Topic: Oil

[Rjgordon0]

Hi, I'm new to this site so hello!!
I've just bought two 1978 CB750F2 for restoration. I was wondering with the leaps in technology since the 70s if it is ok to use a fully synthetic or even a semi synthetic oil in the engine or should I stick to the standard 10w-40 ?
Thanks in advance
Bob.

[slikwilli420]

Welcome to the board and a very hot topic. I will only speak to what has worked for me and you can go from there. I have had great experience with Shell Rotella 15w-40 in both street and racing applications. I switched to Motul 5100 10w-50 oil for my race bike and have zero complaints. Any motorcycle oil that is wet clutch compatible should be more than up to the task for our old engines, especially compared to oils available when these bikes were new.

[Stev-o]

Hello and welcome.

This is a great question and my all time favorite!  What is the best oil to use?!

There have been "leaps in tech" in oils but my old Honda still has a wet clutch, modern oils have been known to cause "slippage".  I suggest using a motorcycle oil made specifically for wet clutch systems.

What bike do you have, BTW?

[PeWe]

NOT 10W-40 in a CB750 during normal spring- summer is my experience, gearbox feels very hard.
20W-50 war recommended by Honda. 10W-40 on the label has a history Hondaman has explained if you search.

I have used several 10W-40 during brake period  in and all caused very hard gear box.
 Next break in 20W-50 since I think 10W-40 as I have tested is not good for the engine.
Harder wear on cam and crank bearings and their friends.

Mineral, semi synth, "full" synth or Ester synth will work fine.
Must be for wet clutch JASO MA on the bottle.

If you search you will find not that old oil threads with recommended oils. Spectro is one of them in any of mentioned types.

I have got the impression that Harley Davidson recommended V-twin oils in 20W-50  is also good for our CB750's.

I have 2 rounds of Eurol HD oil, cheap synth to test in my CB750 K2. I have to ride it 3000km first so I can verify a change and tell others if good.
 
How the gearbox feels when shifting gears and find neutral on a hot engine when standing still are my parameters.

Some think good synth will not work.
My CB750 K6 get Red Line 20W-50, summertime with a mix of  a little 20w-60 too
I bought a box of bottles the warm summer 2018 so I put a bottle in the mix.
But that engine has extra $ power and need good lube.

[Pielz]

Shell Rotella T6 is a fully synthetic diesel oil that's JASO MA and MA2 rated and it's only 20 bucks or so for 5 quarts. A lot of folks run that

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[Johnie]

My choice...Castrol motorcycle oil. Do not use conventional car oils in these bikes as they are not wet clutch friendly.