Breather System Issues - Mini / Midget / A Series
Discussion
I have a problem on the XI with the breather circuit. The engine is an A series from a Midget with an oil separator on the timing cover. Originally this was plumbed to the twin SUs, but I have upgraded to a DCOE.
The first attempt was to plumb the timing cover up to the rocker cover and then take off the rocker cover to a catch tank with a simple filter on the catch tank. This gave me positive pressure in the crankcase and oil went everywhere.
I then tried to supply vacuum to the catch tank (and hence the crankcase) by the Evacupan system of David Vizard, no dice.
Next I welded two stubs onto the inlet manifold to replicate the original system. This I plumbed to the catch tank. At last, vacuum in the crankcase! Took the car for a quick spin and after 2 minutes I vanished in a cloud of smoke, James Bond's wasn't a patch on my smokescreen!. I now have so much vacuum that it would appear it is sucking oil out of the rocker cover, down into the catch tank, filling that then dumping it into the inlet. DOH!
I do not have a PCV valve so this is probably going to be Breather System 2.4b. Anyone else with any thoughts/guidance/pointing and laughing at what the idiot has done now?
The first attempt was to plumb the timing cover up to the rocker cover and then take off the rocker cover to a catch tank with a simple filter on the catch tank. This gave me positive pressure in the crankcase and oil went everywhere.
I then tried to supply vacuum to the catch tank (and hence the crankcase) by the Evacupan system of David Vizard, no dice.
Next I welded two stubs onto the inlet manifold to replicate the original system. This I plumbed to the catch tank. At last, vacuum in the crankcase! Took the car for a quick spin and after 2 minutes I vanished in a cloud of smoke, James Bond's wasn't a patch on my smokescreen!. I now have so much vacuum that it would appear it is sucking oil out of the rocker cover, down into the catch tank, filling that then dumping it into the inlet. DOH!
I do not have a PCV valve so this is probably going to be Breather System 2.4b. Anyone else with any thoughts/guidance/pointing and laughing at what the idiot has done now?
The Aseries is going to get you
no matter how you try
I have a Peter May rear seal kit on my Midget and in general it works pretty well, but mine breathes through an SU HIF44 not one o' they noo fangled Webers
I have heard (no personal experience) that the Weber has too much suck at the throat after the butterfly which makes providing negative crankcase pressure so difficult
but everyone with a Weber has this problem it seems
You could try asking for assistance at
http://www2.mgcars.org.uk/cgi-bin/gen5
This is the MGEBBS Midget and Sprite technical section, loads of helpful people there who will rally round
A thought but only that, are you running through an airfilter?
If so maybe a small diameter cross section pipe at the filter box face could induce a slightly less fierce suck inside the crankcase. Do block off the new holes though
Hope you get help with it, nice cars
Have you tried an HIF on yours, it retains the crankcase venting system of the standard unit
Bill
no matter how you try
I have a Peter May rear seal kit on my Midget and in general it works pretty well, but mine breathes through an SU HIF44 not one o' they noo fangled Webers
I have heard (no personal experience) that the Weber has too much suck at the throat after the butterfly which makes providing negative crankcase pressure so difficult
but everyone with a Weber has this problem it seems
You could try asking for assistance at
http://www2.mgcars.org.uk/cgi-bin/gen5
This is the MGEBBS Midget and Sprite technical section, loads of helpful people there who will rally round
A thought but only that, are you running through an airfilter?
If so maybe a small diameter cross section pipe at the filter box face could induce a slightly less fierce suck inside the crankcase. Do block off the new holes though
Hope you get help with it, nice cars
Have you tried an HIF on yours, it retains the crankcase venting system of the standard unit
Bill
The high vacuum may not be the issue.
Most breathers fitted into rocker covers have a baffle fitted inside the cover to stop oil being thrown at the open pipe and away into the vent system. Some also have a steel gauze to also trap/filter oil from the air and retain it in the cover.
Now your going to tell me the pipes you installed do have baffles fitted.
Steve
Most breathers fitted into rocker covers have a baffle fitted inside the cover to stop oil being thrown at the open pipe and away into the vent system. Some also have a steel gauze to also trap/filter oil from the air and retain it in the cover.
Now your going to tell me the pipes you installed do have baffles fitted.
Steve
Steve.
