Motormite breather

Why don't you cure the leaks instead? Sorry, couldn't help it, but why try to cure symptoms instead of fixing the real problem. Its of course your choice, so disregard my comment if inappropriate.

Hi Steve,

You could give one of these a try.:-

http://motors-parts.shop.ebay.co.uk/Motorcycle-Parts-Accessories-/14780/i.html?_nkw=duckbill&_catref=1&_fln=1&_trksid=p3286.c0.m282

As it is only a few quid it will show if the leaks are related to excess crankcase pressure.

For around £10.00 ( I will check tonight) I could supply you with the Motormite one as I bought a bunch of them a while ago and still have a couple left. This would be on the proviso that you let me know if it makes a difference or not. If this is of interest then email me your address.

I have an 850MkIII that used to have the odd weep and it is now completely house trained.

Regards

Tony Ripley <technical@nortonownersclub.org>

The Yamaha one fitted to the XS650 is quite well made and costs about 20 euros from www.XS650shop.de One of my branch members is playing with a "Bunn breather" cost about £80 and looks like two fish tank valves and a length of hose. He has managed to pump about 150ml into a catch tank in about 150 miles.

Give us a clue as to where the oil is coming from and the "experts" should be able to assist. For instance oil at the front of the head is often coming from the rocker feeds and is drawn forward. Leaks under the engine often come from the alternator grommet. In this day and age of high tech sealants there should be little reason for leaks.

Fitted Bunn breather kit, very expensive for two plastic valves, tubing and filter, but cannot fault the theory. From experience, fitting a single one-way crankcase exhaustvalve creates a significant negative pressure in the crankcase which the pistons are working against each time they go up the bore. Not good for engine efficiency.Also the negative pressure causes additional piston ring leakage so oncompression strokefuel/air mixture is sucked into the crankcase and on exhaust stroke burnt gases and unburnt fuel/air mixture drawn into crankcase. This contaminates the engine oil which is obviously not good, fuel dilutes the oil and corrosive elements in burnt gases don't help engine component life.

Solution is to fit one way inlet and exhaust valves to crankcase. Connect both to catch tank, inlet at bottom, exhaust midway up. In addition two more tubes connected to top of tank each with an inlet and exhaust valve fitted. Inlettube also fit an airfilter which breathes in fresh air, exhaust goes to secondary catch tank which so far in 120 miles has collecteda few drops of what looks like mainly water. Any oil vapour/crankcase gases are blown into first catch tank on piston downstroke. The crankcase positive pressure closes the inlet valves. On up stroke negative crankcase pressure closes exhaust valves, inlet valves open sucking in fresh air and any contents of first catch tank from previous up stroke. Crankcase pressure is approxiamately at 1 bar (atmospheric) and gases are vented to atmosphere. Oil vapour is recycledto be filtered (if you have one)on return to oil tank. Plug the pipe from oil tank neck. Oil tank breather to secondary catch tank. I worked out the primary catch tank set upincluding the four (standard Bunn is two)check valvesafter experiencing, as Dave mentioned, the accumulated oil in single catch tank.

What got me thinking about the Bunn theory was drainingdirty, smelly engine oil from tank during oil change whilst using a single crankcase exhaust check valve.

Steve

Any PCV valve will do the job, or evenan old one way valve off a brake booster/servo. I think that was the Motormite'soriginal function. Alternatively the XS 650 job or one of Norvil's brass marine valves. I have one on my 750which has 850 cases and timing breather with1/2" pipe but they do fittings for 3/8" as well. It's not cheap but is a solid piece of kit that works well. If you Google Marine brass one way valve you'll find this.........http://www.seascrew.com/browse.cfm?BRASS-ONE-WAY-VALVES&l=0000000423It's the 1/2" one Norvil use but with screw in barbed tails. Couldn't see these on that site but they must be there somewhere.

Here is an articlefrom the INOA about the breathers:

http://www.inoanorton.com/docs/BreatherValve.pdf

Breather Valve Fixes Oil Leaks! By Alan Goldwater. ã 2001 All Rights Reserved

(revised from an article in INOA Norton News #124)

