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Brake Servo advice please


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I'm considering fitting a remote brake servo and just wondering how to connect to the inlet manifold take off that's already being used by the crankcase breather system.  

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4 hours ago, Geko said:

You can use a "T" or "Y" brass connector like this. Available at any hardware shop  

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Thanks. Thought it might be something like that or a 'T' piece. I guess  there's enough vacuum to serve both. 

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11 hours ago, Malbaby said:

IMHO...you need a dedicated single vacuum source for the booster to operate efficiently.

Hmm, this is what I am concerned about. I have seen some electric vacuum devices which I guess could be operated by the brake light switch as long as there was not too much lag in starting up. Or, even an electrically operated valve to shut off the vacuum to the crankcase breather when braking?

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Or you could do yourself a favour and get rid of the awful pvc valve by venting the rocker cover either to atmosphere with a pipe down just past the chassis or to a catch tank. One less thing to go wrong and problem solved

Chris

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3 hours ago, ChrisR-4A said:

Or you could do yourself a favour and get rid of the awful pvc valve by venting the rocker cover either to atmosphere with a pipe down just past the chassis or to a catch tank. One less thing to go wrong and problem solved

Chris

Thanks, yes actually a Catch tank is on my bucket list - but I thought they use the same inlet manifold connection? 

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9 minutes ago, rogerowen said:

Thanks, yes actually a Catch tank is on my bucket list - but I thought they use the same inlet manifold connection? 

There's no need for a vacuum connection to a catch tank Roger.

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Just now, RobH said:

There's no need for a vacuum connection to a catch tank Roger.

OK, so blank off the vacuum port of the catch tank? And, no point in getting one with an air filter?

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5 hours ago, ChrisR-4A said:

Or you could do yourself a favour and get rid of the awful pvc valve by venting the rocker cover either to atmosphere with a pipe down just past the chassis or to a catch tank. One less thing to go wrong and problem solved

Chris

Thanks, yes actually a Catch tank is on my bucket list - but I thought they use the same inlet manifold connection? 

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The inlet manifold connection is for a sealed system where the crankcase fumes are sucked into the carbs for burning. Chris and Andy are describing an open system where the fumes just vent to atmosphere. You don't need a manifold connection for that,  just a pipe from the rocker cover outlet to take the fumes to where they can freely dissipate.   (with a drip collecting tank if you prefer, but that must be vented)

 

Edited by RobH
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Cheap catch tank.....1 litre plastic milk bottle attached somewhere under the bonnet by tie wraps. 

Length of pipe poked in the top from the engine breather outlet. 

You could even paint the bottle or cover it with sticky backed plastic for the 'factory finish' effect.

It is what the racers did for many years - Cheap and light.

Peter W

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4 hours ago, RobH said:

The inlet manifold connection is for a sealed system where the crankcase fumes are sucked into the carbs for burning. Chris and Andy are describing an open system where the fumes just vent to atmosphere. You don't need a manifold connection for that,  just a pipe from the rocker cover outlet to take the fumes to where they can freely dissipate.   (with a drip collecting tank if you prefer, but that must be vented)

 

OK, Thanks Rob - but please bear with me and my rather poor schoolboy level science a little longer.

I see the benefit of the vacuum effect from the inlet manifold connection - as in 'pulling' the fumes out of the engine so they don't condense internally within the engine. Without this pulling effect surely the removal of these fumes is going to be greatly lessened. I do remember the crankcase breather pipe on my 2 TR2's that ran down below the chassis and had an angled end to create a venturi effect to pull engine fumes out as the car travelled (this used to get horrendously clogged on both cars).

The standard PCV on my car, after cleaning and only a few miles of driving, shows oil residue in the very small space available to collect oil inside the PCV unit - obviously this will eventually get sucked into the cylinder head (as Upper Cylinder Lubricant???). 

So, I can definitely see the advantages of a metal catch tank - in that hopefully the fumes pulled in will condense on the walls of the tank, the condensed goo will then fall to the bottom of the tank, and relatively clean air will be sucked back into the inlet manifold. Or, am I dreaming!

To add to the conundrum are the catch tanks with air filters! Going for a wild guess here!....... Cooler air coming in from the catch tank air filter assists the condensation of the engine fumes??? But then - surely with extra air coming in to the inlet manifold - the carbs are going to need re-tuning, maybe more to the aft one as it's closer to the vacuum port.

