponding with the engine.  It's a bit odd as the gearbox is not very aware of the engine to which it is attached. Mind you, the same manual says it is a hydraulic gearbox when it is a mechanical box, albeit the clutch plates are engaged by hydraulic pressure.