What could cause this?

[pateco]

So, two weekends ago while we were motoring south down the ICW on our way to the Fort Lauderdale Winterfest Boat Parade, The temp alarm went off, and I had to do a quick shutdown and drop anchor in the ICW. When I went below, the pulley on my raw water pump was completely loose on the shaft of the pump.

I quickly replaced the pump with my spare, and we continued to have a successful parade evening. Later in that week I pulled the pulley off, and recognized that it had destroyed itself. I ordered a replacement, and it arrived in a couple of days. Comparing the new with the old, it was obvious that the squared off sections of the pulley had worn away allowing it to spin on the shaft and eat itself.

The detentes on the shaft still looked perfect, so I replaced the pulley with the new one, and tested the pump, it spins correctly, and the impeller looks to be in great shape.

What could have caused this? I know I tightened the pulley on correctly the last time I refurbished this pump. Could the nylock nut be deteriorated enough that it vibrated itself loose?

 

[justsomeguy]

Could the nylock nut be deteriorated enough that it vibrated itself loose?

They can and do wear out.

 

[Will Gilmore]

I'm not a mechanic in any way but out looks like the pulley without flat spots may have had an insert that is no longer present. The hole is too large and too perfect for wear.
- Will (Dragonfly)

 

[Ted]

The exact same thing happen to me on my maiden voyage delivery while I was going through Hells Gate with a barge in tow close behind me. The engine was a Yanmar 2GM. I reassembled the new pulley using Locktite. Never had a problem again for the 16 years thereafter. I would imagine that the nut came loose and wore away the center hole like you experienced. The hole in my pulley was as large as the washer. I always wondered how that much metal could be worn away in the short amount of time it would take to set off the high temperature alarm without me noticing that something bad was going on. What is interesting to note is that it looks like your pulley was spinning on the shaft after the flat sections of the pulley hole were worn away. The bare metal around the washer seem to indicate that this was happening.

 

[jviss]

I must say that it doesn't look, to me, as if the flats were worn away, it looks like it was always a round hole; it loosened up and this caused the slipping. If it had worn from square to round, where did the metal go? And, it would have taken enormous force to do that.

 

[pateco]

I'm not a mechanic in any way but out looks like the pulley without flat spots may have had an insert that is no longer present. The hole is too large and too perfect for wear.
- Will (Dragonfly)

I must say that it doesn't look, to me, as if the flats were worn away, it looks like it was always a round hole; it loosened up and this caused the slipping. If it had worn from square to round, where did the metal go? And, it would have taken enormous force to do that.

There was no insert. The old pulley looked just like the new one when I refurbished the pump last summer.

They can and do wear out.

Ok so I guess a new nylock nut is on order, and some locktite. Thanks guys

The exact same thing happen to me on my maiden voyage delivery while I was going through Hells Gate with a barge in tow close behind me. The engine was a Yanmar 2GM. I reassembled the new pulley using Locktite. Never had a problem again for the 16 years thereafter. I would imagine that the nut came loose and wore away the center hole like you experienced. The hole in my pulley was nearly as large as the washer. I always wondered how that much metal could be worn away in the short amount of time it would take to set off the high temperature alarm without me noticing that something bad was going on. What is interesting to note is that it looks like the pulley was spinning on the shaft after the flat sections of the pulley hole were worn away. The bare metal around the washer seem to indicate that this is probable.

We were only 10 minutes from the dock when this happened. So it sure didn't take long.

ps: While we were anchored, and I was down below working on this, we must have swung at anchor. Once I was done, and restarted the engine, I pulled the anchor and continued on my way down the ICW only to realize about 15 minutes later that I was headed in the wrong direction. My guests laughed at me for a while for that.

 

[Jackdaw]

I know I tightened the pulley on correctly the last time I refurbished this pump. Could the nylock nut be deteriorated enough that it vibrated itself loose?

As long as you cannot put the nylock nut on by hand, it has locking force sufficient to keep it tight. The FAA allows this on aircraft, so probably OK for your boat.

 

[Calif. Ted]

Were there a lot of metal shavings and shrapnel in the area ? The rounded out hole appears of a greater diameter then the shaft on the pump, I don't see how a rubber v belt could be stronger than the hub.

