breather solutions for early commandos - dare I ask?

Given the heat that this topic has generated over a few years, I am hesitant to raise it, but I have some questions specific to breathers for early Commandos with a frame brace proximate to the sump plug. I have been rereading old threads here on breathers, and in particular breathers on pre 1971 models, which have the timed breather as standard; and what my 1970 has.

My assumption is that the timed breather is not the best solution, and that an improved breather will assist with keeping oil leaks in check and provide some additional efficiency for the motor. I note Jim Comstock’s comments in earlier posts that the timed breather might have been good on smaller motors, but was not efficient enough for the 750 (a lot of the information and assumptions that I am making are from previous Comstock posts on this subject).

I’m looking for a breather solution that is bolt on; one that doesn’t involve drilling holes in the timing case/crankcase, and therefore does not involve stripping down the motor. That counts out the CNW crankcase breather.

The best bolt on solution for most motors would appear to be the Comstock sump plug breather, but this will not work for pre 1971 frames that have the brace across the frame close to the sump plug; that brace fouls the Comstock sump plug breather (see previous posts from DogT advising of his experience). Or does it only not fit on some bikes? Has anyone with a cross brace successfully installed this breather? When I look at my bike and the photos of the Comstock sump plug breather it looks to me like it will not fit. .

I have attempted to post a picture of my sump plug and its proximity to the cross brace; which in the picture is covered in oil. A past owner has welded a nut onto the sump plug to make it easier to take on and off.



I see two possible solutions, each with its own issues. I seek thoughts and comments.

1. A reed valve off the timing case. My 1970 motor has a separate plate at the back of the timing case. I don’t think it would be difficult to attach a reed valve to that plate (in fact I have one of the XS reed valves that I bought before realising that it was pointless to connect to a hose coming out of a timed breather). One way of connecting it would be to have the valve bolted direct to the plate – in a similar way to that done by Grandpaul with the Triumph reed valve; another would be to put in a connector and then have the valve on the hose – as shown by ZFD in another thread; I think that the connector is stock for later timing case breathers.

Jim C has suggested that this solution has problems; inefficiency given that it draws pressure from the timing case as opposed to from the crankcase itself; and an increase in the oil level in the timing case.

If I understand Jim’s comments properly, he has found that a timing case breather encourages high oil levels in the timing case, which in turn generates heat through the timing chain rotating in that oil bath; and that heat is a negative. This can be mitigated by drilling an additional oil drain hole from the timing case to the crankcase; but I think that for all but the most skilled (or those with the appropriate tools) that would involve a strip down of the motor.

And I also understand that there is a basic issue of whether relieving pressure in the timing case will relieve pressure in the crankcase. It seems that by drilling other holes between the crankcase and timing case you can assist the air pressure to migrate from the crankcase to the timing case.

That is not viable for me as it would involve stripping down the motor.

If I attached a reed valve breather to the timing case without any additional holes being drilled between the timing case and the crankcase would the reed valve be effective? At all? More so than the factory timed breather? If I left the timed breather operative would that assist to equalise pressures on both sides of the crankcase and encourage oil to flow back from the timing case into the crankcase to avoid the oil accumulating in the timing case and overheating?

Or would I just be creating more problems than I would be solving (in attaching a timing case breather at all, and also if I left the timed breather in place)?

2. My second solution is totally theoretical; and a variation on the Comstock sump plug solution. And I add the disclaimer that it comes from someone who has never taken a motor apart (I’ve stripped the bike to the frame and rebuilt it totally; but left the motor and gearbox to people who know what they are doing).

Given that the Comstock sump plug breather can’t fit onto early bikes with the cross bar on the frame positioned almost directly under the sump plug, I have wondered whether you could drill right though the sump plug; run a hose out of the sump plug, and then attach it to breather in the hose. The sump plug would have to have a fitting attached on its bottom to enable a hose (or more probably a u joint to which a hose could be attached to it) screwed on to it. The hose / u joint would have to be able to be unscrewed so that the sump plug could be removed without fouling the frame cross bar. The hose would have some sort of inline breather valve attached to it – probably as close as possible to the crankcase – and then would run back to the oil tank like the factory breather, and like the Comstock sump plug breather.

