Engine Breathing
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erictharg
- Posts: 680
- Joined: Thu Jan 29, 2009 7:50 pm
Re: Engine Breathing
Half inch bore in old money will be a good start. Either follow Matt's lead and drill & tap the cover then screw in a 1/2" tail fitting to take the hose, or get a 1/2" tank fitting and drill a clearance hole through the cover (at a point where the back of the fitting will clear the valve gear - it gets tight in there) and you are sorted.
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Engine Breathing
What was the problem you were having with the Evacusump system? It is usually very effective if you have it plumbed correctly, and have all of the holes (including the one for the dipstick) sealed.
What you are trying to do, create a depression in the crank case using intake vacuum, can't work. The higher the crank case pressure, the lower the amount of vacuum your engine produces. At best, you are supercharging your engine with oil mist, which dilutes the intake charge, causing tuning problems, oiled plugs and detonation. When you are driving the car hard, you have just about no vacuum at all, while the engine is pumping its heart out.
While you are trying to restrict the vacuum, you are increasing the crank case pressure. Exactly the opposite of what you are trying to accomplish.
I run three breathers. The front timing cover breather into a small conical filter I stick to the outlet pipe, a rocker cover breather (I braised a nipple with a little baffle welded in behind in my steel valve cover), and a crank case breather, drilled into the fuel pump pad. The crank case and rocker cover breathe into a catch tank with a filter on top.
This reduced oil consumption, and other than the poorly sealing oil cap, there is very little blow by in the engine compartment. Oil consumption has dropped as well. My catch can stays empty, my engine dry.
I am loathe to cut holes in my intake manifolds(certainly not to add crank case fumes), as this always causes tuning problems. I will usually run the breathers into the air filters or air filter housing if required.
If I am not required to re circulate engine blow by, I use a breather can, and drain that back into the timing cover.
Why not just weld a nipple to the side of the rocker cover (I did), with a baffle over the hole (openings at the top and bottom), and have a second breather? it really helps if you have a strong engine, and like to turn it to 6000 RPM and above. Pick a fitting that matches the hose you are using for the front cover breather.
Remember, when the engine is working hard, and crank case pressure is highest, there is no engine vacuum, as you are probably at full throttle. What you get is your intake supercharged with oil. This promotes dilution of the intake charge, detonation, and general loss of performance. The increased crank case pressures will also increase oil consumption, and offer up pumping losses, reducing power further.
The Evacusump produces vacuum from the venturi effect produced at the exhaust system collector to create a depression in the crank case. This pulls the crankcase through the air oil separator so you don't kill every mosquito in your neighborhood. It's a good system, and it makes more power. I am not personally using one, but I have friends who are using the system on BMC A series engines. It works. The harder you run the engine, the more vacuum it pulls on the crank case, reducing pumping losses, and increasing power. It also keeps the blow by out of the combustion chambers, where it does the most damage. If you can make the Evacusump work, it is the best system. Or...
My suggestion is to plug the holes in the intake, get rid of the vacuum lines, and direct the front cover vent, and a rocker cover vent to your catch tank. Your engine will thank you.
If you have a fuel pump pad that can accept a fuel pump (and you are not running one), you can fit a vent there, and run a hose up to your catch tank. After you do that, you wont have any problems with high crank case pressures again. If you are running a mechanical fuel pump, get an electric pump, then drill your cover plate for a nipple and hook a hose to it and run it to your breather tank.
Another idea: Run a cylinder leak down test to see if you don't have a problem with the rings.
Mknight702 wrote:
> I thought I would post up my latest trials and tribulations.
>
> My engine has been breathing heavily through the oil filler cap since I
> replaced the SUs with the Weber. The Weber manifolds don't have a vacuum
> port for the breather circuit so I thought that a catch tank was in order.
> I did flirt with the Evacusump system from Vizard's book but that didn't
> seem to work for me so I relented and had some stubs welded onto the inlet
> manifold that I plumbed to the catch tank to give me negative crankcase
> pressure. (I had also previously modified the route of the breather system
> so the timing cover vented to the rocker cover which in turn vented to the
> catch tank.)
