Timing case holes?

Hopefully someone else can confirm that. I am wondering how the timing case fills with oil to lubricate the chain and gears and I didn’t notice any hole low down from the crankcase or anything discharging into the timing case, so perhaps it is return flow from the head as you suggest…..

Thanks Peter, I didn’t spot a path past the triangular washer and have not had to remove it (yet!)

Thanks all for your explanations, makes sense now. I did look at the diagram in the workshop manual but the detail around the timing case area is not very clear in my black and white copy.

Latest event in my Commando relationship….

Oil in tank midway between the level marks. No oil in catch tank I fitted between oil tank and pancake filter breather connection after a few hundred miles of operation, only condensation, so catch tank removed…this might have been premature! Spirited riding yesterday including a motorway stint, bike ran great but a bit lumpy after the motorway and then stalled at a junction. Noticed a lot of oil in vicinity of the air filter and the level was below the dip stick. Slow ride home where I topped up the oil tank to lowest level mark….1.2 litres….this might have been premature!! Ride 10 miles today, stopped to find an oil slick on the road and oil everywhere else, dripping from the air filter: oil tank was full :-(

So it appears that after the high speed run the missing oil was lurking in the engine, I think in the timing case. What I do not understand is why, during the 30 minutes of slow running (<3000 rpm) after leaving the motorway, any excess oil in the timing case didn’t flow into the crankcase and get scavenged by the pump back to the oil tank.

Ref my photo earlier in this message thread, perhaps the crankcase holes are so small that it takes more than 30 minutes for the timing case level to return to ‘normal’ but the oil was hot and I find this hard to accept. Perhaps there was an adverse pressure differential with the PCV valve fitted in the crankcase breather hose which flows from the timing case, and positive pressure due to piston blow by in the crankcase was opposing oil flow from the timing case. Anyway, it seems that my Commando riding must be sedate in future :-(

Nothing that I noticed, including during subsequent strip of the pump to tighten the gear clearances 

So now I have changed to a breather at the rear of the crankcase as per original 1972 bike and retained the PCV valve which I’d fitted in the line to the oil tank. The non-std breather connection to the rear of the timing chest has been blocked. Oil level is just above the low mark on the dipstick. I rode the bike on the motorway today for 10 miles at around 4200rpm/70ish mph, then pulled over at a junction and checked inside the oil tank filler: a little frothing but good return flow, no discernible flow from the breather and most importantly oil level unchanged! Which all makes me think that the original 1972 setup is fine for normal road use. My conclusion about the problem with the breather from the timing chest in combination with the PCV, which resulted in a large drop of oil tank level at motorway speeds, is that the small flow area (with original holes between timing chest and crankcase) restricts oil flow back to the crankcase and the pump scavenge port, more so when the PCV is lowering the mean pressure in the timing chest relative to that in the crankcase. As the oil level rises in the timing chest it tends to an even more adverse pressure difference because the holes to the crankcase are progressively being covered by the rising oil, impeding gas flow and pressure equalisation. Well that’s a theory which fits the symptoms on my bike anyway!

@Julian, there is foam in the breather now I and hadn’t thought to omit it. I guess it’s intended purpose is to reduce any oil that might be blown into the oil tank but with my combat arrangement that might actually help with scavenging! I would leave at least one perforated plate if it is retained without foam present, as a precaution against a foreign object passing into the crankcase, although an unlikely eventuality?

Regarding the Y, I did think of doing this as I am in possession of 2 breather ‘elbows’ and thought it would help equalise pressure across the chest-crankcase holes, but I want to retain the PCV which does appear beneficial for oil tightness and would have to be ‘above’ the Y, plus I want to encourage oil to return to the tank possibly via the breather line and a Y below the PCV might instead allow the oil to meander between chest and crankcase. It’s difficult to be confident about the actual effects, all I really know is my latest arrangement appears to have stopped a large quantity of oil pooling in the timing chest :-)

10 miles at 4500rpm today: same result as for 4200rpm reported above so all good. Fast enough for me on U.K. roads :-)