Crankcase Breather Pipe Set-up
Posted By : Tom Longley, 12-Jun-2007, 07:48pm
Hi, it sounds wrong. The round contraption is a Smith's valve and was fitted to the MkII Vitesse in an attempt to reduce emissions. I believe that the
SU carburretted 2000/2500s didn't use it; instead there is a pipe from the rocker cover that goes directly into the carburettor (thus using the vacuum
of the carb to draw the crankcase fumes through the combustion chambers where they are then burnt). You describe yours as "the breather pipe straight
into the K&Ns"; if you mean that the pipe is somehow connected to the K&N, I am not sure that this will have quite the same effect, as the
vacuum at the K&N wont be so great. Have a look at the most recent Courier where Dave Rummens has done an article on the this very subject, with
pictures, which might help explain the situation.
Does your inlet manifold have the take-off for the Smith's valve? (I have seen these used for a brake servo, which then means that the Smith's valve is either removed or re-plumbed.) If you do have the take-off inlet manifold then it might be simplest to find a Smith's valve and fit that, obviously ensuring that you block up the hole in your K&N.
Regards,
Tom
Does your inlet manifold have the take-off for the Smith's valve? (I have seen these used for a brake servo, which then means that the Smith's valve is either removed or re-plumbed.) If you do have the take-off inlet manifold then it might be simplest to find a Smith's valve and fit that, obviously ensuring that you block up the hole in your K&N.
Regards,
Tom
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Crankcase Breather Pipe Set-up
Posted By : John Davies, 12-Jun-2007, 08:27pm
What's "Wrong" about it?
Pressure builds up in the crankcase due to blow by past the piston rings, so the case needs a vent.
The crankcase gases also hold a lot of oil in droplet form and fumes.
Early Spitfires and Heralds, as usual at the time, just put a tube on the vent and led it out below the engine.
Early pollution concerns, and the drips of condensed oil from the tube, meant the tube was led to the intake manifold, where the crankcase fumes were drawn into the air flow and burnt in the engine.
While intake manifold pressure is usually lower than crankcase, sometimes it's not, so the Smiths device is just a one way valve to prevent petrol vapour being drawn into the crankcase (Doesn't bear thinking about!)
The gases flowing into the intake manifold are an unknown factor that racers don't like, so they usually lead the crankcase vent to a 'catch tank', where condensed liquids can collect and be drained off cleanly as required. The catch tank should itself be vented, and some will add a mini-K&N or other proprietary filter on the tank vent. This is a perfectly legal and sensible way to manage cranckcase vapours. The MSA Race regs state that for over two litres of engine capacity, the catch tank must be at least three litres in capacity.
Enjoy your Vitesse!
Not how wrong or right it is!
John-
Crankcase Breather Pipe Set-up
Posted By : Stuart Newby, 13-Jun-2007, 08:54am
thanks guys , and have read Dave Rummens' article - I am concerned that he states that the oil seals may go if i continue to not have the smiths valve. I've a servo fitted, so what do you suggest i do as i don't want an expensive job to replace oil seals.....
it's been this way for at least 5 years.
stu-
Crankcase Breather Pipe Set-up
Posted By : Chris Taylor, 13-Jun-2007, 02:38pm
The seals can only leak if the crankcase pressure rises. If you connect the breather pipe to the carbs, or leave it open to the atmosphere via a filter or catch tank, then pressure cannot build up. Connecting the breather direct to the inlet manifold may result in too high a vacuum in the crankcase without the valve, and just blocking it off will result in too high a pressure as the pressure cannot be relieved.-
Crankcase Breather Pipe Set-up
Posted By : Stuart Newby, 13-Jun-2007, 07:37pm
cheers chris....so the article in this month's courier isn't strictly true then???-
Crankcase Breather Pipe Set-up
Posted By : Chris Taylor, 13-Jun-2007, 09:28pm
Yes it is, if you simply block off the valve (pressure is too high in the crankcase) or just possibly if you connect straight to the inlet manifold, where too high a vacuum just might affect the seals.
In general though I would suggest leaving stuff just as Triumph designed it, unless there is a really good reason for changing it.-
Crankcase Breather Pipe Set-up
Posted By : Stuart Newby, 14-Jun-2007, 12:08pm
ok so just leaving it with a mini K&N on the end of the breather outlet is ok then?
The servo has nicked the inlet port.
cheers-
Crankcase Breather Pipe Set-up
Posted By : John Davies, 14-Jun-2007, 12:46pm
Stuart,
Depending on the extent of blow-by, a filter just stuck on the vent will block up quickly or slowly.
The catch tank is to catch condensed oil and water vapour, so that only gas fumes are left to exit via the filter.
The filter life is much longer as a result.
But it's your car, your money!
