HOME and how to join Forum Open Area General Scott topics Updated: cast iron piston, NOT SCOTT RELATED Reply To: Updated: cast iron piston, NOT SCOTT RELATED


malcwebb’s note of caution should be given due consideration but without a first hand knowledge of that particular engine it is impossible to come to a definitive conclusion as to the reason for the problem experienced and how that might bear on Erik’s Premier.

I still consider that if a liner is well done there is little risk. Furthermore there are very real attractions in a liner; the material is guaranteed to be homogeneous and the composition can be selected with particular attention to its wear properties. When a casting is made there are other factors that need to be taken into account, no such compromises are needed when selecting a material for a liner.

The condition of the cylinder, the quality of the original casting and the amount of metal around the bore must be considered but as it has survived more than an average lifetime already it is likely to be a pretty sound casting!

As a rule of thumb I’d say that if there were enough metal around the bore to make a liner of sufficient wall thickness that it takes up no more than 1/3rd of the thickness of the cylinder wall then all will be well. It is further worth bearing in mind that the fins act as hoops and help stiffen the cylinder so the above proportions are probably conservative.

Turning now to C.I. pistons, in many ways it is an ideal material having excellent wear properties and a coefficient of expansion compatible with iron cylinders. It was only because of the advent of higher and yet higher engine revolutions that the mass of a C.I. piston became a very serious problem and as a result the much lighter aluminium piston came to reign supreme but it is really only its low weight that is in its favour.
Lets face it, when it comes down to it a piston is just something moveable that plugs a hole! I cannot then see why a C.I. compressor piston could not be able to do the job; both seal a bore, both are subjected to similar loads. Compressors don’t as a rule run as hot as an I.C. engine, (although I’ve known some that you wouldn’t want to keep your hand on), so clearances might be a bit tighter for a given bore but that is about it and certainly worth a try.