Unfortunately, the front timing cover has the standard vent filled with steel wool. The new rocker cover vent does not, nor does it yet have a baffle. I did do a side of the road modification to take the new rocker vent and blank it off then take the standard vent to the vacuum but it didn't make too much difference.
My curent thoughts are, baffle for the new rocker vent and PCV valve to cut down on the peak vacuum. The car did seem to make less smoke at full throttle than idle and if I remember correctly idle and cruise are peak vacuum and WOT is min vacuum so it would make some sort of sense. PCV valves do 2 jobs, prevent backfires reaching the sump and, more importantly for me, manage the vacuum to minimise the peak loading.
I guess a busy weekend bodging in the garage is required.
Unfortunately, the front timing cover has the standard vent filled with steel wool. The new rocker cover vent does not, nor does it yet have a baffle. I did do a side of the road modification to take the new rocker vent and blank it off then take the standard vent to the vacuum but it didn't make too much difference.
My curent thoughts are, baffle for the new rocker vent and PCV valve to cut down on the peak vacuum. The car did seem to make less smoke at full throttle than idle and if I remember correctly idle and cruise are peak vacuum and WOT is min vacuum so it would make some sort of sense. PCV valves do 2 jobs, prevent backfires reaching the sump and, more importantly for me, manage the vacuum to minimise the peak loading.
I guess a busy weekend bodging in the garage is required.
does the block have the machined out part for the mechanical fuel pump or is this always electric on the midget style a series? I used to run 110 bhp out of an A series many moons ago and didn't have oil issues, although in a mini. I will have to look at pictures and see what I did for the breathers, as did not run it back to the inlet as standard.I would be worried about crankcase pressure from loose bores and rings, although the a series was never a great engine for not breathing.
Can you fab up a fitting in the dizzy hole to run to a catch tank somewhere.I guess you have taken out the distributor drive too. Is this an A+ block ?, as I remember mine had a breather on the back of the engine under the inlet which you could get the followers out without removing the engine on a plate, although it was an S block. Bugger, think my vizard book is in the loft..............
Thanks, I'm going to the scrappy this morning to look for a suitable PCV, failing that, or maybe as well, I'll give the restrictor a go. Plus baffle the rocker outlet.
I could put another outlet onto the dizzy blank, but I'm not sure that will offer any benefit. I may, however, use that as an entry point for a drain from the bottom of my catch tank to stop the oil being sucked out of the engine. The only problem I can see with that, is that with so much vacuum, I may end up just sucking more oil in that way.
I could put another outlet onto the dizzy blank, but I'm not sure that will offer any benefit. I may, however, use that as an entry point for a drain from the bottom of my catch tank to stop the oil being sucked out of the engine. The only problem I can see with that, is that with so much vacuum, I may end up just sucking more oil in that way.
This a common problem. I work for a Morris Minor specialist so I spend a lot of time with 1098 and 1275 inline engines. The crank rear oil seal kit is not Peter May's by the way it is made and distributed by ESM Spares who I believe are the cheapest retailer.
Points to note about this breathing system:
The oil separators get blocked. Cut them open and clean them out! They also get full of rust, another reason to open them up!
You need either consistent +ve pressure or no pressure to avoid leaks. The crankshaft windage causes different pressures inside the crank whether you have blow by or not. You will have some element of piston blow by.
If you are using a +ve pressure system you need a PCV valve or you will end up with lots of suction at idle and little when moving. Volvo used this system but it only draws at high manifold vacuum and use a fresh air breather to vent when the vacuum is insufficient. The breather connection on SU carbs does not expose the crankcase to full manifold vacuum as it is positioned behind the carb piston upstream of the throttle butterfly but will also draw a slight pressure at WOT due the pressure drop at the piston/venturi. It can be overcome by heavy breathing engines though.
If you are venting to atmosphere you need at least two 3/4" breathers on a high performance engine. Sometimes you see A series engines covered in little breather filters....on the rocker cover, timing cover, fuel pump plate, transfer case on transverse. That's because 1/2" OD breathers are far too small on these motors. remember you are not trying to provide adequate venting of pressure but enough breathing to eliminate any significant pressure that will cause leaks.
The Inline cranks rely on the sealing of the Archimedes screw on the crankshaft. If this is worn it is useless, they do work when they are unworn but will always allow a small dribble out over time. The crankshaft oil seal conversions do work but the must be assembled correctly and need a spotless surface on the side of the flywheel mounting boss part of the crankshaft. Usually this has to be machined to give a flat surface.
