Engines/Running gear

Fitting head gaskets with asbestos substitute sandwich to SV engines

Non asbestos gaskets have a layer of material that is more resilient than the ‘old’ asbestos type. The outer layers of copper are also often very slightly thicker. This means that, as you pull the head down onto the block, resistance is felt very suddenly. There is not the gentle build-up that is experienced with the asbestos sandwich that allows torquing down to a pre-set figure with gradual increments.

Use of a torque wrench will usually leave the gasket uncompressed and lead to failure of the joint in a very short time-perhaps as little as a few miles along the road. Hence, a manufacturer recommends the use of the technique that used to be practiced before the advent of torque wrenches.

If the previous gasket blew, do check that the head and block are not damaged; the narrow spacing between cylinders is a danger area. A steel rule held on edge with the light behind can show if there is excessive warping or erosion. The head will not ‘straighten up’ as you tighten it down nor will the gasket fill up a pit caused by escaping exhaust gases.

The gasket should be fitted in the usual way, ensuring that the face of the block and head and the studs and stud holes are clean and any waterways are clear-particularly any of the very tiny ones that are found between many blocks/heads. A smear of light oil can be applied to the faces but no gasket cement should be necessary. Using a ring spanner, the head should be pulled down onto the block by following the sequence given by the manufacturer, which broadly is from the centre outwards. When the nuts feel uniformly tight, add a further one eighth of a turn.

It is most unlikely that you can apply excess torque with a standard ring spanner. That’s why spanner lengths vary-unlike a torque wrench with a long arm and (potentially) considerable leverage.

Start the engine after the water is added etc. And allow it to reach normal temperature and warm through. You may add a blanket over the radiator to speed this up, but keep a close eye on the temperature to prevent boiling. Stop the engine and retighten the nuts while still hot. Invariably they will take up some more. If you have an aluminium ‘aftermarket’ head, retighten when cold.

Use the car normally and after about 200 miles retighten again.

The two re-tightening activities are important to give reliable operation.

With thanks to Ian P. Harris.