1275 Crank case breather question

[Neil MG]

I am fitting a Midget 1275 engine and wondered about options for crank case ventilation. The Midget engine has a breather canister on the timing cover, but this needs to be altered to fit the Minor fan and the ones I have seen have not looked so nice. Is it possible to space the fan without getting too close to the radiator?

Has anyone successfully used the standard Minor timing cover and found a solution? This would be my preferred option, but am concerned at the problems I have heard about these engines struggling to breath.

[philthehill]

You can space the fan away from the water pump by using 7/8" spacer from Mini Spares Pt No: PGX10001 £6.79 inc VAT plus P&P. This spacer was fitted to Minis from 1990 on until twin port cars.
You may also need 3/16" spacer again from Mini Spares Pt No: 12A312 £4.20 inc VAT plus P&P.
You may need a combination of both to achieve the required clearance.
Fitting the spacers is much better and easier than cutting away part of the fan or modifying the timing chain breather.
Make sure that you have enough clearance in front of the fan so when undergoing hard braking the engine does not move forward so enabling the fan to hit the radiator.
You do need to have good crankcase breathing with the 1275cc Midget engine and unless you retain the timing cover breather you are more than likely to have oil leaks. If you just have the rocker cover breather that is totally insufficient for the engines needs. Crankcase vent breathers have been fitted to where the mechanical fuel pump would have been on the side of the block and that may be another option for you to consider.

[IslipMinor]

Ours has a high capacity radiator, which has a thicker than standard Minor core and I tried to space the fan out, but it was too close to the radiator for comfort, so I had to slice the front off the oil separator on the timing cover and weld on a flat cover to reduce its width by about 20mm.

There is no fixed fan fitted (very noisy), it has a thermostatically controlled electric one, but just in case it fails there is the original 2 bladed fan in the boot, and it would not be much use if it didn't fit!

Then a simple connection from the timing cover to the port on the carburettor(s). No connections anywhere else. Use either an unvented rocker cover or block the outlet to the carb if using a non-1275 cover. Use the ventilated rocker cover cap to provide the inlet for fresh air.

The in-line A-Series needs a partial vacuum in the crankcase to keep the oil inside the engine, as without it, oil will get past the rear crankshaft scroll and on to the floor!

I expect there will be suggestions to connect the carb to the rocker cover - there is no oil separator or filter in the rocker cover and it was never done by BMC/BL in any production model with closed circuit crankcase ventilation. It may work, I have never tried it.

[Neil MG]

Thanks guys, that's really useful!

[bmcecosse]

As Richard predicts - I recommend to NOT use the vented cap - which allows nasty smells to waft about the engine bay, and use a rocker cover WITH breather, and connect to the carb - or better still (as suggested by Declan) - to a PCV and thereby directly away into the inlet manifold. You MUST evacuate the crankcase, and you really MUST use the timing case breather......

[mike.perry]

I have a Midget engine and I use spacers on the fan blades with clearance for a 4 blade fan. I have early twin carbs so need to use a PCV into the manifold which needs to be kept clear of mayonnaise. I fitted a crankshaft sealing kit which was a waste of space.
I have a power wash to clean the garage floor!

[IslipMinor]

I am not going to get into another pointless debate about breather systems - what is being suggested was never a BMC/BL design, nor will it provide an effective breather system that also helps to contain the oil within the engine, through creating a partial vacuum. Leaving any part of the system 'open' prevents a vacuum being created and so increases the risk of leaking through the rear crankshaft scroll.

The later 'closed' circuit systems are generally better at keeping the oil inside the engine than the original 'open' systems. The closed system never used any connection to the rocker cover (there was nothing to connect to) - it was either from the tappet chest filter/separator (later 1098 engines) to the PCV, or from the timing cover filter/separator to either the PCV or the port on the carburettor(s). Closed systems always had the vented oil filler cap -where else can the crankcase get the incoming air from?

allows nasty smells to waft about the engine bay

This is not possible with the closed system, as the whole point is to draw air IN through the cap and the crankcase fumes OUT through the combustion process.

[IslipMinor]

I fitted a crankshaft sealing kit which was a waste of space

I talked with Peter May a while ago about fitting a rear crankshaft seal and, although they sell them, they don't recommend them! Needless to say I have not fitted one.

[bmcecosse]

I appreciate that was the plan - but with worn engine, when working hard - the fumes overcome the suction and a smelly engine develops with oil mist mess on the rocker cover. hence my firm conviction that a sealed cap is best - but with a breather pipe from the rocker to the inlet system in some way - be it direct to the carb, or to a PCV if you have one, or even directly to the inlet manifold via a 1/8" restrictor.

[Declan_Burns]

Closed systems always had the vented oil filler cap -where else can the crankcase get the incoming air from?

