Difficulty in breathing

[Chris Y]

No, not me - my engine

My engine is somewhat 'compromised' in the design department. Well, that's a polite way of saying it.. One of the more famous aspects of this design was putting twin Weber carbs right on top of a hot exhaust manifold, leading to severe heat soak in the production version.

Another issue is/was oil breather pipes. The standard car has a breather / separator at the front of the sump, and a breather cap on the oil filler tube, which leads to the side of the block. Neither of those has any sort of baffle plate. The separator at the front is the 'wire-wool' kind.

Anyway, I plan to put a breather in the cam cover. At the moment my engine suffers from quite a bit of blow-by (although the piston rings are in good condition, etc), and chucks out about 1 litre of oil during the 'average' 20 minute race.

Am I right in thinking that a breather at the top end may reduce the blow-by? It was actually Denis Bassom's thread on dry sump installations that reminded me of this.

Apart from that, I'm going to try and put a baffle plate on the front breather to stop the oil being thrown off the crank. Also, I was thinking perhaps using larger diameter breather hoses may work? Possibly less pressure in them, leading to less oil being spat out... Or am I breathing up the wrong pipe here?

[Al Weyman]

Personally don't think it will make a jot of difference, if you have blow by for what ever reason (how do you know the rings are in good condition, are they bedded in correctly to the bore, are the bores not perfectly cylindrical etc. have you done a leak down test?) it is gonna vent where ever you put the breather. There is definitely something wrong to chuck that amount of oil out, thats rebuild time IMHO, I use virtually none in my v8 cars (when they are sealed correctly :-)) and they still breath a little when hot.

BTW what is it?!!

[Tim Falce]

Chris, is this a Ford engine (sounds like it by the decription). If you have an oil catch tank then you may need the breather near the rear of the rocker cover to stop the oil being thrown out under braking,
I used to lose up to a gallon of oil in a race from my Jaguar engine untill I got a pair of tank engine cam covers with the breathers at the rear.

[Alan Raine]

Originally Posted by falcemob

Chris, is this a Ford engine (sounds like it by the decription). If you have an oil catch tank then you may need the breather near the rear of the rocker cover to stop the oil being thrown out under braking

Agreed - It works on Formula Fords, although they are dry sumped.

[Chris Y]

It's an MG Maestro 1600 engine. Rover 'S' series. They're known for throwing oil out through the breathers unfortunately - bad design, same with the carbs on top of the exhaust manifolds.

I'm pretty sure the rings are in good nick. The compression figures are the same as they were when the engine was freshened up last, and the cylinders were honed, new rings, etc. Of course it's possible that things have deteriorated a little over time, but as I say, these engines are known for throwing out oil. I'm just looking for a way to reduce that a little.

I think a lot of the the oil being thrown out is due to the fact that the breathers are on the front, and left hand side of the engine (as you sit in the car), so in right hand corners, the oil's being chucked up the oil filler tube. As I say, bad design.

There's no breathers at all in the top-end, which is something I intend to rectify, and I was wondering if a bit of positive ventilation would reduce some of the blow-by?

[Tim Falce]

Originally Posted by Chris Y

There's no breathers at all in the top-end, which is something I intend to rectify, and I was wondering if a bit of positive ventilation would reduce some of the blow-by?

It could help, I can't see how it will do any harm.

[dtype38]

One thing to keep in mind if you're looking at rocker cover breather is the amount of "oil splash" that goes on under the cover. You'll probably need to make sure that there is some means of baffling the breather takoff, preferably with a plenum with a drain back to the sump.

[Al Weyman]

There are some nice little Moroso breathers available cheaply from Real Steel that may be worth a try, they have the baffles and separators already in them and a fitting for a 5/8" hose plus come with some big rubber grommits to aid fitting so should be a piece of cake to install. Oh they come in gold anodised alloy or chrome so you get a bit of engine bling in the with the bargain! I always use them cause they work!

[Notso Swift]

If there are pressure problems in the bottom end putting a breater in the top may not work. as the gas tries to move out of the engine, through the new hole in the top, it will stop oil flowing back down (bad) and probably pick up some of that oil and spit it out with the gas.
If you are pumping that much oil out (I have had cars that would just do it regardless of how good or otherwise the rings were) I would suggest finding a way of draining your catch can back to the sump, a simple line back with a one way valve will surfices, then it will pull the oil back under vacuum with out pushing it out. I would also have a second or even third vent fitted to the car somewhere else. A top vent may be of value in this situation, but the bottom needs to be right as well.

Also another sugestion, if you are loosing that much oil the temptation is to fill the oil right up, which can exacerbate the problem, if he oil drains back you can run the level lower with confidence.

Finally, there are som some sump exvacuation systems available, I have never used them, but they are fitted to the exhaust and drag pressure from the motor, the theory being that the vacuum created wll give less resisttance for the crank to spin, saving power. As I said, I have never used one but the F1 teams were using this sort of thing in the 80's to help with turbo blow by, so I am guessing it works.

[zefarelly]

I used to get breathing problems with crossflows, I reverted to the std rocker covers with longer necks and breathable caps in the end

I just hang the expensive Ally ones on the wall !

[Chris Y]

eBay Zef, eBay

Thanks for all the tips guys - I will try out a few things at Mallory this weekend. Apologies in advance to the marshals who have to clean up the oil spill