Timing Belt Question(94 xantia 1.9TD)

steviewonder7 · Unread post by **steviewonder7** » 17 Jul 2007, 15:35

Hi folks,
I have a slightly puzzling question,for me it is anyway.
When the tensioner for the timing belt is renewed/refitted after a timing belt change why is the pivot nut and the tensioner
bolt tightened?Why are they not ever so slightly loose so as the tensioner actually applies constant pressure to the
timing belt?This I would have thought would negate the possibilty of the timing belt possibly jumping
the pulley teeth or even worse.
Forgive me as I'm not a mechanic and do not understand the workings of this setup fully,but I would have thought the idea
of said tensioner was to keep constant firm tension on the timing belt .
I say this because i'm currently in the process of renewing my Xantia diesel timing belt and relevant components,but i have
noticed after the removal of the timing belt covers that there was suprisingly some slack in the timing belt between the
camshaft pulley and the injection pump pulley(more than i think should be).This slightly alarmed me thinking I may have been
close to the scenario of belt jumping pulley teeth or worse with even more problems.
I checked the timing belt tensioner to discover that it was tightly done up probably as per instructions from the manual(s) and
probably doing its job,albeit, as far as I'm concerned, 90 percent of the time.I thought the tensioner's job would be to keep constant
pressure on the timing belt preventing the possibility of any undue slack in the belt ever appearing to the extent that it would
also obviously take up any future slack from the belt due to normal stretching.
As it stands at the moment,unless otherwise informed by your good selves,I would be thinking that I need to adjust the tensioner
every so many thousand of miles so as to ensure that the tensioner was taking up any possible slack from the belt.
I may also be tempted ,unless someone advises me to the contrary,to try and loosen off the pivot nut and tensioner bolt a fraction
so there is slight movement in the tensioner to keep applying constant pressure to the timing belt thus hopefuuly negating the possibility
of any undue slack ever making an appearance.I'm not sure though,whether this will bring on premature wear on the timing belt!
What would you say?What would you do?
Perhaps ,and only perhaps,this is why you hear of diesel timing being out and timing belts that have jumped teeth.Who knows???
Can someone,some kind knowledgeable soul enlighten me and put me right before I make a dreaded mistake.
I look forward to any replies.
Thanks for reading Steve

jeremy · Unread post by **jeremy** » 17 Jul 2007, 15:55

The tensioner isn't intended to be used as a spring loaded tensioned while the engine is running - so its construction probably isn't robust enough - or possibly even geometrically correct. As its well hidden its not even as if you can study its function easily as time goes on.

If you leave bolts partially undone they will work loose - especially on a diesel engine which is subject to heavy vibration. The XUD is smooth for a diesel - but if you look at things like 60's diesel Land Rovers you will find that everything shakes loose and even things like the aluminum wings crack at their mountings due to the vibration. Those things which are meant to pivot will have a suitable bearing - even if its only a sleeve to enable the mounting to be tightened fully.

Belts will jump teeth if they become slack - which can be due to belt wear or wear in the various pulleys - or even incorrect installation. Few do jump during their recommended life - providing tensioners, jockeys and water pumps remain sound. Most of these components will make noises before failing.

Unread post by **Peter.N.** » 17 Jul 2007, 17:49

As Jeremy says in his last comment " belts will jump teeth if they come loose". The crankshaft exerts a considerable ammount of 'pull' on the belt, this could be sufficient to compress the tensioner spring and introduce a lot of slack, enough to cause the belt to slip, that's why its locked.

steviewonder7 · Unread post by **steviewonder7** » 17 Jul 2007, 20:22

Thanks for your replies chaps.I'll bow to your better knowledge and follow
the instructions as per manual(s).I didnt realise that the tensioner wasn't to be used in the manner i spoke of.
I've come across tensioners being used in the way I 've spoken in the machines I've maintained in the past.
Last year when I had to renew the timing belt on another car,this being a petrol engine,I found that (a) it was last serviced and had a history of being serviced by the dealership and(b) that the tensioner setup was very similar to the XUD engine and the tensioner bolt was missing on purpose and the pivot bolt was just loose enough to allow the tensioner some minor movement.
This car is still running as is today.Maybe it can get away with it because its a petrol engine and not a shakey diesel one?
Thanks again...Steve