John-
Crankcase Breather Pipe Set-up
Posted By : David Rumens, 14-Jun-2007, 04:56pm
John, using just the catch tank this will not prevent a build up of pressure in the crank case. The best way is to use an electric fuel pump and fit a breather pipe to the hole vacated by the standard fuel pump and then use the catch tank fed from the rocker cover. This will give you an air flow through the engine, as per the 1600 Vitesse.
As for the servo - The option kit for fitting a servo to the 2 Litre Vitesse had a "T" pipe fitted between the Smiths and the inlet manifold to allow an additional vacumn pipe to be fit from the servo unit. Not ideal but approved by Triumph.-
Crankcase Breather Pipe Set-up
Posted By : John Davies, 14-Jun-2007, 06:55pm
Dave,
"using just the catch tank this will not prevent a build up of pressure in the crank case"
How so?
What's to stop gas escaping?
Poiseiulle's Law says that gas flow along a pipe is proportional to the pressure difference across a pipe, to its length and inversely to the fourth power of its radius.
Okay, there will be a constant pressure difference between the crankcase and atmospheric, determined by the above and by the resistance of the final filter - which could block.
But also the hose might kink, the catch tank could fill up, the horse might fly.
Without these unlikely events, why and how could there be a "pressure buildup"?
"The physics cannae stand it, capn!"
John
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Crankcase Breather Pipe Set-up
Posted By : David Rumens, 15-Jun-2007, 07:19pm
John,
The release of the crankcase pressure is limited by the internals of the engine. For the gases to get to the rocker box they have to build up a pressure level that could damage the seals. That why the 1600 Vitesse had a crankcase breather as well as the rocker box breather. The use of a close circuit system placed a slightly negative pressure with the engine and prevents the gases forcing oil passed the seals. Yes its all about theory, but you have to apply the theory.-
Crankcase Breather Pipe Set-up
Posted By : David Rumens, 15-Jun-2007, 07:58pm
John, Just to add that as the oil seals are not pressure seals it only needs a small pressure in the crankcase to force oil passed the them. That's the problem.
It good to see your Vitesse on the track, I wonder if you are using the standard diff and rotoflex set-up.
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Crankcase Breather Pipe Set-up
Posted By : John Davies, 15-Jun-2007, 08:47pm
David,
Thanks for the compliments!
The Silverback has swingspring, lifted up by a 1" spacer, with a Quaife ATB LSD, and extra spring-controlling radius arms.
Part of the re-design inc. an ARB, but it was useless - as it was doing almost the same job as a swing spring!
See you at Silverstone?
But,
"For the gases to get to the rocker box they have to build up a pressure level that could damage the seals"
You must have different cyclinder heads to me.
There are twelve bl**dy great holes between the two on my car.
There's only a push rod going up through each hole, and some oil trickling down, little to impede gas flow.
There should be a dynamic equilibrium between the two spaces.
And of which seals do you speak?
The rocker cover seal, IMHO, usually leaks because the cover is made of thin sheet, and the seal seat distorts with age.
I place mine, sealless, on a flat surface, and twist and gently hammer it until I can see no light passing under it.
Then glue the seal itself to the cover.
That usually gets a reasonable seal, but I still need to wipe the cover down every day.
And granted, I have two vent hoses, one block, one rocker cover, that go to the catch tank.
But that's because a hose WILL offer some resistance to flow.
Two hoses are better than one!
John-
Crankcase Breather Pipe Set-up
Posted By : David Rumens, 16-Jun-2007, 08:11am
John, Its the crank oil seals that given the problem. They are oil seals, not pressure seals and will only handle a very very low pressure. That's why the older non closed circuit engines have the breather system they do. This is basic stuff taught to engineers back in the 1960's and before. I am surprised it is has raised so many questions, but I guess so much knowledge has been lost of the years. I am not getting at you as I know you know your stuff.
Thanks for the info on Silverback.
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Crankcase Breather Pipe Set-up
Posted By : Chris Taylor, 14-Jun-2007, 07:03pm
Since the rocker case and crankcase have several connections between them, how can pressure build up inside if either of them is open to the atmosphere?
I am aware of the two openings to atmosphere in early Heralds and 1600 Vitesse, but have never been able to understand how this actually promotes a through flow of air through the engine.-
Crankcase Breather Pipe Set-up
Posted By : David Rumens, 15-Jun-2007, 07:10pm
Chris, It all comes down to pressure equalization within the engine. At different times there will be a pressure difference between the crankcase and the rocker cover. This will produce air movement within the engine. I always believed most of the air went in the rocker cover breather and out through the crankcase breather. That is until the engine became worn and the crankcase pressure built up to a high level, then it came out of both breathers. A heavy oil mist on the rocker cover and lots of oil pong was the normal sign of wear.
Keep up the good work mate.
