Oil in the airbox/breather

BOBBREEKS · May 25, 2023

Hi Team,
I can't find a thread, so excuse this inquiry if it's a duplicate. My 961 appears to be using the airbox as a secondary oil tank. The catch tank has been filling up quick smart. I have been advised to be careful with the oil levels when checking on the dipstick, and only relying on the lower level to guage the correct level. That being the veruy bottom of the stick.I have just completed an oil change cycle and even before getting any indication on the dipstick of a level, after running the motor for 2mins oil is settling into the airbox. The previous owner told me he fitted a large touring bottle to catch the excess and tip it back in the oil tank at the end of the ride. My questions, is this normal ? And should I be concirned with the amount of oil "breathing" into the airbox? I am loath to fit my new very expensive air filter as the previous one had a level mark on it of old oil !! The new airfilter is actually longer/deeper so it will get wreaked sooner
I have what appears to be a filter in line and a plastic collector tank fitted I was told that my dipstick was a newer factory fitment.
I guess my next job is to see where this is coming from the crankcase or rocker. Any thoughts and wisdom would be most welcome.
(Like fitting a litre bottle catch tank).
Best wishes
Bob

Boss302 · May 25, 2023

BOBBREEKS said:
Hi Team,
I can't find a thread, so excuse this inquiry if it's a duplicate. My 961 appears to be using the airbox as a secondary oil tank. The catch tank has been filling up quick smart. I have been advised to be careful with the oil levels when checking on the dipstick, and only relying on the lower level to guage the correct level. That being the veruy bottom of the stick.I have just completed an oil change cycle and even before getting any indication on the dipstick of a level, after running the motor for 2mins oil is settling into the airbox. The previous owner told me he fitted a large touring bottle to catch the excess and tip it back in the oil tank at the end of the ride. My questions, is this normal ? And should I be concirned with the amount of oil "breathing" into the airbox? I am loath to fit my new very expensive air filter as the previous one had a level mark on it of old oil !! The new airfilter is actually longer/deeper so it will get wreaked sooner
I have what appears to be a filter in line and a plastic collector tank fitted I was told that my dipstick was a newer factory fitment.
I guess my next job is to see where this is coming from the crankcase or rocker. Any thoughts and wisdom would be most welcome.
(Like fitting a litre bottle catch tank).
Best wishes
Bob

Bob
Welcome to the complex and perplexing world of the SG Norton. The subject you describe is among the most common discussions of 961 owners. The problem arises mostly due to the high location of the oil tank and improper correction via the lower end vent system. There are multiple techniques that have been attempted to resolve this and some seem to have results, others not so much. In my experience your main simple effort will be to run a lower oil level in your oil tank. I even extended my dip stick to meter a lower level. A longer dip stick is also available. You are fine running less oil in the tank. Some suggest letting the oil level drop until the amount vented into the airbox and the catch bottle becomes manageable. It will help for you to tell us what year your 961 is and provide a picture of the vent system you currently have from the engine block up to the airbox. How many miles do you have on it?There was a factory mod offered to try to resolve this problem but it did little. Regarding the expensive air filter, there are fram filters for around 50 American dollars that can be modified to fit with minor effort. You will find several members in this forum who are professional Norton mechanics who have worked with this airbox oil problem extensively and have more experience. City Garage(usa), StuBodycote(england), and TonyA(usa) among others. We have all dealt with this problem and many continue to do so. It is a design flaw in the bike. Your bike has numerous other design issues possibly including clutch, valves, timing chest, electrics, exhaust system mounts, etc. Improper assembly and tightening of bolts and rivets was common. My advice is to stay up to date with these threads which are quite active and current. You may save yourself some big headaches.

