belt tensioner question

**toby** · 6th June 2006, 11:29 AM

G'day,

I drive a 96'disco 300tdi, i'm new to this engine (had a V8 rangie), yesterday i changed my coolant and i noticed that with the engine running i could see one of the pulley's (assumed it's the belt tensioner) was moving up and down. It's the one next to the water pump near the top of the engine, the whole bracket seems to move up and down however when the eninge is off i can feel much loose. Is that what it's supposed to do? i read somewhere that they have a bearing inside? could that be the problem.
Hope this makes sense thanks in advance
Toby.

**DiscoDave** · 6th June 2006, 05:11 PM

however when the eninge is off i can feel much loose

Could you explain that a little more?

The belt tensioner does vibrate a little when idling (well mine does) and it does contain bearings which need to be replaced if they are not running freely.

**toby** · 6th June 2006, 08:24 PM

Not sure how to explain it other than the bracket the pulley is held onto (the one near the water pump and up high) moves up and down when the car is idleing, not a lot maybe 2cm or so. Its probably ment to do it (i hope). But just wanted to check, sorry but i cant think of a better way to explain it.

Thanks for the help anyway.

Toby.

**one_iota** · 6th June 2006, 09:27 PM

That doesn't seem normal to me....particularly 2 cm

The main belt tensioner is just that..once it has applied the tension on the belt then it should stay put.

The bearing is in the tensioner pully and wouldn't move that much and usually you get a squealing noise if it is "shot".

The main belt is connected to the crank pully (that drives) the injector pump, the water pump, the alternator, and the power steering pump in that order clockwise. One of those would need to be running strangely for that to happen...have a look at how all of them run.

Now I'm guessing:

Maybe the spring in the tensioner is shot or it hasn't been properly relocated after removal and replacement.

Also the earlier 300Tdi have a different length belt to the later models so maybe not enough tension on the belt.

**incisor** · 6th June 2006, 09:41 PM

2cm is wayyyyy to much movement as mr one says above.

2mm would be my max limit

if it really is 2cm then you have a serious problem of some sort....

**DEFENDERZOOK** · 6th June 2006, 09:48 PM

they do move a bit.....maybe one cm total movement.....
they dont lock into place....the spring holds the tension on the belt 24/7....

try and find another car with the same engine and see if you can move the
tensioner up and down as much as you can yours.....

if yours moves more freely.....the spring may have lost tension......
if you want to put your mind at ease....replace it and the belt......this way you will
know when it was changed......and keep the old parts for spares for your trips.......

**toby** · 7th June 2006, 07:44 AM

It's moving 2cm if not more!! so i think i'll replace it today. I'm heading to the cape in August so i don't want that to let go! Thanks very much for the help.

Toby.

**4bee** · 7th June 2006, 08:21 AM

Have you checked the belt surface in contact with the tensioner for irregularities/rubbish/ belt on the blink?

As that is the only "floating" component, any irregularity will show up here as movement. It would bounce over the other pulleys, but because the tensioner can move it will show up there.
Hope this helps.

british4wd · 7th June 2006, 12:15 PM

The spring inside the tensioner has weakened

**rick130** · 7th June 2006, 02:50 PM

put a ring spanner on the pulley retaining bolt and try to turn it CCW looking at the crankshaft. There should be considerable (spring) resistance, otherwise, as british4wd said, the tensioner spring is cactus.

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