Do boat gearboxes have clutches?

[Hunter34]

This might be a silly question but do gearboxes on inboard diesel engines usually have clutches?
When I say clutches I mean the friction plate normally found on cars etc.
I know the rear crankshaft oilseal has failed on my Perkins 4 108 and I am sure initial takeoff isnt what it should be so I guess if these gearboxes are normally fitted with a clutch plate then it will need replacing too.
My engine manual doesnt realy go into much detail about the gearbox.

Thanks in advance

Andrew

 

[sailorman]

depends on the gear box
my 4108 had a TMP hydraulic box so the gear change was a matter of redirecting the fluid.
similarly with my new Nanni 4150 + PRM box

 

[capsco]

The simple answer to your question is no, the drive plate is bolted to the flywheel and this drives the g/box which drives the hydraulics/clutches

 

[Avocet]

Mine has something a bit like a friction plate but no friction material. The perimeter of the "friction" plate is bolted to the flywheel. The centre of it has a spline to take the gearbox input shaft and around this there are small springs (just like a car friction plate) to take some of the shock loading when a gear is engaged but there isn't anything in there that can "slip" as such. Is there a chance the bottom of your boat has grown a big clump of weed that's making it a bit sluggish?

 

[oldharry]

Mechanical gearboxes frequently do have a form of clutch to engage the gears when changing from forward to reverse, and proiding a neutral position but these rarely have any similarity to car style faced plate clutches. Commonly they are spring loaded cones with no friction surface material, depending on the gearbox oil to provide the necessary cushioning while engaging. This type of clutch is part of the gearbox internals and would be unaffected by a crankseal faliure. Other boxes - Parsons for example - had a brake band which clamped down on an epicyclic or planetary gear housing bringing it into engagement - again within the gearbox internals. When the band wore out the box would be trying to engage both forward and reverse at the same time and the neutral position would disappear resulting in some quite interesting maneovering tactics!

Some very early conversions did use car gearbox and clutch setups, but I suspect that most of these have gone long since to the scrapheap.

Hydraulic boxes always have internal clutch actuation usually part of the hydraulic system.

If the box is not engaging properly, then there is either an internal fault, the shifter cables are worn, or there is some other problem in the transmission chain. But it is highly unlikely to be related to the oil seal failure.

 

[30boat]

The PRM gearboxes have twne for forward and another for reverse.They're of the multidisc type in an oil bath and very similar to a motorcycle clutch.They are activated by oil pressure applied to them through a diverter valve via an exterior lever.

 

[Ruthie]

Hiya.

The answer is yes. Exactly what type of clutch, and whether there is one or two, depends on the type of gearbox. An epicylclic gearbox has a brakeband and a clutch; a two-shaft gearbox has two clutches.

Cone clutches were common on smaller/older engine/gearboxes; disc clutches (which as someone else commented, are a bit like the units found on motorbikes) are more usual.

Control will likely be either by morse cable (or similar) or hydraulic.

If you suspect that your transmission is slipping, the first thing to check is the controls - especially if they are cables. Other wise you can open up the box and check the brakeband or clutches, and adjust if necessary.

And I agree that any problem is unlikely to be related to you oil seal, other than suggesting that various things might be wearing out!

Ruth

 

[PCUK]

There is no car type clutch mounted on the engine flywheel. The clutches are part of the gearbox and are engaged by oil pressure holding the clutch plates together when in drive.

 

[brianrunyard]

[ QUOTE ]
When I say clutches I mean the friction plate normally found on cars etc.
I know the rear crankshaft oilseal has failed on my Perkins 4 108 and I am sure initial takeoff isnt what it should be so I guess if these gearboxes are normally fitted with a clutch plate then it will need replacing too.
Andrew

[/ QUOTE ]

No they don't have a clutch like a car, they may have a damper plate that is bolted to the flywheel. The clutch is integral to the gearbox. So a leaking rear crankshaft oil seal, won't affect the drive.
If the initial take up appears to be slipping, it could be that the internal clutch needs adjusting, whether it's a cone clutch, brake bands or whatever.

 

[dickh]

Hurth Gearboxes have multiplate clutch plates running in oil. Make sure the lever is moving sufficiently. To test remove the cable and manually put in gear and try your drive. Your rear cranckshaft seal has no effect on the gearbox operation. The Hurth gearboxes sometimes 'slip' (as mine did), when stripped could find no obvious cause but fitted new plates and it was OK.