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Crankcase Breather Pipe Set-up
Posted By : Chris Taylor, 14-Jun-2007, 01:48pm
It's not ideal, but I can't see how it can damage the seals as it will prevent a build-up of pressure in the crankcase. It will however do little to ensure any fumes from the crankcase are directed into the engine and burnt. Two consequences are likely/possible. One is a smell of oil fumes in the engine bay that you may get to smell inside the car if it gets near the heater inlet or through any gaps in the sealing of the transmission tunnel. Second is a gunging up of the filter with oil, and possible dribbles of oil from the filter onto the manifolds. This may be a nuisance, or it may cause smoke if it drips onto the hot exhaust manifold. The filter can be washed (in petrol) and re-oiled (with special very thin K&N oil), but this arrangement would be better with a catch tank, or piping to the UPSTREAM side of the carbs (into carb body or air filter) as per Spitfires.
The absence of the (modest) vacuum provided by the Smiths valve MAY exacerbate some leaks from the crankcase, but that would only be because the previous vacuum had been "sucking" any leakage back into the engine, the weakness in seal or gasket having been there all along. It is unlikely to make the underlying fault any worse, and will not on its own "blow" a seal.-
Crankcase Breather Pipe Set-up
Posted By : Nigel Barton, 18-Jun-2007, 01:06pm
Like so much else in the classic world, the thinking and understanding behind crankcase breathing has changed / improved over the years, and engine design is improved to match. It's worth thinking about what we are actually trying to achieve by the crankcase breather system. On older cars the emphasis was very much on avoiding excessive crankcase pressure, and hence leakage, thus the arrangement of pipes open to atmosphere. In theory this improved marginally if the pipe was run under the car where the air flowing past it with the car in motion created a very slight suction effect. Obviously this was improved further by plumbing into the air filter where a slightly greater vacuum exists, and still more by plumbing into the intake via a suitable valve.
Over time though, it was realised that actually more than just a means of preventing excessive pressure was needed. A good flow of air through the crankcase is much better as it prevents condensation of nasty acidic deposits, reducing sludge build up etc. But to achieve this you have to not only have a way of sucking air out of the top, usually by connecting the rocker cover to inlet manifold via a suitable valve, but also a way to get fresh air INTO the crankcase- circulation cannot occur without this, although pressure build up will still be avoided. This is the reasoning, I believe, behind the earlier post in this thread suggesting air be allowed in via the fuel pump apperture etc. It's all much easier on a V- engine like my Rover engined Stag, where one rocker is piped to the air filter to allow it to suck air IN, whilst the other is connected via a valve to manifold vacuum which sucks it OUT. Thus air is contantly circulated in one side, through the crankcase and back out the other.
This theory is all very sound but in practice does not work well on some highly tuned engines, or others liable to excessive blowby, as the blowby gasses upset the mixture being burnt by the engine. This is why these applications go for a catch tank arrangement instead.
There, now that's off my chest!-
Crankcase Breather Pipe Set-up
Posted By : David Rumens, 18-Jun-2007, 06:20pm
Nigel, I agree with your comments and would go on to say in modern highly tuned engines the cranks seals are of a type that can handle the pressure build up in the crankcase. However, the type of seals used in the Vitesse engine are not. The seals have not moved on therefore we still have to apply the 1950/60's theories and limitations to these engines.
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Crankcase Breather Pipe Set-up
Posted By : Stuart Newby, 20-Jun-2007, 10:28am
Gents , I have read these comments with much interest and think I can just about understand the reasons. In my case then , which has the mini K&N on the end of the rocker cover outlet, and the servo plumbed into the inlet, it looks like I have 2 options,
1.) get a T-piece and an old smiths valve and plumb it in,
2.) get a catch tank which somehow gets plumbed in between the rocker outlet and the mini K&N ?
either way running it as is for the last 5 -6 years (after a new engine) has maybe made oil leak out of the crank seals but not in any way damaged them - correct?
cheers Stu-
Crankcase Breather Pipe Set-up
Posted By : Leon Guyot, 20-Jun-2007, 11:03am
Hi Stu,
I have found an oil catch/breather tank works well.
I have temporarily used a plastic tank with K&N, but will upgrade to an alloy tank as funds allow.
Regards
Léon
Crankcase Breather Pipe Set-up-
Crankcase Breather Pipe Set-up
Posted By : Leon Guyot, 20-Jun-2007, 11:07am
You cannot see that there is a petcock, (careful!), at the base of that tank...
But here is another photo, sorry for low quality, taken with phone-camera.
Regards
Léon
Crankcase Breather Pipe Set-up-
Crankcase Breather Pipe Set-up
Posted By : Stuart Newby, 24-Jul-2007, 10:20pm
Leon, many thanks for those pics, most appreciated.
cheers.
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