Many of us have discovered that our Nortons tend to leak more oil as they age. At 30k miles, my 850 started weeping oil out the head joint. Several head gaskets and oily weekends later I realised the leak wasnât from the mating surface, but from the casting around the push rod tunnel. By 40k miles, several other places were leaking , including the case joint and the tach drive (despite the seal mod!). Finally I concluded these symptoms could all be caused by pressure inside the motor. I installed a hose fitting on the intake valve cover and connected a gauge that measured from 10 psi vacuum to 10 psi pressure. Some of you may have seen me riding around with this kludge stuffed in the map pocket of my tank bag this summer. My testing confirmed the theory, showing positive pressure of up to 2 psi inside the motor at 4500 rpm. I tried several types of PCV valves, but none reduced the internal pressure, and some actually increased it. Finally Doug McCadam, of the Colorado Norton Works reminded me of a part mentioned in 1998 on the NOC-UK email list, the Motormite/HELP #80190 brake booster valve. With this valve installed about midway up the large breather hose, pressure at the head dropped to â2 psi (vacuum) at idle. This gradually increased with engine speed, to just slightly negative pressure at 4500 rpm. An extended test ride of 500 miles showed that all of the oil leaks were gone, and oil consumption decreased from 300 mi/qt to around 700 mi/qt. At under $5, this is the most cost-effective Norton accessory Iâve seen, and every Norton with the large breather should have one. Several other Norton Club members have tested this part, and all share my enthusiastic opinion of it. You can find it on the rack at Kragen and many other auto parts stores. The question remains where is the pressure coming from. There was an extensive discussion of this phenomenon on the NOC-UK email list starting in 1997. While several theories had been offered, no on thought to do the simple test with a gauge, so Iâm not convinced any of them were correct. There was a favorable review of the HELP part by INOA member Ben English. Most mechanics Iâve asked think the increase in pressure is due to combined blow-by from worn rings and valve guides. This seems reasonable to me, but the pressure I measured seemed to increase with engine rpm but not with throttle opening, so there seem to be some other mitigating factor(s). What do you think? Send me your theories on this by email magicsound@aol.com

Simon, you say:-

From experience, fitting a single one-way crankcase exhaustvalve creates a significant negative pressure in the crankcase which the pistons are working against each time they go up the bore. Not good for engine efficiency.Also the negative pressure causes additional piston ring leakage.

I am not sure why the negative pressure would causeefficiencyissues. If the pistons are working against the pressure on the way up then then this is balanced out by the pull on the way down so the effect is neutralised.

I also remain to be convinced about the additional piston ring leakage. I do not know what the pressure in the cylinder is when the bang occurs but I would not have thought that the extra 2 psi difference between above and below the rings would have much effect.

I have the Motormite breather on my 850MkIII and have had for about three years. it seems to have stopped all those annoying little weeps (not leaks as such). and I have not noticed any oil problems.

By the way, I weighed the operating bit of the valve ( a small rubber disk ) and it was something like 0.1 gram which I believe is why it works much better than any using something like a ball bearing which just cannot react at high speeds.

Regards

Tony

"Hi I have already got the brass one in the hope that i could pull it apart and fit the internals into the original breather ,but itwouldn'tcome a part withoutdestroyingit."

So are you saying you've been using the brass job and you still have leaks from what must be quite high internal pressures? You mentioned an engine rebuild and subsequent leaks....was it leaking badly before? Do youhave a camshaft breatheror is it the Combat with the rear breather.If it leaks with the brass one installed I don't think even the Motormite willsolve your problem. If its a Combat style then apparently the Colorado Norton one is the business but it aint cheap. Need to clarify whats happening with the brass breather installed because they do work. Its only a light spring and nylon valve against a machined circular seat. Right way round?

My 1972 750 leaked from the tacho drive, I fitted the honda oil seal tacho housing , it still leaked..

I then fitted a PCV valve I got from Burton the car engine tuning folks , similar to part number6011482 in place of the hose adapter up by the oil tank.

Now my front ISO tube is rusting due to lack of protective oil.

I would certainly try a PCV valve if you have oil leaks, I will be getting one of the XS650 breather valves in the future as they are well made and incorporate a nice reed valve,

PCV valves are a proven fix for oil leaks , if you want more opinions I suggest searching the Jerry Doe accessnorton commando site - more commandos went to the USA than the UK and Jerrys site is the definitive place to look for commando stuff.

Previously wrote:

Simon, you say:-

From experience, fitting a single one-way crankcase exhaustvalve creates a significant negative pressure in the crankcase which the pistons are working against each time they go up the bore. Not good for engine efficiency.Also the negative pressure causes additional piston ring leakage.

I am not sure why the negative pressure would causeefficiencyissues. If the pistons are working against the pressure on the way up then then this is balanced out by the pull on the way down so the effect is neutralised.

I also remain to be convinced about the additional piston ring leakage. I do not know what the pressure in the cylinder is when the bang occurs but I would not have thought that the extra 2 psi difference between above and below the rings would have much effect.