And to cap it all, I still haven't found a way of connecting the brake servo..........I'm going to have a little lie down... :wacko:

 

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I believe the reason for sucking the fumes into the carb to be burned was to meet US emissions regulations Roger, not for efficiency of extraction.

The breather pipe on the early cars shouldn't get clogged unless the engine is well past its best (and perhaps only driven for short distances so it never gets really warm).

There was a thread on here a little while ago where someone had filters on a catch tank, which didn't work properly. Unfortunately I don't seem to be able to find it. 

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1 hour ago, rogerowen said:

OK, Thanks Rob - but please bear with me and my rather poor schoolboy level science a little longer.

I see the benefit of the vacuum effect from the inlet manifold connection - as in 'pulling' the fumes out of the engine so they don't condense internally within the engine. Without this pulling effect surely the removal of these fumes is going to be greatly lessened. I do remember the crankcase breather pipe on my 2 TR2's that ran down below the chassis and had an angled end to create a venturi effect to pull engine fumes out as the car travelled (this used to get horrendously clogged on both cars).

The standard PCV on my car, after cleaning and only a few miles of driving, shows oil residue in the very small space available to collect oil inside the PCV unit - obviously this will eventually get sucked into the cylinder head (as Upper Cylinder Lubricant???). 

So, I can definitely see the advantages of a metal catch tank - in that hopefully the fumes pulled in will condense on the walls of the tank, the condensed goo will then fall to the bottom of the tank, and relatively clean air will be sucked back into the inlet manifold. Or, am I dreaming!

To add to the conundrum are the catch tanks with air filters! Going for a wild guess here!....... Cooler air coming in from the catch tank air filter assists the condensation of the engine fumes??? But then - surely with extra air coming in to the inlet manifold - the carbs are going to need re-tuning, maybe more to the aft one as it's closer to the vacuum port.

And to cap it all, I still haven't found a way of connecting the brake servo..........I'm going to have a little lie down... :wacko:

A crankcase breather is simply to accommodate the change in internal volume of that crankcase when there are reciprocating parts.  So for example with a 500cc twin cylinder engine, where both pistons descend the cylinders at the same time, compresses that 1/2 ltr displacement into exactly the same crankcase space (volume) as when the pistons are at TDC.  And that crankcase pressure is enough to blow passed oil seals.  So breather vents and pipes are added to let the air pressure out.  Many such engines have a simple one-way flap valve on this vent, so air doesn't come back in again ..not least because that outside air can contain dust and pollen, outside humidity and road spray,  and  perhaps even the occasional insect. 

But with crankcase air being pushed out by the descending pistons and then only a small amount of air coming back in (when a one-way OUT valve is fitted and the pistons ascend) results in negative crankcase pressure . This (partial vacuum) inside a small engine  ..such as a Citroen 2cv 600cc flat-twin or a larger twin cylinder motorcycle engine, has the benefit that on the piston's power stroke (descent) there is less air pressure to resist its descent.  On such an engine that resistance is said to absorb 2 or 3 bhp of power (..so almost 10% of the Citroen's 33bhp). The 2cv has a one-way vent breather designed into its engine oil filler tube.  This negative crankcase  pressure also helps reduce engine oil leaks.     

NB. larger capacity but compact-in-size parallel-twin cylinder motorcycle engines have the worst ratio of displacement to crankcase internal volume.. which is why they are notorious for leaking.

Naturally on a four cylinder engine, where two pistons are ascending as the other two are descending, there is not nearly so much difference (puffing) of crankcase air pressure.  But there is always some..  because air is pulsating ..at piston speed, from under one piston to another (in effect from one end of the engine crankcase to the other, and this pressure wave pulsates all the way up to the rocker cover).  Added to this is a little more pressure thanks to combustion blowing-by piston rings.  (Tip.., condition of piston rings and bore might be assessed by feeling what comes out of the crankcase breather).  Long stroke engines have a worse situation than those with a short stroke, even though their capacity might be the same, simply because long stroke engines tend to have higher piston speeds. Therefore the air being pushed around inside that crankcase is having to also move faster, which in turn increases the pressure at the air wave front.   

