OK, here's the scoop
The problem with fitting a high output alternator on the Yanmar is belt slippage, wear, and lotsa belt dust. Most high output alternators come with dual V belt pullies, but this won't help you on the Yanmar. And of course, Yanmar makes no upgrade kit.If you look at the front of the flywheel face, there are 4 tapped holes (M8). These are actually used for some sort of Yanmar power take-off kit.Anyway, the trick is to get away from V belts altogether, and go to what's called a K6 Serpentine flat belt. These have great flexability, won't wear like V belts, and one K6 easilly drives what 2 V belts are rated for.Now, you'll notice that the existing V belt goes around the flywheel, up around the water pump, and then loops over the alternator, which gives it the tension. What we're going to do is break this up into 2 belts:A V belt for the water pumpA new Serpentine belt for the Alternator.This has many advantages:Firstly, with a high output alternator, there is a lot of side force tensioning the alternator. It is actually way too much for the water pump, and will damage the bearings over time. So by having the Water Pump on its own V belt, there's harldly any stress on it, and will probably last forever.Also, by dividing up the belts, you won't ever get into the situation where a broken alternator belt "loses" your water pump, and overheats (siezes) your engine.So... Here's how to do this. Note: You'll need access to a machine shop, but nothing fancy.Firstly, the trick is to find a Serpentine pulley that will fit on the yanmar flywheel. Go to Jones Racing Products.http://www.jonesracingproducts.comGet to the area for the CS - 5102 Serpentine PulleysDual Dowel Pin Design. You will probably need about 5.5" or 6". It's not listed, but they make it.All that you need to do is machine a 6" diameter 3/8" thick aluminum plate which picks up the Yanmar flywheel holes, and mount the pulley to the center of this. Use the 4 dowel holes on the pulley to screw it to the 6" plate.Next, You will purchase a Serpentine altenator pulley from Jones as well, and mount it to the alternator. At this juncture you will notice that the crankshaft pulley is about 1.25" forward, (out of line), with the alternator. To remedy this, you pull the alternator, and move it forward by switching the postion of the long 1.5" spacer bushing. Then you will need to "spacer forward" the alternator swing arm by an equal amount. For this, get a simple tube spacer made on a lathe. (Steel)There my be some misalignment where the alternator is too far forward, and out of line with the crankshaft. This is easy to correct. Just put washers between the crankshaft pulley adapter plate and the crankshaft.Lastly, we have to deal with the water pump. You can purchase from a variety of bearing supply houses idler plastic pulleys. You will need to mount a small flat metal plate between the flywheel and water pump, to which you screw on the idler. The function of the idler is to take up tension in the V belt once you've looped it from the flywheel to the water pump.Once this is all done, you should see higher alternator output, (no slipping), along with zero belt wear.Arthur Boas