Alternator belt screech mystery

[Poppin]

I recently installed a new 120A alternator on my BMC 1.8. it was overheating and screeching at high revs so I had it replaced by the seller and just installed the replacement and changed the belt while I was at it.

 

Curiously, the belt itself is screeching when I first start the engine, but within say 5 minutes, all sounds normal. The alternator puts out more amps as these minutes go by, so it would seem the noise goes away as more load is applied, but I'm not sure. What else could make the noise disappear with time? Heated up rubber? 

 

I've noticed that spraying the belt with water while running also makes the noise go for a couple of seconds.

 

Once the noise has gone, after a bit of running, no amount of revs makes it return.

 

Been running daily for about a week now and I've just taken a closer look. The belt is wearing fast and the some of the underside grooves are completely gone!  Turned to powder if the mess on my engine pulley is aby indicator. 

 

What do you guys reckon? Wrong belt or something out of alignment? 

[Phil Ambrose]

Provided the belt matches your pulleys it would be most likely an alignment issue, you may need to add or take away spacers to get the new alternator in line. 

The screeching when you first fire up will be belt related ie slipping because of the initial high load on the alternator coupled with alignment issue.

What was the size of your original alternator and did you change pulleys and belts at all.

Phil

[Nickhlx]

I think the belt is inadequate to pass the power / torque needed to the alternator - assuming it is tightened correctly.  The larger alternator will naturally consume more mechanical power, especially when starting as the battery is likely drawing more power from it, but a cold belt will also have less friction and be more prone to slip - you could no doubt prove this by switching on a heavy load ( microwave ?) just after the initial screeching has stopped after start up, and if it starts when the microwave is switched on, that proves the point...   

 

Things to check is that the pulley on the alternator is the same diameter as previously or about a third to half the size of the crank pulley, and with adequate "wrap" of the belt around it at least 1/2 and preferably 3/4 of the way around the alternator pulley would be ideal.  

 

Hope that helps,

 

Nick

[bizzard]

13 minutes ago, Poppin said:

I recently installed a new 120A alternator on my BMC 1.8. it was overheating and screeching at high revs so I had it replaced by the seller and just installed the replacement and changed the belt while I was at it.

 

Curiously, the belt itself is screeching when I first start the engine, but within say 5 minutes, all sounds normal. The alternator puts out more amps as these minutes go by, so it would seem the noise goes away as more load is applied, but I'm not sure. What else could make the noise disappear with time? Heated up rubber? 

 

I've noticed that spraying the belt with water while running also makes the noise go for a couple of seconds.

 

Once the noise has gone, after a bit of running, no amount of revs makes it return.

 

Been running daily for about a week now and I've just taken a closer look. The belt is wearing fast and the some of the underside grooves are completely gone!  Turned to powder if the mess on my engine pulley is aby indicator. 

 

What do you guys reckon? Wrong belt or something out of alignment? 

If its a single V belt a 120a alternator puts far too much load on the belt especially just after start up, not enough grippage by far. The safe upper limit for a single V belt set up isaAbout a 70a  alternator.  You would need either twin matched belts or Poly multi V belts to drive it without  slippage.  The belt is probably slipping much of the time, but as you say grips better when the belt gets hot and softer.  I assume it is also driving a car type water pump, so 3 points, even less belt wrap.

Edited January 3, 2019 by bizzard

[dmr]

Everything Biz says really, though if you have good wrap you might go a little more than 70 amps.

The cold makes the belt less flexible so more likely to slip......listen to a few cars starting up in the winter, though the initial high load is also a big factor.

 

Water spray certainly does stop the squeal but I'm not sure if its stopping the slip or just stopping the sound. There are spray on lubricants that do a similar job, I did some work on this many years ago,   try typing rubber lubricant into Google.....or on second thoughts maybe not ?

 

.............Dave

[bizzard]

I don't think twin V belts or Poly multi V belt pulley sets are available for BMC 1.8's, if they were the car type water pump bearings wouldn't stand the extra strain.

2 minutes ago, dmr said:

Everything Biz says really, though if you have good wrap you might go a little more than 70 amps.

The cold makes the belt less flexible so more likely to slip......listen to a few cars starting up in the winter, though the initial high load is also a big factor.

 

Water spray certainly does stop the squeal but I'm not sure if its stopping the slip or just stopping the sound. There are spray on lubricants that do a similar job, I did some work on this many years ago,   try typing rubber lubricant into Google.....or on second thoughts maybe not ?

 

.............Dave

Water spray doesn't stop the slip, it's just used as a check to pin point and eliminate a squeal.

[Poppin]

28 minutes ago, bizzard said:

If its a single V belt a 120a alternator puts far too much load on the belt especially just after start up, not enough grippage by far. The safe upper limit for a single V belt set up isaAbout a 70a  alternator.  You would need either twin matched belts or Poly multi V belts to drive it without  slippage.  The belt is probably slipping much of the time, but as you say grips better when the belt gets hot and softer.  I assume it is also driving a car type water pump, so 3 points, even less belt wrap.

