[s-cars] Potential connection between bent valves andsubsequent rod bearing failure?

[Wylie Bean]

Cody
I believe the engine in question had a timing belt issue (back in the winter if this the same one I'm thinking of) where a valve was bent and replaced. 


Wylie Bean (via blackberry)
90 cq
91 90q20v
92 UrS4
08 Q7 3.6P

-----Original Message-----
From: Cody Forbes <cody at 5000tq.com>

Date: Sat, 16 May 2009 13:08:34 
To: David Forgie<forgied at shaw.ca>
Cc: s-car-list<s-car-list at audifans.com>
Subject: Re: [s-cars] Potential connection between bent valves and
	subsequent rod bearing failure?


It is possible that the rod bearing was a cause rather than an effect.  
If the bearing was already bad for whatever reason it could allow the  
piston to travel too far up the bore and hit the valves. Doesn't take  
much.

-Cody
Sent from my iPod

On May 16, 2009, at 12:42 PM, David Forgie <forgied at shaw.ca> wrote:

> We all know that if the timing belt breaks, there will be bent  
> valves (typically intake valves) because
> the AAN is an "interference" engine.  Several of us have been trying  
> to help diagnose a knocking
> noise in a new UrS4 owners car on AudiWorld.  The owner insisted it  
> was coming from the head but
> we were skeptical.  At the suggestion of one poster, the owner  
> bought an automotive stethoscope
> from Harbour Freight and after he got it, he pin-pointed the knock  
> to low in the block.  He dropped
> the oil pan (no small job on an AAN in the subframe) and discovered  
> that one of the rod bearings
> was gone/in pieces (in the pan).  I asked him which cylinder and he  
> replied: "Cylinder 3. So far I
> have burned a valve, then bent two valves and now disintegrated a  
> bearing, all in that cylinder."
>
> I can't help him with the burnt valve, but I am wondering if the  
> bent valves came from a timing belt
> "issue", it could mean that the force of the piston hitting the  
> valves, which would have been
> transmitted to the crank, via the rod and the rod bearing, may have  
> been enough to damage the rod
> bearings.
>
> Does that seem possible?  It's the only co-relation I can think of  
> but it might not be valid.
>
> Dave F.
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