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Old 12-18-2016, 11:02 PM   #1
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Slipping V-belt Sheave advice needed

My boat has a double V-belt sheave that is installed on a 1 1/4" keyed shaft that is bolted on the end of the crankshaft of the Starboard main. It drives and accessory shaft that has alternator, fridge compressors, hydraulics, etc off of it. I recently removed the double sheave as part of an engine painting project I just finished. Everything was rusty and nasty and I had a heck of a time getting it off the 1 1/4" shaft. I ended up using a 3 arm gear puller, and heating the sheave with a torch to get it off. After cleaning it all up it slid back on easily. It has two set screws on it one on the key, and one at 90 degrees to it that bites right into the shaft. This weekend we took the boat out for the weekend for the first time since doing the work and after about 3 hours of motoring, the sheave loosened up and slid partially off the shaft, causing the brand new belt to jump off the tensioner, grind it's self up, and make a huge amount of black rubber dust in the engine room I had just spent a ton of time cleaning. When I discovered it after we had anchored, (I had checked the engine room several times, during the trip, but it must have happened right at the end) I took it apart, cleaned off the anti seize I had put on the shaft so it wouldn't get stuck, and put it all back together, tightening the set screws as much as I dared not wanting to strip them, or break off the allen wrench. I checked it a bunch of times on the way home, but never shut off the engine and checked the tightness of the set screws. When I got back to the marina after about 4 hours of crusing, The sheave was loose again, and the set screws were loose!

What is happening?
How should I fix it?

My thoughts are: Should I put some sort of lock tight on the set screws? Should I put some kind of lock tight on the Shaft? Could that be why it was so hard to get apart in the first place? Is it a thermal expansion issue where the sheave is growing more than the shaft as it heats up? Should I heat it in boiling water, put it on, and tighten the set screws with it hot?

Thanks in advance for any good advice. Other than this we had a fun weekend out in the cold. First time pulling crab pots in the snow.
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Old 12-18-2016, 11:53 PM   #2
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I would use some locktite 620 on the shaft, it is a special product for interference fits and I would also use some of the regular stuff on the set screws. Did you use a drift to get the sheave back on the shaft first? It needs to be TIGHT. I would say that Never-Seize is the wrong product for a shaft. I would also investigate a guard for those belts.

What does that motor on the bench drive?
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Old 12-19-2016, 12:34 AM   #3
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Quote:
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I would use some locktite 620 on the shaft, it is a special product for interference fits and I would also use some of the regular stuff on the set screws. Did you use a drift to get the sheave back on the shaft first? It needs to be TIGHT. I would say that Never-Seize is the wrong product for a shaft. I would also investigate a guard for those belts.

What does that motor on the bench drive?
That sounds like exactly the advice I need. I am not sure what " A drift to get the sheave back on the shaft first" means? The sheave slid right on. It didn't seem to have any play, but it was not super tight feeling either. If I use locktite 620 on the shaft will I ever be able to get it back off?

A few belt guards are definitely on the list of projects. For now I just turn off the engines if I need to get near them, as I don't want to have my arm ripped off, and bleed out, while my wife sits up above in the cabin not hearing a thing over the racket of the diesels. (I may have spent some time worrying about this scenario.)

The electric motor can be used to drive the aux shaft, to drive the fridge and freezer compressors when you are plugged into shore power.
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Old 12-19-2016, 05:55 AM   #4
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Replace the set screws. They should have a hollow point to bite into the shaft. The crown of the point is probably blunted down and not biting in. If the sheave is moving on the shaft, clearly the set screw isn't doing its job. That application may also require dimpling the shaft with a drill bit through the set screw hole to give the set screw a larger contact area.

Ted
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Old 12-19-2016, 06:58 AM   #5
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I would use new set screws, dimple where they seat and use Locktite or JB Weld on the sheave. Heat will loosen the Locktite, etc. when you want to get it off.

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Old 12-19-2016, 07:05 AM   #6
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All good advise, but I'd argue to put the Loctite on the set screw after you got new ones. Can be removed with heat and tool.
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Old 12-19-2016, 07:28 AM   #7
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Sd3.

You ask "whats going on". My guess is that when you cleaned all the rust off the parts you destroyed the fit of the sheeve on the shaft.
It should be a tight fit, like size for size or very slight interference, not clearance like it obviously is now.
Because there is clearance the sheeve will wobble on the shaft and the screws then work loose. They will do this regardless of what you do until you fix the fit. Correct fix is a new sheeve with bore size same as the shaft..... But you can try and measure the clearance ( between shaft & sheeve) with feeler gauges. If the clearance is too small to measure you might get away with it by using loctite on the shaft and inside the sheeve as you slide it on as suggested elsewhere. Do not get loctite in the screw holes and do not tighten the screws until the shaft loctite has cured. Then use loctite on the screws and get them as tight as you reasonably can.
It might work.
If there is a few thou clearance you might also be able to bodge it with a shim brass "liner" inside the bore of the sheeve plus the loctite in and out of the liner.
If you cant get shim brass try a beer can.

