fume vent dumping oil

[soilman]

Hi,

there is a pipe running down the side of the sump, its noted as fume vent on the schematic, ( its not the crankcase breather that returns to the air filter), well it dumped some oil on the road after being out for a drive, never seen this before, what could cause this?

regards

Soilman

[Declan_Burns]

It's a Moggy and it has just marked it's territory!
Regards
Declan

[philthehill]

The pipe described in the above post is the crankcase breather pipe. The pipe between the rocker cover (or cam follower cover) and the air cleaner is also a crankcase/engine breather.
When the engine gets to the point of 'dumping' oil through the crankcase breather pipe it is a good indication that the piston rings/bores are worn so allowing piston compression blow by into the crankcase which then leads to crankcase pressure pushing oil out of the breather pipe.

[soilman]

Just had the engine rebuilt December 2017, done 2000 miles, new sleeve pistons the lot cost me a fortune, so hoping it wil go away,thanks for the replies.

[IslipMinor]

The side 'vent tube' is the early 'open breathing' system. The later 1098 engines were fitted with a 'closed circuit' system using a PCV valve in the inlet manifold.

There are a number of variants of this 'open' system, but they all work on the same principle.

The side vent tube is actually a 'draft tube', which draws air/fumes from within the crankcase, via the front tappet cover when the car is moving forwards at a reasonable speed (?20/30mph+).

Draft Tube.jpg (31.92 KiB) Viewed 3280 times

The oil filler cap must be the 'sealed' type and there also needs to be a hose connecting the air cleaner to the rocker cover.

Early Rocker Covers and Oil Fillers.jpg (56.62 KiB) Viewed 3280 times

For the breathing system to work, fresh, filtered air enters the rocker cover FROM the air cleaner and is drawn down through the crankcase and OUT through the tappet cover and down the side vent tube. Unfortunately, there will inevitably be some drips from the end of the tube, as it is the outlet for the process.

Oil Bath Air Cleaner.jpg (50.43 KiB) Viewed 3280 times

Paper Air Cleaner.jpg (50.92 KiB) Viewed 3280 times

It was never a very good system!

[soilman]

That’s the one, bloody marvellous thankyou

[Declan_Burns]

You can always convert to the closed PCV valve system and that will certainly solve that problem. The valves are expensive though.
Regards
Declan

[moggalot]

Or.. you could find a cannister breather system which was fitted to the later 10V type engines which should enable the oil to find its way back to the sump.

[philthehill]

No matter that the engine was rebuilt 2000 miles ago the engine should not be dumping oil out of the crankcase breather vent Pt: No 2A118.
Engines with good bores and good serviceable pistons/rings will not create enough crankcase pressure to dump oil out of breather vent pipe.

The early metal rocker cover cap oil filer with cable with cable Pt No: 8G612 was not sealed. Air was able to enter the rocker cover via the cap. The rocker cover 2A261 had a breather which was connected to the air filter via pipe Pt N: AAA3979 (early) ACA5353 (late).
Later still 'A' Series engines had either a sealed or breather type rocker cover oil filler cap dependent upon the breather system fitted.

[dudload]

just out of interest Phil - when did the late engines start getting fitted? i've got a 66 traveller that's got the breather in the rocker cover...

[philthehill]

https://www.moss-europe.co.uk/shop-by-m ... minor.html

[KeithL]

Thank you for your interesting post IslipMinor. My 1098 cc Traveller has exactly the arrangement you show in your post with the second oil filler cap pictured and the paper air cleaner. The only difference is that my side vent tube goes up between the exhaust and the bottom hose and then bends over before dropping down to the bottom of the engine. Presumably this is to stop oil dripping out as Soilman describes?

However, I am confused about one thing. You say the air gets drawn from the air cleaner and then down and out the vent tube. I was always under the impression that air was drawn out of the rocker cover through the air filter - a way of recycling the noxious fumes. I'm sure I have seen posts to that effect on the Forum but from what you are saying that is incorrect.

