Drive pulley loose on alternator stopped enginerss

[superheat6k]

My Stbd engine through its drive belt today after a somewhat bumpy crossing from the Needles to Poole.

About an hour before we entered the channel I noticed a jingling sound from the engine bay but could see anything wrong, so plodded on in a nasty southerly swell (crossing the Bridge at the Needles was bloody awful !). Then as we came up the Poole approach channel I opened the engines up to clean off the turbos after 2 hours at moderate revs, when in short order the generator warning light came on then the stbd engine overheated, so I knew straight away the belt had gone.

Thanks to Poole Quay Yacht Haven staff who sent out a posse to help me alongside a simple to get to berth at the entrance.

Then found most of the coolant in the bilge with the belt detached but not snapped. Instead the alternator drive pulley was loose, but the nut was bar taut on the shaft. Managed to get it undone, checked the shaft and re-did it up with plenty of loctite 242, but found it odd that the nut was so tight on the shaft even though it was about two turns loose.

Replaced the belt with a new spare (both engines).

Cummins 6BT5.9M engines ...

1 I noticed about 1-2mm run out on the re-mounted driver pulley on the alternator. Views as to whether this is excessive please.

2 The new ribbed belts were extremely tight to fit with the idler tensioning pulley at max deflection to get the belt on, and only fell back about 15mm from its loosest position as it took the tension up. So as long as the idler moves back a distance is the tension OK.

3 The overheating took the temperature gauge up to 105oC, bit all seems fine after the belt was replaced and the coolant replaced (the qty that leaked came from the pressure cap). Anything else I need to pay attention to on a Cummins 6BT after such an overheat. The engine was shut down within 1 minute of the alternator alarm sounding,

 

[RichardS]

How are you measuring the run-out?

If by ribbed you mean polyvee then they can be tight to get on when new but if you have any slack in the idler wheel then that's fine.

Richard

 

[nigelmercier]

... odd that the nut was so tight on the shaft ...

You haven't lost a wave washer have you?

 

[superheat6k]

Re: Drive pulley loose on alternator stopped engine

How are you measuring the run-out?

If by ribbed you mean polyvee then they can be tight to get on when new but if you have any slack in the idler wheel then that's fine.

Richard

I estimated the run out visually, probably less than 1mm. There is free movement in the heavily sprung idler, but it was damn tight to get the new belts on.

There was no washer under the nut. The driver pulley had a simple taper bush locking it to the shaft. This all seemed just fine. There is barely any spare thread to have a washer present.

I had to tighten it with a 22mm socket gripped tight in my mole grips, with an 8mm Allen key inserted through the socket into the alternator shaft.

My greater concern is that I haven't caused any damage by a brief overheat on the fresh water side.

 

[lw395]

Re: Drive pulley loose on alternator stopped engine

Most car/truck engines, 105 degC would just put some coolant in the expansion bottle temporarily.
Unless there was so much coolant lost that the head was dry in places I doubt you will have any consequences.

 

[RichardS]

Re: Drive pulley loose on alternator stopped engine

I estimated the run out visually, probably less than 1mm. There is free movement in the heavily sprung idler, but it was damn tight to get the new belts on.

There was no washer under the nut. The driver pulley had a simple taper bush locking it to the shaft. This all seemed just fine. There is barely any spare thread to have a washer present.

I had to tighten it with a 22mm socket gripped tight in my mole grips, with an 8mm Allen key inserted through the socket into the alternator shaft.

My greater concern is that I haven't caused any damage by a brief overheat on the fresh water side.

It's a bit worrying that the nut came loose unless someone had been working on it recently, but it looks to me as if the run-out and new belts are OK.

As LW395 says, it's unlikely that any damage has been done. However, the practicality is that it would not be worth removing the cylinder head just to check. The only sensible thing you can do is to keep a very close eye on the levels of coolant and oil for the next few outings, and remove the oil filler cap after a few hours motoring to check for any oil / water emulsion. If the coolant level stays put and the oil stays water-free and any exhaust smoke looks the same as it did before the overheat then I would forget about it.

Richard

 

[superheat6k]

Re: Drive pulley loose on alternator stopped engine

Had to make a slow cruise back home today cutting short our week away whilst I sort the alternator drive out.

We left Poole Quay YH to allow a huge Catamaran called Moose out and because the tide was still foul back to the Solent we went to a buoy for lunch off Sandbanks.

So I took the opportunity to re-check the alternator pulley was still tight, which it wasn't, so spend a joyous hour working out why it was loose again and what I could do about it. Fortunately because the cruise through the harbour was at slow speed the belt hadn't jumped off again, but clearly I couldn't go any distance on it in that state.

Close inspection showed the pulley has a simple taper lock arrangement where the retaining nut loads a conical split bush between the pulley bore and the shaft. The problem was that the bush was entering too far into the pulley bore so the retaining nut was bottoming out on the shoulder of the pulley instead of properly tightening the bush into place between the pulley cone and the parallel shaft. I suspect the alternator shaft has become excessively worn, but why it came loose in the first place I have not yet fathomed, as the nut was not loose.

