Engine Crank Case Breather

Side valve, 803, 948, 1098., 1275 and Vizard mods

Engine Crank Case Breather

Postby DavidF2 » Thu Aug 15, 2013 5:33 pm

Hi, Apologies if this has already been covered, but I have searched and not found the answer.

I have a 1971 Traveller with a canister on the side of the engine (sort of catch tank). Hole in the top that has a pipe that goes to the air filter. All makes sense as far as crank case breathing goes. But at idle and indeed any engine speed, I can put my hand over the top outlet of the can and feel absolutely nothing. I also have a fairly good (bad) leak from what I will assume is the crank rear seal as it drops oil on the floor near the engine/gearbox join. If I remover the filler cap on the rocker box I can feel and hear it breathing very well.

The little catch tank appears not to come apart, no screws, bolts, nuts, etc. When I look down the hole in the top I can see what appears to be steel wool, so I guess this acts as a minor baffle for the breather. However I imagine it needs cleaning. Is it really true that this can only be cleaned after removal from the engine and is it really attached to the large plate I can see on the side of the engine.

Seems odd considering the rest of the car appears to be designed for easy servicing.

Assuming all this is correct is there a filler cap available that fits with a one way flap valve. This would create a permanent negative crank pressure and pretty much eliminate all leaks.  If one does not exist I guess I'll make one.

Any ideas, especially if I've missed something obvious about cleaning the original greatly appreciated.

Thanks,
David
Morris Minor Traveller, 1971, Original, not restored, no modifications, not even a radio. My first MM. Wanted a useful estate classic that could be used everyday. http://www.f2motorcycles.ltd.uk/motorcycles.html
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Postby MM » Thu Aug 15, 2013 10:53 pm

I guess removal and flushing out with petrol or paraffin is the only way to properly clean it.

You are supposed to replace the plastic oil filler cap on the rocker cover every 3 years or so, though I fitted an alloy rocker cover and it has a stainless steel cap.
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Postby DavidF2 » Fri Aug 16, 2013 7:44 am

Thanks, the cap is the unvented type, so don't think I need to replace it as there is nothing to go wrong with it. I spent an hour online last night ordering various fittings and my intention is to make a negative pressure breather in a way that would allow the engine to be converted back to standard quickly and cheaply.
For the drive to work today I took the seal off the filler cap so I have neither neg or pos pressure and the leak when I park has reduced from a 4 inch spread on the concrete to a single drip. I'm fairly hopeful the new breather design will solve the leaking issue completely.
Even cleaning the original will not give negative pressure unless there is a reed valve in there that I don't know about.
I'll post details when it's done and I've proved it works.
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Postby minormadman » Fri Aug 16, 2013 8:05 am

Now there's some positive thinking OR is that Negative  :shock:  :?:  :lol:
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Postby woodywoodchipper » Fri Aug 16, 2013 1:28 pm

the problem with the canister, is it becomes clogged with sludge and no amount of cleaning will cure it,

you can cut it open remove the guaze and reweld it back together,

better if you can find 1 is the early plate which just has a pipe facing down ward with no obstruction, they are interchangeable but make sure you get the bolt as its shorter,

would be intrested in your design for the cap, sounds good,

A,
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Postby Custard » Fri Aug 16, 2013 3:28 pm

Wish I could of just got the old style plate on mine, but the 1275 does not have tappet chest covers.

I know you must never have positive pressure.

Old style is zero pressure though, but piped to carb/air filter should be negative pressure, how much difference does having negative pressure really make?

I was thinking of just piping mine to a catch tank as I could not see the point of putting warm air through the carb.

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Postby minormadman » Fri Aug 16, 2013 3:35 pm

And yet on BAS, that's just what happens,straight from the tappet chest cover via the 90 degree angle pipe and rubber tube straight into the base of the carb to get recycled. :(
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Postby DavidF2 » Fri Aug 16, 2013 4:18 pm

Old style is zero pressure though, but piped to carb/air filter should be negative pressure, how much difference does having negative pressure really make?