Any thoughts? Flawed concept or viable? Better than a timing case breather or not? And of course the major problem is that it doesn’t exist; but I suspect that for someone with a welding kit and and access to the right parts it would not be difficult to create.

I think that the later sump plugs were made with a hole through them into which a magnetic plug screws up to attract metal scraps. I wonder if one of these plugs could be adapted to attach a u joint and hose rather than the magnetic plug. I guess an issue might be whether the hole through the sump plug would be wide enough to make the breather efficient, or whether it would be better to have a male connector pipe on the bottom of the sump plug.

Presumably this arrangement would be inherently less efficient than any breather attached directly to the sump plug or crankcase, but would it be more efficient than the factory timed breather? Again, that might depend on how wide the hole in the sump plug could be, but I suspect that it would be able to be made as big as the hole in the Comstock sump plug; I suspect the area of inefficiency would be the length and width of the u-joint and hose before the breather valve.

One further question, which might be irrelevant. In my reading for this topic, I have found (and lost) some material which suggested that the sump plug is an integral part of the oil pathway, and a diagram which should the oil pathways in the motor converging at the sump plug. Am I correct in assuming that there is no negative impact of having oil flow out of the sump through the sump plug? Presumably there is a minimum level of oil left in the bottom of the sump even with a sump plug breather.

Thoughts appreciated.

Chris, The sump plug is indeed in the flow line of the oil and in fact has a mesh filter in it held in with a circlip. I have seen people drill a hole in the inlet valve covers and run a breather off that with a 90 degree union, you can get valve covers easily and cheaply so it is not something that cannot be returned to stock if required. I myself have not tried this although I amn currently running a 1970 bike with only the timed breather and so far no issues.

Hello Chris
In your search of posts on this topic you may have come across my solution(?) to this question on my 1970 model.
I attached an XS650 reed valve to the blanking plate on the timing case via a short hose and discharged it into a catch tank because I was determined not to route blow-by gases into the oil tank.
This setup is yet to be proven over time.
I believe the timing case had to be used for my arrangement as the crankcase breathers carry a fair bit of oil and so need to be routed to the oil tank.
This modification DID of course involve drilling extra holes between the crankcase and timing case, which I did while the engine was apart for rebuild.

I think Jim Comstock mentioned once that he has drilled into cases without dismantling them, using grease on the bits and much care, but don't quote me on this.
Also, Jim said that the extra oil level in the timing case is caused by the forward tilt of the engine which was designed to be upright, not by breathing through the timing case.

Here's another option if you don't mind a fair bit of work and spoiling the bike's originality:
Remove the offending crossmember and add one in the later position, along with the later type side stand if you want one.
That's what I did, although not for the purpose of engine breathing.
I got a piece of tube from a local trailer builder to make the crossmember (the tube they use for the tie rail is exactly right for the job.) Forming the curve in it was a p###k of a job.
I bought the side stand kit from Norvil, but their fitting instructions for welding the lug to the frame were woeful. Old Britts have Andover engineering drawings on their web site which are excellent.
I didn't discover the Old Britts information until after my job was done, but luckily I got it right.

Cheers
Martin

Chris,

I'm assuming here your reason for a better breather is to stop the leaks which is usually caused by lack of negative pressure in the crank case. Couple of things.

The Comstock breather may have fit on my bike, but not while his breather was together. It may actually fit if it's taken apart, installed and then assembled again, but I'm not sure on that one. Jim may know better. My cradle is within probably 1/4" of hitting the frame brace and I think Jim said that was very close, the one he had was not that close. I just didn't want to install something I had to take apart to remove, so he agreed to take it back.