It is a single v belt. So I would need to change the pulleys to use a poly multi v belt? Because the grooves need to correspond between belt and pulley? 

[bizzard]

11 minutes ago, Poppin said:

It is a single v belt. So I would need to change the pulleys to use a poly multi v belt? Because the grooves need to correspond between belt and pulley? 

As I've just said I'm pretty certain that multi V belt or twin V belt pulley sets are not available for those engines and the car type water pump on the front of the engine wouldn't take the extra strain either. I without any hesitation would fit a 50 or 70a max alternator, the A127 is almost a straight swap.   You are also wearing the inner V's on the metal pulleys caused by the slipping belt friction.

Edited January 4, 2019 by bizzard

[Boater Sam]

A single "A" or "B" width single Vee belt will not drive a 120A alternator and the water pump on a BMC 1.8D.

I have not found anyone making alternative crank and water pump pulleys for these engines.

Even if polyvee or double vee pulleys were available, the water pump and the woodruff key in the crank pulley would probably not withstand the extra loading for long.

I run a 90A alternator on a BMC 1.8D with the standard belt without any problem but the pulley alignment has to be perfect.

[Boater Sam]

8 hours ago, Poppin said:

I recently installed a new 120A alternator on my BMC 1.8. it was overheating and screeching at high revs so I had it replaced by the seller and just installed the replacement and changed the belt while I was at it.

 

Curiously, the belt itself is screeching when I first start the engine, but within say 5 minutes, all sounds normal. The alternator puts out more amps as these minutes go by, so it would seem the noise goes away as more load is applied, but I'm not sure. What else could make the noise disappear with time? Heated up rubber? 

 

I've noticed that spraying the belt with water while running also makes the noise go for a couple of seconds.

 

Once the noise has gone, after a bit of running, no amount of revs makes it return.

 

Been running daily for about a week now and I've just taken a closer look. The belt is wearing fast and the some of the underside grooves are completely gone!  Turned to powder if the mess on my engine pulley is aby indicator. 

 

What do you guys reckon? Wrong belt or something out of alignment? 

On reflection. "--some of the underside grooves are completely gone"   There are no grooves in a normal v belt.

Do you mean that it is a v belt with notches on the inside so that it wraps around smaller pulleys better?

 

If so, and the inside is wearing away I think you have the wrong WIDTH of belt fitted, and it is so narrow that it is bottoming in the pulley not running on the sloping sides.

Or your pulleys could be badly worn.  The proper belt is a B width across the top, 21/32" wide. 

An A is too narrow at 1/2", won't grip the pulley.

 

Have a look at https://www.google.com/search?tbm=isch&q=v+belt+widths&chips=q:v+belt+dimensions,g_1:c+section:2P9e9LCh_gw%3D&usg=AI4_-kTVt-TG-39nCIfJpn8d9fInLwOQbg&sa=X&ved=0ahUKEwj71r-b2NPfAhWPQN4KHX5dBhgQ4lYINCgA&biw=1366&bih=664&dpr=1

 

Sam.

[BEngo]

With any pulley change on a BMC 1.8 you need to be careful not to introduce torsional vibration, which can break the crank.  The 1.5 had a damper pulley to stop TV but I am not sure about the 1.8.  The crank is pretty similar though so I would be very wary of adding extra mass to the pulley set up.

N

[Boater Sam]

1.8D  crank pulley is larger diameter than 1.5D and is 2 piece with a bonded rubber damper between.

Its the keyway and woodruff key groove in the pulley boss that is weak, the pulley cracks through at the keyway to the area on the boss where the oil seal runs, then they leak, until they break completely.

They need to be torqued up regularly so that they don't come loose.

 

The OP needs to look at the bottom of the groove in all the pulleys, if the metal is polished right at the bottom, of even one pulley, the belt is not running on the V as it should.

If its just the alternator pulley, it may need a new one.

Edited January 4, 2019 by Boater Sam

[Alan de Enfield]

Why not just run a dual alternator system ( 2x 70Ah for example) ?

 

[Boater Sam]

There is only one groove in the special crankshaft pulley unfortunately. And bolting another groove ring on loads up the pulley mounting problems even more.

Calcutt got around this problem of 2 alternators on a 1.8D, sort of, by machining a V groove and putting a belt on the flywheel, with an alternator mounted atop the gearbox. 

Bit of a problem with that when it needs a new belt! Taking the gearbox off is not a fast job.

 

I thought of putting a second alternator on the other side of the block and using the same belt but there would be a problem getting a good grip as that is the short run off the water pump, less wrap.

And you still are going to be feeding too much power through one belt.

Edited January 4, 2019 by Boater Sam
added more

[Flyboy]

18 minutes ago, Alan de Enfield said:

Why not just run a dual alternator system ( 2x 70Ah for example) ?

 

Yes that would seem the most sensible option but the problem with the keyway would still be there and even worse.. The extra overhang on the crankshaft may even lead to it eventually breaking.

[BEngo]

There is still the problem of driving the second one. As Sam confirms the 1.8 has a damper pulley you can't just add another pulley for the extra alternator  and working it into the existing alternator and water pump drive will only reduce the belt wrap, giving the same problem.  A Z or A section belt will only do about 70A even with good belt wrap.