I have the Motormite breather on my 850MkIII and have had for about three years. it seems to have stopped all those annoying little weeps (not leaks as such). and I have not noticed any oil problems.

By the way, I weighed the operating bit of the valve ( a small rubber disk ) and it was something like 0.1 gram which I believe is why it works much better than any using something like a ball bearing which just cannot react at high speeds.

Regards

Tony

There will be additional leakage. If you have a positive pressure one side of a seal and negative the other side the pressure will try to balance out. Over time it will balance out. It is a law of nature and physics and so engineering. Where do you get the 2psi from? Approx. 1 bar is atmospheric pressurewhich is approx. 15psi.

If you only have an exhaust valve then how is your crankcase breathing? Surely you need an inlet as well to breath.

Your crankcase and oil will beaffected by additionalring leakagewetheryou notice it or not.

Hi Simon,

I think you and I have a different idea of what the breather system is intended to do. If I understand your thinking correctly you want to get the air in and out as the pistons go up and down. The only way you could do this is to have an enormous hole so there is no restriction.

My idea of a breather is as thepistonsgo down they blow air out of a pipe, this can be fairly small as the first time they go down it is a starting revs so very slow. The breather valve closes. Then as thepistonsgo up a negative pressure (relative to atmosphere) is formed under the pistons. By measurement this is around -2 psi when thepistonsare at TDC(Also if you read the post above with the text from 'article in INOA Norton News #124' this also has -2 psi). If for the sake ofargumentwe assume no leaks anywhere then as thepistonsgo back down the pressure goes back to the same as atmosphere. Thus the pressure inside and outside the crankase is the same and there will not be any reason for the case to leak.

Now there will be a little bit of leakage past rings and guides so as the pistons get down to the bottom there will be a small positive pressure, this is not enough to cause leakage through seals and the small extra pressure will go out via the breather ready for the next upstroke.

Atmospheric pressure is irrelevant as we aretalkingabout the relative difference between the inside of the crankcase and the outside.

Again, the extra leakage past the piston rings will be insignificant as the pressure inside the cylinder would be 100's of p.s.i so an extra couple will make no difference.

I have scope traces of a transducer showing the pressure changes inside the crankcase, I hope to submit anarticleto Roadholder showing my results.

Regards

Tony

Why would there need to be an enormous hole? If you understood my previousposting then simply having an inlet valve would allow nature to take care of things. The one fitted is approx. 4mm dia.

The measurement you quote would be dependent on bore condition, rings etc so to give that figure any meaning it would have to comparative to other methods of crankcase breathing e.g none, one exhaust only, inlet and exhaust etc.

Why as the pistons return down the bore would the pressurebe at atmospheric? You previously stated as an advantage that negative pressure in thecrankcase would suck thepistons down thus negating the negative pressure as they went up. You now state thatcrankcasepressure is at atmospheric approx 15psi? If indeed this is the case with your engine then air is leakinginto the crankcasefrom the rings, guides or other source, and the pistons cannot be pushing airgases/oil out of the cases. You seemed to be a bit confused.

I look forward to reading your report.

Why fit both an inlet and an exhaust valve to the case? If there are two opposite valves, either one or the other will always be open so they might as well both be left out. The average pressure will be close to atmospheric at mid stroke, so a couple of psi above atmosphere at BDC - forcing oil out.

When pistons go down they increase pressure in the cases. Blow by will make it worse. If there is an exhaust valve in the breather pipe, the pressure will balance atmospheric all the way down (depending of course on the capacity of the valve+tubes...) and will ideally be close to atmospheric (zero gauge pressure: 15psi absolute pressure) all the way down to BDC.

Then when the pistons go up the volume inside the cases gets bigger so the pressure goes down all the time the pistons are rising. A minimum of -2psi gauge pressure at TDC sounds plausible. So there's no pressure to force oil out.

So on average the pressure is slightly less up than atmospheric - ranging between close-to-atmospheric at BDC, to a couple of PSI below when at TDC. Of course the system might not keep up with the pumping action if there is too much blow-by - so modern vehicles have these fumes sucked back into the engine air supply.

The Dommie does not need a valve in the breather because it has the timed camshaft breather. And the singles have the timed crankshaft breather. So Dominators and Norton Singles never leak. In theory.