That said, I was looking for ways to stop the continual leak of oil that plagued my bike from the day I got it. First thing I did was remove the chain oiler, crimp the fitting off the small oil tank banjo and solder it shut. That didn't do much. I think my biggest leak was oil coming from the oil tank breather that goes into the air filter, oil leaking down on the filter, through that and on top of the gearbox and on down to the bottom of the cradle/gearbox where it gets blown all over the rest of the bottom of the bike. This is probably due to not using the bike every day and a full of oil crank case which causes oil to get out of the oil tank breather. I had my engine apart and was very reluctant about drilling holes, like you, but mainly because I didn't understand what is going on, so I opted to just put it back together as built and see what I could do. Well, short of it, when it got back together, there was oil on the bottom of the engine after a run. I did 2 things. Installed a ball valve in the oil feed line to shut off the wet sumping 'problem', which is most likely not a problem. Other thing I did was install a catch bottle off the oil tank breather by threading a stud with a hole in it into the breather, taking it out of the air box and routing it into a catch bottle. Since I've done those 2 things, the bottom of the engine is dry and clean.

Now what exactly have I done? I can only assume the ball valve stops the wet sumping and that may stop some leaks from the engine. The catch bottle certainly has stopped any leakage from the oil tank into the air filter. The timed breather is working as good as it can. But I have to say, I never have to empty any oil from the catch bottle. If I didn't have the valve on the oil line it very well may have to be emptied regularly, I'm not certain.

I did think of removing the top of the oil tank and re-arranging the oil lines in there. The line that goes into the air filter goes through the oil in the tank and curves up into the top hat thing on top of the tank. I'm assuming this is their attempt at making a breather/separator so a minimal amount of oil/vapor gets into the air filter. I wonder if instead of just going straight up into that top hat, one would make a loop in it, so it points back down, sort of like an upside down 'P' trap if that wouldn't stop a lot of oil into the air filter without a catch bottle. I don't think it matters where the breather from the timed port goes into the oil tank, mine goes into a spigot on the top hat gizmo, but the later tanks had it going into the top of the main tank. I wonder if this wasn't an attempt to stop oil from getting into the air box breather? Other thing to do is block the oil tank breather from the air box and just take it to the air or a catch bottle. Actually I had my oil tank breather at one point dripping down with a hose below the bike, but it still dripped and made oil all over the bottom of the bike, that's when I put the catch bottle on.

Jim has not recommended using the ball valve for the oil feed line because I understand he thinks it's better to have more oil in the engine via the wet sumping to keep the cam lubed better on start up. It's probably a valid point.

All I can say is it's working for me right now, I'd rather have a better breather (and ludwig's cam trough), but I'm not going to take the engine apart just for that.

Dave

A cheap and cheerful approach to lowering internal engine pressure on the early bikes is drill a hole in the exhaust valve cover, screw in a elbow, then run a hose, either to atmosphere or to a small bottle to pick up the odd drop of oil that might work its way out. I think the ID of the hose I used is about 1/2 inch. It seems to have reduced oil leakage around the gasket joints on one bike and reduced smoke coming out of one exhaust pipe at idle on another bike. If you want, you could add a one way valve in the hose to further reduce pressure.
Stephen Hill

There are some fantastic reed valve products on this site. I will fit one on my 750 shortstroke when I finish the build.

A simple solution is to keep what ever 750 breather you have and add the 850 breather back to a catch bottle or tee to the tank. Works fine, even on combat breather style.

Chris:

I have an Atlas with the timed breather, and share many of your concerns.

First, installing another breather port in addition to the timed breather is likely to be ineffective unless you block the timed port.

Secondly, I don't think the timed port is effective (to obtain negative crankcase pressure) as a reed valve type, but a reed valve in series with the timed port (in the tube attached to the timed port) may be very effective. But this arrangement raises concerns with me as to oil mist fouling the reed valve, unless the reed valve is mounted high with a gravity drain back to the oil tank.

Thirdly, Jim C has advised against tapping the rocker boxes for a breather line, as the breather air will be counter flow to the returning oil in the oil galleries.

I am in the process of testing various reed valve configurations on the Atlas. I have modified an XS valve to screw directly into the timed port. Unfortunately, the Atlas is down waiting on a cam ring. It will be awhile before I can report results.

Guys, thanks for your responses which are appreciated. The range of experience and opinion is interesting.

MFB – I had read your posts and noted that you had drilled your timing case; that is the issue for me; I don’t want to do that; I had read Jim Comstock’s post about it being able to be drilled with expertise; but I don’t want to risk it here unless I get someone that I am really confident about to do it.

