Engines / gearbox problems - whose feeling smart

[IanPoole2]

At the end of last season when getting underway the gearbox would engage in forward so we would stem the tide. When increasing the revs the engine seems to slip out of gear. Reduce revs - kicks back in again.
After some minutes - say 10 mins steming the tide, we can increase the revs slowly, stays in gear and then the gear box behaves perfectly.
Now the boat is out of the water, we cannot reproduce the problem, so I'm thinking it must be something to do with the extra work imposed by the water.

Any ideas?

 

[Topcat47]

It sounds a bit like a clutch problem, either a very worn dog clutch or a worn conical. It takes a load to make it slip...out of the water no/low load conditions = no slip.

 

[RivalRedwing]

What are you observing (or hearing?) when you say it seems to slip out of gear, thinking a bit laterally and assuming that you are observing movement (or not) of the shaft I would ask: how is the shaft connected? could the bolts clamping the shaft need tightening (enought friction at low revs to spin shaft, not enough friction at higher revs so slips, once warmed up, with a bit of expansion, grip is improved)

 

[fluffc]

Either worn clutches, or something up with the gearbox oil pump / seals?

When did you last change the gearbox oil? Is it possible that you've used too thick an oil : postulating this through a thick oil would have just enough umph to softly engage the clutches, but not enough umph to engage them properly.

Once the oil has warmed up a bit, and thus is 'thinner' and more runny it can perform properly and engage the gears properly.

IMHO

 

[IanPoole2]

In the water - definately out of gear. You can hear the engine note go up - no load - and there is not bite in the water.

 

[IanPoole2]

ah! like your thinking - change the gear box oil. During the engine overhaul the engineer could n't find a problem. I'll give him a call

 

[Kawasaki]

Sounds like an adjustement prob.
Once had an old Ships Lifeboat Conversion jobby.
Double ender Clinky thing.
Yer know the type.
BMC Captain 1.5 eng, Damm can,t remeber the gearbox type.
Anyway for ages could not get any sternway/ reverse reaction.
An Old Boy who knew the rig "adjusted" the gearbox and het presto She was a different Vessel.
Forward, Bang, off We went, Reverse ,Bang ,astern We went!
All for a matter of adjustement, I had struggled for 3 seasons before that liitle tweek!

 

[Bilgediver]

Hi Ian

I see the boat is a Cobra???? so probably not a hydraulic gearbox as on bigger boats so oil may not be the problem.

Some gearboxes as on the Volvo 2001/2/3 series were prone to cone slip and this would sound as you descibe. This may also be caused by incorrect adjustment of the gearbox control teleflex wire.

The Volvo problem was sometimes accepted as being a manufacturing problem and they offered a deal on replacement parts which cost an arm and a leg plus the mechanics time to change. I believe a new cone and adacent parts were needed.


John

 

[IanPoole2]

Hi John,
No not hydraulic but I'm getting the oil changed anyway (can n't do any harm). The cable is a possible, but it would also fail out of the water. Parts are cheap (it's a marinised Ford) for the engine. I'll have another look at the gearbox.

 

[Bilgediver]

Don t be fooled...with incorrect cable settings it could work ashore under no load but the cones be resricted from fully engaging enough to take load.

Be sure that there is equal movement of the actuator lever on the gearbox to each side of neutral when you select ahead or astern. You might be giving too much movement to astern but not enough to ahead