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Technical Alternator/ drive belt snapped

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Technical Alternator/ drive belt snapped

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damaguz

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Basically, the alternator belt has been making screeching noise for a while but it snapped off my van today. Is it easy to replace by a novice or It needs a mechanic with the right tools etc?
If I am to replace it, what tools are needed and steps to follow pls.


Thanks
 
Easy to replace, depending on access.
Without aircon, the belt is usually tensioned by moving the alternator on its mountings. Getting the tension right is a bit down to feel, comes with experience. There are guidelines like longest run of belt should deflect by no more than about 5mm under thumb pressure.
With aircon, belt is usually tensioned with a spring-loaded tensioner. Needs a spanner on the centre nut to pull it away to release the tension, and carefully release onto the new belt. If you let go with your fingers in there it will hurt - a lot.

But! Why did it break?
Squealing is usually a sign of undertensioned. To cause a belt to break would normally take a long time, with the noise becoming constant, probably unbearable.
Breakage could just be an old tired well-worn belt.
Or, something it is driving is seizing. What else does it drive apart from the alternator? Some do just that, others can drive aircon, power steering, water pump, or all of these. Any one of those that is trying to seize will cause the belt to squeal. When not running, things may be quite free, so could be difficult to determine. Many alternators these days have a freewheeling pulley, to help reduce the amount of engine vibration that gets to the alternator. These can seize. There have been a few instances of cracked alternator casings due to this, mostly on Multipla, but can affect any vehicle with the freewheeling pulley. If the pulley is seized, and the alternator is OK, new pulleys can be found on Ebay, but take accurate measurements of size and offset.
 
portland_bill said:
Easy to replace, depending on access.
Without aircon, the belt is usually tensioned by moving the alternator on its mountings. Getting the tension right is a bit down to feel, comes with experience. There are guidelines like longest run of belt should deflect by no more than about 5mm under thumb pressure.
With aircon, belt is usually tensioned with a spring-loaded tensioner. Needs a spanner on the centre nut to pull it away to release the tension, and carefully release onto the new belt. If you let go with your fingers in there it will hurt - a lot.

But! Why did it break?
Squealing is usually a sign of undertensioned. To cause a belt to break would normally take a long time, with the noise becoming constant, probably unbearable.
Breakage could just be an old tired well-worn belt.
Or, something it is driving is seizing. What else does it drive apart from the alternator? Some do just that, others can drive aircon, power steering, water pump, or all of these. Any one of those that is trying to seize will cause the belt to squeal. When not running, things may be quite free, so could be difficult to determine. Many alternators these days have a freewheeling pulley, to help reduce the amount of engine vibration that gets to the alternator. These can seize. There have been a few instances of cracked alternator casings due to this, mostly on Multipla, but can affect any vehicle with the freewheeling pulley. If the pulley is seized, and the alternator is OK, new pulleys can be found on Ebay, but take accurate measurements of size and offset.
Click to expand...
yeahthat.gif


Only issue you may have if the belt has come off completly and you have never done one before is working out the exact routing for the replacement.
Certainly worth having a go yourself.

Robert G8RPI.
 
Thanks for the reply. It's got no air con and its a fiat ducato 2.8jtd 2004 .
 
Access isn't too good!
Best I found was to jack up driver's side up. Remove wheel. Support vehicle on axle stand. You can just about see the threaded adjuster rod which is attached to the alternator with a 13mm nylock nut. If you feed your arm over the sub frame and drive shaft you can just about get a ratchet spanner on the nylock nut to adjust a few degrees at a time. You will need to slacken alternator retaining nuts which allow it to rotate on its pivot first. You may need to get a lever on the alternator casing to shift the alternator far enough to get the new belt on. Check the alternator pulley rotates freely without any noise or roughness and it runs true.
As far as I recall the belt only runs around the crankshaft and alternator pulleys with a ribbed belt which needs locating correctly in the poly groove. The belt needs to be pretty tight to drive under load but should have about 8mm deflection on the longest run to not overload the alternator bearings.
Nice of Fiat to think about the logistics of adjusting the belt!
 