And while I appreciate the suggestion of moving the frame support, that is not really an option for the same reason that dismantling the engine is not; I have had the frame powdercoated during the rebuild, and I don’t want to cut it up and attempt to patch it now; and I suspect that the cutting and welding involved would be best done with frame separated from the rest of the bike. For me the stand is not so much an issue; a past owner had replaced the stock side stand with a T120 stand mounted on the standard Norton frame attachment, which works well, apart from the difficulty of sourcing a spring of the right size and dimensions for the hybrid arrangement.

DogT I had also read your post and have pretty much decided that at some point reasonably soon I will put in a catch bottle from the oil tank overflow: I don’t suppose you have the diameter of the outlet tube handy so that I can buy some plastic tubing before I start taking the air filter cover off? Incidentally a past owner of my bike had rerouted the breather tube away from the oil tank and into a catch bottle; I reverted to a stock arrangement when I rebuilt the bike; but I am considering doing that too. I also suspect that a lot of my oil is coming from the oil tank overflow; it intensified after the last oil change.

I had seen threads referring to breather tubes run from the valve covers, This seems to have been a system that has been adopted from relatively early days. But I note the concern that the breather air will be counter flow to the returning oil in the oil galleries. I don’t really understand how this works yet; I need to look more closely at some diagrams of the motor and cylinder head. I think that pressure from the crankcase can come up through the pushrod cavities into the cavity in the cylinder head where the rockers are. Jim C appears not to endorse this breather:

“The area around the pushrod tubes is large but the area around the lifters is not. I have seen racers that tried venting from the head and ended up with a flooded head and a serious smoke trail.”

TexasSlick, I note your suggestion of putting the XS650 valve in series with the breather valve tube, which was my original intention. But will that work? I can see two possibilities.

First, If I understand the function of the timed breather correctly, it only opens when the slots in the camshaft align with the breather hole; so in a sense it is already like a reed valve; open at a time of high pressure to allow exit of pressure; closed when pressure reduces to discourage blow back. Therefore if you put a reed valve beyond that don’t you create a situation where when there is sufficient pressure created between the timed breather and the reed valve the reed valve will open and release that pressure, but the timed breather is already preventing blowback into the crankcase, so you are possibly creating pressure in the cavity that discourages pressure from leaving the crankcase through the timed breather? Jim C has said about this:

“Installing a reed valve on the timed breather is of no benefit. The cam breather is already timed to open and close at the correct time. It's only problem is the tiny hole through the cam is not large enough to carry the volume of blowby created by an engine that has some miles on it. Adding a reed there will not help that problem. Jim”

Second (as I suspect you think will be the case) the insertion of the reed valve will create a vacuum between the timed breather and the reed valve when air is expelled through the reed valve, which will encourage more air to be “sucked out” of the crankcase when the timed breather is open. If that happens the addition of the reed valve will be an enhancement to the existing situation, but presumably will not make such a difference to a timed breather motor as to a motor that just has an open breather that can draw air back in as well as expel it. I had understood from Jim C’s posts that he considered that the addition of a reed valve in series with a timed breather was more likely to inhibit the effectiveness of the timed breather than to enhance it; it will be interesting to hear your results.

If I understand Nortiboy’s response correctly he is suggesting that I stick with the existing breather, and then put in an 850 style breather. Is that just a ujoint and a hose? Do the 850s have any greater cavities between the timing case and the crank case than the 1970 750? Which then begs the question if I have a hose from the timing case will I do any harm in putting an xs650 valve on it? I see that is exactly the set up that Roadrash has on his bike.

I think that Jim C takes the view that a breather from the timing case will be less efficient than a crankcase breather:

"Having a reed close to the engine may help with condensation problems as it will run hotter but it will not create a vacuum at higher engine speeds when the large area of the timing chest is there to dampen the pulses. Jim"

So right now I am not sure what to think. I do recall one forum member saying that he had issues with an XS650 valve and eventually took it off; I can’t find that thread right now, but I think that he was referring to an accumulation oil in the timing chest. That must be a risk without an additional drainhole being added.