>
> Fired the car up in the garage and it seemed good, finally I had vacuum in
> the crankcase. Took the car out for a quick run and after 5 minutes I
> suddenly did a James Bond and vanished in a cloud of smoke. Pulled over to
> the side of the road and popped the bonnet, I now have so much vacuum that
> it was hoovering the oil out of the rocker cover and had filled the catch
> tank and was in turn getting to the inlet. OK so now I quickly rerouted
> the breather to remove the rocker circuit and just take from the timing
> cover, better but not perfect so turn round and drive home looking like a
> Red Arrows display.
>
> Today I have fitted a PCV valve to the vacuum side of the system to
> partially restrict the peak vacuum at idle and cruise, plus rerouted the
> breather circuit more permanently to exclude the rocker. I may also have
> to fit a restrictor to the vacuum if it doesn't have the desired effect,
> unfortunately the weather wasn't the Mae West for further testing today so
> I haven't managed to test it extensively, maybe tomorrow.
>
> One day the car will be finished!
What you are trying to do, create a depression in the crank case using intake vacuum, can't work. The higher the crank case pressure, the lower the amount of vacuum your engine produces. At best, you are supercharging your engine with oil mist, which dilutes the intake charge, causing tuning problems, oiled plugs and detonation. When you are driving the car hard, you have just about no vacuum at all, while the engine is pumping its heart out.
While you are trying to restrict the vacuum, you are increasing the crank case pressure. Exactly the opposite of what you are trying to accomplish.
I run three breathers. The front timing cover breather into a small conical filter I stick to the outlet pipe, a rocker cover breather (I braised a nipple with a little baffle welded in behind in my steel valve cover), and a crank case breather, drilled into the fuel pump pad. The crank case and rocker cover breathe into a catch tank with a filter on top.
This reduced oil consumption, and other than the poorly sealing oil cap, there is very little blow by in the engine compartment. Oil consumption has dropped as well. My catch can stays empty, my engine dry.
I am loathe to cut holes in my intake manifolds(certainly not to add crank case fumes), as this always causes tuning problems. I will usually run the breathers into the air filters or air filter housing if required.
If I am not required to re circulate engine blow by, I use a breather can, and drain that back into the timing cover.
Why not just weld a nipple to the side of the rocker cover (I did), with a baffle over the hole (openings at the top and bottom), and have a second breather? it really helps if you have a strong engine, and like to turn it to 6000 RPM and above. Pick a fitting that matches the hose you are using for the front cover breather.
Remember, when the engine is working hard, and crank case pressure is highest, there is no engine vacuum, as you are probably at full throttle. What you get is your intake supercharged with oil. This promotes dilution of the intake charge, detonation, and general loss of performance. The increased crank case pressures will also increase oil consumption, and offer up pumping losses, reducing power further.
The Evacusump produces vacuum from the venturi effect produced at the exhaust system collector to create a depression in the crank case. This pulls the crankcase through the air oil separator so you don't kill every mosquito in your neighborhood. It's a good system, and it makes more power. I am not personally using one, but I have friends who are using the system on BMC A series engines. It works. The harder you run the engine, the more vacuum it pulls on the crank case, reducing pumping losses, and increasing power. It also keeps the blow by out of the combustion chambers, where it does the most damage. If you can make the Evacusump work, it is the best system. Or...
My suggestion is to plug the holes in the intake, get rid of the vacuum lines, and direct the front cover vent, and a rocker cover vent to your catch tank. Your engine will thank you.
If you have a fuel pump pad that can accept a fuel pump (and you are not running one), you can fit a vent there, and run a hose up to your catch tank. After you do that, you wont have any problems with high crank case pressures again. If you are running a mechanical fuel pump, get an electric pump, then drill your cover plate for a nipple and hook a hose to it and run it to your breather tank.
Another idea: Run a cylinder leak down test to see if you don't have a problem with the rings.
Mknight702 wrote:
> I thought I would post up my latest trials and tribulations.
>
> My engine has been breathing heavily through the oil filler cap since I
> replaced the SUs with the Weber. The Weber manifolds don't have a vacuum
> port for the breather circuit so I thought that a catch tank was in order.