cliffa · May 25, 2023

BOBBREEKS said:
Hi Team,
I can't find a thread, so excuse this inquiry if it's a duplicate. My 961 appears to be using the airbox as a secondary oil tank. The catch tank has been filling up quick smart. I have been advised to be careful with the oil levels when checking on the dipstick, and only relying on the lower level to guage the correct level. That being the veruy bottom of the stick.I have just completed an oil change cycle and even before getting any indication on the dipstick of a level, after running the motor for 2mins oil is settling into the airbox. The previous owner told me he fitted a large touring bottle to catch the excess and tip it back in the oil tank at the end of the ride. My questions, is this normal ? And should I be concirned with the amount of oil "breathing" into the airbox? I am loath to fit my new very expensive air filter as the previous one had a level mark on it of old oil !! The new airfilter is actually longer/deeper so it will get wreaked sooner
I have what appears to be a filter in line and a plastic collector tank fitted I was told that my dipstick was a newer factory fitment.
I guess my next job is to see where this is coming from the crankcase or rocker. Any thoughts and wisdom would be most welcome.
(Like fitting a litre bottle catch tank).
Best wishes
Bob

Welcome Bob, I think this is the thread you refer to...

Unraveling the 961 part two (oil in the air box)

There are two shortcomings with the 961 that have annoyed me the most. One is the idle which I've been investigating HERE The other is oil in places it shouldn't be! Neither unfortunately can be fixed with a cable tie! So this thread is going to deal with understanding the oil in the airbox...

www.accessnorton.com

Out of interest what year is your bike and what mileage.?

Us 961 owners are very lucky to have some very good folks on here as Boss302 mentioned. But in the UK you are double lucky as @Stu Bodycote ( ex Donnington Norton ) specializes in maintaining them. He is based in Derby and is very highly regarded.

Lots of info. on here. The search feature is your friend

Cheers,

cliffa

BOBBREEKS · May 25, 2023

Boss302 said:
Bob
Welcome to the complex and perplexing world of the SG Norton. The subject you describe is among the most common discussions of 961 owners. The problem arises mostly due to the high location of the oil tank and improper correction via the lower end vent system. There are multiple techniques that have been attempted to resolve this and some seem to have results, others not so much. In my experience your main simple effort will be to run a lower oil level in your oil tank. I even extended my dip stitch to meter a lower level. A longer dip stick is also available. You are fine running less oil in the tank. Some suggest letting the oil level drop until the amount vented into the airbox and the catch bottle becomes manageable. It will help for you to tell us what year your 961 is and provide a picture of the vent system you currently have from the engine block up to the airbox. How many miles do you have on it?There was a factory mod offered to try to resolve this problem but it did little. Regarding the expensive air filter, there are fram filters for around 50 American dollars that can be modified to fit with minor effort. You will find several members in this forum who are professional Norton mechanics who have worked with this airbox oil problem extensively and have more experience. City Garage(usa), StuBodycote(england), and TonyA(usa) among others. We have all dealt with this problem and many continue to do so. It is a design flaw in the bike. Your bike has numerous other design issues possibly including clutch, valves, timing chest, electrics, exhaust system mounts, etc. Improper assembly and tightening of bolts and rivets was common. My advice is to stay up to date with these threads which are quite active and current. You may save yourself some big headaches.

Thanks so much for that infomation.
I have a 2014 SF Sport 13000 miles on the clock and the venting system is the arrangement with the blanked off rocker box and the plastic box between the crankcase and the airbox.
So running it with as little oil as you can get away with is the answer? I took the crankcase breather off to check this was the offender and the oil pumps out at such a rate it looks like an oil return pipe. It's no wonder the bike smokes on start up. How was this resolved in the "new" 2023 bikes? Or was it just a case of fitting a larger catch tank and an even longer dipstick.

BOBBREEKS · May 25, 2023

cliffa said:
Welcome Bob, I think this is the thread you refer to...

Unraveling the 961 part two (oil in the air box)

There are two shortcomings with the 961 that have annoyed me the most. One is the idle which I've been investigating HERE The other is oil in places it shouldn't be! Neither unfortunately can be fixed with a cable tie! So this thread is going to deal with understanding the oil in the airbox...

www.accessnorton.com

Out of interest what year is your bike and what mileage.?

Us 961 owners are very lucky to have some very good folks on here as Boss302 mentioned. But in the UK you are double lucky as @Stu Bodycote ( ex Donnington Norton ) specializes in maintaining them. He is based in Derby and is very highly regarded.

