Breathing on 1275 engine
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Re: Breathing on 1275 engine
Why would they have to fiddle with carb and timing to get an MOT on the car??
Re: Breathing on 1275 engine
Well, they wouldn't have to but it is running a lot better now!
Re: Breathing on 1275 engine
I have also been advised to check that the valve stem seals were actually put on, so going to have a look at the head today. Also had suggestions of the cam bearings, and piston rings, any thoughts would be greatly appreciated. Thanks.
Re: Breathing on 1275 engine
Cam bearings have no effect on this - but of course, worn or broken pistons/rings are indeed the likely culprit.
Re: Breathing on 1275 engine
Here's my twuppence worth on how to set up the breathing on a 1275cc engine with HIF44 carb.
No breathers open to atmosphere.
Connect timing cover breather (and breather on side of engine if fitted) to the carb port designed for this purpose.
Vented oil filler cap.
Never connect inlet manifold port to breathers - far too much vacuum at idle and partially open throttle and not enough at full throttle.
This setup should create a partial vacuum in the crankcase minimising oil leaks past the scroll seal etc. There will be no smells coming from the filler cap because it is letting a small amount of filtered air into the engine but not enough to prevent there being a partial vacuum in the crankcase. If you use a non vented cap then there is zero ventilation of the crankcase.
So I agree with IslipMinor
bmcecosse - if I understand you correctly and you are venting one breather to the atmosphere (into the under car airflow) and connecting another to the inlet manifold, then the crankcase breathing will behave very differently depending on how open the throttle is: at idle and low throttle the powerful vacuum from the inlet manifold will pull air in through the 'open to the atmosphere' breather whereas at high throttle when there is virtually no vacuum in the inlet manifold, fumes will gently escape from your open breather. In neither case will there be the necessary partial vacuum in a positive crankcase breathing closed system - which is what the 1275 engine is designed to have.
No breathers open to atmosphere.
Connect timing cover breather (and breather on side of engine if fitted) to the carb port designed for this purpose.
Vented oil filler cap.
Never connect inlet manifold port to breathers - far too much vacuum at idle and partially open throttle and not enough at full throttle.
This setup should create a partial vacuum in the crankcase minimising oil leaks past the scroll seal etc. There will be no smells coming from the filler cap because it is letting a small amount of filtered air into the engine but not enough to prevent there being a partial vacuum in the crankcase. If you use a non vented cap then there is zero ventilation of the crankcase.
So I agree with IslipMinor
bmcecosse - if I understand you correctly and you are venting one breather to the atmosphere (into the under car airflow) and connecting another to the inlet manifold, then the crankcase breathing will behave very differently depending on how open the throttle is: at idle and low throttle the powerful vacuum from the inlet manifold will pull air in through the 'open to the atmosphere' breather whereas at high throttle when there is virtually no vacuum in the inlet manifold, fumes will gently escape from your open breather. In neither case will there be the necessary partial vacuum in a positive crankcase breathing closed system - which is what the 1275 engine is designed to have.
Re: Breathing on 1275 engine
The 'filtered' oil filler cap leads to oil mess on the rocker, and nasty smells in the car. Yes - I agree - the open breather probably DOES emit some fumes when the engine is working hard. It exits below the car in the airstream, so no nasty mess or smells in the car. If it wasn't open, there would be pressure in the crankcase - and fumes would be leaking out of the 'filtered' oil filler cap if I was silly enough to have one fitted! The system I have works v well on my (less than new) v hard worked 1098 (big valve head and large carb) - and it has NO oil leaks.....and no mayo in the rocker cover ..... QED 
Re: Breathing on 1275 engine
Right, I've finally finished my degree and got a bit of time to try and get this oil leak from the rear of the crank sorted. I'm thinking it is probably increased pressure in the lower part of the engine. Would doing a compression test help confirm this and the offending piston? Thanks.
Re: Breathing on 1275 engine
It won't do any harm - but pressure in the crankcase shows readily enough if you run the engine with the oil filler cap removed!
