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MG Midget and Sprite Technical - Engine breather, oil sucking reprise. 🤣

Not wishing to divert from Guy's current persuit of the true path to engine breathing, I thought I'd start a new, but **brief** thread on the subject of engine breathing, aka, PCV.

We could of course also discuss PVC. That too involves breathing. Usually by a sweaty bloke wearing a plastic mack, and leaping out from behind some bushes. 🤣🤣.

But I digress.😄.

For those of you with a curious nature, and a few 'moments' of your spare time to pass, why not look in the technical archives, and fully immerse into, and educate yourselves on, the wonderful subject of A series engine 'oil sucking'.

The best thread is titled (or even entitled 😅), "Engine Breather OIL SUCKING. Yet another engine". 2013.

As Paul mentioned, there's even a movie to watch. Paul also mentioned about 600 posts on the subject in that thread. In total though, across multiple threads, there are in excess of 2000 posts as far as I can tell, and they go back to 1998.

The definitive thread though, is the one mentioned above. A full and thorough analysis of the problem, but alas, no one definitve single cause was identified. And this is because oil sucking depends on fine balancing. It's a goldilocks issue. Just the right amount of oil, at just the right temperature, with just enough suction etc. A minor change, such as a like for like engine rebuild, and bingo; where once there was no oil sucking, there now is.

However all was/is not lost,

If retaining 'PCV', then a properly working solution was identified, and implemented.

I should now like to 'briefly' 😉😄 comment, on some comments from Guy's thread.

Firstly, PCV.
The 'CV' in that, is crankcase ventilation. It's purpose is not only to reduce crankcase pressure and prevent/cure oil leaks. It is also, importantly, to remove the harmful effects of combustion gasses escaping downwards past the rings, which contaminate and degrade the engine oil. In addition to that, it's to remove water vapour from inside the engine.

Just providing a vent or an additional vent, will reduce pressure, but not enough. For CV To act properly, fresh air must be drawn in, pulled through the crankcase to collect all the harmful stuff, and expelled. For the environment, it gets fed into the intake and combusted.

Just sucking on the rocker cover, won't do it properly, unless there is fresh clean air being fed/sucked into the crankcase.

EDIT: Note, tappet cover extraction DOES work, but can't be done on 1275's.

In Jan's solution, he has cured the excess pressure issue, and stopped oil leaking from the rear scroll. But it does not properly vent the engine. It's really a PR, and not a PCV, system. PR, being 'pressure reduction' You can see that the bulk of the air being drawn in, will be in via the vented oil filler cap on the rocker cover, since that is the path of least resistance, -- and not pulled in from where it needs to be. There is less to little suction on the crankcase, and none at all on any reservoir of collected liquid oil, so of course, there will be no oil sucking either. See Jan's picture.

Whereas, in this other picture, an additional connection has been added. This splits the suction from the intake, between a direct connection to the sump (above the oil level), and the original connection to the timing chain cover oil separator. Because suction at the timing chain cover is reduced, no oil sucking occurs. But there is still sufficient suction, the original amount, to draw fresh clean air in via the filtered oil filler cap, to fully vent the crankcase. This method works with both single hiff44 carbs, and with twin hs2's.

Paul, if you are talking about an A series engine with your current customer, look at the split suction solution in my picture.

It works, whilst retaining full function pcv.

It's simplest if you have an engine block that has a pre-drilled hole for a mechanical petrol pump. All you have to do is remove the blanking plate, fix an oil separator, and T it into the original connection from the timing chain cover separator. Alas if no blank, you have to drill the block. Still not hard though. Raise engine, remove sump, cover internals, drill hole, clean up. Or if you feel lucky and have a magnetic hole cutter to collect the swarf and cutout, drill with the sump in situ.

More pictures are available. 😁






anamnesis

I will "bite" on this.
I think that is a good summary, Anam. But then you of all people should know this subject!

I would add that a good balanced pcv system needs a controlled inlet of air as well. This is to ensure a through flow to scavenge fumes, but not allow too free an air entry which would prevent the available suction from creating the ideal slight below ambient air pressure in the crankcase. It is this that ensures a pressure gradient from outside to inside and reduces oil leakage. Even then its a compromise as at higher revs the piston blow by may overwhelm the available suction capacity.