 

[pateco]

Were there a lot of metal shavings and shrapnel in the area ? The rounded out hole appears of a greater diameter then the shaft on the pump, I don't see how a rubber v belt could be stronger than the hub.

Always some rubber dust, but it didn't look any worse than usual. There were some metal shavings on the pump itself.

 

[Gunni]

How could a properly operating water pump strip the flats off a belt pulley? Even if the pulley worked itself loose the pump shaft should still rotate. This could go back to your belt failure mode where an incorrectly aligned belt assembly side loaded the pump shaft bearing and cause it to jam, locking up the pulley. That belt failure showed signs of heat damage and this looks like a culprit.

 

[Michael Davis]

Nylocks were always considered a one-use item in the mill. Anything needing removal got Loctite 242. Maybe we were a little picky, but.....

 

[pateco]

How could a properly operating water pump strip the flats off a belt pulley? Even if the pulley worked itself loose the pump shaft should still rotate. This could go back to your belt failure mode where an incorrectly aligned belt assembly side loaded the pump shaft bearing and cause it to jam, locking up the pulley. That belt failure showed signs of heat damage and this looks like a culprit.

Totally different belt than the failed alternator belt, and this belt did not fail.

ps the cogged belts I replaced the alternator belt with work great.

 

[Ron20324]

I never would use a locknut in a pump situation. Maybe a jam nut first, then a locker, but, no, not just a locknut.

 

[kloudie1]

The washer beneath the locknut is supposed to have the same oblong cut-out as the pulley hub Subbing a round hole washer can cause the washer to hang on the shaft and not let the nut fully squeeze the hub.. also, If the oblong washer is not lined up with the shaft correctly, the washer will stop on the shaft shoulder and not allow the nut to fully squeeze the hub.. The oblong hole washer is Yanmar part number 124070-42420, about $2.00..

 

[pateco]

The washer beneath the locknut is supposed to have the same oblong cut-out as the pulley hub Subbing a round hole washer can cause the washer to hang on the shaft and not let the nut fully squeeze the hub.. also, If the oblong washer is not lined up with the shaft correctly, the washer will stop on the shaft shoulder and not allow the nut to fully squeeze the hub.. The oblong hole washer is Yanmar part number 124070-42420, about $2.00..

Mine definitely has a round washer,

but i think the detente on the shaft is only long enough to protrude into the pulley itself. I do not believe that the washer goes deep enough to reach the detente. However since it is round, maybe it does. I will check

 

[kloudie1]

Round would be ok if it is thick enough to keep the locknut from "bottoming" on the shaft shoulder.. and the hole is fully big enough to go over the shoulder of the shaft.

 

[Newport Bob]

I agree with other posters. Looking at your pictures;
- the round hole is too perfect to be caused by wear
- the round hole is larger than the diameter of the round on the new pulley
- the wear on the surface of the old pulley suggests wobble under the washer when the tightening from the nut relaxed
- no way the metal on the pulley would go without the pump freezing = high temp alarm, belt failure

 

[Ron20324]

Maybe it is my glasses, but are both pulleys the same diameter?

 

[pateco]

Maybe it is my glasses, but are both pulleys the same diameter?

Both pulleys were identical. I thought I had a good picture of it from the last time I rebuilt it, but The ones I have don't show the front of the pulley.

 

[Jake N Eggs]

I would say that the clamping force on the pulley was insufficient and the pulley was working on the flats of the shaft. In time the pulley material wore away and the result is the round hole. It could be that the nut was actually tight but it is hard to tell from the pictures. The flats on the new pulley fit over the flats in the shaft, which is obvious, but if the material thickness of the pulley is even or less than the depth of the flats the round washer could be pressing on the shoulder of the shaft. This would result in inadequate clamping force on the pulley. Again, it is hard to tell from the pictures if the washer inner diameter is sized for the threaded part of the shaft or the bigger diameter. Normally in this type of connection there would be a washer with the same flats as the pulley. This way all of the clamping force of the nut is transferred to the pulley material. To use this type of connection there has to be some of the flats of the shaft protruding through the pulley to index the washer.