I'll let you know when I've done it.
My background (and future) is motorcycles and certainly with single cylinder and opposed twins it makes a huge difference. In both of these designs the change in crank volume is large. A big 500cc single needs to make enough room in the case to accommodate the piston as it comes down the bore, and a twin with both pistons moving up or down at the same time needs twice as much. With an inline 4 as our MM engines are, there is no doubt that at least one piston will be reducing the volume of the case while any one of the others is increasing it so you may assume it does not matter. However taking the oil filler cap off when the standard breather is blocked as it is in my case would suggest that at low speeds at least there would be some advantage to a negative pressure system.  

It seems worth a try to see what happens. It certainly will not make it leak more. I understand the standard MM has a scroll seal on the rear of the crank which says to me you need negative pressure if it's not going to leak.
Morris Minor Traveller, 1971, Original, not restored, no modifications, not even a radio. My first MM. Wanted a useful estate classic that could be used everyday. http://www.f2motorcycles.ltd.uk/motorcycles.html
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Postby DavidF2 » Sat Aug 17, 2013 5:38 pm

Theory is one thing.

So today I removed the canister style breather from the side of the engine and discovered it was as blocked as I suspected. Poured boiling water and degreaser in one side and waited for a few minutes but nothing at all came out.  As you all know these can not be taken apart for cleaning so rammed a screw driver in from the top until all the blocked internal mesh was smashed to small pieces, Washed, flushed, used magnets etc until I was certain the canister was completely empty. refitted it to the engine and now I get a nice healthy blow from it and the engine is breathing well.

Next stage, was to attach a very low pressure one way reed valve to create a negative pressure breather. These valves are from the motorcycle industry and require very little pressure to open. However the pressure in a MM is not enough to open them. So back to the drawing board. I have to say now I know how little positive pressure there is I do wonder if the effort will indeed be worth it.

I still stand by the theory that it would reduce oil leaks, but if I can't find a valve that will open at a low enough pressure I can't try it.

So going back to Sean's question of "how much difference will negative pressure really make" I would say probably marginal.

I'll revisit this if I find a valve that may work.
Morris Minor Traveller, 1971, Original, not restored, no modifications, not even a radio. My first MM. Wanted a useful estate classic that could be used everyday. http://www.f2motorcycles.ltd.uk/motorcycles.html
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Postby MM » Sat Aug 17, 2013 6:38 pm

Strange, that - it must have been very caked in gunge for nothing to come out, though I would have left it soaking in petrol overnight before resorting to gouging out the innards!
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Postby bmcecosse » Sat Aug 17, 2013 10:32 pm

You could refill the can with copper pan scourers - from Poundland... The Mini lads clear the can by setting it on fire - off the engine....      And YES - you MUST have negative pressure in the crankcase.   No need for a reed valve - just connect the can to the tube going in to the side of the carb  - along with the tube from the rocker cover - via a T piece obviously....   This ensures some suction and will handle normal blow-bye in the crankcase.  Some Minors had a PCV (Pressure Control Valve) fitted to the inlet manifold -and to the breathers, and this worked well except they also fitted a vented filler cap - and this tends to vent oily fumes leading to smells and mess - when the PCV can't cope with all the fumes.......perhaps at high revs/working hard.
 









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Postby DavidF2 » Mon Aug 19, 2013 7:50 am

I have noted the original connection to the air box where there should be a constant slightly low pressure, however on my car when you take the pipe of the spigot at the air box the hole in the middle is only a few mm diameter. Really can't see this being enough to cope with the breathing. My rocker box does not have a breather or a vented cap.
All the breathing is done through the now empty canister. I'm sure there is room for improvement and I will keep thinking on this one for a while.
Morris Minor Traveller, 1971, Original, not restored, no modifications, not even a radio. My first MM. Wanted a useful estate classic that could be used everyday. http://www.f2motorcycles.ltd.uk/motorcycles.html
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