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Old 07-11-2009, 10:10   #31
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Put a straight edge across the sheave. If it is not parallel to the belt then it is not in perfect alignment. There is though some allowance for imperfect alignment.


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Old 07-11-2009, 10:25   #32
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Old 07-11-2009, 18:56   #33
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By my late Mentor Pete. S.

Originally Posted by Rick View Post
Because almost no one has a belt tensioning gauge and because pressing on a belt to observe deflection is too subjective I've been able to "optimize" belt life for alternators by doing the following:

Use gloves or put a rag over the alternator fan and rotate the pulley to observe that the crankshaft turns. If the belt slips doing this it is too loose. Tighten the belt JUST until the belt no longer slips and no more. This will be very close to the ideal belt tension.

Because there is usually a 3:1 pulley ratio or greater on most engines I have been able to rotate the crank even on fairly large diesel engines using this method.
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Old 07-11-2009, 20:26   #34

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easy way to align belts in parallel and angular is with a piece of string.
You cannot align with a straight edge or string if the sheaves are of different widths but if you have room check both faces and align so gap is equal both sides. is generally easier with string to get to back side. if truly a perfectionist use drill set as gage to make any gap equal. look at sheaves closely with a tightly focused flashlight an see if faces are polished equally to verify running true. lots of other tricks too....
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Old 02-12-2009, 08:17   #35
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Could it be the water pump?

We have gone through 3 V-belts in the past month on our Yanmar 4JHE 44 hp engine. The first had been on for a few years so we assumed it was just time for a new one. However, the next 2 belts lasted only 35 hours (or 1 week) each. After the 3rd belt, we suspected it wasn’t just a belt issue and went looking. We discovered that the alternator had two bolts that were a half a turn loose so tightened them. It doesn’t seem like much but maybe that is the problem.

When we spin the pulley for the fresh water pump, it turns freely and make a bit of sound as it turns. The pulley for the alternator spins freely and is totally silent. The bottom pulley doesn’t spin but we are assuming that is normal as it would have to turn something inside the engine so has more resistant. Is this a correct assumption?

We spoke to a Yanmar diesel mechanic and he said it is probably the bearing going on the fresh water pump. We are told that Yanmar does not sell a rebuilt kit for the fresh water pump and would need to buy a whole new pump. Are there after market options that we can consider instead of a new $300 pump? The pump is about 2 years old.

Any comments are much appreciated.
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Old 02-12-2009, 08:42   #36
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Okay, what happens when a belt slips? Besides dust (which is particularly good for the guts of your alternator) it polishes what ever it is sliding across. So if you have a set of pulley's that a belt has honed to a shiney surface, the solution is to 1 throw some salt water on them and let them pit up with rust (probably not) or take a piece of crocus cloth and put some tooth in them. When installing new belts (every 4 years when putting on all new coolant hoses, I'm just a preventive maint guy) I always tooth up my pulleys. Dream maker, On the fresh water pump,when the bearings start to go the seal is the first casuality. Coolant starts to drip out the weep hole just below the pulley shaft. As the bearings further deteriorate they "seize up" and the pump stops turning . With the belt still being driven around the immovable pulley it soon heats up and fills your eng room with smoke as it burns itself up with friction heat. Around this time your overheat eng light comes on and the eng shuts itself down. Since you replaced the belt , have you daily checked the tension? Is your pulley shinny? Don't think it has a thing to do with your water pump. Try taking a bad pump to a machine shop where they can press off the shaft and get to the bearings and seals. If they can get the parts it will probably cost 1/2 the price of a new pump. If there is a lot of dust it is a slippage issue. Good luck to all
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Old 02-12-2009, 09:52   #37
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checking alignment is real tough. many variables, sheave thickness etc. I've pretty much gone to getting it close and observing while it is turning....Belts seem to come in many widths also 13/32, 3/8. 15/32 etc... I always thought they were 3/8 or 1/2 until recently....

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