Martin, The Yanmar shop manual says that the KM2-A gearbox for the 2GM was available with 2.21, 2.62 or 3.22 ratios. You would think that after "X"ing out the 2.62 they would have stamped the correct 2.21 ratio on the plate.
Rick Taillieu Nemesis '75 C&C 25 #371 Shearwater Yacht Club Halifax, NS. -----Original Message----- From: CnC-List [mailto:[email protected]] On Behalf Of Martin Kane via CnC-List Sent: September-04-14 21:52 To: [email protected] Subject: Stus-List Yanmar Gear Box Mislabeled I've owned a C&C 29-2, with the 2GM engine and KM2-A gearbox for the past three years. Initially the Yanmar tach would show 2200 rom at WOT in gear and about 3400 in neutral at WOT. In year 2 I replaced the installed 14X9 three blade with a 15X10 folding prop that was spare. WOT rpms in gear decreased by a small amount. In year three I installed a 13 x 7 Campbell Sailor. WOT rpms increased to 2500 (as measured by Yanmar tach). I advised the prop supplier that based on the Yanmar tach and a laser tach that the engine was still not able to reach the appropriate WOT rpms. They offered to resize the prop, but mentioned that the 13x7 prop had produced good results for other owners. Given that info I decided to find out why I was "different" before sending the prop back for rework and proceeded to measure the rpms of the engine and prop shaft at different speeds with a laser tach. The answer is that even though the gearbox plate has ratio of 2.62 stamped on it. The actual ratio as determined by comparing crankshaft rpm to prop shaft rpm, is 2.21. This ratio was also confirmed by turning the crankshaft by hand and observing the prop shaft. So it appears that the gearbox is mislabelled. The only possible hint of this is that the 2.62 has an X stamped through it. I'm posting this in case it helps other listers dealing with an overpropped situation and to see if anyone has ever heard of this happening before. I don't know if the PO had the gearbox rebuilt or if is even possible to switch one or more gears to change the ratio from 2.62 to 2.21 Martin C&C29-2 Recalculating Mimico Cruising Club _______________________________________________ This List is provided by the C&C Photo Album Email address: [email protected] To change your list preferences, including unsubscribing -- go bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
