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Old 15 August 2019, 10:20   #1
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Yamaha 25 astern problem

Hi,

I have a yamaha 25 autolube 2 stroke I recently acquired on a small rib. The boat has a console with yamaha throttle unit. When going into astern at sea at any real power the gears crunch horribly. Out of the water no problems seem apparent at all, and the prop spins as expected, as if the load on the engine makes the gear slip?

Any thoughts would be really appreciated

Many thanks !
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Old 15 August 2019, 10:59   #2
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Originally Posted by nickos_w View Post
Hi,

I have a yamaha 25 autolube 2 stroke I recently acquired on a small rib. The boat has a console with yamaha throttle unit. When going into astern at sea at any real power the gears crunch horribly. Out of the water no problems seem apparent at all, and the prop spins as expected, as if the load on the engine makes the gear slip?

Any thoughts would be really appreciated

Many thanks !
Possibly out of adjustment and not going far enough into gear to fully mesh the gears causing them to jump out under load
Either that or reverse gear and drive dog knackered
Check adjustment first
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Old 15 August 2019, 11:08   #3
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Possibly out of adjustment and not going far enough into gear to fully mesh the gears causing them to jump out under load
Either that or reverse gear and drive dog knackered
Check adjustment first
+1

Sounds like the gears aren't engaging 100%
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Old 15 August 2019, 14:18   #4
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Makes sense. A good test could be to disconnect the gear linkage from the console at the outboard end and have a mate push it over by hand to see if it engages?
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Old 19 August 2019, 01:19   #5
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Possibly out of adjustment and not going far enough into gear to fully mesh the gears causing them to jump out under load
Either that or reverse gear and drive dog knackered
Check adjustment first
Yes def adjustment ! when in forward gear is it better than reverse ?
Corners off dog gear worn through bad adjustment ?
Check prop bush ?
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Old 25 August 2019, 15:28   #6
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Forward is perfect, absolutely no problems at all. It is in astern the problem shows itself
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Old 26 August 2019, 09:38   #7
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I am very confused..

Ok.. So I have replace the gear cable. Problem still shows itself. I test by going astern on the lever and turning the prop against engine compression by hand. I can hear the dog clutch clicking away and can see the gear shaft popping up and down. So this at first guess sounds bad. Then I separate the nuts holding the drive shafts together, remove the locking bar which pulls the locking mechanism down when astern (which I only recently obtained as it was missing when I bought the boat). I manually engage astern by pushing down on the lower part of the gear shaft and manually turn the prop over - hey presto she stays in gear.

It seems to me that the spring tension on the locking bar thing is pulling her out of gear... Any thoughts what to do here?
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