Lots of info. on here. The search feature is your friend

Cheers,

cliffa

Cliffa, mine is 2014 with 13,000 miles, thank's for that pointer. What do the majority of owners do to solve this issue? It sounds unsolvable, short of a complete redesign of the oil tank and plumbing. Thanks again.

cliffa · May 25, 2023

BOBBREEKS said:
Thanks so much for that infomation.
I have a 2014 SF Sport 13000 miles on the clock and the venting system is the arrangement with the blanked off rocker box and the plastic box between the crankcase and the airbox.
So running it with as little oil as you can get away with is the answer? I took the crankcase breather off to check this was the offender and the oil pumps out at such a rate it looks like an oil return pipe. It's no wonder the bike smokes on start up. How was this resolved in the "new" 2023 bikes? Or was it just a case of fitting a larger catch tank and an even longer dipstick.

TVS Norton have not shared much detail on the improvements they made to the 961 unfortunately, but I suspect it is mainly improved quality control and tolerences.

Some bikes seem to suffer more than others with oil in the airbox. It may be down to poor pump scavenge performance or excessive piston ring blow by. Member Iwilson reverted his bike to the original Mk1 setup, by routing the crank breather up to the right rocker cover, then on the left side another hose to an oil / air separator toward the rear of the bike, and from there to the atmosphere. Most of the oil blown up from the bottom end then ends up in the rocker cover, and he reports mostly vapour in the separator. I'm not sure what he did with the breather which runs up to the oil tank though, but I know some folks have routed it to another catch can. Like I said lots to read up on.

Boss302 · May 25, 2023

BOBBREEKS said:
Thanks so much for that infomation.
I have a 2014 SF Sport 13000 miles on the clock and the venting system is the arrangement with the blanked off rocker box and the plastic box between the crankcase and the airbox.
So running it with as little oil as you can get away with is the answer? I took the crankcase breather off to check this was the offender and the oil pumps out at such a rate it looks like an oil return pipe. It's no wonder the bike smokes on start up. How was this resolved in the "new" 2023 bikes? Or was it just a case of fitting a larger catch tank and an even longer dipstick.

You will certainly be getting some responses from the professionals who frequent this forum who have seen the results of several attempted fixes. I have heard some say they have had complete resolution of the problem and others with continuous oil output. My 2015 does not even have rocker cover banjos and just sends the vent from the base to the airbox with the plastic separator Interposed. I have a few questions for the pros also.

Some bikes wet sump more than others and there are discussions of this to be found. My bike seems to output oil more after it has been sitting and has collected oil in the bottom end. Does a recirculation vent outflow occur as the oil returns to the tank after sumping?

What year bikes did or didn't have the rocker banjos involved in the venting?

At this time much remains unknown about the 2023s and information about specific corrections has been hard to come by. Much frustration has resulted from this lack of transparency among the earlier model owners.

TonyA · May 25, 2023

Boss302 said:
Does a recirculation vent outflow occur as the oil returns to the tank after sumping?

When the sump is overfilled with oil there is more oil than usual coming out of the crankcase breather tube when started .

TonyA · May 25, 2023

Boss302 said:
What year bikes did or didn't have the rocker banjos involved in the venting?

By Mk2 2016 this was fully implemented.

TonyA · May 25, 2023

BOBBREEKS said:
Hi Team,
I can't find a thread, so excuse this inquiry if it's a duplicate. My 961 appears to be using the airbox as a secondary oil tank. The catch tank has been filling up quick smart. I have been advised to be careful with the oil levels when checking on the dipstick, and only relying on the lower level to guage the correct level. That being the veruy bottom of the stick.I have just completed an oil change cycle and even before getting any indication on the dipstick of a level, after running the motor for 2mins oil is settling into the airbox. The previous owner told me he fitted a large touring bottle to catch the excess and tip it back in the oil tank at the end of the ride. My questions, is this normal ? And should I be concirned with the amount of oil "breathing" into the airbox? I am loath to fit my new very expensive air filter as the previous one had a level mark on it of old oil !! The new airfilter is actually longer/deeper so it will get wreaked sooner
I have what appears to be a filter in line and a plastic collector tank fitted I was told that my dipstick was a newer factory fitment.
I guess my next job is to see where this is coming from the crankcase or rocker. Any thoughts and wisdom would be most welcome.
(Like fitting a litre bottle catch tank).
Best wishes
Bob

