Yanmar 2GM20F: free wheel or in gear

[glcalahan]

I am wondering what thoughts are regarding placing my Yanmar in neutral (freewheeling) while sailing or locking in forward or reverse.

I rebuilt the engine and am not quite finished with total rebuild yet. Thinking ahead!

Opinions??

Thanks in advance!

[Wotname]

The 2GM20F has a transmission with cones clutches. Yanmar recommends these are left in neutral while sailing.

The upside is less drag, the downside is more noise!

[Gary Mc]

I have a 2gm and always put the transmission in reverse when sailing.

I have a folding prop and assume, or at least hope, that Yanmar's advice to leave it free wheeling is meant for fixed props.

I believe that a folding prop does not cause the shaft to attempt to turn so it will not damage the Kanzaki tranny. Fingers crossed but comments appreciated.

[Davo1404]

I have a 2GM20F coupled to a 3 bladed folding propeller. Sometimes it doesn't fold when the motor is switched off, you can hear it turning. So I select reverse, then back into neutral. Silence prop is folded.

[lockie]

If you look at details of the gearbox on your engine, you will see that the geometry of the helical splines on the output shaft is such that the prop drag torque will tend to reduce the force on the cones (ie pull them apart) if you leave it engaged in forward while sailing. This can lead to slipping and glazing of the cones.

Hence the advice to leave it in reverse, whence the drag torque will tend to push the cones together and eliminate the chance of slipping and glazing.

Glazed cones will quickly lead to engagement problems requiring removal and disassembly of the gearbox.

Wanna know how I found all this out????

A freewheeling prop would probably be ok if you could guarantee no contact by the cones. But if the shifter was even slightly out of whack allowing any contact at all, the cones would very quickly glaze leading to... see above.

I offer no comment on the relative drag of free vs fixed props.

Cheers, Graeme