Originally Posted by
Butchi
A question: Did syntehtic oil exist when our car was made back at the eighties? We all know that the CVH head is running very hard at the cams, thats why the belt is supposed to be changed often compared to other cars. Im willing to think that the mineral oil 20-50w is more likely to sustain the oil film between the cam and tappets and other components.
Yes they were around, however they were very, very expensive so were generally not used/purchased and many places did not stock them for this very reason. Also cars had run fine on mineral oil for so long it took time for opinions to change with the fact to back it up that synthetics are better. At the end of the day engines not only back in the 80's but even now do not know what kind of oil is being used, what the oil is made from and quality is down to the owner. The engine is designed to run on a viscosity (thickness) when hot and in your case it was originally SAE40 @ 100degc.
When you look at the temp ranges of the oil, 20w may look ok as it says for -10degc and that is pretty chilly for the UK, however what it does not say is how well it will flow at those temps... Just that it will flow and compared to a 5w or even a 10w will not flow very well at all, causing your new cam to be starved of oil even longer on start up. No oil = wear.
Cheers
Guy