So.. crankcase air pulsations + combustion blow-by fumes puff out of the breather, and this carries with it oil in suspension (ie., a mist or perhaps even a fine spray of oil, plus any humidity that is trying to escape the hellish environment inside an engine !).  On a worn engine, or one put together with loose tolerances, there can be a lot of oil mist  - with some engine bays being clear witness to this.  What do you do with it (the oil mist) ?  ..Well suck it back in to engine and let the oil get burnt up with the next cycle of combustion, and any moisture will turn to steam and is ejected through the exhaust.  

In short ; the inlet manifold connection is a low pressure connection to take these fumes, without their being sucked actually through the carburettor.   And., serving the same function as the one-way valve on twin cylinder engines, its low pressure works to create a negative crankcase pressure (partial vacuum) to the benefit of both performance and engine oil tightness.  And yes., upper cylinder lubrication is good (..in moderation). A hotter grade of spark plug will keep cleaner with such 'closed' systems, conversely if you were to switch to an open vented system - then a cooler spark-plug grade may be fine. 

So Roger,  you can remove the manifold breather pipe and use that connection for your brake servo,  and then your crankcase breather can be to the atmosphere via a simple rocker-cover cap ..such as on the earlier cars, or via a pipe to under the engine, or to a catch tank ..which is then vented to the air,  or else via pipes to the air-filter side of the carburettor.  The latter will give you some degree of lower pressure but (assuming your air filters are not under size then) not nearly as much as the connection from the air intake manifold.  An in-line one-way valve in the breather pipe (leading to a catch tank or atmosphere) will possibly catch some of the pulsation, but I doubt if it will be particularly effective on a four cylinder engine.   

As to your conundrum regrading catch tanks with air filters..  Perhaps the easiest way to appreciate this is to think carburettor venturi ..where the pinching in of the cross-sectional-area causes the air to accelerate through the carburettor - so that when a jet of fuel is injected into it - that fuel 'mist' stays in suspension all the way through the manifolds, passed the valves, into the combustion chamber, and then swirls around inside to thoroughly mix.   With that understood - just think exactly the same principle but the other way round - where the cross-sectional-area doesn't decrease - but instead is increased to perhaps fifty or a hundred times as big.  Then the air flow velocity slows right the way down  ..and the (crankcase oil ) mist drops out of suspension. The air filter on a catch tank is intended to do just that : so many times larger than the cross sectional area of the rocker's breather pipe.  Oh yes, some oil mist will stick to the wires within the filter and this in turn acts as air filter to help prevent gritty dust, pollen, bugs, etc, from going back up the breather pipe.

Hope that helps, Pete.

 

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9 hours ago, Bfg said:

A crankcase breather is simply to accommodate the change in internal volume of that crankcase when there are reciprocating parts.  So for example with a 500cc twin cylinder engine, where both pistons descend the cylinders at the same time, compresses that 1/2 ltr displacement into exactly the same crankcase space (volume) as when the pistons are at TDC.  And that crankcase pressure is enough to blow passed oil seals.  So breather vents and pipes are added to let the air pressure out.  Many such engines have a simple one-way flap valve on this vent, so air doesn't come back in again ..not least because that outside air can contain dust and pollen, outside humidity and road spray,  and  perhaps even the occasional insect. 

But with crankcase air being pushed out by the descending pistons and then only a small amount of air coming back in (when a one-way OUT valve is fitted and the pistons ascend) results in negative crankcase pressure . This (partial vacuum) inside a small engine  ..such as a Citroen 2cv 600cc flat-twin or a larger twin cylinder motorcycle engine, has the benefit that on the piston's power stroke (descent) there is less air pressure to resist its descent.  On such an engine that resistance is said to absorb 2 or 3 bhp of power (..so almost 10% of the Citroen's 33bhp). The 2cv has a one-way vent breather designed into its engine oil filler tube.  This negative crankcase  pressure also helps reduce engine oil leaks.     

NB. larger capacity but compact-in-size parallel-twin cylinder motorcycle engines have the worst ratio of displacement to crankcase internal volume.. which is why they are notorious for leaking.

