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MG MGB GT V8 Factory Originals Technical - How to set up breathing on a Rover V8?
|Finishing up a conversion with a Rover 4.2, I believe circa 1996 or so. The motor didn't have valve covers when I got it so I found some, I think they are from a P6, which are finned and say "ROVER" on top.|
I don't understand how to set up the breathing/ crankcase ventilation. As you know there is a little tube sticking off of each. I take it I basically run a hose from one of them up to the underside of the air cleaner, and run another hose from the similar tube on the other valve cover to the manifold vacuum port on the base of the carb. Do I need a PCV valve, and if so, which one (part #?), and is there any particular orientation that is necessary? ... or do I need this "flame trap" fitting that they talk about in Roger Williams's book? What I don't want to do -- as I have heard of many times -- is set up a system that sucks the oil vapors so hard that you end up inadvertently burning oil.
Can someone give me a primer?
I also have the P6 covers and the original MGB V8 SU set up. From each valve cover there is a hose to a flame trap and from each flame trap there is a hose to each carburateur. The flame trap is a like on the MG V8 (diameter approx. 1 inch). I don't know the official part. nr. I got mine from the V8 conversion Compagny in the UK.
You could use a T-joint and then run 1 hose to your airfilter or just block 1 off the valve covers pipes and run the other to the airfilter.
I have also seen a lot of V8's with the K&N breather/filter on the valve cover but i prefer my set-up because i supppose the K&N filter makes the engine dirty.
I don't have any problems with burning oil.
|As Peter says the factory set-up involved a pipe from each cover to a carb, which leaves somewhere where the air must get in. This was via a filter (externally very similarly to a fuel filter) right at the back of the block on the RH side. On an Edelbrock conversion of a factory car I have seen this inlet was capped off but I can't recall how the valve covers and carb were then plumbed.|
I'd try a PCV valve for the Buick-Olds 215 if you could find one, in one valve cover, hose running to the carb base. If you can't locate exact proper PCV valve, get one that fits the hole, off a similar sized engine, like a Buick V6, and then just see if it runs okay. On the other valve cover, use one of those inlets, preferably with a filter, for air to come in. Should be a simple but effective way to go.
You understand the need for crankcase ventilation, but Iíll restate it. There is always blow by from combustion leaking past the piston rings and if this isnít vented the crankcase would become pressurized and force oil out the dipstick tube, blow the oil filler cap off or worse. The fumes are typically drawn through the engine to limit pollution.
There are a few ways to ventilate the crankcase and the old Buick design uses a filtered oil filler cap to filter engine compartment air on one valve cover and vacuum from the base of the carburetor drawing the contaminated air from the other valve cover through a PCV valve. The strong vacuum at idle lifts a plug in the PCV to block or partly block the path of the crankcase fumes to prevent rough running or stalling. At higher speeds where the engine can tolerate it, the reduced vacuum drops the plug allowing full flow. Later American designs supply cooler air from the air cleaner through the crankcase, sometimes with the filter relocated in the air cleaner and sometimes with a hose to a filtered filler cap. Cooler air entering the crankcase means cooler air exiting the crankcase to go into the carburetor. Many aftermarket air cleaners have a place to attach the inlet hose and the carburetor doubles as a filter for the crankcase and the whole thing picks up warm engine compartment air. Now at idle when the PCV limits crankcase ventilation, blow by will push backwards through the inlet filter. If the inlet is to the air cleaner the motor burns then the fumes otherwise they are released into the air.
The flame traps were described on previous threads as being filled with something like steel wool so they donít cut the crankcase ventilation at idle, but donít backflow through the inlet filter and the oil vapors condense on them and drip back into the valve covers.
If your 4.2 has the inlet filter that Paul describes then your simplest solution is probably to duplicate the British design because all the parts would fit. The Buick uses a rubber grommet in the valve cover that may not fit your P6 covers. Even if that works, you may find that a PCV with a 90į upper fitting clears the hood better than the straight PCV from the 215.
On my Buick without the Rover style inlet filter I must vent the crankcase from one valve cover to the other Buick style. Iím adapting MG V8 valve covers and canít bring myself to drill a big PCV grommet hole, so Iím mounting the PCV remotely and connecting it to the cover using a hose. Browsing the PCV section in the local auto parts store, I found a small replacement filter that fits the other side.
