Shrieking drive belt on JP3

[starman]

The 90amp alternator on the JP is driven direct from the flywheel rim by a big micro-vee belt. When the engine starts it shrieks like a banshee for a couple of minutes, then whistles for a while before settling down. Aside from this, the system charges well.

Any ideas why? Is the belt too tight or too loose? There's a small amount of play in it under thumb pressure but not much. Someone suggested a freewheeling drive pulley on the alternator would help. Could it?

[RLWP]

Belt is too loose. Now, that doesn't mean you can get it tight enough with your setup

 

Richard

[bizzard]

If its been let to do this for a long time the alternators pulley V groove has most likely worn too wide and the belt is loosing its grip by bottoming out on the pulley V's root.

[Timleech]

Two methods HERE (page 5) for setting tension on polyvee belts.

 

Tim

[Roadsteam]

Micro vee belt? do you mean poly vee as per the link or a small vee belt?

Assuming the belt and pullies are not worn i would say that the problem is lack of belt tension possibly combined with insufficient wrap on the alternator pulley.

[flatplane8]

We have the same setup on our JP3, with a 90a alt driven off the flywheel rim. We have a single 'v' belt and a 3 or 4 inch pulley on the alternator, I can't recall which but it was the biggest we could get at the time. Seems to work ok, so perhaps a new belt or a bit more tension?

[Paul C]

We have the same setup on our JP3, with a 90a alt driven off the flywheel rim. We have a single 'v' belt and a 3 or 4 inch pulley on the alternator, I can't recall which but it was the biggest we could get at the time. Seems to work ok, so perhaps a new belt or a bit more tension?

 

Surely you'd want the smallest possible pulley on an alternator, to drive it more quickly for a given engine rpm. The upper (well, lower - smallest) limit being the max rpm of the alternator which should not be exceeded at max engine rpm.

[RLWP]

Not necessarily. You may not get enough belt in contact with the pulley to drive it,

 

Richard

[by'eck]

The 90amp alternator on the JP is driven direct from the flywheel rim by a big micro-vee belt. When the engine starts it shrieks like a banshee for a couple of minutes, then whistles for a while before settling down. Aside from this, the system charges well.

Any ideas why? Is the belt too tight or too loose? There's a small amount of play in it under thumb pressure but not much. Someone suggested a freewheeling drive pulley on the alternator would help. Could it?

 

Some alternators do whine quite loudly when working hard at lowish revs - its not drive belt slip, just something you have to live with - greatly reduced by increasing engine revs though.

 

Its caused by the reversing magnetic fields in the stator core laminations, much like the hum of a transformer but at a higher frequency.

Edited July 12, 2013 by by'eck

[trackman]

My money is on a slipping belt. Our Travelpower belt is a multi vee one and does this when not tight enough.

I have to use a lot of leverage to get it sufficiently tight BTW.

[by'eck]

Hi starman, does your shrieking alternator sound anything like this:

 

http://k002.kiwi6.com/hotlink/05h4747flp/jp2.mp3

 

This is the sound (above the engine clatter) of two well loaded alternators with engine at fast idle. Definitely not a slipping belt.

 

I hear the same sound from many vintage engine installations probably because of the deliberate high gearing required and the fact that the engine room is usually open.

[Biggles]

Get dome belt jam or dresser

 

Linky

 

Works a treat and you don't have to put megga tension on the belt so saving the belt and bearings.

 

Blog linky about it.

[starman]

Hi starman, does your shrieking alternator sound anything like this:

 

http://k002.kiwi6.com/hotlink/05h4747flp/jp2.mp3

 

This is the sound (above the engine clatter) of two well loaded alternators with engine at fast idle. Definitely not a slipping belt.

 

I hear the same sound from many vintage engine installations probably because of the deliberate high gearing required and the fact that the engine room is usually open.

