Crankcase ventilation
Discussion
Pictures of engine bays in Mini World etc usually show that the owner has removed the PCV tubes that connect the crankcase breathers to the carburettor and replaced them with small air filter like objects, usually coloured. Is this purely cosmetical or is this the preferred method for venting the crankcase these days? If it is what are the advantages over the old method?
The reason for blanking off the crank breather to the vac side of the inlet system is really to improve reliability. If you get just a small leak in the hoses, or the oil filler cap seal, or anywhere else, then the engine will run lean or just run badly.
The best way to correct the problem, IMHO, is to fit a 'catch tank' made from a 1/2 litre polythene bottle under the r.h. wing, fitted to the inner wing. Then make 2 holes to take normal 1/2" heater hose and run one hose from the timing chain cover breather into the catch tank and another from either the flywheel cover housing or the top of the rocker cover (easy if it's aluminium - just use a plumbing fitting).
This seems to work on rallycars and the other advantage is that you can see when it's blowing out oil.
The best way to correct the problem, IMHO, is to fit a 'catch tank' made from a 1/2 litre polythene bottle under the r.h. wing, fitted to the inner wing. Then make 2 holes to take normal 1/2" heater hose and run one hose from the timing chain cover breather into the catch tank and another from either the flywheel cover housing or the top of the rocker cover (easy if it's aluminium - just use a plumbing fitting).
This seems to work on rallycars and the other advantage is that you can see when it's blowing out oil.
if you fit these little filters instead of the standard set up, or the catchtank set up as suggested by cooperman , you'll end up with quite a dirty engine bay, especially if you do any motorway miles.
all the oily fumes from your breathers tend to get spread around the engine bay, and then you get dust and grit sticking to the film.
all the oily fumes from your breathers tend to get spread around the engine bay, and then you get dust and grit sticking to the film.
eccles said:
if you fit these little filters instead of the standard set up, or the catchtank set up as suggested by cooperman , you'll end up with quite a dirty engine bay, especially if you do any motorway miles.
all the oily fumes from your breathers tend to get spread around the engine bay, and then you get dust and grit sticking to the film.
You are absolutely right there, Eccles. Those little filter-thingys keep the dirt out of the engine, but don't stop the fumes getting into the engine bay at all. That's why the catch tank is the best option. Some people put a non-return valve in the hoses, although I don't do this and have not found the need to. One thing you should do is to just have a small hole in the top of the catch tank (plastic bottle) with the rest of it sealed as it could get spray from the wheel into it and partially fill with water.
Two schools of thought depending on application. On a race/high performance engine you are trying to keep the incoming charge optimised for combustion for power (13:1 air/fuel) and so having the by products of the crank case ventilation system (oil fumes etc) into the inlet charge is scene as detrimental (polluting the charge), hence race engines will have positive crank case ventilation (Filters on the oil seperation cannisters or the big bore pipe and catch tank scenario advocated by cooperman).
For a road engine, making the engine run a closed cicuit system will ensure negative crank case pressure and give the oil control rings less to deal with. This is providing the hoses are in good condition and not split/cracked, air leaks will not only bugger the carburation (mixture will lean out) but you won't get the benefits of the oil control either.
For a road engine, making the engine run a closed cicuit system will ensure negative crank case pressure and give the oil control rings less to deal with. This is providing the hoses are in good condition and not split/cracked, air leaks will not only bugger the carburation (mixture will lean out) but you won't get the benefits of the oil control either.
That's why you could fit non-return valves. With the length of hose used to take the oil fumes to the catch tank under the left wing it's not a problem and that's why I don't bother to fit them. Then no positive pressure is needed to open them and there is, therefore, less to go wrong.
When I did a Clubman GT I was able to put the catch tank in the engine bay on the rh side low down just behind the grill. Not quite enough room with the ordinary Mini though.
I have seen it done without a catch tank and with the hoses running down the side of the engine bay to exit at floor level and clipped to the sub-frame. No good for competition, of course, where catch tanks are mandated, but for the road I guess it's OK. It would help keep the rust at bay as well!!
When I did a Clubman GT I was able to put the catch tank in the engine bay on the rh side low down just behind the grill. Not quite enough room with the ordinary Mini though.
I have seen it done without a catch tank and with the hoses running down the side of the engine bay to exit at floor level and clipped to the sub-frame. No good for competition, of course, where catch tanks are mandated, but for the road I guess it's OK. It would help keep the rust at bay as well!!
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