This is a more technical article for all the ones that are also „suffering“ from the Yanmar SD-50 cone clutch they may have installed in their vessels.
Our mechanic in Shelter Bay Marina, Panama simply didn’t check the clutches despite his invoice stating the contrary. So the surprise came in Galapagos, when our port engine failed to engage. A clear sign of a glazed over cone clutch, as it is frequently found in the Yanmar SD-50 that has not been checked and serviced every 500 hours of operation.
After we got over the mild stress induced in a crowded Isabella anchorage with strong winds from starboard, a reef on our port side and no operational port engine we diagnosed the cone clutch defect. The clutch will fail to engage (and thereby transmitting power from the engine to the propeller) whenever two surfaces therein are to smooth. In our case that happened due to the usual wear and most likely due to two incidents involving a line in the affected prop.
As we were very happy to use some very valuable resources from the internet concerning a repair outside a proper boat engine workshop, I decided to improve the respective manuals a bit and post it her. Hopefully, they will help others in their repairs. Yanmar Service in the US was also a great help to us. Whatever anyone may say about their SD-50 Saildrives: Their Service was world class. Thanks for that. Also a big thanks for El Tigre on Isabella. He runs the local car workshop and allowed us to use his vice. We also used some of his scap aluminum to use as brackets in the vice for protecting our clutch shaft from the iron vice brackets.
Please find the attached manual for repairing the Yanmar SD-50 Saildrive cone clutch here: Yanmar_SD50_Clutch_Repair_v03.
By the way: We did use a vice to open the cone clutch assembly. But we also met Laurent of the Catamaran „Sept à Vivre“. Laurent managend to repair / lap the clutch without a vice. He did so by applying lapping paste to the cones and lapping without taking the assembly apart. I guess he performed a very thouroughly cleansing of the unit after that procedure to make sure not to have the agressive paste in it after starting the engine. But the clutch works fine after the process. Thanks for sharing that, Laurent, I think it is a very cool improvisation.
Books: Yanmar SD-50 Service Manual
Georg Forster, Entdeckungsreise nach Tahiti und in die Südsee
U.B. Peter, Europa – Warum wir sind, was wir sind
Neal Stephenson, Seveneves: A Novel