I tried to pack the cone with some silver foil, but that was useless and the thing was loose again within 20 minutes.

So a gentle plod on the port engine across into the solent with the stbd engine available in an emergency and for short running to assist with mooring up.

I have ordered from Cummins a new pulley and retainer which appears from the parts sketch to be a different design.

Tomorrow both alternators are coming off so I can properly get this problem resolved. However, I might order a shorter belt that would fit without the alternator included on the belt run, as at least this would allow me to use the engine should I ever have a similar problem with an alternator in the future, after all one alternator provides more than enough power if I limit the services being used.

 

[RichardS]

Re: Drive pulley loose on alternator stopped engine

Had to make a slow cruise back home today cutting short our week away whilst I sort the alternator drive out.

We left Poole Quay YH to allow a huge Catamaran called Moose out and because the tide was still foul back to the Solent we went to a buoy for lunch off Sandbanks.

So I took the opportunity to re-check the alternator pulley was still tight, which it wasn't, so spend a joyous hour working out why it was loose again and what I could do about it. Fortunately because the cruise through the harbour was at slow speed the belt hadn't jumped off again, but clearly I couldn't go any distance on it in that state.

Close inspection showed the pulley has a simple taper lock arrangement where the retaining nut loads a conical split bush between the pulley bore and the shaft. The problem was that the bush was entering too far into the pulley bore so the retaining nut was bottoming out on the shoulder of the pulley instead of properly tightening the bush into place between the pulley cone and the parallel shaft. I suspect the alternator shaft has become excessively worn, but why it came loose in the first place I have not yet fathomed, as the nut was not loose.

I tried to pack the cone with some silver foil, but that was useless and the thing was loose again within 20 minutes.

So a gentle plod on the port engine across into the solent with the stbd engine available in an emergency and for short running to assist with mooring up.

I have ordered from Cummins a new pulley and retainer which appears from the parts sketch to be a different design.

Tomorrow both alternators are coming off so I can properly get this problem resolved. However, I might order a shorter belt that would fit without the alternator included on the belt run, as at least this would allow me to use the engine should I ever have a similar problem with an alternator in the future, after all one alternator provides more than enough power if I limit the services being used.

Is there a spacer missing which ensures that the pressure from the nut is exerted on the proper place? It sounds unlikely that it could go awol, but if the alignment is also slightly out then it might be something like a missing spacer. Perhaps it's broken off?

I can't see how the cone faces can have worn against each other without you hearing a terrible screeching noise for quite a long period.

Richard

 

[superheat6k]

Re: Drive pulley loose on alternator stopped engine

Is there a spacer missing which ensures that the pressure from the nut is exerted on the proper place? It sounds unlikely that it could go awol, but if the alignment is also slightly out then it might be something like a missing spacer. Perhaps it's broken off?

I can't see how the cone faces can have worn against each other without you hearing a terrible screeching noise for quite a long period.

Richard

The spacer / washer shown in the parts list was absent when I first dismantled the already loose pulley. I can't see that it would have disintegrated and fell out, besides there was no debris beneath or small pieces left when the nut was first removed.

 

[nigelmercier]

Re: Drive pulley loose on alternator stopped engine

As I mentioned in #3, there is often a wave washer. These can fracture, and would travel some distance.

 

[RichardS]

Re: Drive pulley loose on alternator stopped engine

The spacer / washer shown in the parts list was absent when I first dismantled the already loose pulley. I can't see that it would have disintegrated and fell out, besides there was no debris beneath or small pieces left when the nut was first removed.

It's quite possible that the taper fit was hammered on but no spacer fitted and the taper has held for a long time before finally breaking loose. If there is a spacer in the parts list and it is of a diameter (ID and OD) and thickness which will ensure that the pressure from the nut is applied to the correct part of the taper then I am 100% certain that you have found the source of the problem.

Richard

 

[superheat6k]

Re: Drive pulley loose on alternator stopped engine

I removed both alternators today. The port is fine - there is no way the pulley would even start to loosen, but is is a later model than the stbd, so it is going back on 'as found'.

On the stbd the problem was that the loose taper cone has worn away the entirety of the thread beneath the conical retainer split bush right down to the thread roots, which are barely visible, so the bush simply had nothing to grip to when its split side closed.

I have ordered a new alternator from a supplier in Plymouth that should arrive tomorrow. Cummins have sent me a new pulley and retainer cone bush, but have superseded the pulley to a parallel shaft hole, so it no longer matches the non-superseded retainer also supplied. Hats off to their service, shame the parts do not match. Fortunately I can now see the original pulley is just fine, but will need the new retainer.

However, I am not sure having the retainer clamping onto the crests of the shaft thread is an ideal method of affixing the pulley, so I will see if the superseded pulley is a better idea when the new alternator arrives tomorrow.

Now the deep joy of putting the two alternators back on - more chest bruises from leaning in unnatural positions for an hour at a time. Our weeks cruise may resume on Friday after all, besides the weather today was bloody awful.