Cambelt idler failure
jeffw - 10/9/12 at 08:46 AM
Out on a nice run with the Southern Kit Car Club yesterday (with Son in passenger seat) when the engine stopped at a junction near the A26. An
attempt to re-start had metallic top end noises....so lifted the bonnet to find
You can see the failure of the idler pulley which has allowed the cambelt to jump in the pictures. Without the Supercharger frame I think it would
have been gone completely.
4 hrs for the AA to recover the car allowed a lot of time to reflect. Less than 500 miles since the cambelt was changed when the engine was rebuilt
and the idler pulley has failed....not happy bunny.
I can't imagine the idler is under any more strain than it would be in the orginal vehicle (?) so maybe I've just been unlucky (again).
Likely to be head/pistons/valves at a guess...
Davegtst - 10/9/12 at 08:55 AM
Was the idler changed with the cambelt? I never fit a cambelt without changing the idlers and tensioners now unless the customer specifically tells
me not to. I had a nasty experience on a focus once that cost me a fortune and a lot of stress to put right.
jeffw - 10/9/12 at 08:59 AM
I don't know is the easy answer. The whole engine is only 5K old so worse case the idler has that many miles on it although you would expect it
to be less than 500 miles. I'll find out this morning...
jollygreengiant - 10/9/12 at 10:23 AM
quote:
Originally posted by jeffw
I don't know is the easy answer. The whole engine is only 5K old so worse case the idler has that many miles on it although you would expect it
to be less than 500 miles. I'll find out this morning...
I'm afraid its the old story, you change the cambelt and no matter how hard you try to get it the same, you end up with a different tension. Plus
it was probably being driven with a bit more gusto than it was used to.
ashg - 10/9/12 at 12:53 PM
oh dear jeff your not having much luck with the car at the moment.
jeffw - 10/9/12 at 01:02 PM
Pulleys where changed with the belt (500 miles ago). Looks like one of those things. At least I have ARP studs so it doesn't need new stretch
bolts this time. We will be able to skim the head to increase the CR as well.
Hopefully it will only be the valves as it happened at idle and I'll not need new pistons.
Fatgadget - 10/9/12 at 02:17 PM
quote:
Originally posted by jeffw
Pulleys where changed with the belt (500 miles ago). Looks like one of those things. At least I have ARP studs so it doesn't need new stretch
bolts this time. We will be able to skim the head to increase the CR as well.
Hopefully it will only be the valves as it happened at idle and I'll not need new pistons.
Valves and pistons getting up close and personal when something breaks in the linkage, one can never predict the seriousness of the outcome sadly.
daviep - 10/9/12 at 04:38 PM
That's a sickener
It may be an optical illusion but the idler doesn't look as if it sitting properly against the block, as if the bolt has come slack?
Cheers
Davie
Andy S - 10/9/12 at 06:02 PM
quote:
Originally posted by daviep
That's a sickener
It may be an optical illusion but the idler doesn't look as if it sitting properly against the block, as if the bolt has come slack?
Cheers
Davie
Just what I was thinking
perksy - 10/9/12 at 06:07 PM
quote:
Originally posted by daviep
That's a sickener
It may be an optical illusion but the idler doesn't look as if it sitting properly against the block, as if the bolt has come slack?
Cheers
Davie
Was just thinking that myself
Is the bolt loose ?
RickRick - 10/9/12 at 06:16 PM
goes with the damage to the outside of the pulley too
ian locostzx9rc2 - 10/9/12 at 06:56 PM
Looks like a bent or misaligned idler pulley bolt/or idler to me!
hicost - 10/9/12 at 07:13 PM
When you pull it apart, can you get away with putting a pocket on the pistons for the valves, that way it will inimise the damage if it happens
again.
Best of luck
James
jeffw - 10/9/12 at 09:07 PM
It has forged HC pistons with pockets in them already. Also port/polished head with large valves & high lift cams.