Naturally on a four cylinder engine, where two pistons are ascending as the other two are descending, there is not nearly so much difference (puffing) of crankcase air pressure.  But there is always some..  because air is pulsating ..at piston speed, from under one piston to another (in effect from one end of the engine crankcase to the other, and this pressure wave pulsates all the way up to the rocker cover).  Added to this is a little more pressure thanks to combustion blowing-by piston rings.  (Tip.., condition of piston rings and bore might be assessed by feeling what comes out of the crankcase breather).  Long stroke engines have a worse situation than those with a short stroke, even though their capacity might be the same, simply because long stroke engines tend to have higher piston speeds. Therefore the air being pushed around inside that crankcase is having to also move faster, which in turn increases the pressure at the air wave front.   

So.. crankcase air pulsations + combustion blow-by fumes puff out of the breather, and this carries with it oil in suspension (ie., a mist or perhaps even a fine spray of oil, plus any humidity that is trying to escape the hellish environment inside an engine !).  On a worn engine, or one put together with loose tolerances, there can be a lot of oil mist  - with some engine bays being clear witness to this.  What do you do with it (the oil mist) ?  ..Well suck it back in to engine and let the oil get burnt up with the next cycle of combustion, and any moisture will turn to steam and is ejected through the exhaust.  

In short ; the inlet manifold connection is a low pressure connection to take these fumes, without their being sucked actually through the carburettor.   And., serving the same function as the one-way valve on twin cylinder engines, its low pressure works to create a negative crankcase pressure (partial vacuum) to the benefit of both performance and engine oil tightness.  And yes., upper cylinder lubrication is good (..in moderation). A hotter grade of spark plug will keep cleaner with such 'closed' systems, conversely if you were to switch to an open vented system - then a cooler spark-plug grade may be fine. 

So Roger,  you can remove the manifold breather pipe and use that connection for your brake servo,  and then your crankcase breather can be to the atmosphere via a simple rocker-cover cap ..such as on the earlier cars, or via a pipe to under the engine, or to a catch tank ..which is then vented to the air,  or else via pipes to the air-filter side of the carburettor.  The latter will give you some degree of lower pressure but (assuming your air filters are not under size then) not nearly as much as the connection from the air intake manifold.  An in-line one-way valve in the breather pipe (leading to a catch tank or atmosphere) will possibly catch some of the pulsation, but I doubt if it will be particularly effective on a four cylinder engine.   

As to your conundrum regrading catch tanks with air filters..  Perhaps the easiest way to appreciate this is to think carburettor venturi ..where the pinching in of the cross-sectional-area causes the air to accelerate through the carburettor - so that when a jet of fuel is injected into it - that fuel 'mist' stays in suspension all the way through the manifolds, passed the valves, into the combustion chamber, and then swirls around inside to thoroughly mix.   With that understood - just think exactly the same principle but the other way round - where the cross-sectional-area doesn't decrease - but instead is increased to perhaps fifty or a hundred times as big.  Then the air flow velocity slows right the way down  ..and the (crankcase oil ) mist drops out of suspension. The air filter on a catch tank is intended to do just that : so many times larger than the cross sectional area of the rocker's breather pipe.  Oh yes, some oil mist will stick to the wires within the filter and this in turn acts as air filter to help prevent gritty dust, pollen, bugs, etc, from going back up the breather pipe.

Hope that helps, Pete.

 

OK, thanks Pete. After several read throughs - I think I can work out a system. My main concern was the 'pulling out' from the engine - and this effect being reduced by removing the vacuum provided by the inlet manifold connection. So, if this is really of no great importance  - I can run a pipe from the rocker cover outlet to a air filter attached catch tank (blocking off one of the 2 ports). By the way - I never knew of an engine whose pistons travelled the same way together even though I once owned a 2cv. I guess that was to do with balancing a horizontally opposed, lateral power plant.

Cheers,

Roger

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Tiny little catch tanks with dinky filters are a waste of time and money on a TR engine, if you dont want to just vent down and under the car (A perfectly good way of doing it) then at least get a decent sized catch tank with good sized hoses, you would be surprised what you do get in them and if they are vented under the bonnet you will get fumes inside the car. I have one of these and its one of the best systems I have come across.Catch tank

Then you can use your inlet manifold properly for a servo installation.

Stuart.

 

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1960's to 1970's Triumph twins (motorbikes) had both pistons traveling up & down together, one on its compression stroke, the other on it exhaust / inlet stroke. difficult to balance which is why they always vibrated rather a lot.

Bob.

