Possible Yanmar Transmission Damage

[Wotname]

Quite a few threads mention that Yannar recommend that you should leave the transmission in neutral when sailing to prevent gearbox damage.

Leaving aside the thorny drag question (debated at length on many threads), can anyone explain just WHAT damage can be done to the Kanzaki gearbox when the transmission is left in (say) astern.

I am clear that Yanmar oppose this method but I remain unclear as to what damage is possible. I confess to not having a solid understanding of the cone clutch principle which I understand is used in these gearboxs.

I simply see an input shaft (the engine) not turning, an output shaft not turning, a torque applied to the output shaft (by the propeller being held stationary in moving water) and being resisted by the compression of the engine. The coupling between these two forces must be the "cone clutch" but as no movement is occuring and the force "must be" less than supplied by the engine (when running), then where is the damage being done.

Please enlighten me!

[lockie]

The cone clutch relies in part on the shaft torque to push the two parts together hard, and create enough friction to transmit the torque. If there's only a tiny bit of shaft torque, the two parts may not be pushed together very hard, and they may slip. The end result may be polishing, which means the clutch may slip under full engine torque, which means it gets more polished which means.....etc

lockie

[Wotname]

Originally Posted by lockie

The cone clutch relies in part on the shaft torque to push the two parts together hard, and create enough friction to transmit the torque. If there's only a tiny bit of shaft torque, the two parts may not be pushed together very hard, and they may slip. The end result may be polishing, which means the clutch may slip under full engine torque, which means it gets more polished which means.....etc

lockie

I understand this polishing may occur if one shaft is rotating slightly (slowly?) so are you suggesting that the prop shaft might be turning very slowly when the gearbox is engaged while sailing?

And therefore, if it isn't, no damage is possible?

[lockie]

Yes, if the clutch is in the neutral position, the cones are separated. So then if one rotates relative to the other, no polishing occurs.

[Wotname]

To add further confusion, my internet based research comes up with two other explanations as to WHAT the problem is.

Potential wear on the "horseshoe clutch actuator" - not sure if this is just HorseS*^t or serious bit of stuff in the gearbox to worry about

And

Cones locking together making it difficult to disengage.

I don't buy the polishing of the cones theory too much - at least in my installation. When sailing at hull speed with asternl selected, I have marked the position of the prop. shaft and it just does NOT turn so no polishing is possible. Again, this observation is only applicable to my installation, YMMV.

I am currently discounting the "wearing horse clutch actuator" for the same reason - no movement in the gearbox so no wear.

I am keeping an open mind on the cones locking together as others have recounted this experience. But was it a problem, did real damage occur.

I note the Yanmar advisory was published in 2008 but Kanzaki has been these clutches for decades - appartently without the need for an advisory

[SailPenelope]

The advisory also applied to Saildrive........I don't know if it would be different for the straight shaft application.

[ShaunJ]

Good question Watname, I put mine in neutral like Yanmar advises. I do however put it in reverse when the noise starts to bother me. That is usually approaching hull speed.

[boden36]

Are you sure that gearbox has cones? I suspect it may have plates.
We have run our Yanmar 3JH locked in reverse for years with no problems. When you are sailing fast, with the gearbox in reverse, check to see if the shaft is turning. If not there can be no wear.
If you get the boat sailing before engaging reverse, you will have more positive engagement.
Regards,
Richard.

[bill good]

G'day Watname, Never heard of anyone complaining that the reverse gear was slipping but have had slipping in forward. Have heard of locked gear however & that is more likely why the advise to run in neutral. I have 2 bladed folding & find selecting reverse makes sure it is folded then neutral.

It was not a hard job to lap the cone with valve paste to remove the glaze on the cone without need to replace any parts.

regards Bill

[Talbot]

Not all yanmar drives are friction cones. The saildrives fitted to the 3GM30 and the 3YM30 uses a constant mesh with dog clutch. This is the SD20 and its replacement sail drive.

The SD50 uses the friction cone clutches, and are used in engines above 30hp

[sailorboy1]

A little off topic, but for all you with fixed prop running around with the transmission in neutral, does the noise and vibration of the spinning prop make you crazy?

When my Flex-O-Fold hasn't folded I know because of the noise (a quick pop into reverse fixes it and then it goes back into neutral).

[bob_77903]

I think I'll follow Yanmar's recommendations, but then what do they know

[rocma]

Originally Posted by Don Lucas

When my Flex-O-Fold hasn't folded I know because of the noise (a quick pop into reverse fixes it and then it goes back into neutral).

Yet another Yanmar recommendation: do not install a folding or feathering prop under your boat if you DO NOT have a flexible coupling between shaft and gearbox.
By the way, most marine engine manufacturers are not keen on having these props fitted without a flexible coupling. These props generally cause more vibrations, especially when they get older and the opening "klang" is on the long run not good for your gearing.

On topic: on conical Kanzaki gearboxes you should leave your prop free running. In gear, there is constant pressure of the prop wanting to turn. Besides, a turning prop causes less friction (yes I know some people say it is the other way around).

[Wotname]

Originally Posted by Don Lucas

A little off topic, but for all you with fixed prop running around with the transmission in neutral, does the noise and vibration of the spinning prop make you crazy?.......

YES, that is why I select astern and put with the increased drag (and possible damage) rather than listen to the noise.

Originally Posted by Talbot

Not all yanmar drives are friction cones. The saildrives fitted to the 3GM30 and the 3YM30 uses a constant mesh with dog clutch. This is the SD20 and its replacement sail drive.

The SD50 uses the friction cone clutches, and are used in engines above 30hp

Thanks, mine is a 2GM20 with a Kaznaki transmission and I THINK it has cone clutches. I should do more research

Originally Posted by bob_77903

I think I'll follow Yanmar's recommendations, but then what do they know

Well apparently they didn't know too much pre 2008 and when I consider I got my first 2GM back in the mid 80's (with same transmission I suspect) and this one around 2002, I begin to think it is not a big deal. Most likely an a^*e covering exercise.

[sailorboy1]

Originally Posted by Catcruiser

Yet another Yanmar recommendation: do not install a folding or feathering prop under your boat if you DO NOT have a flexible coupling between shaft and gearbox.
By the way, most marine engine manufacturers are not keen on having these props fitted without a flexible coupling. These props generally cause more vibrations, especially when they get older and the opening "klang" is on the long run not good for your gearing.

In years of reading threads on folding and feathering props, including every comparison article I could find; this is the first I have ever seen this. Do you have a link or more iinfo to support this?