Hose from rocker box to air intake experts required!

[pcatterall]

I say experts because I fell it may benefit all of us with no knowledge or whose knowledge is sketchy to understand this fitting and some issues around it.
As some of you will know some of us are trying to reduce engine noise by fitting air inlet silencers ( which have been found to give significant noise reduction)
One issue concerns the connection of the chosen silencer box to the little hose that goes to the rocker.
My ( sketchy) understanding is that oil/vapour can leak from worn valves into the rocker box and the oil needs to be drained and any pressure released.
The little hose does this job by draining/forcing ( there may be an element of venture suction as well) the oil into the silencer box.
With diesels it is important, however, that significant oil is not allowed to enter the engine or the engine may start to burn this oil and be difficult to stop.
As stated my knowledge is very limited and a concise explanation would be very useful to me and ( I think many others).

In my case I want to mount my box some way from the engine intake and would have to fit a very long hose from the rocker box to the silencer box.
I understand that I could optionally fit a container near the rocker box and just allow any oil to drain into that?

I have also looked at these 'universal filter' kits which are essentially just a filter and hose ( sold mainly in pretty colours to car modifiers!) I thought these would be easy fit and may reduce the noise but see that the rocker box hose goes into the main air intake pipe AFTER the filter raising the prospect of oil being drawn into the engine.

So can some kind and knowledgeable person explain this little system to me and others who will find it interesting and useful?

Many thanks

 

[Lon nan Gruagach]

The pipe from the rocker cover is a pressure breather pipe, it is to relieve pressure that builds up in the crank case due to exhaust gas that gets past the piston rings, if it wasnt there then your dip stick will pop out or the rocker cover seal will burst.

Due to the action of cams and tappets the air in the rocker cover is laden with oil droplets. So, where ever that air goes will get dirty. While you are right that in some situations (faults only) it is possible that an engine might run off its own oil leakage. If there is sufficient oil coming from the rocker cover pressure relief hose you have a serious problem, this will not happen in normal running. So it is a perfect solution to dealing with this dirty air to send it straight into the engine air inlet (after the filter since the air will have no grit in it).
So, the pressure relief hose can be connected near the engine, it does not need to go to the filter or silencer box.

One issue you might have is that the air hose from your silencer to the engine, "some way" as you say, will radiate noise. You would be best siting the silencer as close to the engine as possible.

 

[RichardS]

I agree with Dougal but would add that even if there were no piston blow-by the crankcase airspace is being cyclically compressed and de-compressed by the piston action and the breather pipe is probably designed to even out these normal pressure changes.

Sometimes the breather pipe is connected before an air filter and sometimes after but it is often the case that there is a "condensation" path built into the rocker cover to condense out the oil droplets which drip back into the rocker box and to assist in only air going down the pipe, although it is still laden with vapour of course. However, it's unlikely to be sufficient to cause oil-burning overrun which I believe is more usually caused by oil by-passing the rings or the valve stem seals.

I have seen older vehicles with a catch-tank for the breather pipe rather than recycling the vapour through the intake but these days it is always recycled. A sign of the times I guess!

Richard

 

[NickRobinson]

I agree with Dougal but would add that even if there were no piston blow-by the crankcase airspace is being cyclically compressed and de-compressed by the piston action and the breather pipe is probably designed to even out these normal pressure changes.

Sometimes the breather pipe is connected before an air filter and sometimes after but it is often the case that there is a "condensation" path built into the rocker cover to condense out the oil droplets which drip back into the rocker box and to assist in only air going down the pipe, although it is still laden with vapour of course. However, it's unlikely to be sufficient to cause oil-burning overrun which I believe is more usually caused by oil by-passing the rings or the valve stem seals.

I have seen older vehicles with a catch-tank for the breather pipe rather than recycling the vapour through the intake but these days it is always recycled. A sign of the times I guess!

Richard

There will be air displaced/cycled in a single cylinder crankcase, less so in multiples.
The OP should be aware that the aftermarket filters are often sold as colourful free flow devices advertised to help breathing.
They can be seriously noisy.
A poster here some time ago utilised a breaker's yard air box on a 4108(?), transforming the noise for not a lot.

 

[pcatterall]

Many thanks, an excellent explanation ( and you all agree!! more or less!)
Thanks NickR yes I guessed that the aftermarket filters are often used to replace the original fitted air box and filter and could well be noisier than the original but on my 4108 there is no filter at all so I had hoped for some sort of noise reduction.

The breakers yard box referred to is the one I purchased but its 35cm diameter and 25 deep so finding a mounting location near my engine is a problem but I will take the unit out with me and make a temporary fitting to see if the noise drop warrants me finding a place for it.

Thanks again guys

 

[Heckler]

Many thanks, an excellent explanation ( and you all agree!! more or less!)
Thanks NickR yes I guessed that the aftermarket filters are often used to replace the original fitted air box and filter and could well be noisier than the original but on my 4108 there is no filter at all so I had hoped for some sort of noise reduction.

The breakers yard box referred to is the one I purchased but its 35cm diameter and 25 deep so finding a mounting location near my engine is a problem but I will take the unit out with me and make a temporary fitting to see if the noise drop warrants me finding a place for it.