Re: Breathing on 1275 engine
Right, borrowed a gauge from our local garage, got reading of 210psi on all 4 cylinders. Is that a bit high? As they are all the same is it unlikely that damage to a piston ring is causing increased pressure in the crankcase?
Re: Breathing on 1275 engine
Took all the plugs out, screwed the gauge in and turned the engine over a couple of times to get a reading.
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IslipMinor
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Re: Breathing on 1275 engine
Just for clarity (I hope!):
Non-vented oil filler cap - used on all 'open' crankcase ventilation systems in the same way that BMC/Morris originally designed it. The vents are in various positions, rocker cover, tappet cover, etc., but all rely on a very small positive crankcase pressure to expel the fumes through the vent(s), wherever they are located. This can also include the rear crank scroll, which is open to the atmosphere, and which provides a well-known exit path for fumes and/or oil! Open systems include those that are vented into the air filter, as no partial vacuum is designed in and quite often the filter gets clogged up with an oily residue. Using a vented cap in an open system means that fumes/oil could escape from the cap itself, as it becomes just another vent in an open system.
Vented filler cap - used on all 'closed-circuit' crankcase ventilation systems, again as BMC/Morris designed it to be, and relies on a small negative crankcase pressure to draw the fumes into the intake system, with any residue being passed through into the exhaust system. The later 1098 Minors had the PCV in the inlet manifold to create a controlled partial vacuum (the rocker cover vent was deleted at the same time), and the HIF range of SU carburettors have a port on the side that the ventilation system connects to for creating the partial vacuum. With a partial vacuum in the crankcase, no fumes/oil can escape from the cap, as it is now being used to draw air into the crankcase and provides no way out at all (assuming the system is working properly). Also the rear scroll is now being subjected to a small pressure differential towards the crankcase, rather than out into the bell housing with the open system, so this helps to prevent leaks from here as well.
In summary, with any type of 'open' system use a non-vented cap and for the later PCV/HIF closed circuit systems use a vented cap.
For a closed circuit system, either use a timing cover or tappet cover vent that has the oil separator canister attached to it (it also contains a coarse wire mesh filter, if it is still there). The early tappet cover and all rocker cover vents have no oil separator, and if used as part of a closed-circuit system could draw oil into the engine, along with the fumes, so should not be used.
Non-vented oil filler cap - used on all 'open' crankcase ventilation systems in the same way that BMC/Morris originally designed it. The vents are in various positions, rocker cover, tappet cover, etc., but all rely on a very small positive crankcase pressure to expel the fumes through the vent(s), wherever they are located. This can also include the rear crank scroll, which is open to the atmosphere, and which provides a well-known exit path for fumes and/or oil! Open systems include those that are vented into the air filter, as no partial vacuum is designed in and quite often the filter gets clogged up with an oily residue. Using a vented cap in an open system means that fumes/oil could escape from the cap itself, as it becomes just another vent in an open system.
Vented filler cap - used on all 'closed-circuit' crankcase ventilation systems, again as BMC/Morris designed it to be, and relies on a small negative crankcase pressure to draw the fumes into the intake system, with any residue being passed through into the exhaust system. The later 1098 Minors had the PCV in the inlet manifold to create a controlled partial vacuum (the rocker cover vent was deleted at the same time), and the HIF range of SU carburettors have a port on the side that the ventilation system connects to for creating the partial vacuum. With a partial vacuum in the crankcase, no fumes/oil can escape from the cap, as it is now being used to draw air into the crankcase and provides no way out at all (assuming the system is working properly). Also the rear scroll is now being subjected to a small pressure differential towards the crankcase, rather than out into the bell housing with the open system, so this helps to prevent leaks from here as well.
In summary, with any type of 'open' system use a non-vented cap and for the later PCV/HIF closed circuit systems use a vented cap.
For a closed circuit system, either use a timing cover or tappet cover vent that has the oil separator canister attached to it (it also contains a coarse wire mesh filter, if it is still there). The early tappet cover and all rocker cover vents have no oil separator, and if used as part of a closed-circuit system could draw oil into the engine, along with the fumes, so should not be used.
Richard
