Hi Scott - You are not alone! Not long after I began cruising Seahorse I began having problems with the Balmar 165A alternator. The LP668D was then 2 years old (2004). I kept getting dusting, even on a near-new serp belt and began to check for the reason. With a new belt, the tensioner had only minimal travel left before it hit the stop, and that occurred soon after the belt was broken-in. That left the belt too-loose and so it slipped heated the pulley. That heating eventually burned up the front alternator bearing. When I discovered this I queried Alaska Diesel about the belt, which was a 123464. The parts guy and I decided that the shorter belt, 123463, must be right and I bought one, only to discover it was so short it wouldn't fit at all. Then another round of discussions with ADE, which uncovered the fact that they "never" supplied Balmar alternators and that a L-N machine was installed when it left ADE. The yard that sold and installed the engine had replaced the L-N with the Balmar - evidently the pulley was a bit smaller but they didn't bother to check - and now the factory belt was too long. I'm not sure how the PO got away without problems - maybe that's why he had a surplus of belts aboard. The fix, of course, was to get a belt that would allow a 180-degree wrap on the alternator pulley and put the tensioner mid-travel when new. Since ADE didn't have anything that would fit, I determined the correct belt length and ordered one from Michigan Industrial Belting for about 1/3 the price of a Lugger belt. It fit correctly and I haven't had any problems since. By the way, Scott, you might want to check your spares for a "engine low temp switch." This switch, used exclusively on the LP668D engine. When the engine is first started, the injection timing is advanced 10 degrees - when the water temp hits 140 the switch opens and retards the timing back to normal. You can ID the switch (on the thermostat housing) because it has a 2-pole connector on 2" leads. If this switch is bad, the timing will be advanced all the time, which will lower the EGT 50 degrees and make the engine noisier (you can hear the difference). A dead give-away of switch failure will be that if the switch fails (closed) the current draw on the positive wire to the PH engine panel will be about 22 amps. That will show up as low voltage (due to excessive drop) on the engine panel voltmeter and the red and purple wires on the key switch will be overly warm, as will the black Merc connector. Regards, John "Seahorse" > Today I went to consult my spares list and guess what? The number on the belt was R-123463 and my spare was R-123464. My first thought was I had made a mistake transcribing the number. I found the original spares list that Nordhavn provided (an excel spreadsheet probably from another boat) and sure enough it specified R-123464, the belt I had as spare. So now I'm thinking I have definitely written the wrong number down. So I call Barb the parts goddess at Hatton in Seattle (206)283-5501 and she tells me if I can get her the serial number of my engine, she can tell me exactly what belt was put on the motor when it shipped to China. Well I get her the number and she confirms the mechanic was spot on, R-123463, not 464. So I figure, one is a replacement for the other, not true says Barb, a 463 is 1,613 mm long and a 464 is 1,635mm long. The different size belts accommodate different alternators, so between my boat and someone else's they changed alternators, resulting in a different belt. ************************************** See what's new at http://www.aol.com