Second point is just a slight alert. Pcv does mean positive crankcase ventilation,meaning an active system, rather than simple venting to atmosphere by having one or more, often large ventilation routes. But pcv is also used to mean Pressure Control Valve, so the detail in some discussions can get a bit confused. Do you mean the valve itself, pcv, or the total breather system, pcv ? Especially as some of our cars don't have a pcv, but do operate a pcv system!😂😂
GuyW

All good points Guy. For a working pcv 's' you need a working pcv 'v' too.

That is, system, and valve. Which is why I do try to use the word system in my posts. Yep, it can easily get too confused.

Hence forth then shall we say pcvs and pcvv? 😆.

I thought the rear scroll, not by design of course, is the pcv, aka, pressure control valve. 😅😅.

anamnesis

Unless you are talking of the rear scroll as a valve, then later 1275's have positive crankcase ventilation system, but no pcv valve. The amount of suction at the carb is matched to revs, and therefore to some extent, to blow by and crankcase pressure. It's only the manifold connected systems that need the pcvalve to control, umm, err, oil suction!
GuyW

When the rear scroll gets worn enough it allows air to enter....
Paul Walbran

It was a joke Guy. The oil pisses out of the rear scroll, along with the pressure. The scroll is an unintended pressure control valve. No?

Paul, can air from the outside enter, even as oil is being expelled by the pressure on the inside? Of course, if there is sufficient suction from an evacuation system, air must be drawn in from any 'hole' in the engine, including the rear scroll. That's no doubt part of the original design intention, to assist the scroll.

Are you arguing, that drawing air in, in the way Jan T has arranged it, unfiltered gritty contaminated air, is a good way to implement a pcv system?

And as I pointed out, most of the air will enter via the vent in the oil filler cap. I suppose you *could* use a sealed oil filler cap, and rely on air being drawn in via the dip stick hole, the front oil seal, and a badly worn rear oil scroll though. 😆.

The original pcv system with the valve, and later with the 'constant' depression at the Su's, works well enough, except on those engines, not all, that acquire oil sucking. Then you need a solution. The split suction in my picture works.




anamnesis

But Anam, if you have a system that has sufficient extraction, then neither the pressure not the oil escapes out of the rear scroll seal
GuyW

If course Guy. I repeat, I was joking. And what you just posted, is pretty much the answer I just posted myself, to Paul's post.

"Of course, if there is sufficient suction from an evacuation system, air must be drawn in from any 'hole' in the engine, including the rear scroll. That's no doubt part of the original design intention, to assist the scroll."
anamnesis

Now, moving on; ---

I forgot to add. Guy, rev's do have some effect on suction at the pcv port on the carbs, but to a FAR lesser extent, because those ports are at the 'constant depression' area, in the carb body.

"If the airflow into the engine is increased - by opening the throttle plate (usually referred to as the "butterfly"), or by allowing the engine revs to rise with the throttle plate at a constant setting - the pressure drop in the venturi increases, the pressure above the piston falls, and the piston is pushed upwards, increasing the size of the venturi, until the pressure drop in the venturi returns to its nominal level. Similarly if the airflow into the engine is reduced, the piston will fall. The result is that the pressure drop in the venturi remains the same regardless of the speed of the airflow - hence the name "constant depression" for carburettors operating on this principle - but the piston rises and falls according to the rate of air delivery."

However, as was measured previously using a vacuum gauge, there IS some very small variation at the pcv port, which is a low level of depression anyway.

And actually, I have a new theory, as yet untested, regarding oil sucking and that 'constant' depression.

I've been thinking about it for some time, and been tempted to start this thread anyway. Recently, I've been experimenting with the viscosity of the damping oil in my hif44, in order to cure a flat response, caused by my using very thin oil. Then the thoughts crystallised further, when Paul posted this in your thread last week Guy.

"The suction port on the HIF44 and later HS carbs creates pretty much equivalent conditions to the pcv [valve], so are functionally interchangeable.".

Now, we know when the pcv valve malfunctions in the 'right' way, oil gets sucked up -- even in a normally non oil sucking engine.