> I did flirt with the Evacusump system from Vizard's book but that didn't
> seem to work for me so I relented and had some stubs welded onto the inlet
> manifold that I plumbed to the catch tank to give me negative crankcase
> pressure. (I had also previously modified the route of the breather system
> so the timing cover vented to the rocker cover which in turn vented to the
> catch tank.)
>
> Fired the car up in the garage and it seemed good, finally I had vacuum in
> the crankcase. Took the car out for a quick run and after 5 minutes I
> suddenly did a James Bond and vanished in a cloud of smoke. Pulled over to
> the side of the road and popped the bonnet, I now have so much vacuum that
> it was hoovering the oil out of the rocker cover and had filled the catch
> tank and was in turn getting to the inlet. OK so now I quickly rerouted
> the breather to remove the rocker circuit and just take from the timing
> cover, better but not perfect so turn round and drive home looking like a
> Red Arrows display.
>
> Today I have fitted a PCV valve to the vacuum side of the system to
> partially restrict the peak vacuum at idle and cruise, plus rerouted the
> breather circuit more permanently to exclude the rocker. I may also have
> to fit a restrictor to the vacuum if it doesn't have the desired effect,
> unfortunately the weather wasn't the Mae West for further testing today so
> I haven't managed to test it extensively, maybe tomorrow.
>
> One day the car will be finished!
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Mknight702
- Posts: 214
- Joined: Thu Jan 29, 2009 7:49 pm
Re: Engine Breathing
More questions I'm afraid.
I am still having oil loss issues that I am putting down to breather problems.
As I now have the supercharger installed I have had to relocate the breather filter from the timing cover to the distributor blanking plug. I also have a takeoff on the rocker cover but that does not have a splash plate fitted yet so is blocked off at the moment. The hoses then run to my catch tank that has a small filter venting to atmosphere.
The symptoms are massive oil loss (dipstick max to min in 50 miles) not being burned but leaking out round the rocker (new gasket fitted) and being blown out of the filler cap vent.
I have done a compression test and leakdown test and the compression is even across all 4 and the leakdown again is even and very low (circa 5%).
My theory at the moment is that the catch tank venting is so poor that it is causing pressure buildup in the crankcase which is forcing the oil out. I am about to trial an alternative (5l oil can) catch tank with huge venting to see if that helps plus a splash plate in the rocker to stop all the oil pouring out of that breather hose.
I am getting to the point that I want to throw everything away and go back to stock SUs and plumbing.
Hmmm, been doing more reading (not sure if that's a good thing!) and have found someone who seems to have a similar issue to me. A possible cause of cam bearing being fitted incorrectly causing too much oil flow to the rocker so filling the cover has been suggested. Since this seems to fit perfectly the symptoms I have I wonder if that has been an issue all along. (Even going back to Le Mans in 2009 when I used 2 5l cans of oil en route). Given the standard of the work that was done over the course of 6 months
by the "specialist" who machined my engine I believe anything is possible. (I wonder why they went bust?)
Is there a simple way to check cam bearing fitment, I guess knowing my luck it's an engine out job.
I am still having oil loss issues that I am putting down to breather problems.
As I now have the supercharger installed I have had to relocate the breather filter from the timing cover to the distributor blanking plug. I also have a takeoff on the rocker cover but that does not have a splash plate fitted yet so is blocked off at the moment. The hoses then run to my catch tank that has a small filter venting to atmosphere.
The symptoms are massive oil loss (dipstick max to min in 50 miles) not being burned but leaking out round the rocker (new gasket fitted) and being blown out of the filler cap vent.
I have done a compression test and leakdown test and the compression is even across all 4 and the leakdown again is even and very low (circa 5%).
My theory at the moment is that the catch tank venting is so poor that it is causing pressure buildup in the crankcase which is forcing the oil out. I am about to trial an alternative (5l oil can) catch tank with huge venting to see if that helps plus a splash plate in the rocker to stop all the oil pouring out of that breather hose.
I am getting to the point that I want to throw everything away and go back to stock SUs and plumbing.
