Case Perimeter Washers

[chris_seven]

I just had a quick look at a 901/01 we have lying around, I don't think this engine has ever been opened and the washers are slightly rusty and don't appear to be aluminium.



The PET doesn't specify them as Aluminium but this may not be a good indication.

'Aluminium' washers just isn't a good enough definition as there must be many grades.

A typical Aluminium crush washer is made from a 1000 Series Alloy (1050) in a 'soft' condition.

The Coefficient of Friction of this type of washer aganist a steel nut is around 0.5 due the the galling that will inevitably take place.

This will mean that for a given torque the preload will be reduced. The other issue with 1050 is that it is quite likely to suffer from 'cold flow' when the engine warms up and the preload increases.

A 2000 Series Aluminium Washer which was anodised would behave in a very different manner and would probably work well but is likely to have a similar harndness to a mild steel washer so could still damage a Magnesium case although it would notionally reduce Bi-metallic corrosion.

It is difficult to find the material spec of any commercially available aluminium washers and without this information I think I would pass.

The higher the preload of a specific fastener the more likely there will be issues.

With regard to valve cover nuts, we ahve been using dome nuts and Seloc (rubber covered lock washers) for some time now and although they clearly don't look stock, they do solve oil leaks.

These nuts are stainless steel but we have just sourced them in Silver anodised 6061-T6 Aluminium and will use these in the future.