I hope this helps. It's based on personal experience and a lot of leaked oil. If you're venting to atmosphere a catch can helps as it allows pressures to even out between the two breathers and vent the can from a 1" filter, they are available on ebay. If you're working with a worn engine it makes things difficult.
All the best
Tom
Points to note about this breathing system:
The oil separators get blocked. Cut them open and clean them out! They also get full of rust, another reason to open them up!
You need either consistent +ve pressure or no pressure to avoid leaks. The crankshaft windage causes different pressures inside the crank whether you have blow by or not. You will have some element of piston blow by.
If you are using a +ve pressure system you need a PCV valve or you will end up with lots of suction at idle and little when moving. Volvo used this system but it only draws at high manifold vacuum and use a fresh air breather to vent when the vacuum is insufficient. The breather connection on SU carbs does not expose the crankcase to full manifold vacuum as it is positioned behind the carb piston upstream of the throttle butterfly but will also draw a slight pressure at WOT due the pressure drop at the piston/venturi. It can be overcome by heavy breathing engines though.
If you are venting to atmosphere you need at least two 3/4" breathers on a high performance engine. Sometimes you see A series engines covered in little breather filters....on the rocker cover, timing cover, fuel pump plate, transfer case on transverse. That's because 1/2" OD breathers are far too small on these motors. remember you are not trying to provide adequate venting of pressure but enough breathing to eliminate any significant pressure that will cause leaks.
The Inline cranks rely on the sealing of the Archimedes screw on the crankshaft. If this is worn it is useless, they do work when they are unworn but will always allow a small dribble out over time. The crankshaft oil seal conversions do work but the must be assembled correctly and need a spotless surface on the side of the flywheel mounting boss part of the crankshaft. Usually this has to be machined to give a flat surface.
I hope this helps. It's based on personal experience and a lot of leaked oil. If you're venting to atmosphere a catch can helps as it allows pressures to even out between the two breathers and vent the can from a 1" filter, they are available on ebay. If you're working with a worn engine it makes things difficult.
All the best
Tom
Dont complicate something very simple.
Firstly, and most importantly. Any PCV system MUST have proper oil/air separators in order to work.
If you bought a "catch can" off egay, or indeed most places that sell similar products, then I can only imagine it's a useless POS.
Very few out there are actually capable of filtering the liquids from the air you wish to vent.
This will of course be made worse by having no baffles as an initial barrier at rocker cover etc.
And then the actual PCV aspect to the inlet manifold must only be very small as Camelot says. Not a full diameter opening.
And the catch cans must also have the ability to breathe too, assuming there isnt sufficient "vacuum" draw on the system
Firstly, and most importantly. Any PCV system MUST have proper oil/air separators in order to work.
If you bought a "catch can" off egay, or indeed most places that sell similar products, then I can only imagine it's a useless POS.
Very few out there are actually capable of filtering the liquids from the air you wish to vent.
This will of course be made worse by having no baffles as an initial barrier at rocker cover etc.
And then the actual PCV aspect to the inlet manifold must only be very small as Camelot says. Not a full diameter opening.
And the catch cans must also have the ability to breathe too, assuming there isnt sufficient "vacuum" draw on the system
You need to understand the basics of crank case breathing. i.e.
1) You are trying to allow the blowby gasses that have escaped past the piston rings (and to a much lesser extend the valve stems (depending on stem sealing etc). These blowby gases are fast moving and change in quantity (more cylinder pressure = more flow(bigger "leak" and more revs = more flow (more cycles per sec)). As they move into the crankcase they entrain oil mist that is flying off the engine rotating components.
2) You must allow these gases easy exit from the crankcase, with as little pressure build up as possible, and ideally keeping the CC below atmospheric pressure. (but not too much below, depending on your engines sealing arrangement, typically -10kPa)
3) you must try to seperate the lighter gases from the heavier oil mist to prevent excessive oil consumption. You can do this via two main methods: A) allowing the oil to seperate out by reducing the gas mixture to a low velocity, and using a material with a high surface area to "catch" the oil mist so it forms into blobs and then falls downwards and is returned to the CC (std wirewool in the rocker cover method) or B) Deliberatly use a high velocity stream that is made to rotate and centifugal force throws the denser oil to the oustide, gas to the middle. This is the best method and one used by most modern engines.
