combat oil return

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JimC, No advantage, at the time I was using the stock tank which has only one breather inlet and I had two breathers, so I hooked up the 850 "style" to the tank. I now use an alloy central tank which I can weld on two inlets with one 5/8 outlet. I also use a "sight" tube on the side of the tank to monitor quantity of oil.
 
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Wow, this has started something. Wish it had been so clearly documented when I was having trouble back in 98-00.
Hewho's doubt over where the oil goes is understandable. For sure some is in the top end, pipes and filter and even the tank empty. When I was messing around with the original cases I never filled them to see how much they and the timing chest would hold. But, with the crank and rods in place there's a surprising volume in there + the undersides of the pistons etc. Say 0.5 litre in the filter and pipes, 0.2 litre head, 0.2 litre in the tank under the feed, 0.2 litre timing chest. That leaves 1.7 litres or so for the cases and piston insides. It's possible but it does sound a lot.....oh wait a minute that's why it pumps out of the base gasket, into the head and out of the exhaust!!
With the breather sucking air back in or each stroke as well as pumping it to the tank there will always be some extra pressure in the cases from blowby etc. The one way valve minimises that but does not stop it completely. Mine also had an intake cover breather which was eliminated once the root cause was fixed.
 
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Another problem can arise from a severely sumped engine. The drive side main seal might fail and fill the primary chaincase.

However, you'll know it soon...the clutch will tell you. :p
 
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Perhaps I am thick but how the hell do you kickstart a cold engine if the crankcase contains all the oil as some are claiming? I have run Commandos 35 years on the road and a lot of racing,trackdays etc and have never had a lubrication failure and this includes 2oo plus mile runs at motorway speeds eg in excess of 85mph. I often wonder if we are as good at rebuilding engines etc as we think we are and whether we like to admit it or not a lack of skills and care cause the majority of oil leaks for which we suffer endless ridicule. Use semi synthetic 15/40 and get on and use it. Anything mechanical is only as good as the last person to work on it!
 
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Perhaps I am thick but how the hell do you kickstart a cold engine if the crankcase contains all the oil as some are claiming?
Depends how full I guess but yes it would be difficult and is likely the reason some owners end up with more in the chaincase than they'd like. That never happened to me as all of my rides end up in a 30-40 limit when the pump had time to recover most of the oil.

I have run Commandos 35 years on the road and a lot of racing,trackdays etc and have never had a lubrication failure and this includes 2oo plus mile runs at motorway speeds eg in excess of 85mph. I often wonder if we are as good at rebuilding engines etc as we think we are and whether we like to admit it or not a lack of skills and care cause the majority of oil leaks for which we suffer endless ridicule. Use semi synthetic 15/40 and get on and use it. Anything mechanical is only as good as the last person to work on it!
Good point but does that include a Combat? My previous Commando experience was with pre 72 versions and until I found out about the case mod I'd taken the NOC notes on 850 breathers as gospel, so had the PO of my bike. They don't specifically mention the pickup problem/mod as it probably wasn't documented until Mick Hemmings started doing it in the 80's? I'm a slow learner and even slower to put things right but I now know how to assemble these engines for an oiltight result. I too could not believe such a problem existed and that I'd wasted so much time before turning up the solution.
 
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Yes sorry the bike I use for trackdays is a Combat with standard crankcases and it does quite a bit of road mileage. I change oil and filter every 1K miles. If you make a breather in the inlet rocker cover it helps no end as well. I always give at least 10 mile warm up on the road before giving it welly. There is a lot of oil to warm up and this is crucial. I believe Castrol did a temperature test for castor oils many years ago on the IOM and it took one and half laps ( more than 55miles!!!!) before oil temp. was correct for max. performance. Interesting yes.......maybe not :shock:
 
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