[philthehill]

Your engine is fitted with the later cam follower cover with the upswept breather pipe as per the engine in the attached link.
https://www.ebay.co.uk/itm/MORRIS-MINOR ... XQgfZRBjys

Whilst it goes some way to reducing the oil being blown out of the crankcase it will not stop the oil which is suspended in the crankcase fumes being dumped/blown out through the pipe to atmosphere.
The best solution as regards cam follower cover breathers is to fit the front cam follower cover with oil separator canister (Pt No: 12G577 or 12A1212). The canister contains wire mesh which catches the oil which then drains back to the sump.
The wire mesh over time becomes contaminated and blocked so it is a good idea to clean remove the wire and fit a couple of stainless scouring pads into the canister.

I will let islipminor reply to your question regarding air flow to and from and through the engine.

[IslipMinor]

Hi Keith,

Like this?

Later Draft Tube.jpg (130.13 KiB) Viewed 3091 times

Yes, there has been a common misconception that the air filter somehow sucks the fumes into the engine. On the 'draft tube' systems the fumes can get into the air filter housing, particularly with a worn engine and higher than normal crankcase pressure, but the normal process is to draw air from the air filter housing into the rocker cover and down through the crankcase.

If it were to draw the air up the vent tube, it would be unfiltered and full of muck and rubbish being scooped up from under the car!

This extract from the M1000 BMC Workshop Manual describes the later systems for the 1098, using a PCV valve and closed circuit system:

1098 PCV v4.jpg (216.62 KiB) Viewed 3091 times

The the same principles apply to the early systems as well - draw in filtered air from the air filter housing, pass it through the crankcase to collect the fumes and expel them out to atmosphere via the 'draft tube'.

The later PCV systems, and those that connect directly to the carburettor venturi, draw filtered air in via the filtered oil filler cap and expel the fumes via a mesh filled canister that acts as an oil separator and flame trap, into the intake manifold, to be consumed by the combustion process. The canister is mounted on the side tappet cover on the 1098 engines and on the timing chain cover on some other A-Series engines (mainly 1275).

On the open draft tube ventilation systems, the oil filler cap must be the non-vented/unfiltered type (it plays no part in the ventilation system on these engines), and the vented/filtered type on the closed circuit systems and it is the primary entry for the air being drawn into the crankcase. Because the PCV valve and the carburettor venturi both create a small level of vacuum, there will be some air drawn in through the rear crankcase scroll, which helps to keep the oil the right side of the scroll, i.e. in the engine, and also creates a small pressure difference across the timing cover seal, which also helps to keep the oil the right side of the seal.

[KeithL]

Richard,

That is brilliant - thank you. It all makes sense for the first time.

The only thing I need to double check now is that I have the correct oil filler cap. How can you tell a non-vented/unfiltered type from the vented/filtered type?

Keith

[IslipMinor]

Hi Keith,

Courtesy of ESM, a couple of nice pictures showing the two types of oil filler cap:

Oil Filler Caps Variants.jpg (74.68 KiB) Viewed 3075 times

[IslipMinor]

Moderators???

Why has the ability to edit a posting been stopped a few minutes after posting? We used to be able to edit at any time, which was very useful to correct errors in an earlier posting - not everyone reads all the way through multiple pages only to find that the earlier suggestion was actually wrong! Much better to be able to correct at any time.

Please restore the original edit functionality.

[simmitc]

Mods don't control that, it's either something that Mike has done and he'll be along shortly to pick up on it, or Corelous have cocked up again. Sorry for any inconvenience.

[KeithL]

Oh dear, it looks very much like I have a vented oil filler cap which, from what you have said, is the wrong one for my setup.

What are the implications of having the wrong cap? What would the symptoms of this be and, more importantly, will I have caused any permanent damage to anything? It has run like this for 10,000 miles+.

[philthehill]

I would suggest that you will not experience any noticeable problems with the engine.
I have run Minors with the old metal rocker cover oil filler cap, the sealed plastic cap, the breathable plastic cap and aftermarket caps fitted to aftermarket rocker covers and never experienced any noticeable problems but then my engines have always been kept in tip top condition.
Whilst the engine breathing system may not be utilised at its best when having the wrong oil filler cap no permanent or impermanent damage to the engine will be caused by having the wrong oil filer cap as shown by the running of 10,000 miles by your engine.