That raises a question. Can the constant depression port on an su carb, 'malfunction', and show a much greater depression? Reading the description of how the su works, gives a clue to how it could potentially go wrong, and create a much greater depression at the pcv port/pipe, and cause oil sucking.

What if the piston sticks, and does not equalise the depression? What if the spring is too strong? What if the damping oil is too thick? The first two would be obvious all year round, and at any engine temperature. But the damping oil changes viscosity in the warmer months, and because as the engine heats up so does the carb body, and piston containing the oil.

One of the most distinctive features of oil sucking, is that it is worse, or only happens in cold weather, and ceases when the engine reaches a particular temperature.

If a vaccum gauge is connected to the pcv port(s) on a single su or twins, and the piston(s) is(are) prevented from rising quickly enough as the throttle is opened, will the gauge show a significant increase in vacuum?

I'm thinking that maybe, a too thick damping oil, esp' in cold weather, may be partly or perhaps even more than partly, responsible for oil sucking.

Time to experiment. Maybe even a new movie. 😁

anamnesis

Yes, the much lower suction at the carb connection, generally less than -5psi, and then also better matched when when blow-by is at its least, is why those cars don't need a pcvalve!
GuyW

Don't know about the science but my system appears to work. If I remove the now sealed oil filler cap the engine revs change so the PCV must be doing something. Why do some A series engines have the stub on the rocker cover anyway?

Jan T
J Targosz

Earlier engines had a different system for crankcase ventilation Jan.

The earliest was a draught tube. And that would also have had a rocker cover outlet fed to the air filter cannister. Then came the semi closed pcv system, using the pcv 'mushrom' shaped valve to control/regulate the suction. Initially that used the tappet cover, but later the timing chain cover. This too I believe, retained the rocker cover spout, fed to the air filter.

Perhaps you've read much of it Jan, and seen the fantastic picture of Guy's inflated rubber glove, demonstrating that the pcv system can be overwhelmed at higher rev's? I don't have it to hand (pun intended). Perhaps you'd be so kind Guy. 😁. That is what the spout relieves.

Then came the last iteration. The valve was replaced by the connection to the constant depression ports on the su carbs.

Mini A series engine have varations of this, with an additional filtered port on the gearbox/bellhousing, and I think also retained the rocker cover spout.

The system was never perfected, and developed further on A plus engines I think.

On Spridget 1275 engines, I wasn't aware that the spout was retained on the rocker cover. But people fitted them. I did too at one time, in an attempt to defeat oil sucking. A spout there, fed to the air filter, is a good idea, it creates a closed pcv system if the filler cap is sealed, and the pcv system air intake is then the carb air filter. It's clean air.

Is that's new information Jan? I didn't notice you'd said you had sealed your oil filler cap.

Of course then, as I said, you have cured the oil drip and smoke. And now you have a closed pcv, you may be venting the crankcase nicely too.

But it's not a good system/solution.

You've blocked the tappet cover, and not added a filter to allow air to enter there. You've done the same to the timing chain cover, and not added a filtered air entry there.

You've just about fully reversed the flow of venting air.

But your source of air, is unfiltered and gritty; coming as it does via the rear scroll, from inside the bellhousing, and contaminated with clutch dust and any other dust and fine metal grit than gets in there too. Not good for your oil and engine.

If that was a good solution, no doubt BMC would have given it a try, not least because it is very simple and costs less than the systems they did use.

Another question.

Your engine is a 1275. Were there any 1275 engine blocks with side tappet covers?
anamnesis

Early cooper S
Bob Beaumont

Ah right. Not inline then. Can a transverse block be used inline? I never thought to do that.
anamnesis

The transverse blocks don't have a scroll seal so that would have to be fitted. Probably a machine shop job as the tolerance to the crank is critical
The later S blocks ('65 on I think) are the same as the Spridget ie no tappet covers. Finding an early S one would be a challenge!
Bob Beaumont

Right, thanks Bob. So Jan's 1275 is a bored out 1098 then, probably.
anamnesis

Possibly although the biggest I think you can stretch a 1098 to is 1150
Bob Beaumont

AFAIK all Cooper S engines had tappet chest covers.

