Originally Posted By: FetchFar
Thanks, I had no idea this has ever been attempted. I'll bet many of us "invented" this in our heads over the years when thinking about what tribology we want for cams vs. stuff near the combustion chamber.
I'd think the old Fiat SOHC cams in an oil bath might overheat, not sure, but that seems to be a good way to go to separate cam oil properties from piston/rings/crank oil properties. Assuming it was ez enough to change the Cam Oil up there in the "attic", and how long it would last. Also, having a bath there eliminates the need for a second oil pump.
Anyway, a fellow I know that works for GM hinted (leaked?) at an SAE meeting that this will be done soon. Can't wait to see that. It looks like some engine folks are dissatisfied with oil properties compromised to work over the entire engine, with vastly different boundary oil conditions.
Interesting comment from GM. With belts, it's easy to imagine, however with chains, how will they do it? Group the chain and head into one 'oil case' and the rest into another? I can see the chain shaft being used as a head oil drain perhaps, and the head oil pickup being at the crank sprocket area (sealed from the rest of the crankcase).
Originally Posted By: Shannow
Interesting question...
When I was at University, and we were studying engine lubrication, my lecturer was a proponent for separate compartments and lubricants for the bearings and the pistons.
Multigrade for the crank and bearings, and 30 straight for the pistons and rings...sort of makes sense when you see some of the ring seal studies.
Now you really need three...one for the valvetrain too !!!
I remember an old chart comparing wear rates between different types of oils in an old MB OM, the straight 30 provided the best ring protection vs multigrades at, wait for it, wait for it, cold start!
Originally Posted By: FetchFar
Would the valvetrain one be higher viscosity, more EP additives, for example?
Would the valvetrain one have very long OCIs?
1: yes
2: yes
May do something like this in the future, because there is a SOHC engine with a taller deck height that I want to use a DOHC head on; same gasket pattern except for the oil drainback holes. Was thinking of closing the drain holes on head and block, sealing the head feed jet, and refeeding the head with an external pump and it's own oil case, with the head drainback channels tapped into for an oil return.
r
Ideally, I'd use high viscosity for the valvetrain, ie 40 grade, with minimal artificial viscosity spread (ie un-VMed, high-VI base oil), and the additive pack of a race oil, no need for over-basing (TBN) as combustion gasses are not expected to contact the 'head oil' (barring bad stem seals), and allowing the add pack to work more effectively. Straining and magnetic filtration inline.
Bottom end sees a lot of windage and high-speed friction (rings). I'd be keen to use a low- to non-artificially VMed 30 grade (turbo), or 20 grade (NA), with high VI base stocks and a standard, based addpack. Crankcase ventilation to be tapped at the top of closed oil return passages and fed to air intake.
