Head Gasket shape

Having spent my working life in gaskets – much of it with the company that made the original parts for Citroën – and having fitted dozens of these myself,  I confess I had been aware of – but never considered – this apparent anomaly.  Alex’s question therefore compelled me to investigate further.

First of all, I can confirm the unusual gasket bore shape is correct.  Here is a shot from a period catalogue which shows that, unlike others on this page, the bores of both 40.000 and 40.531 are not circular.

40.531 is the original “Perfo” CHG and 40.000 was for a RWD saloon with a similar bore and stroke.

I can also confirm that the CHG for the 6-cylinder engine also has the same, non-circular, bore shape.

The critical sealing area is where the gasket sits on the top surface of the liner. Chris’s suspicion is interesting but longitudinal movement in any one direction would amplify the possible offset at the other end so I doubt that is the likely reason. Nevertheless, I cannot think why this bore shape was considered necessary.

As the enlargements are on the exhaust valve side of the bores, I wonder if it could be to minimise the chance of gasket damage from the exiting exhaust gases?

There has to be a very good reason for this because the cost of tooling for an iregularly shaped hole will clearly have been considerably higher than for a round one.

If somebody else can throw more light on this, I should love to be educated.

B….

Glad to know you are back up and running.

B….