Another difference with transverse engines is that they don't have a thread for the oil pick-up pipe.
Dave O'Neill 2

OK, my 2 bob's worth.

1. Oil sucking is a real issue that affects some 1275 engines.

2. Cause: the famous video shows pretty clearly the oil level in the cover rising to such an extent it enters the breather port in the timing cover. Assumption: that's when the oil suck starts.

3. Why? For the level to rise like that, oil must be entering the cover faster than it is draining away. Sources of oil are discharge from the cam bearing and main bearing, and splash through the hole linking to the crankcase. Oil drains back to the sump via holes in the main bearing cap. When oil sucking starts, something has upset the original balance between all these.

4. Interesting and relevant fact: The car presently in our workshop was not an oil sucker until #3 rings broke up and it started burning oil heavily. Once new pistons and rings were fitted 2-3 years ago, the general oil burning stopped .... but it was left with an oil sucking problem which wasn't there before (big smokescreen 5 min after start-up, clearing after a couple of minutes). Possible explanation: carbonaceous crud from severe ring blow-by deposited in the crankcase and in particular the holes draining the timing cover, reducing their effective size.

5. This car stopped oil sucking when the breather was redirected to the rocker cover, following Jan's observation on the other thread. Like Jan's engine, it is also no pushing oil out the seals as it did when vented to atmosphere.
Note also that this system retains its vented oil filler cap.

6. Based on the above, I don't agree with the proposition that venting via the rocker cover and a vented filler cap is effectively short circuiting the breather system and not doing anything for the crankcase. There is clearly enough negative pressure to address oil leakage. There well may be a negative pressure gradient, in which that in the rocker cover is greater than the crankcase, but the change in behaviour of the oil leaks clearly indicates a change in crankcase pressure for the better.

7. In support of (6) I note that the breather in a number of modern engines is also connected to the valve cover, with the inlet vent also going to the valve cover.

8. So we could debate this aspect for another enjoyable 600 posts, but to me the key thing is that it works - it both reduces oil leaks and feeds unpleasant fumes back through the engine rather than the cockpit. And it doesn't suck oil. What else could you want from it?

9. Regarding air getting sucked in through the rear scroll ... if the breather is doing its job and creating negative pressure in the crankcase, then the pressure difference across the scroll means that air is going to get drawn in there regardless of whether there is an inlet to the system at the filler cap (or elsewhere). The inlet position may affect the amount (by changing the negative crankcase pressure) and yes, the air comes from a dirty area, but the gap is only a few thou and lined with oil. That arrangement makes a reasonably effective job of trapping dirt, and is the same principal as the gauze filter in the filler cap.

That's my view of it, it is just a theory that tries to fit what we do know, but also relies on a fair amount of guesswork about what the pressures and airflow paths inside the engine would be. Others may well have alternative theories that are deduced in the same way but come do different conclusions due to different assumptions and guesswork involved. Hey, it would be boring if we all thought the same!

It would be really cool if someone set up some gear that could actually measure the airflow speeds and directions, and the negative pressure gradients, and the yuk contamination factor, all under different scenarios. But until that happens we are all taking an educated guess, hence a lively fun debate.

For me, what matters is the result. No more oil suck, no fumes inside and lots less oil leaks, and less $$ spent, is what matters to me. I did contemplate fitting an external oil separator to this one, with a drain back to the sump but there is no handy blanked off fuel pump hole. And in any event, it would have cost 5 times as much and achieved a similar result.

BTW we have fitted PCVs a number of XPAG engines with worn scroll housings with good success. The size of the PCV is critical, too big and it sucks oil (there's a surprise!!). But because of the wear in the scroll we have intentionally blocked off any inlet to the rocker cover. In terms of dealing to leaking oil, the results are outstanding - 6" puddle reduces to 1cm. Hard to argue with.
Paul Walbran

The Haynes manual says a 1275 has one of two crank case ventilation systems. Earlier cars had a PCV valve, sucking from the canister on the timing chain cover with air entering from the oil filler cap bleed hole which is filtered. My car had this system. Later cars were fitted out with a very similar system but instead of a PCV valve suction was provided by tappings in the carbs via a "Y" piece. My car sufferred from oil being sucked out of the cannister, through the PCV and then causing copious smoke from the exhaust. My car is a Sprite and the rocker cover has a outlet pipe stub (and also an Austin badge) In an attempt to cure the smoking I connected the PCV valve to this stub and blocked off the outlet from the cannister. The oil filler cap is close to the stub and fearing the PCV valve would suck fresh air straight from the cap rather than the crank case I sealed the cap and relied on a throughput of air from the dip stick. The appears to be working fine and has stopped the rear crank oil drip.