Hmmm, been doing more reading (not sure if that's a good thing!) and have found someone who seems to have a similar issue to me. A possible cause of cam bearing being fitted incorrectly causing too much oil flow to the rocker so filling the cover has been suggested. Since this seems to fit perfectly the symptoms I have I wonder if that has been an issue all along. (Even going back to Le Mans in 2009 when I used 2 5l cans of oil en route). Given the standard of the work that was done over the course of 6 months
by the "specialist" who machined my engine I believe anything is possible. (I wonder why they went bust?)Is there a simple way to check cam bearing fitment, I guess knowing my luck it's an engine out job.
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Engine Breathing
Why not just put three breathers on the engine into a breather tank?
One through the fuel pump boss, one from the front cover, and one at the valve cover. No vacuum at all. I had similar problems on a couple of other BMC As and this cured the problem. My catch tank usually has only water (condensation), and just a trace amount of oil. Oil consumption is less than a pint 1200 miles.
This three breather line configuration seems to be standard for most racing BMC A race engines.
I use this system on all the engines I build, and have no problems with blow by, even with a 7200 RPM redline.
Running the blower, you will have more breather problems if you try to use manifold vacuum as the pressure will bleed over into the crank case
The easy way to make everything work is to keep it simple and stupid. One block breather line, one at the front cover (air oil separator) and a third at the side of the rocker cover, up near the top. Also, make sure that there is a baffle in the rocker cover to keep the oil in, and to let the air out.
If you have a problem with too much oil at the top end, you can put in a restrictor, but I would be careful about that. If your engine is sucking out the oil from the head, it may be the location of the breather, rather than a cam bearing conspiracy. I fixed an identical problem on an engine that I built after the owner put the rocker cover breather in the wrong place.
With the blower, it is likely that you might get more blow by unless you get rid of the excess crank case pressure. Nothing beats a couple of extra breather holes.
One through the fuel pump boss, one from the front cover, and one at the valve cover. No vacuum at all. I had similar problems on a couple of other BMC As and this cured the problem. My catch tank usually has only water (condensation), and just a trace amount of oil. Oil consumption is less than a pint 1200 miles.
This three breather line configuration seems to be standard for most racing BMC A race engines.
I use this system on all the engines I build, and have no problems with blow by, even with a 7200 RPM redline.
Running the blower, you will have more breather problems if you try to use manifold vacuum as the pressure will bleed over into the crank case
The easy way to make everything work is to keep it simple and stupid. One block breather line, one at the front cover (air oil separator) and a third at the side of the rocker cover, up near the top. Also, make sure that there is a baffle in the rocker cover to keep the oil in, and to let the air out.
If you have a problem with too much oil at the top end, you can put in a restrictor, but I would be careful about that. If your engine is sucking out the oil from the head, it may be the location of the breather, rather than a cam bearing conspiracy. I fixed an identical problem on an engine that I built after the owner put the rocker cover breather in the wrong place.
With the blower, it is likely that you might get more blow by unless you get rid of the excess crank case pressure. Nothing beats a couple of extra breather holes.
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Mknight702
- Posts: 214
- Joined: Thu Jan 29, 2009 7:49 pm
Re: Engine Breathing
With the exception of the breather on the timing cover, as that is currently fouled by the drive belt, I am pretty much already doing as you suggest. The location of my breather on the rocker is on the front edge next to the thermostat towards the top. Unless the rocker is filling with oil then I don't see how I can get a steady flow of oil into the catch tank, to expell the quantity of oil I do surely means that it isn't oil vapour or mist it must be liquid flow. The underside of the bonnet shows where oil is staining it above the filler vent and the rocker cover has oil all over it filling the indents where the two T handles go.
When I had the evacupan system running I managed to suck enough oil out of the engine to completely fill the catch tank and then get sucked straight out the exhaust in about a mile. The location of the breather was the same so I guess I have had the same issue since the engine was built but it only manifests when I use the rocker breather circuit.
When I had the evacupan system running I managed to suck enough oil out of the engine to completely fill the catch tank and then get sucked straight out the exhaust in about a mile. The location of the breather was the same so I guess I have had the same issue since the engine was built but it only manifests when I use the rocker breather circuit.
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allymally
- Posts: 70
- Joined: Fri Jul 29, 2011 6:20 pm
Re: Engine Breathing
Hi, this is just a thought! Adam had a problem with his car when all of a sudden the catch tank kept filling, he has roller rockers the plug from the end of the shaft went missing and oil was filling the top end! its worth a look.
