to add an additional question to his, if i am unsure if my bike (87 honda shadow vt700) has been running conventional or synthetic, am I safer running conventional?
I pm'd back and forth with another member, and they provided me with the below. Would everyone agree? If not, why not? Just trying to get as many opinions as possible to keep my bike damage free.
"A caveat about synthetics and old bikes. If your bike has never had synthetic, you may want to avoid it. Conventional oil builds a waxy film on the inside of an engine that's harmless, but is the nature of conventional oil. Over time, which our bikes have had plenty of, this film prevents oil from actually touching the metal surfaces inside the engine cases, which prevents the gaskets from being wetted by the oil. The gaskets dry out, which is also harmless since the film inside the engine is a good sealant. However, the powerful detergeants in synthetic oil strip this film away, and if the gaskets are dry, you develop leaks. I've switched a good number of '80s bikes over to synthetic and developed leaks in about 1/3 of them, casuing me to have to tear down and replace gaskets. For air-cooled bikes, it's worth it to me. For a liquid cooled engine, the benefits of synthetic oil are reduced, so if you want to save yourself trouble on a bike that's never had synthetic oil in it, you may want to hold off on switching. I use Rotella-T conventional 15W-40 ($16/galloon at Walmart) and it's great."