1. hello i have been reading this andi would like to add my two penith if i may. Ihave owned full race spec car engines built at great expence by top engine tuner they have no fancy breath system just 3/8 bore pipe and did not leak or pressurise the crankcase i drive a landrover and its crankcase is delibertly pressurised so when in dusty parts of the world or in deep water contaminates or not drawn into the engine past seals. Yes i know this has nothing to do with Nortons but the point is this if there is pressure that is causing a leak this is because either the leaking part is faulty or the pressure should not be there and the seal or joint face was not ever intended to contain it. Pistion rings fitted to our engines have a gap so will always leak add to that ware on ring and bore (size wise)the surface of the bore (IE to rougth the ring cannot seal). At low RMP like 1000 every time the crank rotates once the piston has up 500 times and down 500 times it is after all connected to the crank so work out for yourself what happens as the engine speed increase to 6000rpm or more ( when we all hope the piston is still connected to the crank!!) So as you can see the time these gas have to blow by the ring is small to say the least. the pressure above the ring is vastly higher than that below and so will always try to pass the ring no matter what slite differance the fancy breather valve may make. To add to all of this what about leakage past valve guides into the head witch will then find its way into the crankcase by oilways an pushrod tubes etc. So are gapes in the engine where gas can pass without said gapes the engine will seaze but these gaps must be kept to the minimum dont fit worn parts and think they wont leak they will if a seal is old and hard or the part it seals on has the slitest sine of ware it will not work as well as it should the same goes for joint faces. If it leaks then it or some other part of engine need fixing if you can live with it fine its your engine and after all when it was made new it may have laeked things did back then it was seen as normal. But if no find the reason why and fix it and if you half do the job dont be supprised if its only half fixed. Spend money on good parts no fancy breaths

Hi Karl,

Car engines do not need fancy breather systems as they tend to have the some pistons going up while others age going down so the net effect is zero, the only breather requirement is to cope with the blow by which is hopefully small.

Hi David,

Thanks for your response, this save me having to explain to Simon who the confused one is.

Regards

Tony

my point about the car engine was it did not leak it was larger engine (2000cc) than commando with larger piston and valve areas so increasing the chance of leakage it produced 185 housepower at 7850 rpm no bad for a 1980s ford pinto but it was built with extreme care and all parts in it were modifed and up rated it had a windage tray fitted in the crackcase ( a plate on to crankcase inner wall extending toward the crank assembly to within a millimetre leaving just enougth space for crank an rods to rotate past it) as you may know these are to trap the oil that is thrown of the crank as it will slow the rotation of the assembly by making an oil ladden fog inside the crank and thus sap horsepower. The point here being the mean factor inside the crankcases is the rotating crankassembly at even low rpm any tiny amounts of low pressure witch may for a breif instant will not have time or enough energy to move to another bore past the massive draft being generated by the crank assembly. Plus as the piston then fail they or gone and replaced by positive pressure these constainly changing small amounts of pressure or at best trapped under the piston that generates them as if they go into the crankcase they will be over come by the far greater forces that exist reguardless of the number of cylinders or or their direction of travel at any one time. There is leakage form the valve guides to address as there is no out let for this it like the oil will find its way down to crankcase in time fitting breather to a rocker cover would help minimise this but Norton did not see the need for this. When these bikes where made they where using engines and many other parts that where much older and out dated designs back then some leakage was normal butif care is used when putting it together ( after all we are not on the assembly line so no need to rush) it should and can work correctly. Any pressure leakages (there are clearances needed so there will be some leaks) will be minimal and the breath will cope but once the breather can nolonger vent the pressure than it is the leakage of pressure that must be found and addressed. As Tom said at the start fix the leak this I know is without question a bigger job than changing the breather but it is the problem not the breather. I am sure we all ( me included ) would like a leak free machine an have those little jobs that we put off untill we can nolonger put them off any more but fix the bit that needs fixing not the part being asked to do more than it should because another part is failing. Karl

Previously wrote:

Hi Karl,

Car engines do not need fancy breather systems as they tend to have the some pistons going up while others age going down so the net effect is zero, the only breather requirement is to cope with the blow by which is hopefully small.

Hi David,

Thanks for your response, this save me having to explain to Simon who the confused one is.

Regards

Tony

Sadly, you are missing the point, assuming the blow-by 'is hopefully small' (Karl), or assuming 'a little bit of leakage' (Tony). There is always leakage past the rings, even in a cylinderwhich has been bored to piston manufacturers clearance,then honed to within 0.0002" of round, using the correct grit and included angle to achieve the desired surface finish and assuming use of top quality rings gapped to size. The job of the breather is to flush the crankcase and so rockerbox of the damaging gases, deposits from combustion, fuel etc. Thanks for answering the points I raised Tony, oh, you haven't.