Apart from that the three breathers as mentioned before should be more than enough.
All the very best
Apart from that the three breathers as mentioned before should be more than enough.
All the very best
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adamwilkinson
- Posts: 187
- Joined: Wed Jun 29, 2011 12:17 pm
Re: Engine Breathing
I was just about to post the same comment as Malc.
Take the rocker cover off and start the engine. If too much oil is getting to the top end you'll soon see where from. I suggest at least 2 pairs of eyes and someone by the ignition key to switch off quickly. Might I also suggest 2 containers, one each end of the rocker shaft just in case it is a similar issue to mine - oil coming out at 80+psi makes a mess.
If you want a hand just shout and i'll pop along.
Take the rocker cover off and start the engine. If too much oil is getting to the top end you'll soon see where from. I suggest at least 2 pairs of eyes and someone by the ignition key to switch off quickly. Might I also suggest 2 containers, one each end of the rocker shaft just in case it is a similar issue to mine - oil coming out at 80+psi makes a mess.
If you want a hand just shout and i'll pop along.
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Mknight702
- Posts: 214
- Joined: Thu Jan 29, 2009 7:49 pm
Re: Engine Breathing
I will have a look tonight. I have a new rocker shaft as well as the last one snapped!
I was wondering if that, because the breather to carb circuit is disconnected, the crankcase is now under more pressure than before and this is stopping the oil in the rocker draining down as it should. So connect the crankcase breather to the catch tank and the catch tank to the carb for vacuum, then block the rocker cover breather off so that the vent on the rocker is an inlet. That should mean that the crankcase is a lower pressure than the rocker so helping to pull the oil back down. This is basically the stock circuit with the addition of a catch tank.
I was wondering if that, because the breather to carb circuit is disconnected, the crankcase is now under more pressure than before and this is stopping the oil in the rocker draining down as it should. So connect the crankcase breather to the catch tank and the catch tank to the carb for vacuum, then block the rocker cover breather off so that the vent on the rocker is an inlet. That should mean that the crankcase is a lower pressure than the rocker so helping to pull the oil back down. This is basically the stock circuit with the addition of a catch tank.
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erictharg
- Posts: 680
- Joined: Thu Jan 29, 2009 7:50 pm
Re: Engine Breathing
Matt - your cam bearing misfit root cause sounds likely given that you've had consistent problems with no other obvious cause. I run just the two breathers and have had no problems to date, other than the dipstick lifting when racing and allowing some oil to blow out over the RHS of the block. Now held in place with a spring...
No oil at all in my catch tank.
No oil at all in my catch tank.
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jonclancy
- Posts: 943
- Joined: Tue Nov 01, 2011 9:30 pm
Re: Engine Breathing
Hi Folks,
I need to address this! Currently running just one breather pipe from the timing cover to carb. The small K&N filter I fitted to the top of the cover direct just filled with oil and made a mess!!
With the pipe to the carb, I do a Red Arrows impression which settles once th ecar is really warm. I think a catch tank and modified steel rocker cover and fuel blanking plate would work well.
Is there anyone that supplies these already modified? I'm out of time to do any of this myself - in the midst of a house move and a two month course starts tomorrow morning!
I am just down the road from Merlin Motorsport, and could ask Gary at Loaded Gunn if he could weld on the pipes required to my spare rocker cover. Any links to the correct fittings gratefully received!!
TTFN
Jon
I need to address this! Currently running just one breather pipe from the timing cover to carb. The small K&N filter I fitted to the top of the cover direct just filled with oil and made a mess!!
With the pipe to the carb, I do a Red Arrows impression which settles once th ecar is really warm. I think a catch tank and modified steel rocker cover and fuel blanking plate would work well.
Is there anyone that supplies these already modified? I'm out of time to do any of this myself - in the midst of a house move and a two month course starts tomorrow morning!
I am just down the road from Merlin Motorsport, and could ask Gary at Loaded Gunn if he could weld on the pipes required to my spare rocker cover. Any links to the correct fittings gratefully received!!
TTFN
Jon