Reasons for broken teeth on the gear wheel

[Dannycool]

We bought a f80 yamaha only 8 months ago and already the forward gear wheel is busted, two teeth sheared off. This is not the first time this has happened, three time before on the same engine model.

The prop may have hit a piece of debris during operation because it was bent, but surely the rubber bush would be the failure point.

Could it be improperly adjusted control cables? Also at times it pushes up to 5 tons of load.

What else should be looking at?

Thanks Fellas!

 

[racerone]

Hitting something is bad for gear teeth.------The propeller just moves water and that is the load on the motor.----2 or 5 tons does not matter.-----They just do not make this stuff as strong as they used to , in my opinion.

 

[Sea Rider]

Is this the second occasion in which said gear component has been replaced ? If so was it a DIY work or at a Yam dealer facility ? Gear boxes have fine gear adjustments done with proper tools whether at the factory or at a dealer facility.

Now a days parts metallurgy is made light in order to be screwed faster compared to same 8 HP older versions that used to last much longer. Anyway there's a huge gear box stress difference accounted for when pushing a one ton boat compared to a 5 ton one with same recreational portable motor.

As an example, our local fishermen which loves powering their 25-30 ton fishing boats with 7X Yam's 60 HP motors ends screwing their entire gearboxes often due to running motors not intended for such heavy duty commercial task instead than going for proper HP inboard motor installations.



Don't know if heavy duty gearbox components are market available to cope for that.

Happy Boating​

 

[racerone]

??----The motor develops the same amount of thrust whether it is pushing a wee boat or a barge !

 

[Sea Rider]

??----The motor develops the same amount of thrust whether it is pushing a wee boat or a barge !

There's a huge thrust loss difference running a motor at the extreme lugging side of the wot rpm range compared to running it at the higher end while pushing heavy boats with same motor. The issue is that everybody runs wrongly propped motors on heavy applications...

Happy Boating​

 

[racerone]

If motor is running too slow ( not at it's rated RPM ) it will put less load on the gears.----Not good for pistons and rings but no bother to the gears.

 

[Sea Rider]

So it's much preferred to screw the entire powerhead when lugging a portable or a under powered motor while pushing heavy applications and save the gearbox ? It's one or the other....

A 2 stroke story : A Tohatsu dealer offered our local fishermen well priced 70 HP recreational motors to power their 25-30 ton fishing boats as shown in previous post, guess what, the gearbox didn't stand 2 months of daily marine tough operations, Yamaha motors rules for commercial fishing applications, although those guys blows their gearboxes from time to time, end of the story...

Happy Boating​

 

[racerone]

It is up to the operator to select the correct propeller to allow the motor to rev properly.----Power / speed / load seems to be near the top of the list of things that are confusing.