Thanks again guys

Which way are you going now Peter!
Stu

 

[oldharry]

Crankcase breathers are needed so as to allow the crankcase to remain at atmospheric pressure. Air expands as it heats up, and even ona new engine there is some leakage of pressure past the rings. In an older engine this icnreases significantly. Many engines incoprorate an oil separotor in the breather particualrly if the breather is mounted low down on the crankcase. There is little oil spray in the rocker box apart from run off from valve lubrication, so many engines have the breather take off there. Normally the amount of oil lost via the breather is miniscule.

It is a very good crude test of engine condition to block off the breather for 10 seconds while the warm engine ticks over. If there is a whoosh when you release it, the bores are well worn. I had a Perkins Perama which was blowing so badly through it s breather that if you ran it hard it would dump enough oil in the air intake for the engine to run away on it for about 20 seconds. Spectacular, but scared the pants off me the first time it happened. OK the second and third time as well! After that we rebuilt the engine which was in dire need of a rebore! the point is that if anything more than a trace of oil is coming up the breather then you havea bad problem with the engine.

The breather pipe should not be a serious noise source: noise from the engine air intake is almost all induction noise and the air filter should be designed to reduce it. The chaceristic puttering of a Seagull outboard was very largely induction, not exhaust noise! Most modern outboards are fitted with induction silencers. Take it off you will notice a big difference particularly if the engine is working hard!

 

[pcatterall]

Which way are you going now Peter!
Stu[/QUOTe

Coral Wind ?..........Cagliari to Burriana ( near Valencia) via the Baleares
Air silencer?.........Who knows? will test the dustbin lid and report back
Myself ?................generally down hill but gracefully!

 

[Colvic Watson]

I'm fitting one of the Ford Ranger filter boxes on the new engine installation. All the K&N type filters are designed to boost performance but also I suspect deliberately to increase noise! The Ranger box would need adapting but fortunately my JCB doesn't breathe through the air intake so no modifications needed. Reports suggest a noise drop of about 8db which is very significant.

 

[pcatterall]

I'm fitting one of the Ford Ranger filter boxes on the new engine installation. All the K&N type filters are designed to boost performance but also I suspect deliberately to increase noise! The Ranger box would need adapting but fortunately my JCB doesn't breathe through the air intake so no modifications needed. Reports suggest a noise drop of about 8db which is very significant.

8db would be wonderful!! I guess ( after reading the advice) that I can mount the box a bit away from the engine and run the crankcase breather into the pipe near where it joins the air intake.

 

[Colvic Watson]

yes and I'm adding sound insulation to the air pipe from the intake to the filter box, not a long run in my case but pointless not to do so otherwise it will just act as a rubber loud speaker!

 

[anoccasionalyachtsman]

Since the thread on air filter boxes is buried, I'll throw this in here.

I read that the designers of the Jag V12 engine, Sayer and Hassan, reduced intake noise playing with intake speed, and mention was made of supersonic. I've just done a quick calculation using 40mm as the diameter of each of two inlets to the air filter boxes (one each bank) on a 5.3 litre engine and that gives 10,000rpm as the point where they'd go supersonic.

My guess would be that they didn't want it to enter the supersonic region because the inlets would have to be special and variable shapes, but they wanted the engine to effectively 'swallow' as much of the induction noise as possible. This is the shape that they chose.



So it might be worth reducing the intake diameter to achieve the same, but at a more sensible rpm, say 6,000 or just at your 'redline'?

 

[pcatterall]

Since the thread on air filter boxes is buried, I'll throw this in here.

I read that the designers of the Jag V12 engine, Sayer and Hassan, reduced intake noise playing with intake speed, and mention was made of supersonic. I've just done a quick calculation using 40mm as the diameter of each of two inlets to the air filter boxes (one each bank) on a 5.3 litre engine and that gives 10,000rpm as the point where they'd go supersonic.

My guess would be that they didn't want it to enter the supersonic region because the inlets would have to be special and variable shapes, but they wanted the engine to effectively 'swallow' as much of the induction noise as possible. This is the shape that they chose.

View attachment 57357

So it might be worth reducing the intake diameter to achieve the same, but at a more sensible rpm, say 6,000 or just at your 'redline'?

Interesting! that looks like a very small intake on the engine for such a powerful beast!
So a long box with a normal intake on the box going down to a very small engine intake.
My 'red line' is more like 3000 though!
In my trials with ebberspachers it seems that the intake noise is generated around the mouth of the intake when I put on a short pipe it moves to the mouth of the pipe, when I put on the short 'silencer' it is mainly at the mouth but reduced. I'm inspired to do some more tests using my sound app.

 

[anoccasionalyachtsman]

It's the only thing that is small on the engine, it's flipping massive! Big gulp when it was unloaded from the lorry it came on!

I see that I wrote supersonic in the third para, where I should have said transonic, oops. And I wrote 6,000 because I can't remember what the redline is for small yacht engines - and although about 3,000 is the most I've ever used I didn't want everyone to rush out and fit tiny tubes and have their filter boxes implode just as they need max power avoiding a supertanker.

Have you tried a flared opening on the Eber? There are good reasons for the bell mouth on all these things, turbulence is noisy.