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graham.hassall
Monza


Joined: 29 May 2009
Posts: 174
Location: Somerset- 996 C4S


PostPosted: Sun Jul 09, 2017 9:51 pm    Post subject: lower idler pulley Reply with quote

Hi All
Last night after I accelerated hard a strange screeching sound started at the rear of the car. I stopped and the engine seemed fine and gears were OK so I returned home (1mile away) thinking the alternator was giving up. On closer inspection I discovered that the lower idler pulley was loose. Very loose in fact as the M8 screw holding it to the block had sheared off at the block and the belt was holding the pulley in position. The remnants of the bolt and coverplate (washer) had disappeared.

Gloom and doom how do I get the remnants of the stud out, as it was flush with the block apart from a small burr. Well as luck would have it by placing my finger on it and discovering I could turn it and unscrew it!

Well this could be the end of the saga. I will buy a new M8 x 55mm screw (does anybody know the pitch) and washer probably from Porsche. I may buy a new pulley as well as there is some marking on the pulley wheel. I have looked up in the manual section 13 77 20 and see that the tightening torque is only 17ftlb. This seems very low. Should I be using some threadlock as well?

The only thing that now concerns me is why did it happen? The pulley rotates nice and smoothly. Could the screw have started to loosen through vibration and created an eccentric load which then sheared of the screw?
Is this common my car has covered 117k?

Thanks in advance for any feedback.

Graham
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Current car 2004 996 C4S Tiptronic

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Demort
Paul Ricard


Joined: 21 Mar 2015
Posts: 3003
Location: Sussex


PostPosted: Mon Jul 10, 2017 7:32 pm    Post subject: Reply with quote

Link here for the part numbers and to be honest i would just get the parts from OPC ..

http://www.deroure.com/diagrams.asp?TBL=2515&MAK=3&MDL=25&SMA=0&SMO=0&ST=&SC=0

Why did it happen though ? not common at all im afraid and i dont rember seeing it on a 996.

Gen 2 997 and yup they have problems .

Check the seating area it bolts onto , should be nice and flat so the pully will sit flush ( kinda doubt theres a problem here but i aint got much for you ) .

Check the tensioner , im thinking is it siezed .. well it cant sieze but unduly tight perhaps.

Im thinking it was just metal fatigue and finally let go though and thats why you could undo it with your fingers .. no bolt tension when it had snapped !

Torque is low but a lot of the bolts on these are and i wouldn,t advise thread lock .. you can if you want to for piece of mind but it really shouldn,t need it.
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graham.hassall
Monza


Joined: 29 May 2009
Posts: 174
Location: Somerset- 996 C4S


PostPosted: Thu Jul 13, 2017 11:06 pm    Post subject: Reply with quote

thanks Demort for the feedback.
I checked the mounting surface which was flat and the tensioner seems fine so I can only assume like yourself that metal fatigue of the bolt was the problem.

I have replaced the belt, bolt and special washer from Bristol OPC and all seems OK now.
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Current car 2004 996 C4S Tiptronic

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