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Old 02-10-2007, 12:10   #16
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I wouldn't bother with the gauge. Tension was probably ok as you surmise. Not much more to go on. If you can eyeball the alignment and it looks good, it's probably not the problem. (I would not add yet another variable my changing it now.) I would replace that TopCog belt that was a little worn but was working and see how it goes.
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Old 02-10-2007, 13:47   #17
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Aloha J,
I usually buy two belts to have a spare aboard in case something weird happens like it did to you. If you install another new one and it breaks then you definitely know something is out of whack.
I'm betting that you have a misalignment or had a defective belt. Misalignment is easy to check. Belts are pretty cheap considering what they do for us. If one of a certain brand broke I don't think I'd go back to that one. Cogs might be cooler but they have less meat on them. There is a product called belt dressing that can help a bit with belt life. If your wife wears panty hose you can make an emergency belt from them so its always a good idea to have a pair of panty hose aboard.
The twisting the belt with your fingers trick will indicate different tensions because some fingers are stronger than others. I would think the 1/2" deflection theory is a pretty good one but I like my belts a bit looser than that. Its easier to replace a belt than a bearing or water pump.
Sorry for the ramble.
Just some thoughts.
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Old 02-10-2007, 14:04   #18
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Thanks for the info SkiprJohn. I had bought two of these belts, but after that one broke I felt it better to go back to the other one rather than tempt the gods!

Re a temporary fix, the link below is to a link belt that I use on my table saw, I am going to try it just between the crank and water pump pulley as an emergency super fast to stick on there get me moving now repair. Bypass everything except the water pump, don't need alternator in an emergency when you've got a big house bank to draw on. I've used this for years without problems on a 5 HP saw that rips 4" hardwood and I think for emergency it would work better than pantyhose and takes no tools to install.

http://www.leevalley.com/wood/page.a...at=1,240,41067
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Old 02-10-2007, 14:55   #19
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Great idea on the link belt. I'll have to get one of those for my emergency spares kit.
Thanks.
JohnL
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Old 02-10-2007, 17:51   #20
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A heuristic method for establishing proper belt tension

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 02-10-2007, 21:55   #21
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Quote:
Originally Posted by jdoe71 View Post

I've never had problems with vbelts before, on our last boat the vbelt lasted 6 years and was still going strong when we sold the boat. It is not beyond the realm of possibility that is was just a defective belt.
Bingo! - My grandma had two sayings -

"If it ain't f**ked up. Don't fix it."
"If it is f**ked up. Go back to the last thing you f**ked around with."

Yes - My grandma was a longshoreman...

Seriously - You've mentioned this dust several times. I can't recall ever having a belt "dust" on me. It could be a bad lot or a really old belt or whatever.

V-belts have been around for a bazillion years. They are very tolerant of our bad behaviors.

As far as the cog belt and the heating issue? Who cares - seriously. Cogged belts run cooler so the manufacturer can lower the rubber spec - right? I don't know but I do know a solid cross section is stronger than a cogged one. I presume the non-cogged belts (which have been around for the aforementioned bazillion years) have worked pretty good.

Using grandmas 1st rule - stick to what you had.
Using grandma's second rule - go back to what you had.

If you toss a belt after that go back to the next last thing that was messed with (the alternator).

2 cents mode off...
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Old 03-10-2007, 06:55   #22
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grandma was right

Quote:
Originally Posted by Ex-Calif View Post
"If it ain't f**ked up. Don't fix it."
"If it is f**ked up. Go back to the last thing you f**ked around with."
Thanks for the humour Dan! Granny is right. I did think it was f**ked up because when we got the boat there was:
1./rubber dust all over the front of the engine and bulkheads in the engine room
2./two really skinny worn out solid belts on the boat
3./a skinny worn out Dayco TopCog belt on the engine
4./an alternator that was screwed, totally, mechanically and electrically
5./only 370 hours on the engine of a 16 year old boat.

This all added up to a problem to me and still does. My experience is that drive belts last a lot longer than 100 hours and it seems like this boat was averaging that at best. It was only daysailed so likely P/O's never viewed this as a problem, now it gets used more and it is a problem and I need to get it figured out. The good ideas from folks on this board will help sort it out. Thanks again for the day brightener.
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Old 03-10-2007, 10:12   #23
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Just a couple of things:

Alternator belts will sqeak when the batteries are discharged and the alternator is putting out full charge, happens a lot in the cold weather with cars, just tighten up til they stop squeaking. In your case I would loosen the belt a bit, overly tight belts are as bad as looser belts, tight belts make alignment problems worse and wear out bearings faster.

Some V-belt pulleys have an adjustable width to help set the exact speed ratio, these are very common on furnace fan motors. If they are set all the way in or out then they won't work to well.

Have a look if you have one of those on the alternator set it in the middle of its travel.
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Old 03-10-2007, 10:39   #24
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"Yes, there are belt tensioning gauges." But they are getting hard to find, and damned expensive even on eBay used. This because new cars are using self-tensioning pulleys, eliminating a lot of the need for gauges.

