Towards fall of 2001 the well served 1980 Volvo-Penta MD5A of my Senorita was becoming tired, spitting diesel fuel into the sea, and getting more and more difficult to start. Failure of the electrical side was the last nail: troubleshooting in the fall rain was less than tempting.

Another motivational factor was that 7.5 hp had proven not quite enough when pushing against a strong wind and waves. A new stronger engine was due, at a favorable cost, of course. Yes, I know that rebuilding the MD5 is an option. Putting together the piston, cylinder head + lining etc. totaled a handsome figure – and it still would have been an old engine. So I pulled out the MD5 and started looking for a replacement.

Selection criteria

• New motor should preferably fit to the existing S110 sail drive unit (1.66:1 gear ratio) and engine bed, to avoid glass fibre jobs. The original 12"x 6" folding propeller should be used if possible.

• Motor should fit into the rather compact engine locker of Senorita

• It should be lighter than MD5: she was floating a bit tail heavy

• Fresh water cooling would give longer life and easier fall service (well, MD5 lasted a good 23 years…)

• And the price had some significance, too.

The option with least weight was the SailDrive: a Honda 2 cyl with an S50 drive, 45 kg. But it has a different mounting bed, and uses gasoline.

Little used VP engines are pricey and, at best, a very cramped fit in Senorita’s engine space. There are several manufacturers who offer an adapter to S110 sail drive. After some research, making dimensional drawings about the fit into available space, and looking at the service points of the engines, I took a closer look at the Kubota engines ‘marinated’ in France and UK, and ended up with a Kubota Beta 10. It is a 2-cyl. 10 hp diesel with fresh water cooling, and it gives the max power already at 3000 rpm.

Why Kubota Beta 10

• The motor is available with an adapter for S110 from the factory

• The power and torque curves of Beta 10 coincide and are above those of MD5 in whole rpm range: even with the lower gear ratio of S110 (1.66:1) Beta 10 can run at the same rpm – and same prop – as MD5 which mostly is used at 1500 - 2000 rpm. Beta 10 then has power reserve up to 3000 rpm, which will help in head winds and waves.

• The engine is available with a shallow oil sump: no need to cut the engine bed for more space. Oil change pump is available as accessory.

• Weight saving of 20+ kilos compared with earlier

• The local rep promised to make mounting supports which are 5 cm wider than standard, to fit directly over the mounting posts of MD5.

The same engine is available as a 14 hp version, which gives power and torque at higher rpm: this engine would have required a new prop and/or a new gear ratio to run at optimum power range. The new engine, painted bright red, arrived to the local rep. I brought the S110 to him and he mounted to the flywheel a flex plate which spline count matched that of the S110. Good to keep in mind that the bolt patterns etc. of S110 drives vary from year to year and between models: give that info when placing the order, to avoid unpleasant surprises.

Installation

For getting the experience, I decided to install the engine by myself. A truck lift hoisted the engine into the boat, and the work was started.

Preparations

I had to reroute the heater air duct in the engine room, to make space for the new engine. Cold start and stop control cables of MD5 were removed: Beta 10 has glow plugs and electrical stop. The engine control panel fits into the hole of MD5 panel when you make a fill plate out of plastic or plywood. The control cable bundle is long enough to go through the same route used for the cabling of MD5.

A fuel return line was installed. I connected it to the fuel tank with a T-connector at the tank vent tube. Old fuel line hose was replaced, too. The old exhaust line was used as such. Since the exhaust diameter of Beta 10 is 5 mm larger, a piece of larger exhaust tube was pulled over the old tubing and engine exhaust.

The local rep for Beta had extra wide mounting irons made. With these, the mounting /vibration damping feet of the new engine were almost on top of the old MD5’s. I had to make two adapter plates from steel, with holes for the old MD5 mounting screws and for the new engine’s damping pads.

I used the opportunity to replace the sail drive main gasket (recommended replacement interval: 8 years). I replaced the rear damping foot of the sail drive, too (200 EUR for a piece of rubber !).

At the engine, the pipe between the impeller pump and heat exchanger was removed. Two rubber hoses are used to connect the anti-siphon valve into the circuit there. The valve is one used for Volvo-Penta’s 20..30 hp motors, with 19mm hose connections. The motor slid into its place with a bit of effort. There is some (but not much) space on each side of the engine. The oil change pump is mandatory because there is not much room below the oil sump.

The lower part of sail drive slid into its hole, the rubber gasket and its holding ring into their place as described in the instruction booklet. The upper half of sail drive is matched to the adapter, the drive shaft splines slide carefully into the flex plate, and the mounting bolts are tightened carefully crosswise, checking often that the drive shaft rotation is free. Do not use force !

After that you can start mounting the sail drive together, as described in the instruction manual. Remember to use gasket cement (Hermetite, Permatex ) at the stepped inner lip joint between the oil and cooling water channels (not for the main rubber gasket): the O-ring alone is not enough to seal the oil space (don’t ask me how I know). Installing and tightening the bolts for the engine mounting feet requires some acrobatics and a long extension bit for the socket wrench.

The electrical side is connected - as at MD5 – at two points: + and - . The engine has a 40A main fuse. The control cable bundle is connected with a pre-wired plug.

The movement of the throttle cable is larger on MD5 than on Beta 10. Therefore, an extension is added to make the Beta 10 throttle lever at the injection pump 2…3 cm longer. The throttle cable fits into the bracket at the engine without problems. The internal wire of the throttle cable needs an extension of 5 cm. Cooling water is taken from the sail drive to the pump at the front of the engine. The pump takes a 19 mm dia hose; the shut-off valve at the sail drive unit has a 16 mm dia valve which could be swapped. The gear shift cable is attached, tank filled with diesel fuel, fuel circuit primed, and that is it.

The mounting takes a weekend, if you do the preparations in advance and if you are somewhat inclined into this type of work as hobby. I spent more time on it, mostly because the work is enjoyable.

The experiences from one summer

• Two cylinder engine runs smoother the old single

• Cruising speed is a bit higher: the hull speed is reached already at a rather leisurely rpm so that there is plenty of reserve.
• Fuel consumption is not much different

• 10 hp is sufficient to maintain the speed even against wind and waves

The annual service work requires acrobatics:

• The cooling water pump is at the front of the engine (facing rearwards), accessible through the opening which you reach under one of the cockpit benches. Replacement of the impeller at the beginning of each season is recommended, because you do not want to do it on the sea.

• Oil filter is next to the water pump, accessible on port side. Kind a hard to reach, but you need to get there only once a year.

• Fuel filter changingand fuel system priming can be done easily from the rear of the engine

• Oil changes are easy with the special pump.

Overall, I think Beta 10 makes a nice fit with Senorita.