Anam has now advised that my system will suck in dirty air since there is no filter on the dip stick hole. I have now lashed up a simple filter using a pad from our Vax cleaner and connected this to the cannister. I have also sealed the dip stick with tape. My system now works in reverse to the original. The PCV valve sucks air from the rocker cover and since the cap is sealed then from the crank case itself. Air now enters the engine via the cannister and not from it. If it works I will make up a more workman like filter.

I had never thought about Anan's comment about negative crank case pressure pulling dirty oil and dust through the scroll and rear main. The vacuum in my crank case is the same as original, it just flows in the opposite direction and it doesn't appear to have been an issue with the factory so I am leaving as is.
J Targosz

🤣🤣🤣🤣.

In no particular order.

1. I know what I know from months of experimenting.

2. I don't care at all what anyone does or doesn't do with pcv or lack of. 😉

3. The oil drains for the timing chain cover, are 2 small holes in the front main cap. In the 3 engines that sucked oil, that I stripped and examined, they were completely clear. Those drain holes are simply inadequate to cope with the level of oil in the timing chain cover, once it reaches the internal entrance of the oil separator cannister. This is because, as well as being too small, those drain holes are opposed by both suction from the cannister supplied by the induction (pcv valve or carb ports), and by pressure in the sump. The holes can't be made any bigger. Of course if those drain holes are clogged by carbon or anything else, the problem is worse, but not the cause.

4. Jan, my description was based on your earlier descriptions, of a sealed cannister, sealed dipstick hole, and a sealed oil filler cap. The only other place air could enter then, is reverse flow through the scroll. But now you've opened the cannister and filtered the air, I agree, it should work, and indeed, you report it does.

5. However, I considered doing what you've done Jan, but concluded that drawing air and oil vapour up through the block, via the drainage route that oil takes to return to the sump from the rocker cover, opposes that drainage. It seems better to me to assist that drainage and stick to the original direction of flow.

6. You say it was never an issue with the factory. Not sure I understand that comment. The factory never implemented pcv on Spridget engines in the way you are Jan.

7. The Haynes manual. 😅😅.

8. Nothing really matters, anyone can see. 😁 https://tinyurl.com/25cj8xj3

9. Modern engines are not Spridget engines, and hence are designed with a different and better ventilation systems.

10. There should always be a 10, but I can't think of a perfect ten in this instance. The picture will have to suffice.

Once upon a time, I decided to find and elliminate **the** cause. I never did. Instead I found a good working solution that maintains the same flow direction for vented gasses.

The holy grail does not exist. But No.2 does, and I am a free man, not a number. I will not be pushed, filed, stamped, indexed, briefed, debriefed or numbered.

https://youtu.be/-8QTPMj63Tw

https://youtu.be/M3LT98uOwck

This thread is like Airplane vs airport using airport transfers sevenoaks 1975. 😁😄






anamnesis

Nothing really wrong with the as designed systems, periodically upgraded as capacity, compression, power output and blow-by increased.
Problems arise because of attempts to modify (guilty) and due to normal wear process.

System can be improved, but if you are happy with a 1960 - 1980 design of car, then just accept that is what you have. But if you like experimenting, there are lots of options for anyone interested enough to try.
GuyW

I agree Guy. A small amount of oil from the rear scroll isn't really a big deal. It's way better than some of the total loss systems kicking around back then, that were deemed acceptable. I think a catch tray under the rear of the sump is a much better solution, compared to changing the pcv system if those oil drips are the only worry/problem.

