Yamaha Malta outboard - slipping clutch?

[West Coast]

I have a 20 year old Yamaha Malta which began to play up a bit today. Symptoms were running under load at full throttle when engine would begin to overrev with a simultaneous loss of speed. Classic slipping clutch symptoms. When throttling back, drive would seem to return ok, revving again, same loss of power.

It has a forward/neutral lever, which was positively engaged. Will remove the leg bung to make sure this mechanism is still working properly. But other than this, any ideas what is perhaps wrong?

 

[macd]

Not sure about the precise set-up with your engine, but sounds like the prop's not spinning with its shaft. Either a broken shear pin or a rubber bush is no longer bonded to the prop.

P.S. It seems you're far from the first: http://www.ybw.com/forums/showthread.php?174816-Yamaha-Malta-o-b-clutch-problem

 

[RIBW]

Mine was a slipping rubber bush. Drilled and tapped through the old prop to make a temporary shear pin (i.e. shaved a lot off the brass screw end so there was a fair chance it would shear) until a new prop could be sourced (~£45).
Cheers
Bob

 

[VicS]

I have a 20 year old Yamaha Malta which began to play up a bit today. Symptoms were running under load at full throttle when engine would begin to overrev with a simultaneous loss of speed. Classic slipping clutch symptoms. When throttling back, drive would seem to return ok, revving again, same loss of power.

It has a forward/neutral lever, which was positively engaged. Will remove the leg bung to make sure this mechanism is still working properly. But other than this, any ideas what is perhaps wrong?

Outboards have dog clutches so do not slip like friction clutches, although if badly worn by gentle engagement rather than snapping sharply into gear they can jump out of engagement.

What you describe are the classic symptoms of a spun prop hub ie the failure of the rubber bonding / bushing.

But check the drive/ shear pin to begin with

Check the hub by marking the end of the prop shaft or prop retaining nut, with a corresponding mark on the prop itself. Give it a quick run and if the marks no longer line up it confirms the failed prop hub.

Other than this there is very remote chance that it could be a fractured drive shaft.

 

[West Coast]

Have removed the prop, no shear pin but a rubber bush as suggested. Inserting a flat screwdriver into the inner spline bush I can with respect to the prop with respect to the bush (just, so explains why slipping at high power but regaining Drive at low power). So this seems to be the problem.

Thanks all for hints and tips.

Question now is if this old outboard is worth £45 for a new prop. It is working fine at present but if something else goes wrong, it will be hard to fix as some key bolts have seized.

Edit - just looked through the old post (thanks macd) and so reckon repair with a home-made pin is best way forward.

 

[anoccasionalyachtsman]

It's a Yamaha Malta, which a lot of us think is the best small outboard ever made. So, yes, fix it and keep fixing it.

With patience, and the right tools, the seized bolts can be removed and the threads in castings helicoiled very cheaply.

Signed

A Malta owner.