Hi Bob , If your bike wet sumps you must fix this first . Determine how much oil and how long it takes to drain to the sump .
Next find out what length oil dip stick you have , measure from the bottom of the cap to the end of the stick (150mm) from memory. Oil can run back down the oil tank vent tube to the back of the head especially under heavy breaking . A newer stick is available of the longer length. Last run a compression test and get back with the results when you can .
Look Here :

Norton 961 Compression Test

Hello , I thought I would test my compession again and I was surprised to find it so high. I was expecting 150-160 psi and I was wrong. Left cylinder 176 psi Right cylinder 180 psi Current mileage

www.accessnorton.com

Boss302 · May 25, 2023

BOBBREEKS said:
Hi Team,
I can't find a thread, so excuse this inquiry if it's a duplicate. My 961 appears to be using the airbox as a secondary oil tank. The catch tank has been filling up quick smart. I have been advised to be careful with the oil levels when checking on the dipstick, and only relying on the lower level to guage the correct level. That being the veruy bottom of the stick.I have just completed an oil change cycle and even before getting any indication on the dipstick of a level, after running the motor for 2mins oil is settling into the airbox. The previous owner told me he fitted a large touring bottle to catch the excess and tip it back in the oil tank at the end of the ride. My questions, is this normal ? And should I be concirned with the amount of oil "breathing" into the airbox? I am loath to fit my new very expensive air filter as the previous one had a level mark on it of old oil !! The new airfilter is actually longer/deeper so it will get wreaked sooner
I have what appears to be a filter in line and a plastic collector tank fitted I was told that my dipstick was a newer factory fitment.
I guess my next job is to see where this is coming from the crankcase or rocker. Any thoughts and wisdom would be most welcome.
(Like fitting a litre bottle catch tank).
Best wishes
Bob

Bob
Be sure to download (Richard Coote service manual) for free online. Just search those words. Very informative and well done. You can send him a donation if you like but it's free otherwise.

cliffa · May 26, 2023

Boss302 said:
Bob
Be sure to download (Richard Coote service manual) for free online. Just search those words. Very informative and well done. You can send him a donation if you like but it's free otherwise.

Actually they and many other useful publications are available in the “Resourses“ section.

regental · May 26, 2023

On my 2013 bike without the anti wet sump valve, I always checked the oil while the engine was running - it quickly drained back once the engine was turned off so gave a false reading on the dipstick.

BOBBREEKS · May 26, 2023

TonyA said:
Hi Bob , If your bike wet sumps you must fix this first . Determine how much oil and how long it takes to drain to the sump .
Next find out what length oil dip stick you have , measure from the bottom of the cap to the end of the stick (150mm) from memory. Oil can run back down the oil tank vent tube to the back of the head especially under heavy breaking . A newer stick is available of the longer length. Last run a compression test and get back with the results when you can .
Look Here :

Norton 961 Compression Test

Hello , I thought I would test my compession again and I was surprised to find it so high. I was expecting 150-160 psi and I was wrong. Left cylinder 176 psi Right cylinder 180 psi Current mileage

www.accessnorton.com

TonyA, thanks for your help. I will compression test it in the next couple of days to give some hard figures to look at. The dip stick is 153 mm to the bottom of the threaded base. What was wrong with the old MK1 closed crankcase breather system? It would seem like an elegant solution with the excess oil draining down, and the "mist" heading for the airbox. Clearly something was not quite right with this system as it was abandoned foe something which didn't work very well either.
Expediency would suggest a largebore drain pipe from the air box and a huge 1 lt catch tank at this stage if the compression test doesn't suggest a ring/barrel job.
Thanks also to Boss302, Cliffa and Regental for your help.