The Idler pulley has failed causing the belt to jump. Just how or why it has failed remains to be seen.
ashg - 10/9/12 at 11:49 PM
looks like the bolt has come loose to me.
unfortunately jeff it may be a case of the age old saying. "If you want the job done properly do it yourself." failing that have you
thought about getting dick to have a look at it? i don't know of a person that has a bad word to say about him,and he is one of the very few
people that i would allow to touch one of my cars.
jeffw - 11/9/12 at 06:50 AM
I think you maybe correct
jeffw - 11/9/12 at 05:19 PM
And today I ran over something on the M25 which has buckled the 19" alloy on the Jag. I had to change the wheel on the side of the motorway for
one of those stupid space savers and then gone on to Birmingham. New wheel and tyre will be required
six mad - 11/9/12 at 06:22 PM
Oh thats Bad luck, hope you get it sorted soon.
I would suspect as the belt tension has become slack, this has allowed the cambelt to ride on the top of the pulley
causing the belt to become very tight which in turn has bent the idler pulley mounting bolt.
This could have been caused by incorrect tension on the cam belt in the first place.
daviep - 11/9/12 at 08:04 PM
quote:
Originally posted by six mad
Oh thats Bad luck, hope you get it sorted soon.
I would suspect as the belt tension has become slack, this has allowed the cambelt to ride on the top of the pulley
causing the belt to become very tight which in turn has bent the idler pulley mounting bolt.
This could have been caused by incorrect tension on the cam belt in the first place.
Wouldn't be my first guess as to probable cause, not sure which pulley you think it would ride on to the top of?
Ever heard of Occam's razor?
Cheers
Davie
snakebelly - 11/9/12 at 08:14 PM
Am i seeing things or is there a hairline crack radiating from behind the tensioner bolt at approx 3 o'clock?
six mad - 11/9/12 at 09:13 PM
quote:
Originally posted by daviep
quote:
Originally posted by six mad
Oh thats Bad luck, hope you get it sorted soon.
I would suspect as the belt tension has become slack, this has allowed the cambelt to ride on the top of the pulley
causing the belt to become very tight which in turn has bent the idler pulley mounting bolt.
This could have been caused by incorrect tension on the cam belt in the first place.
Wouldn't be my first guess as to probable cause, not sure which pulley you think it would ride on to the top of?
Ever heard of Occam's razor?
Cheers
Davie
Nah, I use Gillette
Tooth on tooth- cam belt against exhaust cam pulley, The belt is even trying to ride the pulley in the pic.
jeffw - 18/9/12 at 10:39 AM
Idler had seized/failed and then bent the bolt holding it on :shock:
Damage is 4 exhaust valves and 2 inlet, guides are fine and the pistons have some very minor marks..
ian locostzx9rc2 - 18/9/12 at 11:49 AM
Now you need to why it happened!!!!
Nick DV - 18/9/12 at 12:26 PM
quote:
Originally posted by daviep
quote:
Originally posted by six mad
Oh thats Bad luck, hope you get it sorted soon.
I would suspect as the belt tension has become slack, this has allowed the cambelt to ride on the top of the pulley
causing the belt to become very tight which in turn has bent the idler pulley mounting bolt.
This could have been caused by incorrect tension on the cam belt in the first place.
Wouldn't be my first guess as to probable cause, not sure which pulley you think it would ride on to the top of?
Ever heard of Occam's razor?
Cheers
Davie
I agree with you Davie, it wouldn't be my first thought. Probably nothing more than a manufacturing problem with the pulley.
Yes, I have heard of Occam's Razor - many years ago in 6th form - but more recently from Jodie Foster in the film 'Contact!' 
Geoff, bad luck but I hope you get it sorted soon.
Cheers, Nick 
jeffw - 18/9/12 at 12:52 PM
There is going to be a metal idler fitted which should alleviate the issue happening again.
jeffw - 28/9/12 at 01:03 PM
6 exhaust valves, 2 inlet and it is back...
Turns out the valve clearances where all wrong (tight) and the engine has gained another 30 wheel HP on the Dyno (300 at the wheels now)...so not all
bad then.
The Tensioner had failed (replaced with a metal manual tensioner), probable some miles ago and the M8 bolt through the idler had sheared .....
[Edited on 28/9/12 by jeffw]