Hi, thanks for the audio clip. Yes, mine does whistle like this but also shrieks! After the engine's started it runs quietly for a minute or so then it shrieks loudly and de-stabilises the engine idling for a while before sorting itself out. Am I right in guessing this is the extra load when the Smartbank gizmo asks it to charge the leisure batteries? If so, it probably is a slightly slipping belt

[by'eck]

Hi, thanks for the audio clip. Yes, mine does whistle like this but also shrieks! After the engine's started it runs quietly for a minute or so then it shrieks loudly and de-stabilises the engine idling for a while before sorting itself out. Am I right in guessing this is the extra load when the Smartbank gizmo asks it to charge the leisure batteries? If so, it probably is a slightly slipping belt

 

Yes I guess this may be the case. Difficult to describe a sound in words but the whistle you heard on mine does get deeper and maybe louder at lower (idle) revs (banshee wail). Any extra load on the alternator(s) will definitely increase this and leave you vulnerable to belt slip if its not correctly tensioned or of inadequate size.

 

For the record I have a single "A" grove belt driving my 90 amp alternator, which I admit is marginal although it works without slip, and twin similar belts driving the 160 amp one. Both from a custom 15" pulley mounted in front of the flywheel.

 

When I operate my bow thruster, the load on the alternator is immediately apparent by the change in alternator sound unless they are working flat out anyway as at start of a days cruising.

[Timleech]

 

Yes I guess this may be the case. Difficult to describe a sound in words but the whistle you heard on mine does get deeper and maybe louder at lower (idle) revs (banshee wail). Any extra load on the alternator(s) will definitely increase this and leave you vulnerable to belt slip if its not correctly tensioned or of inadequate size.

 

For the record I have a single "A" grove belt driving my 90 amp alternator, which I admit is marginal although it works without slip, and twin similar belts driving the 160 amp one. Both from a custom 15" pulley mounted in front of the flywheel.

 

When I operate my bow thruster, the load on the alternator is immediately apparent by the change in alternator sound unless they are working flat out anyway as at start of a days cruising.

 

Is this actually alternator (electro-mechanical) noise or belt noise (not slip)? I don't know the answer, could be both.

I do know my CAV AC7 (60A @ 24V) makes no sound audible above the engine even at full output, & it is driven from the timing chain.

It is, though, a slightly different beast from the modern units, runs at a lower speed

 

Has the OP adjusted his belt tension 'by the book' yet, and if so has the problem gone away or not?

 

Tim

[bizzard]

If it is belt noise by splashing a little water on the belt whilst the engine is running the noise should either disappear or the sound alter.

If so the noise will return or the same noise will return as the water dries.

Edited July 19, 2013 by bizzard

[plainsman]

The 90amp alternator on the JP is driven direct from the flywheel rim by a big micro-vee belt. When the engine starts it shrieks like a banshee for a couple of minutes, then whistles for a while before settling down. Aside from this, the system charges well.

Any ideas why? Is the belt too tight or too loose? There's a small amount of play in it under thumb pressure but not much. Someone suggested a freewheeling drive pulley on the alternator would help. Could it?

 

I had similar experience and eventually found the problem to be a drying out flywheel bearing. I found it hard to believe as I thought the drying bearing would have screeched all the time but not so. Try running the engine without the belt to eliminate any probs with the bearing.

[starman]

Has the OP adjusted his belt tension 'by the book' yet, and if so has the problem gone away or not?

 

Tim

Not yet Tim, I wanted to get a spare belt before playing with tension on a 'just in case' basis so will adjust the belt when I'm back off the river. The shriek is pretty raucous and usually only lasts a minute or two which does suggest belt slip when it first comes under load. I'll report back when I've had a tighten-up.

[bizzard]

Not yet Tim, I wanted to get a spare belt before playing with tension on a 'just in case' basis so will adjust the belt when I'm back off the river. The shriek is pretty raucous and usually only lasts a minute or two which does suggest belt slip when it first comes under load. I'll report back when I've had a tighten-up.

When its shrieking under load splash water on it and see if it stops it, as I've already mentioned. Not a good idea to tighten it more if its something else shrieking.

Edited July 19, 2013 by bizzard