Delayed prop turn - PRM120D

[lampini]

Wot it says in the title...

Start engine, into gear and nothing - for about 5 seconds and then the prop starts churning properly. It happened when we set off from the mooring on our last cruise but then all was good for the rest of the cruise. Gearbox PRM120D transmission fluid about 1-2cm above mark on dipstick.. difficult to tell as is clear fluid!

Got OH to observe driveshaft and it is THIS which starts to turn really slowly at first and then suddenly speeds up, so i may be wrong but don't suspect the prop.. v difficult to access weedhatch!

 

Help?

 

(Beta 38 engine btw....)

[Tony Brooks]

As long as the control lever on the box has its full travel I fear slipping and thus worn out ahead clutch. Take the control cable off the gearbox lever and operate the lever by hand to see if it cures it. If it does then you need to lok at cable adjustment and possibly repositioning the cable on the lever in the control.

[Chewbacka]

 

As long as the control lever on the box has its full travel I fear slipping and thus worn out ahead clutch. Take the control cable off the gearbox lever and operate the lever by hand to see if it cures it. If it does then you need to lok at cable adjustment and possibly repositioning the cable on the lever in the control.

 

But if it doesn't then sadly it's time to get the gear box serviced..........

[lampini]

 

As long as the control lever on the box has its full travel I fear slipping and thus worn out ahead clutch. Take the control cable off the gearbox lever and operate the lever by hand to see if it cures it. If it does then you need to lok at cable adjustment and possibly repositioning the cable on the lever in the control.

 

 

Thanks Tony (again!)

 

- will try the test and report back - probs tomorrow now as am at my mum's trying to make the fairy lights work... a bit more of a simple job - for me - lol!

[Ryeland]

I had exactly the same symptoms. Forward clutch shot. Suggest you contact Primrose Engineering (RWLP of this parish) for a rebuild.

 

Richard

[AndrewIC]

Gearbox PRM120D transmission fluid about 1-2cm above mark on dipstick.. difficult to tell as is clear fluid!

According to the manual the dipstick mark is a maximum, so you may be overfilled. Unfortunately I can't remember whether the level is supposed to be read with the dipstick screwed all the way in or not! You can see the level by placing the stick onto a piece of white tissue/kitchen paper/loo roll, then the red ATF shows up much more clearly.

[lampini]

According to the manual the dipstick mark is a maximum, so you may be overfilled. Unfortunately I can't remember whether the level is supposed to be read with the dipstick screwed all the way in or not! You can see the level by placing the stick onto a piece of white tissue/kitchen paper/loo roll, then the red ATF shows up much more clearly.

Level IS read when screwed right down - sezzit in the manual! Will do the kitchen roll thingy tho -

Excellent wheeze there Andrew....

 

I won with the fairy lights btw... Has probs given me an over-inflated sense of my own mechanical abilities now! God help that poor gearbox...

Interested to see if it is red fluid - it really seemed just this clear thin stuff..... Hmmmmmm...

[Tony Brooks]

I understand the change to red ATF was because of "clutch troubles" but have no further info.

[AndrewIC]

Level IS read when screwed right down - sezzit in the manual!.

Thanks, I couldn't find it in my scanned copy, all I could remember was that it's the opposite way round from a Hurth box!

[Tony Brooks]

However if you just place the dipstick in the hole without screwing it in the minimum mark then becomes the maximum and the end of the dipstick the minimum.

[mross]

I realise now that the 120 is mechanical, not hydraulic

 

One way to get the best life out of hydraulic gearboxes is to never go straight from ahead to astern or vice versa without letting the revs drop to idle. In emergency you can go from full-ahead to full-astern but it will cause wear on the clutches. This is true for many marine gearboxes.

Edited December 12, 2016 by mross

[lampini]

 

 

However if you just place the dipstick in the hole without screwing it in the minimum mark then becomes the maximum and the end of the dipstick the minimum.

Oo - er! Think I geddit...

 

Even tho we liveaboard I have pulled 4 days of 10 plus hour shifts so I'm not gonna be able to sensibly have a look-see with the cable until Friday realistically... This is with my sensible head on - realising that sticking my head in the engine bay after a day like I've had wouldn't be sensible at all ... Grrrrr... Wanna play with my engine!!!

[lampini]

I realise now that the 120 is mechanical, not hydraulic

 

One way to get the best life out of hydraulic gearboxes is to never go straight from ahead to astern or vice versa without letting the revs drop to idle. In emergency you can go from full-ahead to full-astern but it will cause wear on the clutches. This is true for many marine gearboxes.

