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Old 01-10-2007, 08:15   #1
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How to Check Pulley Alignment

How does one check to ensure the drive pulleys on the front of the engine are aligned correctly? Eyeball test says they are and there is no sign of the alternator mounts being bent or weak and flexing but I want to be sure.

Our boat had a Dayco top cog drive belt on it that looked a little worn. So last month I put a new Gates Premium XL belt on it, having read that a cogged belt dissipates heat better. Yesterday while motoring across the bay to our winter storage, this belt with only 30 hours on it blew itself apart, which caused an anxious moment while my brain tried to decipher why the tach would suddenly quit but the batteries still had full voltage showing. The temp gauge needle skyrocketing up quickly gave the answer within 20 seconds or so. Anchor down, put the spare on and carry on.

This belt was properly tensioned, I check it daily along with oil levels and a general visual of the engine. It looks to me like there was a void in the inner belting material but there is a lot of material missing, it blew individual cogs all over the engine room. The outer casing of the belt is intact and there are no nicks or marks that might indicate it hit something so I really feel the belt was defective but that has to be really rare. Or not?

When this belt was installed, it left rubber dust all over the place for the first hour or two, then after re-tensioning it settled down and did not do that anymore. I wipe the oil filter down as that's the easiest place to see whether it is shedding dust or not and it was not after that initial hour or two. Was motoring at 2200 rpm and had just increased revs to 2500 when it blew, we have run it as high as 2700 with that belt on there and no issues. The batteries were fully charged, having been on the float cycle of the charger, so there was little load on the belt, just the water pumps.

Because the P/O had left other belts on board that looked pretty thin, I am wanting to make sure the pulleys are aligned. There is a fair amount of rubber dust on the front of the engine and bulkhead beside the belt. Engine has 480 hours on it. Does any of this sound like pulley alignment might be a problem?

And as a side issue, does anyone have any comments on choice of belt? This is a Universal M3-20, stock 51 amp alternator and stock everything else. The Dayco Top Cog is supposed to be good but it's odd because the cogs are on the top not the bottom which is why I went to the Gates cogged belt. Comments? Thoughts?
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Old 01-10-2007, 08:29   #2
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If the pulleys are not bent put a straight edge across the faces. If one is thicker than the other use the thick one and eyeball it or carefully measure to both sides of the thin one. Then put it on the other pulley up to the edge of the thicker one.
If there is good seperation between the pulleys you will see any misalignment very easy

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Old 01-10-2007, 09:35   #3
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Gates Premium XL are excellent belts.

Drive Alignment Fundamentals
http://www.dodge-pt.com/pdf/brochure...g/RAPS-030.pdf
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Old 01-10-2007, 09:58   #4
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Gates belts are slightly wider than TopCog. V-Belts should always be seated down in the pulley and flush at worst case.
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Old 01-10-2007, 10:25   #5
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Thanks for the feedback and link Gord, I got the Gates belt because it was recommended to me as being a good product. I am sure this one broke from a defect in the middle layers but I will take a steel level to the boat next week and see if the pulley faces are lining up.

stevemac00, I noticed the Gates belt sat a little higher than the pulleys but within the first two hours was sitting down close to level though still above. The Topcog one had sat well below the pulleys so I felt it was worn more than I liked. Perhaps not? The Gates dealer gave me this belt after cross-referencing it from the Topcog number.
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Old 01-10-2007, 12:04   #6
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A new belt should last a long time. To check your alignment place a long enough straight dowel in the pulley slots with the belt off. It will become apparent if the pulley is not in line. A burr or bit of rust on the interior face of the pulley can be a problem but I'm certain you've already checked that? Belt tension is proper if you can twist it around half way with finger pressure.
Hope this helps.
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Old 01-10-2007, 12:24   #7
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Old 01-10-2007, 12:25   #8
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It's not alignment that has caused this failure. It is slipping. What size is the Alternator? 80A is the largest you should spin with a single belt. Above that, you should be looking at a twin belt system.
If the belt sat higher in the pulley, did you have the right "section" belt. If the belt does not sit down int he "V" properly, it will also slip. Slip will tear a belt apart very quickly.
As for alignment, a system can actually tolerate a fair bit of misalignment. Certainly something you would be able to visually see. So if the pulley looks inline, then it should be close enough.
When a belt is correctly tensioned, you should be able to move the belt about 1/2", at the mid point of the greatest distance between pulley's. There is a set of rules for max distance between pulleys for belt section, where upon greater than recomended will require an idler. But as most engines are well within those tolerances, that should not be an issue.
To me, it sounds like you put a B section belt on an A section pulley, or something similar.
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Old 01-10-2007, 12:50   #9
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51 amp stock alternator with stock internal reg. Batteries were fully charged at the dock and the only electrics turned on where the VHF and chartplotter. I checked the internal water pump pulley and it is spinning freely as is the alternator. The raw water pump is not driven by the belt.

This belt was supposed to be the correct part based on the Topcog Xref, I was given that by the Napa store where I bought it. Maybe they did give me the wrong belt, that would be an easy fix. I will get the Topcog part number and check the Xref myself on the web.

If it was slipping wouldn't I see rubber dust or smell rubber burning? I saw some rubber dust for the first hour or two but after that none and didn't smell rubber burning. I checked carefully for this because there was a lot of rubber dust on the engine.

