[urq] Cylinder head retorque

[qshipq at aol.com]

 L-A
Checking a heat cycled stretch head bolt after install is like using a torque wrench setting to measure removal of a road wheel....  It means nothing.  A head bolt that has not been heat cycled can be reused, a head bolt that 'has' been heat cycled should not be reused (not sure I care what the notations say in the manual).  I measured heat bolt stretch years ago in my shop, both heat cycled and non heat cycled, 10vt and 20vt.  IIRC, the heat cycled bolts will stretch approx 5mm (compared to new), the non heat cycled bolts appeared to be within production specification.  

The procedure is 29-44- +180 (2x90 ok).  Threads in block should be clean, threads on bolts should be wet (10w-30).  Me, I'd get a new HG and a fresh set of head bolts.  You can lift the head off the block without much 'removal',  just enough to grab the head gasket, clean the mating surfaces and put it back down.  Clean out the block threads with compressed air, lube the threads on the bolts, and do the procedure again.  WRT other manufacturers, retorquing, and 'checking', none apply to the 10vt or the 20vt Audi engines, nor does doing any 'other' procedure mean anything at all.

Years ago I spoke to a well known Audi race engine builder.  He gave me a 'set' torque spec for the 'final' 180 (in lieu of that +180), but the 180 procedure is valid, and has been used millions of times.  Interesting too, he didn't care for 'studs', esp on 20vt motors, as he claimed if a head gasket is going to blow, you want it to without studs to add warpage to the head...  I digress.

Start fresh and do it again, HG and Hbolts.  If you still have issues after doing it per factory procedure, you likely have some other issue (warped head, warped block, wrong bolts, wrong/bad  head gasket, weak threads, etc)

HTH and my .02

SJ

 


 

 

-----Original Message-----
From: Louis-Alain Richard <laraa at sympatico.ca>
To: 'Peter Golledge' <petergolledge at gmail.com>
Cc: urq at audifans.com; quattro at audifans.com
Sent: Fri, Oct 15, 2010 12:22 am
Subject: Re: [urq] Cylinder head retorque


Peter,

What puzzle me is this : our other car, a Saab 9-5, had a small oil leak
from the back of the head. A Saab technical service bulletin was published
about retorque/bolt replacement. The instructions on that TSB were like this
: first try to retorque the bolts. If the spec is not attainable, replace
the bolts. 
When we first tried to retorque the bolts, it was clear that we wouldn't
reach the spec, as the bolt was almost impossible to torque with a standard
24 in. torque wrench. It would need a lot more force to add the 90 degrees
after the gentle initial torque. So, in my mind, a dead stretch bolt is
elongated to the point of being stretched to its limit and would break if
given more force. The problem on this engine was the bolts themselves : they
changed the surface finish to give the bolts more grip in the engine block.
See this image :
http://www.saabnet.com/tsn/members/gallery.html?memberID=112&do=show&id=746.
After the bolts replacement, the engine is fine.


On the urq, it was not the case. It was relatively easy to add 180 degrees
like in the initial operation. They acted exactly like if the bolts were
new. Or maybe these are not stretch bolts ?

To add to the confusion, in the Bentley book there is some notes, page 15.13
:

Caution : do not retorque cylinder head bolts at first service or again
after repairs.
Note : It is not necessary to replace polygon head bolts when making engine
repairs. Bolts can be reused. However, new bolts are to be used in sets
only.

So, maybe the holes in the block were not clean enough to keep the clamping
force ? However, the block was cleaned in a caustic tank and prepped by a
reputable shop. More, we installed the head and all exhaust plumbing on the
engine while it was in my shop. We then installed the complete drivetrain
from under the car in a single step.

Any ideas to prevent this loosening to happen on the upcoming rebuilt ? I'm
a bit tired of pulling the head on this car, since it is such a big task to
do it in situ with all the plumbing attached to it. 

Louis-Alain 





-----Message d'origine-----
De : Peter Golledge [mailto:petergolledge at gmail.com] 

AFAIK all I5 Audi head bolts are TTY "Torque to Yield" AKA "stretch" bolts.
I'd not expect them to have the same
torque + turn after heat cycling but I don't know if that would explain the
120 Deg difference?


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