Oil again

casamere · Post by **casamere** » Wed Nov 07, 2018 4:02 pm

I hardly dare ask this question on here but am hoping some members in the UK can answer it.
I have been running my rebuilt CA77 engine on minerel oil 20/50 for 3 years now and everything ok, but i have bought 4ltr of Motul 5000 10/40 as I read on Google it is a mineral oil but some posts there are saying it is part/semi synthetic.... who is right as i don't want to put it in the bike and suffer clutch slip I would rather take it back to the shop and get my money back.

e3steve · Post by **e3steve** » Thu Nov 08, 2018 2:37 am

This is worth a read:

https://www.xjbikes.com/forums/threads/ ... cle.43702/

John Watson · Post by **John Watson** » Thu Nov 08, 2018 7:19 am

I doubt you will have any problems with this particular oil, Steve. From what I've seen, it is a specific motorcycle oil, safe with a wet clutch.
The problems occur when oils with friction modifiers are used with wet clutches, and are normally well advertised on the container, one such modifier is molybdenum disulphide.

Tim Allman · Post by **Tim Allman** » Thu Nov 08, 2018 12:44 pm

John Watson wrote:I doubt you will have any problems with this particular oil, Steve. From what I've seen, it is a specific motorcycle oil, safe with a wet clutch.
The problems occur when oils with friction modifiers are used with wet clutches, and are normally well advertised on the container, one such modifier is molybdenum disulphide.

I agree. As long as you stay away from lawn mower sold in the hardware store and the very thin 0W20 etc. oils that cars use these days, you will likely be fine with something appropriate from a major manufacturer. Something labelled as motorcycle oil will be compatible with a wet clutch.

For reasons I don't understand there is a certain revulsion to synthetic oils. They are not "too slippery", whatever that means, and survive the shear forces in the transmission better than pure mineral oils. The down side is that they cost more but that's not a huge problem for these engines.

casamere · Post by **casamere** » Thu Nov 08, 2018 2:44 pm

Thanks for taking the time to reply guys but I also sent an e mail to "Opie oils" here in UK and their guy confirmed it would be ok as with the engine being rebuilt everything should still be tight.
Thanks again.

jkv357 · Post by **jkv357** » Fri Nov 09, 2018 9:23 am

I agree with Tim - synthetic oils are not any more "slippery" than conventional oils - just stronger because they have a closed molecular structure. The closed structure helps them flow better in cold temps and resist breaking down in extreme temps. It also keeps them from picking up free oxygen atoms and "oxidizing" - so there are benefits of using synthetic oil even during storage.

The "Friction Modifier"- thing may be an issue for the clutch, but they are only present in oils 30-grade and under - so no 10W-40 will have them anyway.

The bigger issue with some oils is the lack of adequate ZDDP (Zinc and Phosphate) additives used to protect solid (non-roller) valvetrains used in most cycle engines. Current automotive oils, conventional or synthetic, do not have adequate levels of ZDDP and should not be used in cycle engines.

If you don't want to go with a synthetic motorcycle-specific oil, the best low cost alternative is a diesel oil like Rotella or Delvac. They have adequate levels of ZDDP and no "Friction Modifiers" in any grade.