I had been using 1/2" play between the alt and crank pulleys as that was what the engine manual said. Thought I was doing this right so it's a concern that this thing blowed up real good. Thanks for the input.
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Old 01-10-2007, 13:07   #10
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Get your Top Cog number. Likely it was 15370. The "15" means it was 15/32" wide (at the top). The 370 means it was 37 inches long. As I was saying they are not quite the same and while you may get a cross reference to closest match doesn't mean it's an exact fit. If your TopCog fit well I'd stay with that (although I use Gates).

Interestingly, you said the original reason for switching was the cogs offer better cooling. I think that's why the cogs are on top of the Dayco belt - top offer more surface area for heat dissapation.
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Old 01-10-2007, 13:40   #11
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The Gates belt I have here and it is 25-7355. It broke right under the number, how handy. The top of this belt appears to be a tiny bit over 3/8" wide. I don't have the Dayco belt here but I *think* it is 15355. But that can't be the right number because if it was 15/32" wide at the top it would have sat way higher than the Gates does. The Gates belt is 12/32" wide, unless my math skills have declined more than I thought...Maybe it was 13355, I'll find out on the weekend. Regardless, it was sitting well below the top of the pulleys which is why I thought a change was in order.

What I read was that the belts with cogs on the bottom build up less heat because there is less friction internally in the belt as it bends around the pulleys due to the spaces between the cogs. If that's true, the Dayco would be at a disadvantage since they are a solid belt in the pulley side and while they would dissipate heat as well as the bottom cog style they would have more heat to get rid of.
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Old 01-10-2007, 14:44   #12
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I just looked up Dayco part numbers, there is no 13355 so it has to be 15355. Compared that to the Gates 25-7355 which is actually a NAPA number, the Gates number is 7355 but Gates website says they make the Napa PremiumXL belt.

Effective length of Gates 35.6", Dayco 35.5"
Angle of both belts is 36 degrees.
top width of Dayco is .44", Gates is .41"

So that makes it look like the Dayco was even wider than the Gates when new therefore it is certainly well worn since it is sitting down lower in the pulleys than the Gates did. And if the Dayco survived even though it had to be sitting higher on the pulleys than the Gates, it's hard to understand why that would cause the problem with the Gates unless it's related to the bottom cogs.

The worst of this is I can't find the specs for the original belt from Universal it is either part #302084 or 301965 but I can't find length, width or angle for either of them. Perhaps I'm going to have to bite the bullet and order a factory one at 3X the cost to find out what should be there and work from there.

But first thing is going to be thorough exam of the pulleys and alignment. I can't have this thing blowing belts off, this one was no issue to deal with because of the location but if that had happened in other circumstances it obviously could be a huge problem.

Thanks everyone for the input, much appreciated.
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Old 02-10-2007, 09:36   #13
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Of course check alignment but I (and others) find that a little doubtful. Alignment would cause belt dust but I can't see belt breaking unless it was too tight.

Stop worrying about the belt dissapating heat. Was the Gates belt bottoming out in the pulley? If so, the gates belt was too narrow (sounds like the case) and this would cause it to break. V-Belts should bear the force on the sides of the belt - not the bottom.
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Old 02-10-2007, 11:21   #14
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I don't think alignment is the problem either but I have to rule it out. The alternator was rebuilt this spring and I did not believe at the time that I got my alternator back and still don't think I did. I think they just gave me a similar one off the shelf that was already rebuilt. The shop disputes that and I didn't record any numbers off it when I took it in so I'm stuck with it. It's also possible they shimmed the pulley wrong since the case had been assembled wrong when I got it back and it wouldn't clear the exhaust manifold.

The Gates belt was not bottoming out for sure, I checked that as I know vbelts take their load on the sides. It was sitting with the top of the belt higher than the pulleys. The worn out Dayco belt, even though it is sitting low in the pulleys is not bottoming out either. There is no glazing or sign of slippage on the sides of the Gates belt.

I don't believe it was too tight based on the 1/2" deflection thing, but the problem with using deflection as a gauge of tension is how hard do you push on the belt? Moderate pressure? How much is that? My moderate may be way less than your moderate. SkiprJohn mentioned being able to turn it half way around with finger pressure, that at least sounds a little more accurate than 1/2" deflection. Is there a gauge that can be used for this purpose?

One fellow on the boat association board said Torreson's told him that as long as the belt wasn't squealing it was tight enough. Squealing when? With no charging load? Or full charging load? And how do you adjust for that? Back it off until it squeals with dead batteries then tension it some more? So far there does not seem to be a history of belt problems with this engine from the responses on that board. One fellow said his broke 2 belts last year but never had a problem before or since and another fellow said his original belt lasted 7 years, other people reported lots of rubber dust but no breakage or excessive wearing out of belts so there's no consistency there.

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. Had a cam drive belt break from a defect once so it can happen. Thanks again for the input, it's appreciated.
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Old 02-10-2007, 11:43   #15
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Quote:
Originally Posted by jdoe71 View Post
... the problem with using deflection as a gauge of tension is how hard do you push on the belt? Moderate pressure? How much is that? My moderate may be way less than your moderate.
... Is there a gauge that can be used for this purpose?
As a rule of thumb, “moderate pressure” for measuring belt deflection, is about 20 pounds.

The belt should deflect about 1/4-inch if the belt span (centreline distance between pulleys) is between 7 to 11 inches, and around 1/2-inch if the span is between 12 to 16 inches.

There is a formula for calculating belt tension at:
http://www.alliedbearings.com/downlo...tensioning.pdf

Yes, there are belt tensioning gauges.
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