Excess Oil in Primary Chain Case

I just drained more than twice the correct amount of ail from the primary chain case. I was the last one to have it apart, and filled it carefully with the correct 200 cc. The engine oil is down a little, but it burned some from start after wet sumping after a long sit.

Found two posts that deal with this: https://www.accessnorton.com/Norton...l-in-primary-suspected-leaky-main-seal.39548/ and https://www.accessnorton.com/NortonCommando/oil-in-primary.21590/

My conclusion: Owning a Commando is a love-hate relationship. Heresy I know, but I'm wishing I'd gotten another old reliable BMW boxer.

swolh said:

I just drained more than twice the correct amount of ail from the primary chain case. I was the last one to have it apart, and filled it carefully with the correct 200 cc. The engine oil is down a little, but it burned some from start after wet sumping after a long sit. Any ideas how excess oil would get into the primary chain case?

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Starting a wet sumped engine can push oil past the crank seal and into the primary.

If you’re unlucky, it can push the seal out of the case in the process.

The other way a wet sumped engine can add oil into the primary is the oil level in the crankcase going higher than the lowest bolt of the 3 bolts that hold the primary case inner onto the crankcase. Parking on the side stand will make this more likely due to the leaning direction. Using loctite when fitting these bolts will eliminate this route.

If a reed valve breather is fitted to the big strainer / plug on the bottom of the engine, routed to the oil tank. Any oil collecting in the crankcases. will be transferred to the oil tank as soon as the engine is turned over

Andy Higham said:

If a reed valve breather is fitted to the big strainer / plug on the bottom of the engine, routed to the oil tank. Any oil collecting in the crankcases. will be transferred to the oil tank as soon as the engine is turned over

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That's the first I've heard of a reed valve breather fitted to the big strainer / plug. Where would I get one of those?
Mine is a 73 750.

After posting this thread, I found these two helpful threads: https://www.accessnorton.com/NortonCommando/oil-in-primary.21590/ and https://www.accessnorton.com/Norton...l-in-primary-suspected-leaky-main-seal.39548/

For wet sumping: in 2015, I installed a MK III timing cover and MK III oil pump, then in 2017 I shipped the MK III timing cover to Alternative Motorcycle Repair in Sahuarito, Arizona (520 762-1429 to have the right angled plug in the anti-wet sumping valve machined to use a round plug, less likely to hang up/stick slightly open. This seemed to stop wet sumping, until it sat for the last two years (my bad, don't ask).

If it hasn't already been done, it occurs to me the info and threads about oil in primary case ought to be linked or added to threads about wet-sumping. I recall reading all about wet-sumping back in 2015 and 2017, but don't remember reading that it could cause leaking oil (through threads on the bottom bolt or main seal) into the primary. Could be in some threads about wet-sumping and I'm just having a senior moment not remembering it.

I was able to use this one on my '74 bitsa engine. The XS650 breather that had been previously installed wasn't working properly, so I removed it, plugged the timing case hole, and went with a sump breather.

Te reed valve helps to clear the sump quickly on startup plus keeps the internal pressures down, but if the oil has already leaked into the primary then its too late to help on that. A MK3 oil pump leaks like a pre MK3 oil pump once worn. Your pump can leak internally between the feed side and the scavenge side, AMR can add o rings to the shafts to stop this. I do this mod myself and use X rings.

Or make your own, use a scooter emission reed valve and modify the strainer. This is work in progress, the vertical leg of the elbow needs to be extended above the strainer.

kommando said:

Te reed valve helps to clear the sump quickly on startup plus keeps the internal pressures down, but if the oil has already leaked into the primary then its too late to help on that. A MK3 oil pump leaks like a pre MK3 oil pump once worn. Your pump can leak internally between the feed side and the scavenge side, AMR can add o rings to the shafts to stop this. I do this mod myself and use X rings.

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Thanks. And thanks