[DML] Head bolt torqueing - warning

[Martin Gutkowski <webmaster@xxxxxxxxxxxxxx>]

The manual describes a procedure which was fine on a new engine, however 
on a 22 year old engine that's probably overheated at some point (why 
else would you be taking the heads off?), the threads in the block into 
which the head bolts screw are likely to be dirty and contaminated. The 
angle torque specs make these threads work extremely hard, and stripping 
them out is a distinct possibility.

Our PRV guy (a renault 30 owner and veteran of many engine builds as 
well as many PRVs during his time as a Renault workshop manager) told us 
that the type of head gasket on the PRV means the 
re-torquing-once-warmed-up procedure can be skipped IF the heads are 
prepared properly before being bolted down. He also said that unless we 
wanted to strip the threads in the block, ignore the manual and torque 
the bolts (in the correct sequence) to 90 ft-lbs. Then assemble the 
engine and run it to temperature once for the gasket adhesive to flow 
and bed in.

The proper preparation for the heads is to face them - this ensures they 
are perfectly clean, and also perfectly flat. Contradicting the manual, 
these can be faced - if the heads are so warped that to get them flat 
you have to take too much off, you needed new heads anyway.

Head gasket jobs are rare, but I've personally done three. On one car, 
we replaced a head due to a messed-up manifold stud. That same engine 
overheated massively about 3 months later (nothing to do with our work!) 
and the gasket on the head we _didn't_ change, blew.

Just make sure your water pump, thermostat and rad fan switch work! It's 
a tiny outlay compared to a head gasket job!

So, to Mr T. Just take off the rocker covers and check all the head 
bolts are torqued to 90 ft-lbs. As long as they were prepared properly, 
you'll have no problems.

Martin
DMUK





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