timing case oiling

Rather than screw up someone else's thread which should be focused on their bike rebuild, I thought I would start a new thread to get some opinions.

Recently I modified my '70 commando by adding a reed valve breather to the blanking plate behind the timing cover. I drilled 2 new holes between the crankcase and the timing chest. I drilled one slightly above the crank bearing height to allow air movement, which should make sense because air needs to travel from the crankcase towards the timing chest to the reed breather in order to evacuate air pressure where it's being generated. I also drilled a smaller diameter hole down low behind the oil pump to allow oil to flow back to the sump from the timing chest side.

Danno stated that I've probably screwed up the oiling in the timing chest by lowering the oil level by drilling a hole down low, so I have some questions

How is oil normally supplied to the timing chest?

Is there normally an oil bath height inside the timing chest which is governed by the lowest hole between the timing chest and the crankcase?

How does the timing chest return oil to the sump when timing chest and crankcase holes are plugged for crankcase located breather modifications??

Obviously, since I have already drilled the hole behind the oil pump to allow oil to drain back to the crankcase, I am more than interested in the answers and opinions regarding my above questioons..... thanks...

Some oil comes from breather blow-by mist, but the bulk comes from the timing case oil ways directly from the pump past the conical rubber seal to the cam and pinion support bushings. The oil level is controlled by the height of the drain hole which is normally up by the camshaft drive axis. Jim Comstock posted about drilling a hole level with the drive pinion to reduce the level somewhat. Drilling a hole down by the pump means only the oil pump drive is submerged upon cold startup and as long as the pump has the sump clear.

I didn't say you screwed it up, I just said you lowered the oil level in the timing chest beyond which seems healthy for the timing drive. If anyone has done this without harming anything over the long run, I would be interested to hear about it myself.

Just found one thread where Jim says not to drill the drain hole by the oil pump unless you are using the reed valve crank case breather mod that requires case machining and mounting at the rear of the case.

Danno said:

Some oil comes from breather blow-by mist, but the bulk comes from the timing case oil ways directly from the pump past the conical rubber seal to the cam and pinion support bushings.

Click to expand...

Oil fed to the timing cover gallery from the pump goes to the crankshaft and valve gear (and some may be recirculated back to the pump inlet from the OPRV when cold pre- MkIII cover) but it isn't fed to the cam/bushes etc..

o0norton0o said:

How is oil normally supplied to the timing chest?

Click to expand...

Oil from the inlet side of the head also drains into the timing case.

https://www.oldbritts.com/oillines.html

The majority of the oil in the timing chest comes from the intake valve side drain from the head.

The new oil drain you drilled is OK with the reed breather on the timing chest. There is still going to be enough oil in the chest to lube everything properly.

DO NOT drill the lower drainback hole if the engine is going to be used in a vertical mount chassis like an Atlas.

DO NOT plug the upper ventilation holes unless you are using a crankcase mounted reed breather or a sump plug breather. Jim

Thanks Lab and jim. I appreciate the comments.