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Air breather rocker cover pipe, why?


Blitz
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Right my spit4 shouldn't have a breather outlet from the rocker cover only a breather on the oil filler cap. However I have a newer cover so it does although it's capped off. 

Two questions really. First will opening this up and adding some piping help me in any way ?  Secondly why are these breather pipes usually attached to the carbs and do all the SU carbs allow for this or only later ones. 

Thanks 

Grant 

 

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My SU2 carbs don't have the fittings for the breather pipes. The Su hs4s do (I think). The pipe from the rocker box just dangles behind the main bulkhead, just below the engine so that the fumes don't go inside the car. No doubt Uncle Pete will have something to say about my dangly bit!! Before I fitted the pipe, the back of the carbs were covered in a coating of oil spray and other yuk,

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The "middle aged" cars had a pcv valve fitted into the inlet manifold. And the late cars to the carbs (as posted)

Applying the inlet vacuum helps keep the crankcase pressure low and reduces oil leaks. At high rpm it is amazing how much blowby pressurises the engine. I have seen a tr6 racing engine fitted with a 32mm hose from the rocker cover to a catch tank.

For an engine that is in decent condition and not revved over 6000rpm any of the normal solutions work. Be careful if the hose just goes to the road that it doesn't drop ANY oil, really that just causes danger to other road users, when a simple catch tank would solve the problem. ie a coke bottle etc will do, cable tied in place. 

The other solution is to run the breather hose to the air filter. I am looking into this for my car if I can find a place to attach the hose (proving difficult, but then again mine is not typical)

Whatever you do, do not think poking the hose into the chassis is a good idea. Saw that, chap though oil mist into the chassis rails was a good idea. What he forgot was that most of the stuff that comes out is water.....

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i guess this is a alloy cove r? with a outlet stub about central ready for the later breather ??

what would concern me is you now wont have the gauze filled and vented oil filler cap, the early cars all used

breathing is air transfers from in through the tube mounted in the o/s crankcase and out via the filler cap or the other way round it can flow both ways but the tube has no gauze  so this is generally the exit  

this is an open breather system , you need to open the plugged spout and  fit a filter to the cover outlet  or a  short  hose into a catch  tank 

leaving it plugged will restrict the breathing  so air moved freely between the two vents , 

ideas see    https://www.carbuildersolutions.com/uk/filterSearch?adv=true&cid=0&q=%23bfil15&sid=true&isc=true

there are 10/12/15/25 mm inlet dia.

pete

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51 minutes ago, dougbgt6 said:

The purpose of the gauze is as a fire trap (Pete didn't want to tell you that for fear of causing anxiety and panic :o) A lot of alloy jobbies don't have it and expect an external trap.

So should the arrangement i have have a gauze fire trap in the spout off the rocker? Cos it don't ?

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you want something like this ,  commonly  used on many 70/80 cars,  good at filling with mayo as they get cooled in the air flow

http://www.paddockspares.com/603330-engine-flame-trap-v8.html?gclid=Cj0KCQjwpcLZBRCnARIsAMPBgF3l4v8GDkKloYlJO1dLNSqe3PVwBQJQzIo2xaXKwe1DnqKZi6S80jYaArstEALw_wcB

no idea what the hose diameter is on this idea

 

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"Flame trap"?    Where from and to?  The nearest flame is in the combustion chamber.   In the way are piston rings and a very narrow clearance piston to bores, and a long path to the inflammable fuel-air mixture, but I really don't see how the flame can get past the pistons, unless one is holed. Anyway, oil mist saturates the crankcase gas beyond inflammability.

IMHO, the gauze is there as a droplet catcher and condenser.      Oil filtered out drips back into the rocker cover and thence to the sump. Remaining oil, and yes, water vapour, escapes through it.

If you can't, or don't want, to direct to the inlet, then a catch tank, but let's use a bit more tech than just a bottle on the bulkhead (and not some old plastic pop bottle either,please!).   

The catch tank is away from the engine, cooler so will allow more oil and water to condense, but gases remain and need a vent.    Small air filters, cylinders the size of an apple, do a similar job to the gauze, so that its mostly gas and some water that escape - less polluting!   

Now you have two choices.   Empty out the catch tank regularly - those with a sight tube on the side are useful - or have drain tube in the bottom that goes back to the sump.  Water will be returned too, but no harm there, as long as you change the oil regularly.    This needs the catch tank to be higher than the block, but gives you an excuse for a smart alloy tank on the bulkhead.   Shiney-shiney!

John

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Thanks for the replies. Yes I'd hered about the Mrk 1 gause filter. So mine has the crank case air inlet pipe I guess but no decent air out as it's a later rocker cover with just the little hole in the filler cap.. I will investigate opening the breather pipe and looking at an oil trap of some sorts on the end. 

Many thanks chaps

Grant 

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The original engine design had two breather. i.e. A crank case and a top breather (Oil filler cap). Two vents were required because one alone would not vent off the pressure built up throughout the engine. Due the revolving parts and temperature differences within the engine it is not possible to vent off all the pressures with one breather. Hence the designers used two. 

With the induction of emission regs venting oil fumes directly out into the surrounding air was considered a bad thing to do. So the close circuit systems were introduced where the oil fumes are introduced into the inlet gasses and then burn in the engine. The system operates at a small vacuum to ensure no pressure builds up in any part of the engine. This system only works with one breather because it maintains a small vacuum.

The problem with only using only one breather that vents out into the air is there is no vacuum hence pressures can still build up within the engine. In the case of only using the top breather then crank case pressures can build up and cause leaks from oil seals. You can end up with what is known as a sweaty engine as oil film appears all over the engine.

I have seen some of the track cars using an electric fuel pump and a breather pipe fitted, pointing upwards to stop the oil leaking out, to the hole vacated by the mechanical fuel pump. You have to be careful to ensure the engine oil does not leak from the breather, hence the V design of the original crank case breathers.  

Dave  

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Quick update. 

Fitted an oil catch air breather yesterday. Run the pipe round and sat the canister in a nice place next to the starter motor so I didn't have to drill for brackets etc. Not driven her yet so fingers crossed the location is ok. 

Grant 

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  • 4 weeks later...
On 6/25/2018 at 12:53 PM, dougbgt6 said:

Odd then that most call them flame or fire traps.  And what is that strange arrangement on the late GT6 MK3 rocker cover? An assembly of interleaved plates that can't do much as a droplet catcher? 

Doug

I have not seen that particular system. But interleave plate coolers etc work by virtue of the rapid change of direction of vapour flow and heat transfer and deposit droplets due to the motion and temperature changes. All sorts of Physics are involved, 98% of which I have forgotten it being that long since I did them. (Boyle and Charles laws etc?, along with others).

Pete

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