For further reading I suggest you look at www.bunn.co.nz and www.britcycle.com/products/breatherkit . Also Classic Bike June 2005 features an article by Peter Williams re crankcase breathing, I think he knows a thing or two about engineering.

Mr Bunn very sensibly does not tell how how his device works. But he does hint at part of it - at 4000rpm that valve has to have very short reaction time (vibration natural frequency) if it is to open and close at such speeds. It must be whistlinglike a flute (4000rpm is about 4 octaves above middleC I think).

On a 4 cylinder car engine the fluctuations should be small and all the valve needs to do is allow blow-by to be vented. But in a 360 twin it has to move fast enough to react. So the mechanically timed breather makes more sense since it always goes as fast as the engine. Maybe Mr Bunn just has a very light diaphragm (he says it's very expensive stuff) - and all the rest of the tubes are there to make a good impression!

, which utilises a reed valve in a housing mounted directly on the crankcase. This is the same method used on modern Ducatis. I was too much of a cheapskate to pay their prices, so I machined up a similar housing to take a two stroke reed valve that cost a couple of quid. Luckily for me it fits directly onto the 1972 style crankcase which has a breather hole on the back of the crankcase, but for other types it requires a mounting flat and connecting holes to be machined. He has just developed a rather elaborate valve housing that mounts in the oil drain hole for people with non 72 engines who don't want theirs machined.

You do not need valve that can flow a large volume of gas except on the very first downstroke, and as this will be very slow it does not need to be that large a hole. The following description assumes the Motormite fast reacting one way valve is fitted:-

Once the pistons have gone all the way to the bottom the pressure inside the cranckase will be atatmosphericas all the air will gave gone out through the one way valve (I hope you agree with this bit Simon). The one way valve will close as soon as the pistons start to go up. Once the pistons are at TDC the pressure will be roughly -2 psi. That is 2 PSI less than atmospheric. If you are just turning the engine over on the kick / electric start then the pressure will go between atmospheric and -2 psi as the pistons go between BDC and TDC. Again Simon I hope you agree with this bit.

Once the engine is running there will be a small bit of blow by as you say, this means that when the pistons get to BDC the pressure will be slightly higher in the crankcase than atmospheric and the valve will open to allow this very small amount out.

I have put the breather pipe into a bucket of water and I get a large stream of air initially and this is followed by a small stream of bubbles. This is the blow by or maybe suck in from somewhere else.

The measured pressure goes between slightly positive (less than 0.5 psi above atmospheric) and about 2 psi below atmospheric on each cycle.

Now Simon, If you are correct when you say that the reason for a breather is to flush thecrankcaseof damaging gasses etc. then I am completely wrong and I hold my hand up.Obviouslyyou will need something that will allow 850cc of air (in the case of my MkIII) to get smoothly in and out of the engine when running at any RPM. I am not sure what size pipe will be required, maybe someone can suggest.

Tony

Previously wrote:

You do not need valve that can flow a large volume of gas except on the very first downstroke, and as this will be very slow it does not need to be that large a hole. The following description assumes the Motormite fast reacting one way valve is fitted:-

Once the pistons have gone all the way to the bottom the pressure inside the cranckase will be atatmosphericas all the air will gave gone out through the one way valve (I hope you agree with this bit Simon). The one way valve will close as soon as the pistons start to go up. Once the pistons are at TDC the pressure will be roughly -2 psi. That is 2 PSI less than atmospheric. If you are just turning the engine over on the kick / electric start then the pressure will go between atmospheric and -2 psi as the pistons go between BDC and TDC. Again Simon I hope you agree with this bit.

Once the engine is running there will be a small bit of blow by as you say, this means that when the pistons get to BDC the pressure will be slightly higher in the crankcase than atmospheric and the valve will open to allow this very small amount out.

I have put the breather pipe into a bucket of water and I get a large stream of air initially and this is followed by a small stream of bubbles. This is the blow by or maybe suck in from somewhere else.

The measured pressure goes between slightly positive (less than 0.5 psi above atmospheric) and about 2 psi below atmospheric on each cycle.

Now Simon, If you are correct when you say that the reason for a breather is to flush thecrankcaseof damaging gasses etc. then I am completely wrong and I hold my hand up.Obviouslyyou will need something that will allow 850cc of air (in the case of my MkIII) to get smoothly in and out of the engine when running at any RPM. I am not sure what size pipe will be required, maybe someone can suggest.

Tony

May I suggest (once again) further reading. www.bunn.co.nz www.britcycle.com/products/breatherkitor, if you can find a copy of Classic Bike June 2005, article by Peter Williams on crankcase breathing.