4) you need a vacuum source to provide the "Pull" to do the centrifugal method, and also a vaccuum source allows the CC to be maintained below atmos pressure.
5) Understand the 2 system breathing concept:
A "part load" breather uses manifold vacuum, that is metered by a PCV valve (that is a sprung variable orrifice) to suck blowby gases out from the CC. The PCV valve controls the maximum negative pressure in the CC by sliding to a smaller opening area as the delta pressure across it increases. Effectively finding a balance point where the flow rate is balanced by the pressure drop of the valve.
This "part load" breather however cannot provide CC scavanging during wide open throttle (WOT) operation (or even during the high part loads on forced induction cars, which require a one way valve or special PCV that incorporates one)
For this reason the "full load" breather system uses the intake depression caused by the intake air filtration system at high mass flows to take over from the part load system as the manifold vaccum decreases towards WOT. (vents BB gas to clean air duct after airfilter and before throttle)
Additionally, to ensure sufficent mass flow for the centrifugal seperator to work, a lot of modern cars have a "make up air" breather system, where a large constant pressure diaphram valve opens a pipe between the clean air intake tract and the crankcase to maintain a controlled negative pressure.
Generally this makeup air pressure control valve is using the full load breather pipework in reverse when operating (pulling make up air from the clean air duct)
So to design a successful breathing system you must consider both the removal of the entrained oil, and how your system will maintain the correct massflow and pressure during all zones of engine operation
(or alternatively, just push a bit of hose pipe into a hole on your rocker cover, and stick the end into an old 5litre plastic oil bottle with a few holes drilled in it........ ;-)
1) You are trying to allow the blowby gasses that have escaped past the piston rings (and to a much lesser extend the valve stems (depending on stem sealing etc). These blowby gases are fast moving and change in quantity (more cylinder pressure = more flow(bigger "leak" and more revs = more flow (more cycles per sec)). As they move into the crankcase they entrain oil mist that is flying off the engine rotating components.
2) You must allow these gases easy exit from the crankcase, with as little pressure build up as possible, and ideally keeping the CC below atmospheric pressure. (but not too much below, depending on your engines sealing arrangement, typically -10kPa)
3) you must try to seperate the lighter gases from the heavier oil mist to prevent excessive oil consumption. You can do this via two main methods: A) allowing the oil to seperate out by reducing the gas mixture to a low velocity, and using a material with a high surface area to "catch" the oil mist so it forms into blobs and then falls downwards and is returned to the CC (std wirewool in the rocker cover method) or B) Deliberatly use a high velocity stream that is made to rotate and centifugal force throws the denser oil to the oustide, gas to the middle. This is the best method and one used by most modern engines.
4) you need a vacuum source to provide the "Pull" to do the centrifugal method, and also a vaccuum source allows the CC to be maintained below atmos pressure.
5) Understand the 2 system breathing concept:
A "part load" breather uses manifold vacuum, that is metered by a PCV valve (that is a sprung variable orrifice) to suck blowby gases out from the CC. The PCV valve controls the maximum negative pressure in the CC by sliding to a smaller opening area as the delta pressure across it increases. Effectively finding a balance point where the flow rate is balanced by the pressure drop of the valve.
This "part load" breather however cannot provide CC scavanging during wide open throttle (WOT) operation (or even during the high part loads on forced induction cars, which require a one way valve or special PCV that incorporates one)
For this reason the "full load" breather system uses the intake depression caused by the intake air filtration system at high mass flows to take over from the part load system as the manifold vaccum decreases towards WOT. (vents BB gas to clean air duct after airfilter and before throttle)
Additionally, to ensure sufficent mass flow for the centrifugal seperator to work, a lot of modern cars have a "make up air" breather system, where a large constant pressure diaphram valve opens a pipe between the clean air intake tract and the crankcase to maintain a controlled negative pressure.
Generally this makeup air pressure control valve is using the full load breather pipework in reverse when operating (pulling make up air from the clean air duct)
So to design a successful breathing system you must consider both the removal of the entrained oil, and how your system will maintain the correct massflow and pressure during all zones of engine operation
(or alternatively, just push a bit of hose pipe into a hole on your rocker cover, and stick the end into an old 5litre plastic oil bottle with a few holes drilled in it........ ;-)
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff