The problem with Castor oil is that it tends to form a varnish which can clog up your carburettor and gum up your rings and well as leaving a deposit on the piston.
on the other hand it has a far higher film strength than synthetic oil.
Synthetic oil on the other hand has less tendency to varnish and a higher lubricity (lower friction) than castor oil.
And then there is semi-synthetic (like Castro 747) which has both synthetics and Castor in the same base.
Tabor's favoured policy is to use Castor (R40) for running in, where the ability of the oil to repair the film when it has been torn by the ring shearing off the imperfections of the liner is an aid to protecting the engine. Once run in, then use synthetic or semi-synthetic (R747) to race the engine.
Others suggest that provided you do a proper runnning-in process you can use a synthetic or semi-synthetic oil for both.
Castrol suggested that they might use 747 to bed the engine, as the lower film strength allowed a quicker cutting of the cylinder and using the high film strength of a pure castor to protect the walls under race conditions....but added the proviso that he was talking about highly stressed motors which last for the length of one race only, while our motors are relatively lowly stressed in comparison. The final advice was that if castor then synthetic worked....use it.
In theory, post the run-in, using synthetic or semi is faster and certainly less gummy than a castor.
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Castor or Synthetic Oil? by 'GillardKid' (09 May 2010 @ 22:41)