N

[David Schweizer]

We had a screeching problem when I installed a higher output alternator on our BMC 1.5 engine. The solution was suggested and carried out by Jonathon Hewitt at UCC  Braunston, when he re-built the engine. He opened out the groove in the engine pulleys, made up a wider groove alternator pulley from two standard ones, and fitted a wider belt. Problem solved.

Edited January 4, 2019 by David Schweizer

[dmr]

I can JUST drive my 100 amp alternator off a single "A" (1/2 inch) belt on my JD3, though can't use the smallest diameter of alternator pulley. I believe the official Beta fix for this alternator was to fit new pulleys and use a single "B" belt.

However from what other more knowledgeable people here say its sounds like the BMC pulley is not really strong enough.

I find that my alternator produces a lot less than its full output once it gets hot.

I think some alternator controllers (Balmar?) can limit the alternator current, dunno how well this works,  so a possible approach would be to fit a 100 amp alternator but limit its output to maybe 70 amps just to avoid that burst of full current for the first few minutes of engine running.

 

................Dave

[bizzard]

I'm surprised that a 120a alternator has a single V type pulley and not fitted with a multi V pulley. Although by hunting around there are single V pulleys that will fit, My Hitachi 70A alternator originally had a multi V pulley and I found a single V pulley that fitted. It is on a Lister ST2 so plenty of belt wrap there being only two pulleys.

[dmr]

Whenever I buy a replacement for my 100 amp alternator it turns up with a multiV pulley and I have to find away to get that off and put my single V pulley on instead.

 

I would love to use a multiV pulley on the engine but its a big 13 inch diameter jobby and there is nothing available off the shelf. If anybody knows a machine shop who would make something without charging an arm and a leg......??????? 

 

...............Dave

[BEngo]

I may be able to turn the current  V groove off and put poly-V grooves on, depending on the pulley. If you are interested please PM exact size diameter and thickness of the pulley as is (It will be close to my max swing) and a piccy  so I can see if there is room enough for the grooves.

It will help to know what sized grooves are on the Alternator pulley.

Beer money and shipping at most.

 

N

[Boater Sam]

The BMC 1.8D pulley is strong and OK providing it is kept well tight.

The slightest bit of relaxation of the crankshaft bolt though and it starts to fret on the keyway till its slack and then the impact of the torsional vibrations rapidly wrecks it.

If they are not badly cracked and haven't lost a bit completely I weld them up and refinish the seal surface because they are quite expensive new.

But loading it up with a big double or poly vee pulley may be just to much. After all it was designed in the '30s, last built in the UK late '70s and designed to run a 27A dynamo!

 

You are going to struggle to run that 120A alternator.

As a trial I would use a B width belt and get the alignment spot on. Don't try over tensioning the belt in a vain attempt to cure the problem, the water pump bearings will not withstand it.

There may ne a small advantage on using the water pump pulley made for the direct cooling marinisation, it has a larger diameter for the belt so you need a longer belt. It gives the pump an easier life by reducing its rotational speed slightly.

[dmr]

31 minutes ago, BEngo said:

I may be able to turn the current  V groove off and put poly-V grooves on, depending on the pulley. If you are interested please PM exact size diameter and thickness of the pulley as is (It will be close to my max swing) and a piccy  so I can see if there is room enough for the grooves.

It will help to know what sized grooves are on the Alternator pulley.

Beer money and shipping at most.

 

N

Thanks, but there is just not enough metal there, it needs a new pulley making from scratch. Its a big pulley, its face registers with and bolts to the existing small front pulley. it then has two V grooves, one for the water pump/engine alternator and a second for the bigger domestic alternator and its this one which would need to be polyV. There is not quite enough width to put a set of polyV grooves on.

 

..............Dave

[Boater Sam]

Could you shrink fit a thin band onto the pulley where the belt runs now with polyvee grooves on the outside?

[BEngo]

29 minutes ago, dmr said:

Thanks, but there is just not enough metal there, it needs a new pulley making from scratch. Its a big pulley, its face registers with and bolts to the existing small front pulley. it then has two V grooves, one for the water pump/engine alternator and a second for the bigger domestic alternator and its this one which would need to be polyV. There is not quite enough width to put a set of polyV grooves on.

 

..............Dave

Do you have a local steel profiler? I made my big multi-V pulley by starting with a 300mm  flat circle of flame cut plate.  Mine was IIRC 18mm but they should be able to cut up to about 50 mm thick  From your description it might be practicable to add a new poly V pulley to the existing one, if you fit some longer bolts and provided there is something to centre it all up.  You would then have a spare V groove?!  Domestic  Alternator alignment might be an issue.

Shrinking or epoxy bonding a ring on is another possibility, but first one has to find a suitable ring.  That always seems to be harder than finding a suitable bit of plate and making (lots of) swarf. Getting profile cut rings always seems more expensive than just buying a circle too.

 

Sam, do you know any good steel ring stockists?  I have a couple of improvements  in mind that would be easier if I started with a steel ring.

N