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1 hour ago, rogerowen said:

OK, thanks Pete. After several read throughs - I think I can work out a system. My main concern was the 'pulling out' from the engine - and this effect being reduced by removing the vacuum provided by the inlet manifold connection. So, if this is really of no great importance  - I can run a pipe from the rocker cover outlet to an air filter attached catch tank (blocking off one of the 2 ports). By the way - I never knew of an engine whose pistons travelled the same way together even though I once owned a 2cv. I guess that was to do with balancing a horizontally opposed, lateral power plant.

Cheers, Roger

.

Roger, I'm glad you're managing to get you head around crankcase breathers.  Your previous post imply concern about moisture inside the crankcases, to which I simply ask - how does that moisture get in there ?   And that would be through a non-regulated (by one-way valve) crankcase breather system allowing atmospheric humidity to be freely drawn back into the crankcase.  The early TR's with an open vented breather system were like this, and so your experience was to see a lot of creamy coloured condensation goo dripping out of the end of the breather pipe, and so quite understandably are now keen to extract it.   But pressure regulated (one-way valve) and closed breather systems are quite effective in preventing that humidity from getting inside in the first place  (the inside of your oil filler cap for example should be clear of any such creamy coloured residue).  Aside from that, the everyday practical advantage of a closed breather system is to provide negative crankcase pressure which helps avoid crankcase oil being pushed out of the engine seals. 

A brake servo maintains the vacuum until the brakes are released (.. note the characteristic hiss of articulated lorries when they stop),  but 99% of the time its valves are closed,  ie. whenever the brakes are in use or not in use - it's only the very short time-span of brake release where the vacuum is lost, and that soon recovers even though the engine is just ticking over.   So what I'm saying is that Y or T connector from the inlet manifold connector will all but maintain the partial vacuum of the original closed crankcase breather system.     

However if you Y piece connect to an open vented system (either just a drop pipe or via a catch tank) then the vacuum in the brake servo is compromised, and a one way valve in line (see Stuart's photo) to the breather is necessary to prevent air coming back in through that pipe.  Should the one-way valve, or the Y connector pipe to it, fail - then you loose your brake servo.  So as Malbaby suggests  "a dedicated single vacuum source for the booster to operate efficiently"  and is the safer option.

Regarding the twin cylinder engines. The 2cv has a boxer engine where the crankshaft is a 180 degrees - so the pistons go the opposite direction at the same time (ie. both simultaneously going away from the crankshaft, or both coming towards it).  And yes these masses tend to balance each other out.  However their firing is one side and then the other so they still rock.  Four and six cylinders are naturally very much smoother.  

Parallel twin motorcycle engines were at one time commonplace. Most had a 360 degree crankshaft  (both pistons go up and down together) - primarily because a top-hat shaped crankshaft is easier (and therefore cheaper) to make, and it's stiffer (for the same weight) than an S-shaped 180 degree crankshaft.  Drillings to feed oil to the big ends is also much easier, and less oil pressure was needed.  And then, although the reciprocating mass of the pistons and con-rods needed counter balancing with bob-weights on the crankshaft,  the engine's secondary balance (felt as sideways rocking on a motorcycle) was much better.   
.

Edited by Bfg
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1 hour ago, Lebro said:

1960's to 1970's Triumph twins (motorbikes) had both pistons traveling up & down together, one on its compression stroke, the other on it exhaust / inlet stroke. difficult to balance which is why they always vibrated rather a lot.

Bob.

Explains why Triumph motorcyclist always carried spanners! My 250cc twin was a 2- stroke - so different set up.

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1 hour ago, stuart said:

Tiny little catch tanks with dinky filters are a waste of time and money on a TR engine, if you dont want to just vent down and under the car (A perfectly good way of doing it) then at least get a decent sized catch tank with good sized hoses, you would be surprised what you do get in them and if they are vented under the bonnet you will get fumes inside the car. I have one of these and its one of the best systems I have come across.Catch tank

Then you can use your inlet manifold properly for a servo installation.

Stuart.

 

photo1754.jpg

Nice engine bay! I notice the indent on the o/s inner wing which came up on a recent post that some thought might be to allow more room for Webbers???

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Just now, rogerowen said:

Nice engine bay! I notice the indent on the o/s inner wing which came up on a recent post that some thought might be to allow more room for Webbers???

No that was originally for a servo if factory fitted.

Stuart.

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