Sorry should have mentioned that you have to remove the driver side lower engine plastic cover to get to the crankshaft polyvee pulley. Might make life a bit easier on re fitting the new belt.
 
Thanks all for the replies. I will certainly have a go on my day off work but one more question is how do i get the 8mm deflection etc right ?

The person I bought the van from told me the belt had to be tightened hence the squealing noise but I left it too late till it snapped.
 
damaguz said:
Thanks all for the replies. I will certainly have a go on my day off work but one more question is how do i get the 8mm deflection etc right ?

The person I bought the van from told me the belt had to be tightened hence the squealing noise but I left it too late till it snapped.
Click to expand...

Find the longest section of belt, and push with a finger or thumb. Guess or measure the deflection. Tighten or slacken the alternator position to achieve the correct tension. Then tighten the alternator mountings and recheck.

The squealing was a slack belt slipping when asked to work. The demand from the alternator was greater than the tension on the belt could transmit. The belt will first polish its gripping surfaces, causing more slippage, then gently tear itself apart.
It will also polish the running surfaces of the pulleys. If too polished, they'll never grip properly again. Cleaning them up with very fine abrasive paper is a long and tedious job on a multi-vee pulley. New pulleys may be expensive.
 
Its worth taking out the battery so you can see what you are doing and using a small ratchet spanner for tensioning - theres very little room for a socket and ratchet in there and you can only get a fraction of a turn on a regular spanner.

You can do the tension with a guitar tuner app on a smart phone and the belt mass constants from the gates sonic tensioner manual.

Formula:
T = 4 x M x W x S2 x f2 x 10-9
Where:
T = Belt span tension (Newtons)
M = Belt mass constant (gf/m/mm)
W = Belt width (mm) or number of belt strands
S = Length of the span to be measured (mm)
f = Natural frequency of the belt (Hz)

PK belt mass constant is 18g/m

Gates say 187lbs for a new 6pk belt which reduces to 90-125 after 5 minutes of running, When you recheck tension its supposed to be on a cold belt.
 
Thanks all. Will try it out . Removing he battery on a ducato is a pain though (the positive terminal) .

One more question. Can I move the van (with no fan belt on) so that I can have enough space to do the job.
 
portland_bill said:
Find the longest section of belt, and push with a finger or thumb. Guess or measure the deflection. Tighten or slacken the alternator position to achieve the correct tension. Then tighten the alternator mountings and recheck.

The squealing was a slack belt slipping when asked to work. The demand from the alternator was greater than the tension on the belt could transmit. The belt will first polish its gripping surfaces, causing more slippage, then gently tear itself apart.
It will also polish the running surfaces of the pulleys. If too polished, they'll never grip properly again. Cleaning them up with very fine abrasive paper is a long and tedious job on a multi-vee pulley. New pulleys may be expensive.
Click to expand...

Is it safe to move the van without the drive belt around the drive just to have enough space to work with?
 
Not many of us know the van in detail.
One post said he thought the belt only drove the alternator, but this has not been confirmed.

If it only drives the alternator, you can run the engine for some time before the battery runs out of power.
If it drives the water pump, you need to sort its position quite quickly, as there will be no coolant circulation, which may allow hotspots within the engine. I wouldn't want to risk more than a minute, but that may be over-cautious.
If it drives the power steering pump, steering will be very hard work, so care is needed not to run out of space.
There is also a vacuum pump to provide the brakes with their servo effect. These are usually driven from the camshaft, but I have seen one driven from an auxiliary belt, but cannot remember what vehicle. If your belt drives this pump, you will have no brakes. Or at least, you will have brakes, but they will require a huge effort to stop, even from very slow speeds.
Hopefully you can make a decision based on this.
 
Hello. I had a mechanic look at the van and he said the alternator pulley doesn't roll and alternator needs changing. Is £80 a fair labour charge to replace the alternator? Thanks
 
Its in a very awkward spot and there's a good chance the bolts are all seized if the alternator pulley is so could take 80 worth of time to change
 
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