Wud-E-Nuff |
A 20ft |
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YANMAR YS ENGINES
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I bought a boat in December 2003 with a YSE12 single diesel engine, and have now learned something about them. I'm documenting this with a view to helping others with information, however some of what I have learnt is only hearsay, and some speculation and opinion, so this will require verification. I have only recently discovered the E B & M stand for Early Between and Modern for the YS engines. From photos I have seen, there are visible differences in the engines, due to bolt on parts, but basically the YSE & YSB are similar, with the YSM having a different design and ancillaries. |
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I have been told by several with experience that these engines were taken from an original design as a flat twin, made by Coventry Climax in the mid 1930s. Designed to go in the stern of landing craft, these engines were made so servicing could be from the front, the engines low height allowing them to be tucked away in the stern. Yanmar made the modified design for a single in 1974, making the YSE from 1974 to 1977. Modifications were made for the YSB for 1 year, before a redesign, including a different fuel injection pump for the production of the YSM from 1978 until ceasing production in 1980. I have also been told that to identify these engines, the YSE has a cast iron gearbox housing, the YSB & M having an aluminum housing. The YSE & B have a fuel injection pump bolted onto the front of the engine, while the YSM has a different type of pump, which is bolted in the cylinder block. Another difference is the front pulley is on a layshaft on the YSE & B, only being on the crankshaft on the YSM. There is an identifying plate on top of the flywheel housing, but this is missing on my engine. The engine is raw water cooled only, so operates at a low temperature. I was told by an experienced mechanic, not to run slowly for long periods; the manual states to run flat out for an hour after trawling for a few hours. I can only assume this is to prevent high wear on the heavy horizontal piston at low speeds, and low temperatures. The oil level can be critical, as oil blow by causing the engine to race out of control seems common, from what I have read on the forums etc. This is when the engine runs on it's own sump oil, instead of the diesel through the injector. Could this be caused by high wear on the piston and rings, and the design being only 'half' an engine? The engine has no oil filter, relying on an oil strainer. This consists of a series of thin rings on a shaft that is turned by a T handle on the front of the engine. Thin plates between the rings; scrape the debris from the oil. The dipstick is on the oil filler, both for the engine and gearbox. Levels should be taken with the screw filler caps resting on the threads, not screwed in. Care should be taken however, as the engines are not always mounted level in the boat. My engine tips backwards to allow alignment to the propshaft. The manual states 30sae oil, but multigrade oil can be used, as this oil is superior, and was not around when the engine was manufactured. Care should be taken to only use a mineral oil, and not one of the synthetic, or semi-synthetic oils around today. These can damage the bearings of older engines. Before buying mine, I traveled a considerable distance to view a boat with a YSE12. The old and worn engine had no oil pressure so luckily I didn't buy that boat. However this fault has now appeared on mine at startup. Running the engine briefly, sometimes having to stop, and restart will get the oil pressure up, and good pressure at that. This signifies the bearings and oil pump are in relative good condition, given the age, and design of the engine. I can only assume this is caused by debris entering the oilways, and lodging behind the pressure relief valve. This is held open, allowing no pressure, until the action of restarting, or the warmth of running the engine briefly, causes the valve to seat. Removal of the front cover to clean the oilways and pressure release valve appears to be quite a major job, as it requires dismantling much of the front of the engine. So as long as the problem does not get worse, and oil pressure is achieved after 20 or 30 seconds, living with the problem seems the best option. I have read these engines can suffer from low oil pressure, and despite not having a gauge to check, the oil light goes out as soon as the engine is turned over. Once oil pressure has been achieved, pressure is immediate if there is no delay between stopping and restarting. The YSE and B have a poorly designed govenor. A needle valve in the pump releases the injection pressure, hence only about 1/3 of a turn of a fine threaded bolt is required from full throttle to stop. After all these years, the needle valve seats are worn in the pumps, causing erratic running, stopping, and poor starting. New needle valves are readily available, but I have found the best way to avoid this, is to remove and replace them, resetting the governor linkage at very frequent intervals. If the engine dies at low revs, and will not start, particularly when hot, pulling the governor linkage when flat out will sometimes overcome this problem. My engine was supposedly recently overhauled when I bought the boat, and now I have had occasion to remove the head, and grind the valves, I can see it is in relatively good condition. Even with low compression it started well, although it was a fuel starvation problem from the tank outlet, that prompted me to check the compression in the first place. I have also read the exhaust elbow can become blocked, or corrode, and may need replacing. Apparently these are expensive. On inspection mine seems to be clear, and in fact could have been recently replaced. I have also heard of the water pump requiring attention, and the impeller should be frequently changed, as a broken blade can find it's way into water galleries of the engine, causing a blockage that is difficult to remove, and may require some dismantling of the engine. The gearbox of the YSEs can be 2 to 1 or 3 to 1 reduction. The reverse is very slightly lower geared, but on mine with 2 to 1 gearing, there is little noticeable difference in engine speed. After using the boat last year with first a prop of the wrong rotation, then one a bit too big, I have finally machined one to be correct. On my boat, a 20ft Mahogany clinker the prop is now 14 x 10. This allows the engine to run without labouring, yet is still not running flat out. I was underpropped, partly to having to run in reverse when I got the boat. This was quickly damaging the gearbox, so the boat could only have been used for an hour or two since the engine was fitted, in this configuration. After displacement speed of around 6.5mph the engine would smoke. My first prop with the correct anti-clockwise rotation was much to big, and once again black smoke billowed out and the engine would do little more than tick over. Speed appeared to be around 6.5 mph. Checked with my GPS (now sadly lost through stupidity. I must have left it on the cabin roof after fastening the canopy). The 15 x 10 allowed the engine to reach approx. 2000 of it's 3000 rev maximum, and once again black smoke if trying to go faster than 6.5. It will now rev to an estimated 2700 with black smoke above 6.5 mph. The prop is still large enough to give good stopping in reverse. A noisy engine, with the worst diesel knock I have heard, however it is economical, using approx. 1 to 1 1/2 litres of diesel an hour. Despite their age, parts are still readily available for these engines, although the cost of repair is becoming uneconomic in some cases, according to some people I have been in contact with. There are forums and websites to help so here are a few links. I have found a manual to download, and have a few clear YSM drawings of the parts list. http://www.yanmarhelp.com/msgboard.mv http://forums.torresen.com/sailing/ Phone number for a UK supplier is 01326280214 |
