Oil drain question

I was cleaning up the cases on 69 750 yesterday and while blowing out the oil drain hole from the rear of the right cylinder barrel, the one that drains oil from the area of the intake valve springs, I noted that when it get into the timing side case it makes a hard right and empties into the rear of the timing chest. My question is why doesn't it simply drain straight down into the crankcase. There must be some reason for it's path as Norton went out of their way to drill another hole (and add an additional machining operation) but It seems that there is already plenty of oil in the timing chest waiting to be drained back into the crankcase. Wouldn't it make sense to just drill the hole straight down into the crankcase? I was tempted to do that but thought it might be best to seek the thoughts of those who know.

Cheers

Norton thought the oil pump return would be or could be, at times, effective enough to keep oil level below that needed in TS case so diverted some head oil just in case, not enough leaked out the crank feed seals.

I would leave the oil return into the timing chest. It may be possible under some conditions to run the timing chest low without it. Jim

I think a cover screw can plug the drool while addressing surfaces before resealing or floor after obvious oil removed.
Jim you made us aware of benefit of lowering the TS case oil level and noted less heat off the cover. Any idea what may be the main reason, less heated engine oil collecting in there or lack of windage oil shear friction? Oil shear seems to be a good part of the oil temp issue. Also how good an oil path is a spinning bearing like the superblend with the TS shield but not sealed on either side? Is that why there's a TS oil level drain hole? Any idea if a proper pump and shaft seals leak at peak operation or hold tight? Of course if they are bad fit or blow out that'd loose oil to the TS case galore.

Nit picky builders polish the insides they say to allow faster drain off, I wonder if what would even be detectable somehow in a Norton? Pretty picture for one thing. That'd take a lot of Commando worshiping rituals.

hobot said:

I think a cover screw can plug the drool while addressing surfaces before resealing or floor after obvious oil removed.
Jim you made us aware of benefit of lowering the TS case oil level and noted less heat off the cover. Any idea what may be the main reason, less heated engine oil collecting in there or lack of windage oil shear friction? Oil shear seems to be a good part of the oil temp issue. Also how good an oil path is a spinning bearing like the superblend with the TS shield but not sealed on either side? Is that why there's a TS oil level drain hole? Any idea if a proper pump and shaft seals leak at peak operation or hold tight? Of course if they are bad fit or blow out that'd loose oil to the TS case galore.

Nit picky builders polish the insides they say to allow faster drain off, I wonder if what would even be detectable somehow in a Norton? Pretty picture for one thing. That'd take a lot of Commando worshiping rituals.

Click to expand...

I lower the oil level with a new hole. Basically that lowers the oil level in a Commando timing case to about the level in the Atlas motor.
When they tilted the motor forward for the Commando they did not change the drain hole position in the timing case - so then the oil level gets very high.
When the timing gears are completely submerged in oil then the turbulence creates a lot of heat. Jim

Oh ok Jim, that makes perfect Commando canted engine Norton factory oversight sense. This could influence where one might have an external intake rocker box drain end up if the engine had a large enough bore to take out the cylinder drain path.

Thanks guys, that's the kind of info I was looking for. I didn't mention it but one of the reasons I questioned the factory's drain routing was I remembered Jim's suggestion to drill an additional drain hole in the timing case to lower the oil temp (which I plan to do) so I didn't think there was need for more oil in the TC.

One other thing troubled me during my case cleaning session, namely the flow of oil through the sump drain plug back up to the return side of the oil pump. It appears that the oil in the sump passes thru the filter gause then out through the holes drilled around the circumference of the plug body, however, only one of the holes can line up with the passage cast in the case to return to the pump. And the alignment of that hole depends (essentially) on the thickness of the sump plug gasket. It looks to me like possible mis-alignment of the plug holes and the case passage could cause significant restriction in the return line to the oil pump. I'm not sure if I've explained this clearly but if one looks at the drive side case with the sump drain plug in place the cause of my concern should be apparent. I've considered marking the sump plug bottom and measuring the gasket thickness while it's apart to ensure proper alignment when reassembled. Or oval out the most likekly hole. Meanwhile, I think I'll start polishing all those oil passages (thanks for the idea Steve).