Technical Alternator Belt - how tight is too tight?

[Gman88667733]

Changed the belt a good few weeks ago now and it has chirped on startup since. I have re-tightened twice but it is still obviously not quite tight enough.

When I drive through large puddles now, the belt squeals for a few seconds.

I know I can get it tighter, but I don't want to over tighten it and ruin it.

Do I need to lever the alternator back with quite some force and then tighten the bolts to get the correct tension? Currently I've been pushing the alternator back by hand/with a light leverage of a spanner and tightening.

Thanks

 

[Gman88667733]

I have been out and done it again, I put a bit more pressure on the spanner used to lever the alternator back to tighten the belt before tightening the bolts.

No squeaks on the first few start ups, but driving through water will show for sure.

The belt felt about as tight as I'd dare do it, with about 5mm of movement maybe each way? Hard to say for sure.

 

[portland_bill]

Be careful when levering any alternator, the alternator body can easily be twisted, which will destroy it when rotating parts foul inside. Only ever lever it on the part with the adjuster attachment.

Pushing by hand should be enough, although access can be difficult.

Why did you change the belt? Normal age-related or servicing timescale, or because there was a problem? If the old belt was slipping, the pulleys may have become polished, reducing the belt grip. A tedious task, but the pulleys may need scuffing a bit with fine abrasive, very difficulot with the tiny multi-grooves. A good scrub with a stiff brush and carburettor or brake cleaner might work.

Water on the belt will act as a lubricant and cause slip. Trying to tighten it to prevent this will likely destroy the alternator bearings. Better to keep out of deep puddles, or at least moderate your speed to reduce the splash. Don't assume your delicate underbonnet electronics are completely waterproof.

A chirp on startup is common with a weak battery, if it has given almost all it has to start teh car, its recharge demand is high, more so if you steer immediately, as the electric power steering demands a lot of current.

 

[Gman88667733]

The old belt was quiet, but well worn and overdue

I did not lever hard at all, just slightly, enough to move the alternator back a touch more than I could by hand
The belt was definitely the culprit for the squeak on startup I believe.

 

[Gman88667733]

As a representation, this is how I levered the alternator back.
Obviously I did not use a ruler. But I levered it just so that the alternator moved forward enough for the belt to be a touch tighter.
I reckon there is 10-12mm of movement in the belt... Hard to say for certain though, could be a touch less

 

[DaveMcT]

If it is still noisy with the belt slackened, the noise will be elsewhere. Water pump maybe, but check the alternator bearings are not getting rough.

Obviously ignore the charge warning light until you have belt tensioned again.

 

[Gman88667733]

The noise has gone now I've properly tightened the belt. Water pump was replaced a month ago, so that's fine. Sounds lovely now

 

[DaveMcT]

The noise has gone now I've properly tightened the belt. Water pump was replaced a month ago, so that's fine. Sounds lovely now

Fabulous.

 

[Gman88667733]

Now just got to figure out why my mpg is slightly below what it should be (first quarter of a tank still drops within 50ish miles)
And fuel smell at idle!