Urgent Yanmar gearbox info needed please.

[dralex]

Before I go guddling in dark holes with a torch, does anyone know the reduction ratio of a Yanmar 2GM20 gearbox from 1990, or are there lots of variations. The original gearbox went to a shaft drive and the original 2 blade folding Gori prop.

I have to post my old prop to a supplier so they can match it up.

Thanks

 

[ShipsWoofy]

lots of variants. The sort of standard is 2.21:1.

You should find the ratio noted on the plate on the box, it is stamped so even if rusting you should still be able to make it out.

 

[dralex]

Mmm- so I do have to go guddling in deep dark holes.

 

[Steve Clayton]

Try asking here
http://www.freeboards.net/index.php?mforum=yanmarhelp&showforum=2

 

[snowleopard]

This is not a simple question. There are several models of gearbox and each has several possible ratios. Yours may be model KM2-C which could have ratios of 2.21 2.62 or 3.22. Alternatively you could have model KM2P with the same ratios. Presumably you don't have a saildrive whose ratios and direction of rotation are different again.

 

[wrr]

If you cannot read the ratio on the box, borrow a laser tachometer, put a piece of reflective material on the flywheel or crankshaft pulley and on the hub of the propellor shaft connector. Run engine in gear and measure RPM of engine and prop shaft over a few throttle settings and calculate ratio.