Why are cam belt tensioners always replaced when the belt is?

[joeb]

Hey guys,

I'm intending on changing the cam belt in my mk5 gti and I'm wondering if it's essential to replace the tensioners too?
Only asking as it's considerably cheaper to get just the belt by itself and why are new tensioners needed anyway?

Cheers!

[shail]

I didn't think the tensioner was too expensive to buy. 

Changing the tensioner is a bit like changing the water pump during a cambelt change.  A large cost for the job is the labour, so while you have everything apart it makes sense to change them.

It makes more sense with the original cambelt imlntervals, but vw now recommended such short intervals I can see people doing tensioners every other cambelt change.

[pudding]

Because roller bearings wear out, and so do water pumps, hence why doing the whole lot at once.   Technically you CAN get away with doing just the belt, and even then that only needs doing because of rubber ageing/heat cycling....but why risk it?  Would you rather pay £250 for a complete belt/pump/tensioners replacement every 4/5 years, or £4000 for a new engine?