Help 4.2 belt vibration

[whereisgibson]

The 4.2 has gone through two AC belts recently. After a bit of googling, I've turned my attention to the two belts coming from the crank and I'd like to know if what I'm seeing is normal.

The two belts run nice and smooth on idle, but manually adjusting the throttle gives them a bit of a vibration, around 1.5cm in total, which is how far they can be finger pushed when not moving. Is it normal for them to vibrate on throttle, or should they be rock steady regardless of revs? I'd appreciate if someone could pop the bonnet and have a quick check on a healthy 80

Thanks!!
Martin

 

[Towpack]

As you mention belt(s) I'm guessing that you mean the alternator belts here as the AC has a single belt. 15mm is a little on the slack side, the max being 11mm for a used belt measured on the top (loaded) run with 22lb of pressure applied. Can't say as I've noticed the belts on mine vibrating to any degree. If the belts are wearing out quickly, assuming they're decent quality, there could be some issue with the pulleys. Do they all spin easily with the belts off, excluding crank of course and are they all perfectly aligned and undamaged?

 

[Dave2000]

Also while in there paint a white line (Typex?) across the face of the crankshaft, it has been known for the outer ring to come away from the inner as the bonding between them can fail. After a short time of running recheck the line is still intact and not staggered as the parts start to move independently.

regards

Dave

 

[whereisgibson]

Thanks. Yes the alternator belts. It looks a little like the belt in this video, idle is like at 1:24, and giving some manual throttle is like at 1:47. Maybe half as pronounced.
https://www.youtube.com/watch?v=oFL81TrkUAw&start=84

The crank pulley looks to be nice and smooth, no visible vibration. The AC idle pulley has about 1mm of play and is currently the main suspect in the belts coming off, but I'm checking it's nothing more serious at the crank.

I'm unfamiliar with belts so im not sure if i should expect any vibration in them when operating at all, or some is normal on the slack side, or...

Thanks again!
Martin

 

[Shayne]

I would say that's just the belt riding up the side of the pulley which they all do especially if too tight , but yours doesn't look to tight so just spray some wd40 on it to help the belt wear in comfortably .

WD40 is mostly water so it will evaporate quickly with the heat and doing it once is unlikely to cure it . It's counter intuitive but alls your doing is helping the belt slip so it polishes the side wall of the pulley to stop the bite .

 

[whereisgibson]

Thanks, I shall give that a go on the new AC belt.

It would put my mind at ease if someone would be kind enough to pop out, pop the hood, and just take a look at their alternator belts when pulling on the throttle. The belts have ~40k on them and won't have ever been adjusted since fitting...

I'm half tempted to try adjusting it, but if it ain't broke... just need to see if the belts are shouting "I'M ABOUT TO BREAK" with that vibration, or whether it's business as usual under load.

 

[frank rabbets]

If the car stands for a long time the belts can get pulled in to a not round shape. The same as tyres which if stood for a long time causes the car to vibrate especially with cross ply tyres which not many people will have experienced. Cheap belts is another possibility. Looks like the belt needs tightening though so try that first. I have a machine which I don't use much with belts and it vibrates really badly until they have run for a bit and got supple.

 

[whereisgibson]

Hmmn OK I shall watch them on Friday (500 mile day) and monitor how they change before tightening / interfering. Thanks for the info.

If it does let go, are there any replacement / equivalent alternator belts available on the high street? I've seen the AC belt listed in Halfords....

 

[Shayne]

Roughtrax and Milner are both popular for LC parts and often you get genuine mr T from them . Also if you search the forum for Simon Holton he is our friendly me T who will supply genuine parts

 

[whereisgibson]

Yes I'll definitely have to stock up properly in the New Year, thanks for the contacts!! Naturally I've left this supremely last minute, I'm off on Friday and I suspect not much business is being done 24/25th :/ Hence Halfords etc.