In autumn 2009 we stumbled across an old two stroke outboard which it’s owner was trying to sell. Although the motor had severe overheating issues, the price was very interesting. After some surfing on the net it was identified as a Yamaha 15A built sometime between 1972 and 1978. We were even lucky enough to find a complete parts list with diagrams. As could be guessed from the model number it is a 15 hp motor. It came with a 9 1/4 x 11 1/4 propeller and weights about 37kg.
The first part to be tested was the thermostat, that turned out to work. This was very good news as getting the old one out would have been a big challenge. Next on the list was the impeller of the water pump. Detaching the lower unit proved to be more difficult than expected: most of the bolts were seized and would only come out after repeated treatment with WD40, heating and careful application of brute force. Once the last bolt of the impeller case was out, it was immediately clear what the problem was. Just have a look at the picture! Small wonder the motor kept overheating…
While we were at it the gaskets of thermostat housing and water pump were also changed. Before the reassembly the oil of the lower unit was drained, this permitted us to have a look at the gears. They seemed to be in excellent shape. The fresh oil made a noticeable difference, the shaft opposed much less resistance. As part of the standard procedure new oil drain plugs and gaskets were installed.
On the 24th December everything was ready and the first sea trials were carried out. The motor started and ran fine. Now with the new impeller a nice jet of water was noticeable where none was before. Being a short shaft motor we could not evaluate performance however, grandpa’s motorboat needs a long shaft. Click here for a short video of the sea trial!
Happy that our first power plant seemed to work we made for port and already knew what the Easter Project 2010 would be: a hull on which we could test the 15A. The plan is to build a hull suitable for testing during Easter and then equip it with foils during summer.
Here is some video footage of the project: