XS 650 PCV valve on a MKIII

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crusadersports

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Hi All, I've been trawling through a fraction of the posts here concerning crankcase breathing. I have one of Mike's XS650 breathers but I'm not sure how to plumb it in on my 850 MKIII? As far as I can tell it goes between the crankcase breather pipe running from the back of the timing case, before this pipe reaches the old tank. If I've got it right that would mean the engine breathes into the oil tank, which in turn breathes into the separator and airbox on a MKIII. If you ditch the airbox as I have, is it ok to vent the oil tank breather straight to the atmosphere, sixties style with a long pipe terminating at the rear mudguard? Any pictures of this set up very welcome.

Thanks All
 
I got a MK11, I run my breather into a catch bottle that sits inbetween my engiine mounts, it catches any oil that dribbles out which isn't very much over a year. you could do the same with your MK111, I have been doing this set up for 33 years now, I have just set up the XS 650 PVC valve in my breather line.

Ashley
 
You can plumb it either way, from crankcase to valve to tank or from crankcase to valve to catch bottle. It makes no difference. Currently, your MKIII is breathing into the oil tank (a big catch bottle). Introducing a reed valve in the crankcase breather line is hardly going to change what's going to the oil tank. K&N makes a terminating filter you can use for the oil tank vent.
 
crusadersports wrote;
If I've got it right that would mean the engine breathes into the oil tank, which in turn breathes into the separator and airbox on a MKIII. If you ditch the airbox as I have, is it ok to vent the oil tank breather straight to the atmosphere, sixties style with a long pipe terminating at the rear mudguard?
Click to expand...
,

In answer to your question yes, you can do what you say and vent to atmosphere.
But, what I have done is vent the oil tank into a small plastic container (such as what cod liver oil capsules come in or similar, 3" tall or so) without it's lid attached which I have mounted in front of the battery , mines a mk3, with some cable ties that penetrate the bottle 3/4 of the way up. It can't be seen when the bike is dressed partly because I have painted it black. It gets less than a quarter full per seasons riding which is probably 2,000 miles or so (I do ride my other bikes as well).

Works for me an is a bit tidier than an ugly pipe to atmosphere, and a lot cheaper than a purpose made catch bottle.

Regarding the XS650 breather, I have since put one of Jim Comstocks crankcase breathers on as on my bike the XS 650 breather kept blocking with emulsified oil. I am very pleased with it.

I'd post a picture but for some reason when I paste the img code from Photobucket it doesn't link. It used to, so I don't know what 's gone wrong.
 
I am in the process of installing an XS valve on an Atlas. It is my estimation that keeping the lead in tube short will increase the effect of the valve. I intend to make measurements of crankcase pressure for various geometries, and will post results on this forum, but that will not happen for several weeks. At this point, my recommendation is to mount the valve as close to the crankcase as space allows.

Reggie's post above points out a concern of mine....that oil mist will foul the XS valve unless the outlet port is turned down to allow gravity drainage.
 
I ran my check valve's oulet to the oil tank as per the original vent line routing, then took the oil tank breather and parked it on top of the K&N air filter where the engine could draw the fumes in to be burned, rather than dumping them out raw. Of course, oil introduced into the intake has the undesirable effect of lowering the octane rating of the fuel, but I haven't noticed any knock issues. Nathan
 
texasSlick said:
I am in the process of installing an XS valve on an Atlas. It is my estimation that keeping the lead in tube short will increase the effect of the valve. I intend to make measurements of crankcase pressure for various geometries, and will post results on this forum, but that will not happen for several weeks. At this point, my recommendation is to mount the valve as close to the crankcase as space allows.

Reggie's post above points out a concern of mine....that oil mist will foul the XS valve unless the outlet port is turned down to allow gravity drainage.
Click to expand...
:) precisely why I ended up high on the backbone, drainage.
 
I never got an airbox with mine. How was the original set up? Did the mist return to the airbox via the oil seperator #37 and # 38?
Where did tube #39 and #40 go?
XS 650 PCV valve on a MKIII
 
Numbers 39 and 40 went to the balance tube between the carbs (or so mine came anyway).
 
texasSlick said:
I am in the process of installing an XS valve on an Atlas. It is my estimation that keeping the lead in tube short will increase the effect of the valve. I intend to make measurements of crankcase pressure for various geometries, and will post results on this forum, but that will not happen for several weeks. At this point, my recommendation is to mount the valve as close to the crankcase as space allows.

Reggie's post above points out a concern of mine....that oil mist will foul the XS valve unless the outlet port is turned down to allow gravity drainage.
Click to expand...

+ 1
Jim Comstock has stated the importance of positioning the reed valve as close as possible to the source of the pressure pulses, and his valve is mounted directly to the case.
The farther the valve is from the case, the more the pulses are damped which reduces the effect of the valve.
I took note of that when mounting my valve:

The catch tank is a home made effort, as is much of the air filter.
I have bypassed the oil tank to keep blow-by out of the oil.
Cheers
Martin
XS 650 PCV valve on a MKIII
 
Martin,
I advocate a reed breather from the crankcase -not the timing chest.

Having a reed close to the engine may help with condensation problems as it will run hotter but it will not create a vacuum at higher engine speeds when the large area of the timing chest is there to dampen the pulses. Jim
 
Hi
This is the way I did it. Maybe not the easiest way, but I think it is a good and elegant solution. Close to the cage, and I have hidden the ugly breathing tube. And this solution works perfectly.

Vidar

XS 650 PCV valve on a MKIII

XS 650 PCV valve on a MKIII

XS 650 PCV valve on a MKIII

XS 650 PCV valve on a MKIII

XS 650 PCV valve on a MKIII

XS 650 PCV valve on a MKIII
 
vidar hjelm johansen said:
Hi
This is the way I did it. Maybe not the easiest way, but I think it is a good and elegant solution. Close to the cage, and I have hidden the ugly breathing tube. And this solution works perfectly.
Click to expand...

Whether that's an elegant solution or not is a matter of opinion but I preferred to put mine just in between the existing breather hose somewhere near the top of the battery completely out of sight and it works perfectly :)
 
Plus 10 with comnoz replies, I have two bikes with reed valve breathers in the crankcase as Jim advocates, I have just finished a hard weekend with my new race bike and that proved the reed valve worth.
Regards Mike
 
Brooking 850 said:
Plus 10 with comnoz replies, I have two bikes with reed valve breathers in the crankcase as Jim advocates, I have just finished a hard weekend with my new race bike and that proved the reed valve worth.
Regards Mike
Click to expand...

No doubt about Jim's crankcase breather being the best available! For road use (no high revs) the cheap timingside PCV breather valve is perfect to eliminate minor oil leaks.
 
to vidar johanssen:

Very elegant installation....looks like you had access to a milling machine.

to Jim c.

If the timing chest dampens the pulses and enhances reed valve performance, will tapping the intake rocker box cover to mount the valve provide a similar damping and performance factor? Elevating the reed valve to rocker box height will allow gravity drainage back to the oil tank (at least in an Atlas).
 
If blow by not very much then the little amounts of blow by passed up the head drain paths may still allow good drainage of oil but at some point blow by may hinder pressure relief or oil drainage from a rocker breather exit.
 
texasSlick said:
to vidar johanssen:

Very elegant installation....looks like you had access to a milling machine.

to Jim c.

If the timing chest dampens the pulses and enhances reed valve performance, will tapping the intake rocker box cover to mount the valve provide a similar damping and performance factor? Elevating the reed valve to rocker box height will allow gravity drainage back to the oil tank (at least in an Atlas).
Click to expand...


I would not recommend a breather from the cylinder head. All the air that needs to be vented comes from the crankcase. [ring leakage] If the breather is on the head then that air needs to go up the pushrod tunnels and head drain passage to get there.

Since the oil drainback from a Norton head is pretty well restricted in size you do not want air going in the opposite direction to the oil to hinder it's return to the crankcase.

If you can't connect directly to the crankcase with a reed breather then the next best place is the timing chest. You will not get much case depression but you will vent the excess pressure that way.

Of course you could always drill and tap a hole for a hose nipple and put the breather here as I did on the 1007. There was not room on the lower rear of the engine for my regular breather. Any breather directly from the crankcase will need to be returned to the oil tank as there will be some oil vented with the air. Jim

XS 650 PCV valve on a MKIII
 
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