Last night we checked the tension on the head bolts and that was quite surprising. All of them torqued down quite a lot. They all went down around 45-60 degrees to reach the manufactures spec of 45ft lb which is what I originally set them at when the motor was assembled. So much for monotorque!

We are going to pull the head off and fit a new gasket. We will also be checking the tension of the head bolts after every meeting from now on.

I have to confess that the idea of a single tensioning of the head bolts after fitting a cylinder head is something I have never been comfortable with generally. Even moreso on a race engine.

You're not alone on that one. What I'd maybe suggest is not doing them too many times. I used to do it 3 times, 4 max.

There's a bit of difference of opinion (and I honestly don't have anything I could put forward to favour one over the other) as to 'how' to retension them. This is a general - 'not specifically datto a series' comment mind you

Some people raise issuesthat if you loosen and re-tension the bolts (by just cracking them loose, one at a time, then retensioning, then moving to the next, loosening and re-tensioning, in the same order you'd tension them first time around) - that oil or other fluid could get under the bottom of the bolt and hyraulically 'lock' and stop the bolt going tighter, but it'll register on the torque wrench as being tight. SO they just go one by one, don't loosen any bolts, and just re-tension.

THe 'other' side raises the issue that the bolts can slightly 'seize' and need to be 'cracked' then re-tensioned, or that stickiness will otherwise just make the torque wrench read a high value, but the actual clamping force isn't as high as it could be.

Both have some relevance I guess. For whatever it's worth, I've done the 'loosen one, then re-tension' then move to the next one etc method on practically all motors.

I tend to run studs on anything that has to be re-tensioned a lot. That way the threads in the block won't wear out, they are only pulled once in a blue moon, if changing the head gasket altogether. SO that saves the threads in the block. It also means that you are only loosening the nuts at the top, not the stud, so you have no worries at all with the 'crack one loose, then retension' method. It also was a bit of a bonus on things like holden red motors, as they have bolts going into the water jackets, so you need to run sealer (instead of anti-seize lube) on the threads to prevent seepage past the threads - which is then a real pain when you have to re-tension them (and arguably the sealer also leads to slightly less consistent torque wrench readings for the same clamping force. But with nuts at the top, you can seal the threads in the block, and use anti-seize on the top threads/nuts.

For a streeter i wouldn't bother too much with studs, but they have a decent advantage with more competition oriented stuff.

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Hopefully the head hasn't gone soft/annealed (due to overheating) and caused this..

Jmac, The thought had crossed my mind to have stud kit installed.

You're right about the need to back off the bolts before retensioning. The torque needed to get them moving will exceed the torque needed to keep them moving and thus give potentially a false correct reading.

When I checked them I simply put the torque wrench on to see how tight they were and they moved as described ,no backing off first.

I doubt if there would be much oil getting past the threads on the oil feed head bolt to cause an hydraulic lock.The point is well made though.If you removed and then reinstalled the bolt then I agree that it would become an issue then as any oil around the bolt will go to the bottom of the stud hole.

Fandatstik, Interesting you should mention that. I am aware of that problem however have no experience of that with the the Dato engine. I wonder what temps would be needed to cause that on a Dato head? The temperature recorded is viewed by others as not as bad as it sounds.

If the head has softened I query if it can be re-heat treated or is it then just a fancy looking block of silver swiss cheese ?

Hey Guys been looking at this topic for a while now and I just wanted to clear something up ACL hasnt gone broke nor are they in liquidation the are still up and running and doing fine if you have any issue with thiere gaskets give them a call they were great when I had an issue with mine and as it turned out it was an issue with my head not the gasket at all