Yamaha spun hub or busted dog clutch?

[thomashoebus]

My Yamaha outboard 2.5 hp (2003) revs up when giving more throttle without gaining power (on the contrary). There are 2 problems: when turning the propeller by hand you can either let the dog clutch jump over the rotating components without the clutch engaging. To do this you need to turn the propeller with a quick jerk. When opening the clutch there is some wear on the 2 components but just a little. When you turn the propeller slowly the clutch engages and will not disengage only when forcing to disengage with a quick jerk of the propeller. On the other hand when turning the propeller and locking the axle the propeller turns around the hub even without applying to much force.

So the question is: is the the hub spun or is the dog clutch busted or both.

 

[fergie_mac66]

somebody will come on who knows engine but does it have a shear pin ? if so check it

 

[VicS]

It does sound a bit like a broken shear pin, with the broken parts catching but releasing again if jerked. If it has one!**

Check the shear pin before doing anything else.

If the shear pin is OK or replaced. Check the prop hub by marking a line on the end of the shaft and on the prop. Run it to the point where it slips then check the marks. If they don't still line up then the prop is spun.


**However I dont see a shear pin on the diags (assuming these are the correct ones)

http://www.boats.net/_search/images/parts_yamaha/62/03/0498/0016.png

http://www.boats.net/_search/images/parts_yamaha/62/03/0498/0017.png

#36 in the first diag is the clutch dog

It sounds as though the prop is spun or the splines are cream crackered AND that the dog clutch is worn, probably because it has been engaged gently instead of sharply all its life.

 

[Scarron]

If it's the same a Yamaha Malta [which it probably is] the rubber to metal bonding in the hub can break, of you are lucky it will still drive at tickover but slip if you give it full throttle.

 

[thomashoebus]

Vics,

There is no shear pin. I opened the clutch but it seems ok to me. Nevertheless compared to a similar engine the clutch from my engine disengages far more rapidly when the propeller is turned with a jerk. I couldn't start disassembling the other engine of course. Anyway the propeller spins around the hub when the axle is locked and the propeller is turned by hand. Is it so that propeller and hub should never slip regardless the strain? And is there a difference in sound and power output between a spun hub or a busted dog clutch?

Fact is that a new propeller and gear+clutch comes at nearly 25% of the new value of the engine.

 

[VicS]

You should not be able to turn the prop on the shaft by hand!

The dog clutch should not slip in the way you describe. My guess is that the corners have been rounded off the dog. Possibly the gear where the dog engages damaged too. It is often caused by engaging gear gently instead of snapping it in sharply. BUT I am not so sure that you can properly assess the condition of the clutch with the current state of the prop hub.

Cost of the parts from Boats.net (where the diagrams have come from) are Prop $60.30, dog $15.54, gear (if needed) $78.58.

Have you been quoted some rip off prices.

Should have stuck with a British Seagull!

 

[thomashoebus]

Indeed the dog and clutch are a bit rounded.
So, I will start with a new prop and see from there.

 

[steve28]

maybe see if you can borrow a prop to prove the point.

 

[agurney]

Vics,

There is no shear pin. I opened the clutch but it seems ok to me. Nevertheless compared to a similar engine the clutch from my engine disengages far more rapidly when the propeller is turned with a jerk. .

Are you sure ther's no shear pin? I have a Yamaha 2hp and the shear pin is inside the propeller which is attached with a split pin. There's a rubber clip on the tiller with spare pins.


Alisdair

 

[VicS]

Yes the 2 hp has a shear pin #40 in THIS DIGRAM. #41 is the offset split pin that holds the prop on.

The diags of the 2.5 do not show a split pin.