Timing belt change - tensioner and guide pulley studs

[0wl]

Hi,

Can anyone confirm the correct procedure for changing the tensioner and guide pulley studs on a 1.9 PD TDI (AWX) with the friction damped tensioner - I'm aware there are issues with the tensioner stud in particular potentially snapping when reused.

From the documentation I've seen, the replacement tensioner stud should be tightened into the engine block to 15Nm and then final tightening of the tensioner nut onto the stud should be 20Nm with a further turn of 45 degrees once the initial torque value is reached - but some people think this is too much?

For the guide pulley I can't find any info on the stud to engine block tightening torque - does anyone know what this value is? I believe the guide pulley securing nut should be tightened to 22Nm.

The replacement tensioner stud doesn't have any threadlocker pre-coated but the guide pulley stud does - is it worth putting a dab of blue thread locker on the tensioner stud when installing to the engine block as I've read conflicting advice on this.

Thanks in advance for any advice / guidance / confirmation of the above.

0wl

[rotodiesel]

In my experience, the specified torque of 20Nm + 45deg for the tensioner stud nut is excessive and stretches the stud. After the second timing belt change, the stud often fails. The specified 20Nm for the guide roller nut is OK and causes no problems. I fit new nuts on each stud.

 

If you are replacing an original belt, the tensioner stud is likely to be OK but I tighten a (new) nut to either 23Nm - as recommended by Litens - or to 20Nm + 20deg. In practice, these two methods give identical results. I have never had a tensioner let go at the lower torque figure.

 

There seems to be confusion in the Fatherland over the fitting of new studs. Originally, the VAG kit did not include a new stud - but later kits do. I fit Continental kits - which originally included the stud, but which now don't. Make of this what you will. I fit new studs on engines with unknown histories, or where a dealer has used white paint - the trademark of utter incompetence when fitting these belts.

 

As long as sufficient threads are engaged in the head, the tightening torque of the stud is immaterial. Just wind it in securely with a couple of nuts locked together.

 

rotodiesel.

[0wl]

Thanks for the advice rotodiesel.

I've already got an INA kit from Eurocarparts that includes the studs. It also includes a Litens tensioner, INA guide pulley (obviously since it's an INA kit!), the two nuts and I think a Gates belt.

[0wl]

Found this on the contitech site - maybe they don't include the studs now to avoid any potential liability?

http://aam-europe.contitech.de/pages/newsletter/newsletter-technical-info/12_029/service_einbautipps_12_029_en.html

[rotodiesel]

I think that illustration makes the point that if the M10 portion of the stud is not fully screwed into the head, the contact face of the tensioner will sit on the stud shoulder and not on the flat face of the head - a recipe for certain failure.

 

The whole design is a VAG c o c k up. The Litens tensioner is a well engineered and very well made component which requires an M8 stud to accommodate its eccentric mounting. The older VAG engines all used an M10 stud - so their fix for the PD was to use a stepped stud. This is a potential disaster from a stress failure aspect as many customers have discovered to their cost. I suspect VAG now know the stud is a weakness but don't want to admit it by revising the tightening torque - which itself would carry some risk. Besides, the specified torque is actually moulded onto the belt cover. Putting a new stud in the kit costs peanuts and lets them off the hook.

 

I will re-use a stud which has been tightened only once during engine build to the stipulated torque. On assembly, the 20Nm is applied with a torque wrench, but I turn the final 20 deg with a short ring spanner, marking the head face for position. If the stud is about to undergo plastic deformation which will lead to failure, this can clearly be detected when tightening. I would then fit a new stud.

 

rotodiesel.

Edited 26 August, 2014 by rotodiesel

[Tech1e]

The original studs where threaded up to the cylinder head, these could fail and were recalled on VW's.

 

The later ones are only threaded at the top end and so stronger in the cylinder head.

[rotodiesel]

Thanks for that - I wondered if they had done anything about it. Any chance of a couple of pictures?

 

Anyone who designs a stud with a step in it and then tightens it to yield point needs their head examining...

 

This is the "Jesus nut" of the engine.

 

rotodiesel.

[torq]

HI guys,

found this forum and thread while mooching about the web looking for a bit of info.  I don't have a skoda but I do have a Seat Alhambra with the AUY (115bhp) code 1.9pd engine and 152k miles on the clock.  And I know all about the tensioner pulley stud issue.  I replaced my belt kit including the stud 25k miles ago, all was well until one day while doing 70mph on the M6.  I took my foot off the accelerator and lost all power, coasted to the hard shoulder and she wouldn't restart.  Popped off the top belt cover and found the tensioner free to move around, the stud had snapped.

 

So what was the damage?  Every valve is bent, the cam lobes are dented and the hydraulic lifters are smashed where the valves tried to punch through them.  One badly designed stud has written off the top end of the engine.  I'm in the process of putting a lower mileage galaxy head on to get her back on the road as the school run has started again.  A mechanic I know always drills out the tensioner to fit a larger stud but I'm sticking with standard until I get around to building a 270bhp street sleeper people carrier.

That's it for now!

Torq

[rotodiesel]

When you replaced the belt and stud, did you tighten the tensioner locking nut to VAG's stipulated torque? This is a very silly design.

 

rotodiesel.

[torq]

When you replaced the belt and stud, did you tighten the tensioner locking nut to VAG's stipulated torque? This is a very silly design.

 

rotodiesel.

I wish I could say no and take some of the blame myself but unfortunately the answer is yes, I did set and torque to the correct values.  What I found was an absolute pain is that when setting the 4mm gap at the hydraulic damper, as soon as you tighten the nut the gap reduces.