How to trace execessive oil consumption 850 MK2

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Hi Experts.
After setup the carb by your support my Bike is running now well but the next issue pops up.
Since I have the bike spark of left cylinder always shows a different colour compare right side. After new setup of carb we do a longer ride and I discover that the motor burns a huge amount of Oil. Means 100ml at 50 km!
Surrently I wait for a professional compression tester for checking the cylinder. For the bike exist no history so I have NO idea about the engine condition.
Target is to fix the issue fast to enjoy the rest of summer. A restore of Motor would be a desaster in time.
My question: Is such high consumption of oil posible by valves which worn-out?
Or ist it more the point of worn-out cylinder?
What would you do to trace that failure?
Thanks in advance for kind support. Regards Lorenz
 
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Normally you would have blue smoke coming out of the side that is burning oil, if the blue smoke is on acceleration then its likely rings, blue smoke on deceleration then valves, guides, inlet guide seals. My 850 MK2a was blowing blue smoke out of the left hand side as I pulled away from traffic lights, fitted new rings and honed the barrels and its not smoked since. Seems the left hand side wearing out the rings first is more likely than on the right hand side as the left side is furthest away from the oil pump so I also refurbed the pump at the same time. A leak test will show you were the issue is if you cannot see blue smoke.
 

Nater_Potater

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Not knowing the history of the bike, it could be a number of things:
1. Broken oil control ring. This probably won't show up in a compression test, as that's dependent on the upper rings.
2. Worn valves? Possibly loose guides allowing oil past the valve stem, and/or broken/missing intake valve seal. Those can be seen through the access plate over the intake rocker adjusters at the back of the head.

Search the threads for recent posts about this same issue and the means to troubleshoot the issue based on when the smoke appears, even going as far as to interrupt oil flow to the head for a brief period of time to eliminate bad valve seals.

As far as any major internal work of the engine being a disaster of time, I think you'd be pleasantly surprised as to just how easy a top-end overhaul is on these old girls, assuming you have the proper wrench set.

Nathan
 
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Thanks for the reply.
Hopefully the compression test shows a bit more informations.
Lorenz
 
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What oil are you using and where are you? Old engines and modern oils don't always go together.
 
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My bike burns about the same. I did a check a few months back and I seem to remember 300ml per 100 miles at its worst. It did vary and I thought the variation might be down to type of oil. My right cylinder does not run as wellasthe left though probably close enough to be acceptable. I had the cylinder head and barrels off and really could not pin it down. Check inlet valve seals is probably first action (after leak down test). If the leak down test is good then rings and valves are probably OK, it only leaves the valve guides and positive pressure as potential problem areas I think. Let me know if u find a cure, I will investigate again over winter. I suggest you do the same, use cheap oil and enjoy the summer!
 
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How high on the dip stick do you put the oil in the oil tank if you put it up to the high level mark it is to much and will blow out of the vent hose keep your oil level in between the low level and high level and see how it goes, I found this out when I first brought my Norton new and kept topping it up to the high level weekly once I started to fill only to the half way mark it never needed topping up and kept at that level.
When the oil is at the top mark there is not enough air circlation in the oil tank and because of that the oil will blow out of the vent hose, most experience Commando owners only fill to the half way mark, give it a go before you do anything else, when I first only filled to the half way mark my bike never need any oil top up between oil changes, the 850 Commandos don't have a very big oil tank and when full to the top level not much air ciculation.

Ashley
 
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I would agree with Ashman about oil level. Ive seen this in other engines not just bikes. Just keep a sharp eye on the level though.
 
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Thanks for replies.
I use 20W50 Oil but not syntetic style. Oil for old bikes.
Since I discover excessive oil consumption I fill oil to top level.
But it doesn't matter. Oil consumption is higher then a 2 stroke engine.
There is no automatic chain oiler assembled.
I interviewed friends yesterday. Impossible to reide behind me, huge amount of soot left side accelartion / deceleration doesn't matter, not blue, dark!
Will open the engine on weekend.
I afraid to destroy the whole motor once I drive withn this failure.
 

baz

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If it's black smoke it's running way too rich
If you run it like that it will wash the oil away from the bores the rings will rip the bores up
Don't over fill the oil tank ,just fill to the lower level on the dipstick
 
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Better safe than sorry and adds to confidence to know all is well.

The rear stud needs a home made/thinned/ground down ring spanner if this is your first time. Pushrods need to be held up into the head which is not so easy with oily fingers. It's an art.
 
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Black sooty smoke as spoken will yes mean a stuck float or an old carb float that has developed a leak or old stuck float bowl needle. How old are the carbs ?
 
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Hahahaaa it seems a new challenge! We measured compression. Not so easy with kicker.
Left side (with extreml soot) 7.5 bar right side With good brown spark color 7 bar.
I guess my concentration should be fixed on the head! Weekend and special grinded tool is needed !
 
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The rear stud needs a home made/thinned/ground down ring spanner if this is your first time.
Hi Robin.
Which size the ring spanner must have? Will order two of them before weekend for a grinding session! I assume strait ring spanner
 
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Sounds to me like you have two different issues. There appears an issue with the left carb, jetting, loose needle, sticking float, all needs examining and possibly knackered guides. I would check and confirm carbs match, internals as well first, then rebuild the head. Both compressions are similar but could still be an oil control ring for the oils.
 

baz

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Sounds to me like you have two different issues. There appears an issue with the left carb, jetting, loose needle, sticking float, all needs examining and possibly knackered guides. I would check and confirm carbs match, internals as well first, then rebuild the head. Both compressions are similar but could still be an oil control ring for the oils.
He has a single carb according to his thread
 
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I would check and confirm carbs match, internals as well first, then rebuild the head. Both compressions are similar but could still be an oil control ring for the oils.
Ok thanks for reply. Carb is not issue, but beside the compression and better compression on that side where the oil consumption appears it make sense to lift also cylinder once I have lift the head? I will do and check the rings
 
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