As regards alterations, there really is no need if the engine isn't a sucker. But we do love to tinker, don't we? 🤣

Speaking again of the scroll and air entry there. If likening the scroll clearance to the mesh size in the oil filler cap, then, a) it must also be considered that the cap is a service item, to be replaced when the mesh is contaminated, b) the scroll and it's cap are fixed, c) the air entering at the oil filler cap is likely to be considerably less contaminated than it is inside the bellhousing.



anamnesis

I also think it is easy to overlook the real complexity of constantly changing dynamics of the system, all largely beyond the control of the owner. As you drive it, all of these are constantly changing: blow by, with revs, ambient air pressure and air temperature, throttle position, oil viscosity, pumped oil volume, sump oil capacity, oil surge, crank splash, oil distribution/ share between crank, camshaft, bearings, valves...etc. all constantly changing with every twitch of your right foot!

I'm not terribly convinced about dirt getting in via the rear crank seal. Most of the time the surfaces will be sealed with oil, or being flushed outwards with oil, even on a good behaving system. The rest of the engine would need to be very well sealed to prevent any air entry at all, and most air entry that does come in will be at high pressure from the cylinders.
GuyW

Re scroll dirt. That's my point Guy. If you have sufficient suction to counter the blowby pressure, and seal everywhere else, such that the only air entry point becomes the rear scroll, having stopped and even reversed the flow of oil through the scroll, dirt entry there is likely, heading to certain. Why risk it?

Everything else you say must be right too. It's impossible to compensate for all those variables on old engines like ours, and pointless trying. Modern engines are massively changed, and have sophisticated management systems that can't be used on our engines.
anamnesis

I think even the best set up of our engine pcv systems only cope up to mid range revs. At lower revs there is sufficient suction to scavenge the crankcase but probably not strong enough to pull much if any dirt through the rear scroll. At higher revs blow by is likely to provide all and more of what the suction can cope with!

Of course if you use the proper filtered and size-matched oil filler cap then the same will apply, just higher up the rev range. Use a proper vented cap and at least give it a quick rinse and re-oil when you do an oil change.
GuyW

My engine was rebuilt by Southam Engineering who are A Series experts. They said a 1275 engine from a Maestro can be made to fit but a lot of machining work is needed. This engine does have a proper lip seal to the rear of the crank though.

I disagree that the odd drip from the bell housing isn't a real issue. Before I sorted the Sprite I was embarrassed many times when the car left a rainbow in the road or worse still on a friends drive. I recall a Classic Car event in Glasgow only drivers with a drip tray were allow in. I wonder what is the more eco unfriendly, crank case fumes into the air or oil washed down the drain.


Jan T

J Targosz

I'm confused Jan. I thought you said you had a scroll. Now you say you have a lip seal.

My Sprite only has the odd scroll drip, hardly a big deal, and the normal pcv system, along with a tendancy to suck oil if I let it.

Some of that bellhousing oil is likely coming from the gearbox input shaft.

Old cars vehicles drop oil. Of coure they're bad for the environment, that's why ice is dying out. But our aged cars don't contribute a significant amount of pollution anymore.

anamnesis

Those on this website who are members of MASC may be aware that I developed a simple supplementary oil seal that can be fitted to 948 and 1098 (small and big journal) engines for under £5 details of which were published in Mascot.
It is a face type seal and requires no actual machining of the engine other than cleaning up the face of the rear main bearing housing.
As noted in my article even if it only keeps out the debris from the clutch friction plate that would otherwise be drawn into the sump oil via the drain holes of the scroll seal.
Unfortunately a similar approach cannot be applied the the 1275 blocks directly however it MAY be feasible to make up for the lack of metal in the critical location using a metal loaded epoxy applied to suitably prepared surfaces requiring only minimal development.
Similarly I have modified both types of gearbox front plate to provide a rotary shaft seal in place of the original scroll.
S G KEIL

annam The Maestro (and Montego) 1275 engines ran a lip seal. This was the first A series engine where the crank flange was machined to be concentric, before that they were only machined to be smooth.
The Maestro had an alloy adapter to mate to a VW golf 4 or 5 speed gearbox, hence why you can get a 5 speed A series engined Maestro and Montego.
This alloy adapter was about 1" deep and the crank flange was made deeper to enable a machined concentric area for a lip seal to run. The lip seal was fitted in the alloy adapter.
Interestingly (considering it used a lip seal) the alloy adapter also had a breather with oil separator connected to the HIF44 carb vacuum port. Maybe it was a case of "belt and braces"
Another interesting thing was the Golf gearbox of the time had a clutch operating rod which passed through a hollow first motion shaft.
Another interesting thing is because the Maestro and Montego used VW gearboxes it is possible to mate the gearbox to the Audi 5 cylinder engine. Now that would be something unusual.
Rob
MG Moneypit