BOBBREEKS · May 26, 2023

TonyA said:
Hi Bob , If your bike wet sumps you must fix this first . Determine how much oil and how long it takes to drain to the sump .
Next find out what length oil dip stick you have , measure from the bottom of the cap to the end of the stick (150mm) from memory. Oil can run back down the oil tank vent tube to the back of the head especially under heavy breaking . A newer stick is available of the longer length. Last run a compression test and get back with the results when you can .
Look Here :

Norton 961 Compression Test

Hello , I thought I would test my compession again and I was surprised to find it so high. I was expecting 150-160 psi and I was wrong. Left cylinder 176 psi Right cylinder 180 psi Current mileage

www.accessnorton.com

TonyA, thanks for your help. I will compression test it in the next couple of days to give some hard figures to look at. The dip stick is 153 mm to the bottom of the threaded base. I was wondering if taking the the crankcase breather up to the rocker box wasn't a smart move? What would be wrong with this/ or would it over pressurise the whole engine, if such a thing was possible

TonyA said:
When the sump is overfilled with oil there is more oil than usual coming out of the crankcase breather tube when started .

Just to add to this, I did a complete oil change, inc the filter, I even removed the sump, (to replace the woeful drain plug with tiny allen key), so my sump was effectively dry when I started it up the "first time", within seconds the air box was filling with oil,
so I know for sure this wasn't from the sump.

TonyA · May 26, 2023

TonyA said:
Hi Bob , If your bike wet sumps you must fix this first . Determine how much oil and how long it takes to drain to the sump .
Next find out what length oil dip stick you have , measure from the bottom of the cap to the end of the stick (150mm) from memory. Oil can run back down the oil tank vent tube to the back of the head especially under heavy breaking . A newer stick is available of the longer length. Last run a compression test and get back with the results when you can .
Look Here :

Norton 961 Compression Test

Hello , I thought I would test my compession again and I was surprised to find it so high. I was expecting 150-160 psi and I was wrong. Left cylinder 176 psi Right cylinder 180 psi Current mileage

www.accessnorton.com

Look here :

New Oil Dipstick from Norton Factory UK

Hello , This is the NEW oil dipstick from Norton Factory UK . Many thanks to Richard Pearce (BlightyBrti) for sending this information. The stick measures 150mm from the bottom of the threaded cap to the bottom of the stick. I have ordered this stick and when I get it I will have the original...

www.accessnorton.com

TonyA · May 26, 2023

BOBBREEKS said:
The dip stick is 153 mm to the bottom of the threaded base. I was wondering if taking the the crankcase breather up to the rocker box wasn't a smart move? What would be wrong with this/ or would it over pressurise the whole engine, if such a thing was possible

It looks like you already have the longer dip stick. Taking the breather to the rocker box was how it was plumbed originally. On my machine this arrangement resulted in oil in the air box also. So you can try it and see if it works better for you. I would leave the air/oil separator inline between crankcase and r/h banjo . Then take the l/h banjo to the air box fitting and see how it works .

Stu Bodycote · May 26, 2023

Check scavenge side, from the pick up gauze thats accessible after first removing the sump plate, through to pump and back up to oil tank. At that age it may have a one way valve on the return oil line near to the frame at the front....check that is operating correctly. Oil change for engine after a complete drain is roughly 1.5ltr.
Half the problem is not through design, but through shite tolerance quality control. This is why some guys experience zero oil breather problems, and others are strapping 500ml coke bottles to their breather pipes....Norton's fix is a band aid repair.

TonyA · May 26, 2023

Stu Bodycote said:
Check scavenge side, from the pick up gauze thats accessible after first removing the sump plate, through to pump and back up to oil tank. At that age it may have a one way valve on the return oil line near to the frame at the front....check that is operating correctly. Oil change for engine after a complete drain is roughly 1.5ltr.
Half the problem is not through design, but through shite tolerance quality control. This is why some guys experience zero oil breather problems, and others are strapping 500ml coke bottles to their breather pipes....Norton's fix is a band aid repair.

Hi Stu , Thanks for replying . His may not have the pickup gauze screen installed. Some dealers did not bother to install or messed it up like I did . Mine also have the one way check valve in the return line but has never given me any trouble . All great points to check , it may not be scaveging very well.

Stu Bodycote · May 26, 2023

To be honest, some of the early castings wouldn't allow for the screen to be fitted. But I've had them partially blocked up with lint before.

Oil in the airbox/breather

Similar threads