Is this still relevant, and therefore good. Practice for mechanical gearboxes then?

 

Please feel free to plant any gearbox gems you may have here - I won't be doing much apart from work and read this in my breaks until friday ... Mind you - gearbox on my bus sounded like it was grinding washers today.. "Oh it'll be fine - just a bit noisy!" No Sh%t Sherlock!

 

All gearbox jokes gratefully received too... :-)

[mross]

Well, your gearbox contains cone clutches and I imagine you will get a better life out of them if you change gear at idle . Here's a link to the workshop manual

[lampini]

Well, your gearbox contains cone clutches and I imagine you will get a better life out of them if you change gear at idle . Here's a link to the workshop manual

 

Cheers - funny how it says to use engine oil not ATF innit?! ??

 

There's ATF in there and that's wot they say in the Q&A on their website; and a couple of other places wot i cannae remember right now - but mucho confusiferlous eh?

[lampini]

A final question before I manage some daylight and another pair of eyes to check wots going on at the weekend......

 

Assuming the worst and it IS the clutch... Given that this delay in prop rotation only happens in the very first burst of forward gear, and that it seems to perform as normal thereafter - how fast can I expect this situation to degenerate until I have no prop turn at all? Or is that impossible to say?

Cheers!!

[mross]

PRM hydraulic gearboxes use engine oil but mechanical ones use ATF. The link I sent you for the workshop manual specifically says ATF if you read it! If the ahead clutch is on the way out it will suddenly start to slip and you might get stranded. So I recommend that you do something before planning any long trip!

 

http://www.ebay.co.uk/itm/PRM-80-PRM-120-Gearboxes-/162305350028?hash=item25ca27198c:g:LVYAAOSwx-9WwO1u

 

http://www.ebay.co.uk/itm/Pmr-120-Marine-Boat-Gearbox/282291004582?_trksid=p2047675.c100009.m1982&_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D38661%26meid%3D3a14f342b4c04bbfbadba4fe2b27b686%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D162305350028

 

But you need to check if the latter has the correct ratio. Prm120 is obsolete, replaced by the 125.

Edited December 14, 2016 by mross

[ditchcrawler]

PRM hydraulic gearboxes use engine oil but mechanical ones use ATF. The link I sent you for the workshop manual specifically says ATF if you read it! If the ahead clutch is on the way out it will suddenly start to slip and you might get stranded. So I recommend that you do something before planning any long trip!

 

http://www.ebay.co.uk/itm/PRM-80-PRM-120-Gearboxes-/162305350028?hash=item25ca27198c:g:LVYAAOSwx-9WwO1u

 

http://www.ebay.co.uk/itm/Pmr-120-Marine-Boat-Gearbox/282291004582?_trksid=p2047675.c100009.m1982&_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D38661%26meid%3D3a14f342b4c04bbfbadba4fe2b27b686%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D162305350028

 

But you need to check if the latter has the correct ratio. Prm120 is obsolete, replaced by the 125.

Mine died on the Chesterfield Canal, thankfully not on the Trent getting there.

[mross]

If ahead clutch fails you can get home by going astern!

[ditchcrawler]

If ahead clutch fails you can get home by going astern!

Up the Trent against the flow ?

[mross]

Well, better than going downstream with no steerage! Even if you can't makes any headway you can get to the bank and throw a mud anchor!

Edited December 14, 2016 by mross

[sailor0500]

Wot it says in the title...

Start engine, into gear and nothing - for about 5 seconds and then the prop starts churning properly. It happened when we set off from the mooring on our last cruise but then all was good for the rest of the cruise. Gearbox PRM120D transmission fluid about 1-2cm above mark on dipstick.. difficult to tell as is clear fluid!

Got OH to observe driveshaft and it is THIS which starts to turn really slowly at first and then suddenly speeds up, so i may be wrong but don't suspect the prop.. v difficult to access weedhatch!

 

Help?

 

(Beta 38 engine btw....)

I had same problem. Almost as cheap to buy new box if you shop around for best price as the clutch cone is expensive plus labor of stripping. Try ASAP Supplies.

[mross]

I had same problem. Almost as cheap to buy new box if you shop around for best price as the clutch cone is expensive plus labor of stripping. Try ASAP Supplies.

RCR will recondition for £350 as per my earlier eBay link.

[sailor0500]

RCR will recondition for £350 as per my earlier eBay link.

As opposed to £600 for a brand new box. You pays your money.............

[ditchcrawler]

I bought a reconditioned one when mine failed, it was a mistake as it came with a 6 months guarantee and only lasted a year.