Tell us which system you use.
|George, I sort of get it ... but when you mount the PCV valve remotely, e.g. in a hose, I assume it must be in the vertical position? As I understand what you guys have said, you want something that closes under high vacuum but opens at low vacuum. |
Anyway, reading everyone's posts, I went to Pep Boys and, stunned at the variety of PCV valves they sell, bought one for a Mustang 5-liter. But I'm not sure it works ... it seems to always remain open. One problem I have is that with a big cam in the car the vacuum at idle is very low. It's quite high at cruise -- maybe 18-20 inches -- but at idle it's like 7 or 8. So at idle it isn't nearly strong enough to pull this PCV valve shut. I don't know if it does so at cruise, I'll have to figure out a way to find out.
(One thing is clear -- they've never heard of a flame trap at Pep Boys. But if I understand, you just mean a small canister filled with steel gauze. Since it sounds like that doesn't open and close like a PVC valve is supposed to, I take it when you British guys say "goes into the carbs" you simply mean to a ported vacuum source -- i.e. above the throttle blades -- only. Or are you talking about the full manifold vacuum port? ... if so, wouldn't that cause a vacuum leak?)
|7 or 8 at idle sounds more like ported than manifold. The 'UK' system is sort of ported, in that it uses a carb port but it is not the distributor port but another port that has greater vacuum at idle than the distributor port. Yes, it does sort of cause a vacuum leak, but the inlet to the crankcase is highly restricted as well as filtering which stops it affecting the mixture more than a very small amount. Removing the oil filler cap at idle is a different matter though, this affects idling considerably.|
|> 7 or 8 at idle sounds more like ported than |
Definitely manifold, Paul. On an Edelbrock carb there's no mistaking!
There may be different designs of PCV that have a valve that can be mounted in various angles and some with a ball that must be mounted vertically. I plan to mount mine vertically as thatís the way it was when mounted in the valve cover.
Some cam designs cause the vacuum to be too low to use power brakes, so they may be too low to shut a PCV. I donít know, I have never heard of this. Probably because most people that choose a wild cam bypass the PCV for additional performance.
|George, I dunno, maybe I should bypass it. I could just put open breathers on the valve covers and be done with it ... but I was thinking the engine bay would get filled with oil spray over time, which would be kinda disgustin'. Or do you think I should just run an open breather on one side, and plumb the other to the underside of the air cleaner? ... it seems like that would do pretty much the same thing as the PCV setup.|
|Two open filters are not uncommon on hot rods where performance is paramount. After all motors donít run as well on polluted air any more than people do. Normally, an open filter is a source of air into the crankcase and the exit is through the PCV to the strong vacuum source at the base of the carburetor. A connection to the air cleaner is a replacement for the open filter as a supply of air into the crankcase. Although I said earlier that air cleaner air would be a cooler source of air into the crankcase if the air to the air cleaner is supplied from the outside, Iím sure that the reason manufactures went to that system was so crankcase gasses went down the carburetor when the PCV was shut at idle. This sound like your plan would work, but the manufactures donít use it and thatís probably because you still have an open filter that releases some gasses and the air cleaner wonít supply as much vacuum as available at the base of the carburetor (except in motors with little vacuum do to wild cam grinds). |
If you have low vacuum then maybe you donít need to use a PCV to cut the flow of crankcases gasses completely just as the Rover system doesnít.
|I have followed this thread with some interest|
With my Rover 3.5 I have placed Flame Traps on both rocker covers, that's it. On the back of the engine there is a small pipe which goes into the lifter gallery. On this pipe I attached a rubber hose and put that into the recycle canister on the passengers side. All seem to work fine. When the light is right I can see the vapors coming out of the flame trap and thus figure the crank case is breathing properly.
