The K Series head gasket failure and stretch bolts at the MGF / TF
The bolt set 
An update on the bolts!
After stripping a new Steptronic/Stepspeed we discovered the bolts have
been changed to un-plated bolts but still the same strength steel. The
cars now have the new steel dowels to locate the head so the later cars
should have a better HGF failure rate.
On another note (same car) I noticed a possible reason for HGF that hasn't
been observed before and caused us to have an hour or so of head scratching!
The head bolts on cylinders 3/4 on the front of the engine when screwed
in to check them for length were binding and not screwing down enough
on checking the threads. They appeared to be under some stress 8-[
After checking the available thread depth it appeared that the bolts were
in fact hitting the sump pan and if assembled would not give the correct
torque between the head and block.
The sump does in fact have a raised section in this area and is very near
to the bottom of the bolt especially the one between cylinders 3 and 4
to the front.
Solution was to shorten the bolt by 5-6 mm.The old gasket was fractionally
thicker at this point indicating full torque hadn't been reached,the car
had covered 7200Km.
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The thing to check is the height of the head, say this measures 100mm.
Screw the bolts into the block before the head is fitted finger tight
and measure the remaining height from block to bolt flange. The gasket
will account for 1.5mm but ignore this for safty margin. If the remaining
height is approaching the 97-100mm then it is time to investigate the
problem.
The bolts will leave
a healthy margin on cylinders 1/2 as the deep part of the sump is below
the danger areas.
A problem could be on cyl 3/4 on the front two bolts where the sump is
close to the oilrail/clamp plate.
The bolts are approx 412 long with 72mm thread,the block is 282mm height and the oil rail is 25mm thick. The critical bolt is the front one between 3/4 cylinders because if the bolt is fitted to the block the measurement before it hits the sump is around the 99mm mark, from block to u/s of bolt head.
So if you have a head skimmed and it is say 99.5mm when bolted in position there is a strong danger of this bolt bottoming on the sump and not stretching as it was designed. There is approx 72mm thread on the bolts into a 25mm plate so removing the 4/5mm will not affect the depth of thread in the plate as the bolts protrude 8-9mm below the plate into the sump area. I doubt there is a danger of the bolt running out of thread as the block and head measure approx 382 and the unthreaded section measures about 340 this would mean the bolt would have to stretch some 42mm!!!
The ideal solution
is to have bolts that measure 405mm long IMO. I hope this is clear enough
but to summarise the bolt between cyl 3/4 on the front of the engine needs
to have a safe margin of say 97mm protruding above the block face when
screwed in finger tight.IMO.
If this is NOT the case remove 3-5mm from the end of the bolt, ensure
the threads are recut as this would affect the torque settings.
Mike Satur (message to the MG Cars BBS on 1.12.2001)
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