UK Monster Owners Club Forum » .: Technical :. » Engines, Clutch, Gears » Crankcase breathing

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Old 04-11-2019, 05:07 PM   #1
the lodger
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Crankcase breathing

I want to check that the crankcase breather set up on my M900 is clear. There is a canister behind the vertical cylinder. Is it supposed to be removed for cleaning , if so how does it come out ? Out of interest, what is in it ? There is a large breather tube from the canister to a black plastic box just under the top of the frame and just behind the LHS of the petrol tank. Is this box just a void or is there something in it ? I think this setup is standard but would like to understand how it is supposed to work. Many thanks .
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Old 04-11-2019, 06:24 PM   #2
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It's all part of the emissions control. The hot engine will vent a bit of vapour with oil in it, the boxes should allow the oil in the vapour to be trapped and dribble down back into the motor. The remainder gets sucked into the airbox and burnt.
It also allows the closed circuit on moisture that can allow the oil emulsion to form in the motor.
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Old 04-11-2019, 09:23 PM   #3
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Quite a lot has been written about this subject over the years, especially regarding the removal of the breather to be replaced with a mini 'K&N' style filter.

This is generally considered a bad idea and detailed here:

http://www.ducati-upnorth.com/tech/breather.php

As Nick says, the original set up is driven by emission regulations but the canister behind the vertical cylinder actually houses a one way valve to prevent anything returning into the crankcase, leaving any vapour to either become liquid in the black plastic catch tank mounted on the frame or to be recycled hot oily air taken in via the air box thus meeting any emission regulation originally set out during those production years.

However, the system can easily be made a little better without affecting the crankcase pressure by removing the pipe that returns the hot oily air from the breather catch tank to the air box (ideally you'll need a little extra pipe to vent the box away to the free world).

This set up will then let your motor only take in nice cool, fresh and clean air from the outside world through whatever air filter you're running.
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Old 04-11-2019, 09:26 PM   #4
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the cylinder on the crankcase has a reed valve in it. the black plastic box has to chambers, designed to slow airflow and allow oil droplets to fall out of suspension.
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Old 04-11-2019, 09:35 PM   #5
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Quote:
Originally Posted by slob View Post
the cylinder on the crankcase has a reed valve in it. the black plastic box has to chambers, designed to slow airflow and allow oil droplets to fall out of suspension.
And any water that has condensed to drip back into the engine oil.
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Old 04-11-2019, 09:59 PM   #6
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Quote:
Originally Posted by Darren69 View Post
And any water that has condensed to drip back into the engine oil.
Exactomondo ..
I fitted a K&N on my 750 and within a day or so the oil was clear. Up to then I was running about 50 miles a day so the motor was up to temperature but then once that initial moisture was into the motor it didn't really go away.
My S2R always gets warmed up and doesn't do any small distances but with the standard vent system in place is making mayo.
I'm not convinced that the oily emulsion is actually hurting the motor but it can't be doing any good ??
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Old 05-11-2019, 09:09 AM   #7
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Thanks for the replies. Does the canister reed valve ever need cleaning or fail ? Is it capable of being removed for cleaning ?
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Old 05-11-2019, 10:09 AM   #8
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yes; it and the pipework will get full of oil/water sludge. It unscrews from the crankcase so you can clean it. The earlier ones are 2 piece that are clamped together, later ones are I believe one piece.

Better quality aftermarket ones are also available. Have a look on ebay or such like.
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Old 05-11-2019, 06:31 PM   #9
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For the record I couldn't unscrew the canister but decided it wasn't worthwhile anyway. The whole system was clear of oil and there were just a few drops of moisture in the black plastic tank. No residual evidence of any dirty air having got to the airbox and left deposits; the top of the reed valve that I could see was a nice shiny brass colour.

So presumably all good therefore I need to look elsewhere for the explanation of excessive oil consumption.
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Old 08-11-2019, 08:50 PM   #10
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Does it blow a puff of smoke on start up?, if so probably worn valve guide seals, once warmed up does the exhaust gas smell oily?, if so maybe wear in the cylinders/rings although I’m told that’s not common with these engines, how much oil does it use?
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Old 09-11-2019, 09:53 AM   #11
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Tbh I'm a bit puzzled by the bike. There is a stong smell on start up but no blue smoke .There is some smell on moving off from idle when warm but no smoke. There are no signs of smoke when rolling off the throttle , which I think would be a typical valve guide/seal symptom. I haven't had the bike long enough to be sure but my current estimate is that it's doing about 500 miles per litre. This is a bike that was very well looked after by the previous owner who had it for 15 years , used it moderately and did annual oil changes with decent oil. It has done 17k miles.

Next step is to do a compression test , which may take a while as I don't currently have a tester. Maybe Santa will come good.
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Old 09-11-2019, 10:16 AM   #12
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This is odd.
The exhausts on my 900 can be quite smelly/fumey. Mrs Gazza complains of this if she is about when I come home after a run.
The exhausts blacken very quickly at the tail pipe, but not with a soft deposit, more a hard stain.
Strangely the plugs are clean and have virtually no deposits to speak of. I get near as dammit 70mpg, so not running rich, she has never used a drop of oil on any length of run in any weather. So I wouldn't read too much into the smelly exhausts.
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Old 09-11-2019, 12:08 PM   #13
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Thanks for the replies. On reflection I don't think we would necessarily see blue smoke nowadays unless the engine was very worn, which I don't think mine is My son has a Yamaha TDM 850 which uses a lot of oil but I never see any blue smoke from that , just a stong hydrocarbon-burning smell when I'm following him.

I want my bike engine to run as well as it should do and I will continue to investigate this over time but I know I have to be sensible about potentially fixing any issue. Tearing the engine down for a major refurb is not an option, if it isn't really needed. My annual mileage is not going to be much if any over 500 miles and that's just a litre of oil - max £15 - for top ups between annual oil changes.
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Old 09-11-2019, 03:44 PM   #14
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I'll second Mr G's thoughts on this as my 1997 carb'd 900 does smell like it's running rich but always needs choke to start from cold, is on the button when warm whether it's stood a couple of minutes or half hour. The plugs are a nice colour and the fuel consumption is usually around 48mpg's average and more on a steady run.

I've owned it almost twenty years and it's done 35,000 miles and never uses any oil whether it's a short fifteen miles for an escape to get a cup of tea or an all day 400+ miles while on a long weekend away.

A litre every 500 miles is a lot to me when you consider the total capacity the motor holds (I've had two strokes that have used less ) so I would have thought it must be going somewhere.

I know I've read somewhere, a permissible oil consumption figure which I remember being (in my mind) surprisingly high so you might be within it but either way, it won't thank you for only doing 500 miles a year!

In my experience Ducati's do not like being left un-used for extended periods of time- seals dry out and things start to get gummed up or corroded and the best ones I have known are used regularly and have got good mileages on them.
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Old 09-11-2019, 05:05 PM   #15
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Thanks for the input. I pulled the plugs this afternoon. The horizontal plug is fine but the vertical is not. It is shiny , which I think is an indication of oily but all views are welcome. Hopefully a picture of both appears below



I also took a picture inside the vertical cylinder via the sparkplug hole. I'm not sure it shows a lot other than a surface that looks a bit like a strawberry but here it is for interest

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