As a side note I have had oil leaking problems (either rear mail seal or oil pan) and at first thought this might be because I was not venting the crankcase as previously mentioned, but after seeing the vapors coming out of the passengers side flame trap (I have been told that one flame trap, drivers side, will suck in and the other, passengers side in this case, with blow out) I feel it must be breathing, it certainly is not pushing oil out the dip stick nor blown the oil filler cap off. But I still have that pesky oil leak to deal with. I am planning on pulling the engine this winter, remove the tranny/flywheel and use a drill to get the pump running so I can locate the leak.
|Do open breathers work as well to avoid oil leaks, etc.? Seems like that'd be the simplest solution. If the concern is oil spray in the engine bay, presumably you could just run a hose from each valve cover to an open breather underneath the car. This arrangement might save you from burning oil unnecessarily as manifold vacuum can pull a fair amount of suction from the valve cover fitting when the PCV valve is open; out of curiosity I hooked up my Mityvac to the PCV valve that came on my Rover and you have to crank it to around 28 inches to pull up that weight and close the PCV valve! ... I don't believe 28 inches ever occurs in operation. I attached a clear hose to the PCV fitting just to see what happened and after a single short drive it had noticeably discolored with oil ... surely it is snorting oil into the carb. I'm thinking open breathers like the good ole boys run around here.|
|From this and other discussions I gather that the PCV serves two functions, both restricting airflow at idle (high vacuum), and acting as a check valve/flame arrester at low vacuum, particularly when starting. One particular tale sticks in my mind, from a fellow who says that two mornings in a row he had his valvecovers blown across the street because the PCV was lying horizontal. I would expect that the effect of crankcase gasses at WOT would be minimal, and if fresh air is drawn into the crankcase from the air cleaner any blowby would go the same place anyway, though the mixture could be affected marginally.|
I don't like the Buick vented oil filler. Always messy. Still that's exactly what I have on the Olds.
I also would like to know of a PCV with a lower vacuum requirement. The only one I know of that has been tested shut at 28" vacuum. Not very helpful I wouldn't think.
I wonder how that Rover crankcase vacuum system would work with rope main seals. Is there actually an inlet for air into the crankcase? Or is the system designed to only collect blowby? Is there any restriction to flow in the system other than the rings and seals? And finally, do the seal areas of the crank wear any faster in these engines than in engins with an 'open' PCV system from dirt being drawn into the seals?
|There has always been an oily film around the filtered oil filler cap of my Buick, around the PCV grommet as well. |
Paul Hunt said earlier there is an air inlet on the back of the Rover.
I doubt there is much wear to the main seals whether they are rope or neoprene. Both touch the crankshaft so should wear some but should not allow air to pass through.
A couple of days ago I took a ride in a hoodless car with four open breathers. At standstill the haze output was clearly visible, but at speed it dissipates too quickly. It is an easy system to setup, but the main reason to do it is to ensure the carburetor get nothing but cool clean air for maximum performance.
Something I mentioned before when the subject came up about crankcase gasses and the performance and pollution factors was the racing device that creates a high vacuum from the exhaust and draws from both valve covers with no inlet. This not only removes gasses to prevent pressurizing the crankcase causing oil leaks, but it creates a partial vacuum in the crankcase so as to cause less resistance to the backsides of the pistons during the power stroke. Of course it doesnít send any hot oily fumes to the intake either. This should also keep the valve covers as well as the rest of the engine compartment clean. Sound like the perfect system unless you have smog checks in your area. Iím sure the technician would not be very friendly if his tailpipe sniffer gets blasted with oily crankcase fumes.
|I wonder what the state of evolution is for those header vacuum setups. I say this because of seeing vacuum pumps in the Jeg's catalog, designed to pull a vacuum on the crankcase. Anyway, not being all that power concious, I expect I'll stick with the existing system for now.|
|Those vacuum pumps sound like the best way to go, but man are they expensive. I think the smog aspect might be OK as far as sniffing the tailpipe, because the vacuum pump doesn't dump its output into the exhaust AFAICT. I also don't know where I'd hang it from the engine, as there is a big steady bar rigged on the LHS. I think maybe a pair of open breathers situated under the car (so the engine bay doesn't get misted over time) sounds like the simplest solution. Or maybe you could fit one behind the grille where the air's a bit pressurized and the other under the car, where it's less so.|
|I just added a PVC valve to my system and low and behold the oil leaks have stopped|
This thread was discussed between 09/10/2001 and 25/10/2001
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