Might last you till you get a new sheeve, thats the correct fix.
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Old 12-19-2016, 11:22 AM   #8
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Is the key way fit correct?
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Old 12-19-2016, 11:26 AM   #9
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Quote:
Originally Posted by O C Diver View Post
Replace the set screws. They should have a hollow point to bite into the shaft. The crown of the point is probably blunted down and not biting in. If the sheave is moving on the shaft, clearly the set screw isn't doing its job. That application may also require dimpling the shaft with a drill bit through the set screw hole to give the set screw a larger contact area.

Ted
This is what I would do .
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Old 12-19-2016, 01:40 PM   #10
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Get a taper lock pulley. That will SOLVE the issue. A straight bore pulley with setscrews will not handle the torsional energy on the front of a diesel crank.
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Old 12-19-2016, 04:00 PM   #11
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Get a taper lock pulley. That will SOLVE the issue. A straight bore pulley with setscrews will not handle the torsional energy on the front of a diesel crank.
Best idea yet. I work at lumberyard/ sawmill . We use them on all kinds of applications. I've never seen one fail .
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Old 12-19-2016, 05:03 PM   #12
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Get a taper lock pulley. That will SOLVE the issue. A straight bore pulley with setscrews will not handle the torsional energy on the front of a diesel crank.
Ditto this. I have seen pulleys held only with setscrews walk off the shaft more times than I care to count. Taper lock or bushing bore pulleys are easy to deal with on and off, but will NOT move on the shaft once properly tightened.

https://www.mcmaster.com/#v-belt-bus...lleys/=15jhosv

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Old 12-19-2016, 06:15 PM   #13
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Ditto taper lock pulley. You're probably taking too much hp thru that style pulley and over time the pulley heats up and expands. Any expansion renders the set screws loose. The taper lock pulley will solve that. If you wait too long, you'll have the shaft all scared up.
You can buy a pulley online or at most tractor or farm suppliers.
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Old 12-19-2016, 08:05 PM   #14
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Get a taper lock pulley. That will SOLVE the issue. A straight bore pulley with setscrews will not handle the torsional energy on the front of a diesel crank.
Fully agree this is the best solution
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Old 12-19-2016, 08:13 PM   #15
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Alright,

Well I'm with you fellas
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Old 12-19-2016, 10:50 PM   #16
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Thank you all for the good advice. I like the theory that the pulley is heating up and expanding effectively loosening the set screws. I think I will try the lock tight, and new set screws first at it is cheaper, and somehow this existing set up has worked well for 25 years until I came along and started messing with it. I am confident that I didn't change the fit of it. It was rusty on the outside, and I media blasted it, but I was careful to tape off the machined surfaces so I didn't destroy them. They weren't really rusty and cleaned up quickly with a little solvent and scotch bright. It is probably a little looser than it should be, but there is no where near a beer can thickness of clearance. I would be surprised if I could get it on with a sheet of tin foil in there.
If that doesn't work I will pursue the tapered shaft option.
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Old 12-20-2016, 01:22 AM   #17
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You don't need a tapered shaft. You can buy a pulley with a tapered bushing that fits on a straight shaft. Snug the lock bolts and the tapered bushing grabs the shaft firmly.

Done.

Forget the set screws and locktite etc, those will fail here.
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Old 12-20-2016, 03:28 AM   #18
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I like the tapered pulley best too, I had a notion the one you removed had a taper too, but then I confess I didn't look that hard at your photos. The cost of not buying the locktite will more than pay for the new pulley. I rebuilt an old 944 one winter for shyts and giggles and I bought some of that no-spin stuff for that project but I'll be darned if I can remember what I used it for; but I do remember it worked great!
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Old 12-20-2016, 06:47 AM   #19
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I think if you want to save money and keep using the pulley, why not drill and tap more set screws into the pulley. If you have 3, goto 6, and drill into the crank small dimples a place for the set screws to sit.
And use a loctite on the pulley. But if the old pulley is wobbly loose forget it and go with the new pulley.

Odd the crank nose has no center bolt and washer holding a machined pulley onto the shaft?
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Old 12-20-2016, 08:58 AM   #20
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Use green locktite on shaft and pulley-let it cure(6 hours) then blue locktite on "New" set screws. If you have to remove pulley again you will have to use a puller and torch. Start the engine before putting on the belts and check that pulley is running true.
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