Trevor ,
The need for retightening a 6 cylinder Bristol is really dependant on the condition of the head stud , head stud washers , head stud nuts and the way it was tightened previously . The other thing to consider is the type of head gasket used, I don't know what BODA supply. When the workshop manuals were produced the only readily available head gaskets were the steel shim type from BCL which I have never used ,but imagine will not compress.
Now most people fit a thicker composite type of gasket which will compress slightly over time due to the torque of the studs and due to heat produced in the engine .
I usually tighten the head studs down at least three times before I start a rebuilt engine, then again after about 500 miles and of course re adjust the valve clearance .
The alloy in the heads seem relatively soft and the original head stud nuts and washers deform the machined surface on the head where the washer sits . I always machine that surface flat . Thick hardened washers and flanged nuts spread the load on the head over a greater area which reduces the deformation of the surface of the head , which retains the torque on the studs.
I also bevel the head stud holes on the head's bottom face , this allows a small cavity for any excessive gasket material to go , due to any inaccuracies in manufacture of the head gasket .
So my recommendation is to retighten the head studs.
Geoff
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