Early Engine Oil -
Detergent vs. Non-Detergent
When early engines (prior to 1954) were new, oil filters were an accessory item and non-detergent oil was the type of oil used. Original, unrestored engines have most likely been run on non-detergent oil. If you are running an early unrestored engine that is not spotlessly clean internally, it is imperative to continue to run it on non-detergent oil. Otherwise there is the risk of damage to the engine.
Non-detergent oil was used before oil filters became standard equipment. This type of oil would "stick" contaminants to the sidewalls and valleys of the engine to prevent dirty oil from damaging bearing surfaces. Engines that have been run on non-detergent oil for many years will have a thick "sludge" buildup. Sludge will appear to be oil that has turned to gelatin except that it will be very black with contaminants.
Using detergent oil in an engine that had been running non-detergent oil would allow these contaminants to be released to flow through the engine. This could result in serious damage to the rod, main and cam bearings as well as other engine components such as lifters and plugging of oil lines.
After an engine has been rebuilt or thoroughly cleaned, use straight grade 30 WT or multi-grade 10-30 or 10-40 WT detergent oil to keep the engine clean. Early oil filters only filtered a small portion of the oil flowing through the engine. Unlike modern, full flow filters, these add-on filters are more of a decoration than real protection for the engine. Even if your engine does not have an oil filter, the number of miles a vintage car is driven is much less than when these cars were new. The simple solution is to change your oil more often. Every 500 miles or a minimum of once per year is a good rule of thumb.
An oil additive such as Lucas is recommended when using modern detergent oils. This additive will give additional protection to engine bearing surfaces and increase oil pressure as well. Keeping your engine oil clean is vital to extending the life of your engine. Be sure to use the proper oil and change it often.