Tranny Oil

So I found a manual for the Honda Express NC50 on the mopedriders.org site, which is great because  I wanted to know what sort of oil I should put in the transmission case. The manual specs 10-W40.

Great, but hold on a sec. I had a vague memory of hearing that car and motorcycle oils are different. Further research revealed that this is very true. According to the stuff I read  (totally credible...probably) motor oil for cars doesn't have to lube the transmission, just spinning engine parts. Motorcycle oil, on the other hand, lubricates the transmission as well as spinning engine parts. The motorcycle's clutch is getting bathed in this oil, and it has to grip when things are in gear to transfer power from the engine to the rear wheel. The motorcycle oil has to balance the slip with the grip. The stuff in cars just needs to be as slippery as possible, the transmission has its own separate fluid situation. It seems like putting automotive stuff in your bike would mess with your power transfer and probably make your bike slower.

If you read the comments on this article, I think some people have gotten into this situation. They said after they changed the oil on their Honda Express, it was slower. Most of them seemed to be using oil meant for cars (some even said they were putting in mobil1) and so they're probably getting some extra slip on the shoes in their centrifical spring clutch.

I mean, I think that's what's happening, I'm no expert mechanic, but I think I figured something out. I also realize that I bought a quart of the wrong stuff a few months back. At least I didn't put it in just yet.

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Wait... I kept digging after I wrote this first part and saw something on the honda rebel forums that said car oil is fine as long as it doesn't have certain additives. I don't know how much I trust Honda rebel forums. First off, forums are not always super credible. Second, Honda rebels are lame bikes.  Actually, I shouldn't really say anything. All I have is a non-running noped, but I still don't trust forums.

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Okay, so after getting pretty nerdy and reading about wet and dry clutches and shearing viscous chains, I'm still going to use motorcycle oil instead of automotive oil because I think my clutch will slip less and lose less power.