STOP - Only use a synthetic oil. Using a NON synthetic oil will cause the viscosity to change rapidly in the Triumph engine. Non synthetic MULTI GRADE oils have viscosity modifiers that break down when subjected to "choppers" such as gear trains in our transmissions. The 15W-40 will rapidly become a 15W only which will not give enough protection to the main and rod bearings resulting in ^&&$#@!$$! (Big mess). Synthetics do not have this problem.
That's why they are needed in our engine/transmissions. If we had a separate transmission which used a gear type oil, then a non synthetic oil could be used in the engine proper.
