Timing Belt Failure broken pulley bolt
#1
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Timing Belt Failure broken pulley bolt
I had last week a timing belt failure on my 86.5 5 speed.The bolt for the timing belt pulley broke at fast driving (140 mph) on autobahn.
The laso pump was 2 years old and ok and the belt was 25000 miles and also 2 years old.
In the last time a few pulley bolts broke on the old design of the s pump.
A few members of the German 928 community think we should replace this 8 mm bolt every timing belt job.
I don´t know if the porkensioner has this critical piece?
After disassembling the engine I know the collateral damage of this failure.Luckily I have a set of spare heads.
I think after 235000 km I should rebuild piston rings,rod -and crank bearings.
A new complete gasket set is also needed.
The laso pump was 2 years old and ok and the belt was 25000 miles and also 2 years old.
In the last time a few pulley bolts broke on the old design of the s pump.
A few members of the German 928 community think we should replace this 8 mm bolt every timing belt job.
I don´t know if the porkensioner has this critical piece?
After disassembling the engine I know the collateral damage of this failure.Luckily I have a set of spare heads.
I think after 235000 km I should rebuild piston rings,rod -and crank bearings.
A new complete gasket set is also needed.
#2
Are you talking about the pivot arm bolt? The one that holds the tensioning arm in place?
#3
Rennlist Member
Sorry to hear of the failure. I always wondered about that bolt, when I bought my car and did my first timing belt the PO replaced that shoulder bolt with a bolt and sleeve that I found bent. I switched to the Porkensioner with my last TB job, shoulder pivot bolt is not used, much better system IMHO.
Good luck with the rebuild.
Good luck with the rebuild.
Last edited by Glen McCartney; 03-23-2011 at 04:34 PM. Reason: Spelling
#4
Race Car
Do you have pictures? I am having a hard time visualizing how the bolt holding the timing belt pulley could break... Or are you talking about the shoulder bolt that holds the arm?
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C 475hp/460lb.ft
#5
Inventor
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Sorry to hear that, Karsten.
Let me know if you need anything.
145K miles is not that much. I think you could just put the new heads on?
(BTW: how did the V3 chips work on the autobahn before the engine went quiet? )
Let me know if you need anything.
145K miles is not that much. I think you could just put the new heads on?
(BTW: how did the V3 chips work on the autobahn before the engine went quiet? )
#6
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Thread Starter
My car is at the shop and my friend tells me the diagnosis after pulling the engine.He says the S 4 design hasn´t this weak point any more.
I think he means the shoulder bolt.
Ken, I drove at 7000 rpm in 5th gear..... ;-)
Joke aside, I received the chips the day after.
Loosing the belt at high speed isn´t spectacular.Quietness,a lot of lights in the instrument cluster and no more the feeling of sitting on the tip of a saturn 5.
A little cloud of oil in the back mirror and than waiting for the yellow angels( the german car club )
I think he means the shoulder bolt.
Ken, I drove at 7000 rpm in 5th gear..... ;-)
Joke aside, I received the chips the day after.
Loosing the belt at high speed isn´t spectacular.Quietness,a lot of lights in the instrument cluster and no more the feeling of sitting on the tip of a saturn 5.
A little cloud of oil in the back mirror and than waiting for the yellow angels( the german car club )
#7
Inventor
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No shoulder bolt with a PKT.
(You don't even need the pulley{s} under the crank gear as in this pic.)
(You don't even need the pulley{s} under the crank gear as in this pic.)
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#9
Under the Lift
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A thread with pictures of the offending 8mm bolt gone bad:
https://rennlist.com/forums/928-foru...apart-omg.html
Here's some damage from one that broke:
#13
Burning Brakes
+1 the Porkensioner convinced me immediately, it was actually the first part I changed on my 928 since I have it :-)
Great work Ken! (I replaced all my fuel lines under the bonnet recently, so it's about time I get the s300s chips + fpr)
Major bummer to have the belt go at high speed/rpms.
Hope the engine is repairable with your new heads and some €€€ :-(
Great work Ken! (I replaced all my fuel lines under the bonnet recently, so it's about time I get the s300s chips + fpr)
Major bummer to have the belt go at high speed/rpms.
Hope the engine is repairable with your new heads and some €€€ :-(
#14
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Shoulder bolt is a bolt with large nut with a large barrel where the bushings ride but a smaller threaded stud which attaches it to the pump. So it looks quite robust and a large wrench fits BUT easy to over torque. The S-4 uses a stronger stud with a support brace added.
#15
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