Richard,
That's the trick-through the scroll and oil sump rear seal-that's how my MG is set up and it works. Air going in keeps oil from coming out
Regards
Declan

[Neil MG]

The earlier 1275 Midgets had the timing cover connected to the inlet via a PCV and breathed in through the cap, the later cars were connected directly to the carbs. Am I right in supposing that what BMC is saying is that the crankcase is not satisfactorily evacuated this way and the engine also breathes out through the cap?

I am aware of two problems highlighted by Midget owners (who have varied from standard) regarding breathing and they are excessive oil intake after overrun (big smoke from the exhaust) and excessive oil leaks from the crankshaft rear seal due to over pressure in the crank case. It seems there is a delicate balance here and so I am keen to hear from those who got it right.

It seems there is a general consensus about one thing so I am definitely keeping the timing cover breather. I also have a vented rocker cover, so I just need to know the best way to connect up!

I intend to use the standard 1098 Minor manifolds and carb (I am not looking for more power) so I have no take off on the inlet manifold (so far).

So, my first thought is to vent the timing cover breather to atmosphere (same as the Minor tappet cover breather) and take the fresh air from the air cleaner. This will replicate the early BMC open breather systems with the only difference being that the crankcase is evacuated from the timing cover instead of the tappet cover. A partial vacuum is created when the car is moving at least...

[mike.perry]

That is the whole point. Whilst on the 1098 it is sufficient to allow the crankcase pressure to evacuate to the atmosphere the 1275 operates on a negative crankcase pressure which is created by sucking the fumes from the sump into the carb or PCV.

[Boris64]

Mike,

Thanks for the eloquence, I couldn't decipher the technical stuff but you have nailed it in a sentence.

Pete

[Neil MG]

Not strictly true! As I understand, the method that BMC used on the earlier A and B series engines also creates a negative crankcase pressure once the car is moving. The air is sucked out of the pipe by venturi effect creating a partial vacuum and filtered air is drawn into the engine through the rocker cover breather. The big advantage of this system is that oil mist is not drawn into the combustion chambers (the disadvantage is that is gets discharged into the countryside!)

But has anyone tried such a set up?

[IslipMinor]

Neil,

I don't understand what this earlier venturi system is? Can you explain more please?

Going back to your slightly earlier post, our 1380 has the standard 1275 closed circuit system connected to the port on the HIF6 carburettor. 1380's are known to have less than perfect piston to bore sealing, but we have virtually nothing leaking from the real scroll, and absolutely no fumes from the oil filler cap breather - it does exactly what it designed to do! The rocker cover stays perfectly clean, other than if I spill a drop whilst topping up, which isn't very often as it does about 1,000 miles per litre.

My belief is if the design can cope with a well modified, hard driven 1380, it will cope with most other things. The solution to well worn engines lies elsewhere I think?

Smoke on the overrun is usually worn valve stem oil seals - always fit the later lip seal type.

You could fit the later Minor inlet manifold with the PCV - single connection to the timing cover and cap off the rocker cover.

[bmcecosse]

In my experience - there is no need to let air in to the crankcase - the idea is simply to make sure there is no pressure - inflow of fresh air is not necessary. I do think the PCV is a great idea, connect all the breathers to that - but I would NOT use a smelly vented cap...

[IslipMinor]

I cannot agree - you risk just sucking out all the oil! The system is designed to have an air flow through the crankcase, how is that achieved if you block up the entry point?

Final comment is use a proper closed circuit system based on the original design - it works!

[Neil MG]

Mike, this is also what the Minor (and others) used until almost the end of production. I stole this off the MGA Guru's site:

"The original draft tube on MGA and early MGB works as a venturi when the car is in motion to draw a slight vacuum on the crankcase and produce air flow. Suction inside the air cleaner (pressure drop across the filter element) is very small compared to the vacuum level created by the draft tube. With the draft tube in place and the car moving air goes in through the air cleaner, then through the vent hose to the valve cover, through the crankcase, and out the draft tube. This is amazingly effective at road speed moving a lot of ventilation air through the crankcase.

Operation of the draft tube as a vacuum venturi is easy to demonstrate in your kitchen sink. Fill a tall glass with water and drop in a soda straw (not more than two inches from top of straw to water level). Cut the top end of the straw at 45 degree angle and turn it so the opening faces away from you. Blow across the tip of the straw at a right angle and the vacuum generated can draw water up the straw to produce an atomizing spray."

I agree that using the original Midget design should work, and if I can find a PCV inlet I think that is the way to go. In theory the original Minor design should work too, but there is a difference between the point of exit from the tappet cover to the timing cover...

[bmcecosse]

I've used it - and never sucked up all the oil, so far. But if in doubt, leave one breather open - by 'open' I mean lead it well away from the engine compartment , down into the air stream under the car - where any fumes will be taken away.

[IslipMinor]

The MGB (and MGA?) has a 'proper' rear crankshaft oil seal, so less prone to leaks, with or without positive crankcase ventilation.

Where is the 'draft tube' on a Minor?