You can't trust that the PO used the right belt, or that the alternator shop used the right pulley (in the right place) or that anything really was "on spec" on a used boat. Finding black rubber dust or any signs of chafe and wear are signs to look further and question everything. Compare the profiles of the two pulleys (main and alternator) to make sure they match, then by all means use a straight-edge of some kind (a piece of aluminum box tubing or similar is one good way) to see if they are lined up properly. If someone has worked on the alternator, the "new" one may not quite be in right.

And sadly, the guys in the parts stores, even the NAPA guys, may never have touched a v-belt unless you are in farm country. They're obsolete in cars. I've been given some really unimpressive "Uh, this probably would work" lines.[g] I made a point to actually write the correct belt number, in magic marker, on the pulley itself.

Last of all...Gates, Firestone, Goodyear...all the premium brand name "rubber" makers have had problems with counterfeiting. You take a $1 Brazilian belt, paint "GATES" on it, and now there's another ten bucks profit. Odds are that wasn't your problem, but a call to Gates should get you confirmation on all the other points of how to make sure you've got the right belt, in the right setup.

That overpriced hard to find belt tension gauge is worth getting, too. If the belt is too loose--it slips and wastes power and glazes. If it is too tight, you waste power and put excess wear on the alternator bearing and engine. Once you've calibrated your finger, you can always sell the gauge again.[g]

Typical V-belt tensions might be 165# when new, 120# after break-in, so there's quite a bit of range on them just depending on whether they've stretched in.
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Old 03-10-2007, 12:32   #25
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This is becoming a long thread. As Dan has stated, keep it simple.
Rubber dust means one thing and one thing only. Excessive wear due to slip. Three things can cause slip.
Belt is the wrong section profile. Fix by fitting correct profile.

Belt is too slack. Remedy by tightening. Squealing belts are slack belts. Not squealing doesn't mean they are not slipping.

Load is too great for the number of belts. Remedy by increasing pulley and belt section profile. Or....increase number of pulley sections and number of belts.

As I said earlier, 80A is the limit for one belt. Over 80A you should be looking at a twin belt system.
Maximum load and thus slip, will be at initial start up, when both house and engine start banks are at their lowest. From then on, the current, thus load, will continue to drop as the bank charge states begin to rise.
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Old 03-10-2007, 12:52   #26
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Rubber dust also comes from misalligned pulleys, other parts rubbing on the pulley, very old belts can slowly disintegrate and form rubber dust, excessive vibration and shock loads can also cas rubber dust.

Increased load may cause rubber dust as above, but this can come from worn bearings, or overly tight bearings as well.

All V-belts slip, when driving all but minimuim loads.
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Old 03-10-2007, 14:13   #27
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While I've heard the old saying of having a pair of panty hose for emergency use, I actually had to try that. On my size engine (62 hp) it was worthless. You are NOT going to be able to turn the internal water pump and either the alternator or raw water pump with a pair of hose - they are WAY to elastic. If you are going from the cranckshaft pully to just the alternator ... might work .. unless you have a load on the alternator. The REAL alternative? Carry extra belt (S) - that really isn't an area to be stingy on.

::itching my $0.02 (Canadian - now that they are worth the same):::
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Old 03-10-2007, 16:10   #28
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The ruthless approach...

If I understand the situation correctly none of the components involved is particularly expensive so why not just replace everything.

That is pulleys (go to double or trebble ones if possible), belts, alternator, alternator mounts, external voltage regulator (if used) and so on.

Belts have been replaced. Time to move up the food chain.
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Old 03-10-2007, 16:50   #29
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Aloha Thomas,
Must have been Chinese/Brazil made panty hose. I like the link belt idea for an emergency fix.
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Old 07-11-2009, 11:06   #30
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More on belts - Yanmar part

Thanks to all for all of the useful information. I've still got a couple of questions and comments.

While motorsailing through the Bahamas earlier this year I broke two alternator belts and that makes me very paranoid. The PO left several belts on the boat and I had replacements but now I'm going to need a few more belts to make the trip from the Turks and Caicos to Puerto Rico. I don't want to risk it without plenty of spares. I'll take all of the advice and try to be sure that things are well adjusted. Unfortunately I'm in Puerto Rico right now and the engine (Yanmar GM30) is on our boat in Provo. The PO installed a large Balmar alternator, I don't know the output rating but it's a pretty big one. It only has one belt. A diesel mechanic in Provo recently made a few minor repairs and he told me that the Yanmar part number for the belt is 25132-0037000 and that agrees with information from Yanmar sites on the web. I'd like to buy some good belts from one of the auto stores here in Puerto Rico before going to Provo but haven't been able to find any cross references to the size. If anyone knows a cross reference or a way to find it...I'd sure appreciate it.

I also read in some Balmar literature that the belt tension should be pretty high. But I think I like the advice in this thread. I also understand that there are different cross sections to belts and that the Japanese use a different angle than the Americans so there could be different "types" of pulleys on the motor and on the alternator.

Again, if anyone can help me figure out the belt size, that would really help...if not I guess I'll figure it out in Provo.

Bill
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