SG. That sounds interesting. How many people have copied/installed your design? It sounds good, esp' if with a bit more work it can be made to work on 1275's too. Likewise the mod's to the gearboxes for those still with ribcases and the like.

Rob. Yep I know the later A series had rear oil seals, but didn't know there was built in extraction vented to the hif44. Yep, probably belt and braces. The oil seal alone, still not able to hold back the crankcase pressure, still needed a bit of help.

If only the Spridgets had been continued, and fitted with later engines; what could have been eh?

Only confused about what engine Jan has, since he said he has a rear scroll that had an oil seal conversion he removed, but also says --

" This engine does have a proper lip seal to the rear of the crank though. "



anamnesis

Anam, all that Jan said was that the company that rebuilt his engine were knowledgeable about A series engines and mentioned the lip seal version of the Maestro. He didnt say it was his engine.

Even with a lip seal, an engine still needs a crankcase breather system to scavenge air, and probably even more important not to build up excess pressure which will blow the crankcase seals.
GuyW

Right. "This" vs that Guy.

Absolutely Guy, oil seals can blow out.

I mentioned previously that some mini engines had a plumbed in vent/breather on the gearbox/bellhousing, really called the clutch cover. So it predates the Maestro, but is there for the same reason.

I hadn't researched it on minis before, but I just did. And it seems there is just as much discussion, dissension, misunderstanding, wrong thinking, and right thinking about pcv, on mini forums too.

There's even talk of liquid oil potentially being sucked up.

If only we had access to actual bmc design documents and notes, explaining what they knew about the limitations of their success in controlling crankcase ventilation on A-series engines.

Here's what one chap posted in one mini forum thread. Quite an intereting comment.

--- "Just going back to the two breathers on the 1275 engines, the Cooper S Engines only had one breather and that was from the tappet cover, however when the non-S blocks came about, they had no tappet covers and reading the old technical bulletins, it's clear BMC had Ring Sealing Problems around this time too, so at a guess I'd say the second breather was included at that time as a just in case. I'd also guess that it wasn't fully reviewed for am change at any time during production and / or they wanted to retain it rather than get a reputation (imagine that!) for having engines / cars that spat oil on the roadway after blowing out oil seals."
https://www.theminiforum.co.uk/forums/topic/311234-engine-breathing/


On another mini thread, a chap posted this about the need for proper breathing/venting in minis, and generally.

--- "Your piston rings never make a perfect seal, so you get what's called blowby - basically exhaust gases passing by the pistons into the crankcase, (this is about 20 litres/minute for a 2 litre production engine - not sure about a mini).

This would pressurise the crankcase, however you can stop it doing so by fitting a pipe back to the inlet, (recirculating gases and fumes), on a 998 this is a take off pipe from the right hand tappet chest cover.

On the 1275 they fitted two breathers, one from the timing gear cover, and one off the clutch casing, these were originally fed back into the inlet manifold to go back into the engine, but now in some cases fed through seperaters, (the black canister), and filters to atmosphere.

Back to the first paragraph, 20 litres / minute sounds a lot, but think a 2 lite car at 5000rpm is passing approximately 10,000litres / minute, so 2 litres is only a fraction of a percentage." ---

https://www.theminiforum.co.uk/forums/topic/65074-clutch-breather/

anamnesis

HI Guy,

You are spot on. The engine that Southam rebuilt was the original 1967 A Series 1275. I had visited them to discuss the rear oil seal and they then mentioned the Maestro engine. They said the conversion to fit one of these to a Spridget was complicated and these engines are now very rare.

Cheers

Jan
J Targosz

This thread was discussed between 30/04/2023 and 04/05/2023

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