I think I will mull it over for a while yet; but in the meantime will run a tube from the oil tank overflow to a catch bottle as per Dave’s solution.

You could remove just TS cover to tap a vent in the mag face area and mount the reed valve or a MotorMite brake valve in line to expel what the cam one can't. Its not a bad idea to put check valve on the cam hose so it don't suck back what the TS vents out below ambient. A decent light action check valve will not hinder the cam breather. I wonder if a manifold vacuum pulse operated fuel pump might draw off enough to seal w/o dribbles.

Chris T, I got my 750 from a top kiwi norton specialist in New Plymouth. Combat breather and 850 breather. Combat breather to tank and 850 breather to bottle. He liked to open the motor up so it had less chance of building crank pressure rather than create a negative pressure with a reed. Bike goes hard and does not leak a drop.
Unless your racing you probably would not pick the difference.

Chris,
The catch bottle for the oil tank breather is problematical. I used a 5/16 bolt, cut the head off, drilled it through the center, so I had a 5/16" 'close nipple' we call them here. You may be able to buy one in brass, or even a pipe thread of that dimension with a proper hose nipple on it. Then I tapped the oil line in the tank where it goes into the air box with a 5/16" tap, threaded the nipple in that and glued it in with JB Weld. Put a hose on that and brought it out the front of the ham can cover and just dropped it down between the engine and GB with a large size pill bottle with the hose going in one hole in the top and another hole to the air. I did buy a real catch bottle but have not done anything with it. Fortunately for me, the PO had put a hole in the ham can cover that I put a rubber gasket in to feed the hose through. It makes taking the air box off a job, but I always seem to have to take the carbs off to get mine out anyhow, so it's not a big issue for me.

You could just as easily add another breather in the oil tank, take that to a catch bottle and block off the one into the air box, but I suppose eventually it will fill up with oil, but so what as long as it doesn't leak.



I bought an extra central oil tank with plans to try to re-arrange the breather system to my liking, but haven't gotten around to it.

Dave

My sump plug breather will not clear with your frame crosstube. I have tried a couple of different designs trying to get something that works well with that frame but I haven't had very good luck so far.

The extra length of hose required to get from the sump plug to a point where there is enough room for a reed block has dampened the pulses enough that the reeds will not resonate with the crankcase pulses, and then it becomes nothing more than a pressure relief valve. Not that a pressure relief valve would not help -but it will not create the depression I was looking for at cruising speed.

Sorry I don't have any good suggestions on that one without drilling somewhere. Jim

Comnoz - Maybe a "hard" hose/metal tube that won't pulsate and thereby attenuate the vacuum signal? Determining the diameter of that tube would be problematic, balancing volume against signal against routing.

he extra length of hose required to get from the sump plug to a point where there is enough room for a reed block has dampened the pulses enough that the reeds will not resonate with the crankcase pulses, and then it becomes nothing more than a pressure relief valve. Not that a pressure relief valve would not help -but it will not create the depression I was looking for at cruising speed.

Click to expand...

Thanks Jim; I think I am now beginning to understand the difference between your breathers and the others. Assuming the only viable option for me is a 'pressure relief' type of valve do you see any negative in me attaching a reed valve direct to the timing side cover? In particular I note you past comments about the oil level in the timing case. And are there enough cavities between the crankcase and timing case to make that work (to some extent) without additional drilling?

xbacksideslider said:

Comnoz - Maybe a "hard" hose/metal tube that won't pulsate and thereby attenuate the vacuum signal? Determining the diameter of that tube would be problematic, balancing volume against signal against routing.

Click to expand...

A rigid tube will not mitigate the damping Jim is talking about. The volume pulses ejected thru a long tube are damped due to the interacting effects of viscosity, density, and frequency. In short, the crankcase pumps up with increased RPM due to the damping of the ejected volume. Best to mount the reed valve close to the crankcase, or keep the lead-in tube short.

The happenings inside a tube with air (or any fluid) moving back and forth in response to a cyclical pressure signal, becomes rather bizarre to the layman when the frequency of oscillation gets high. The value of "high" depends on the interrelationship of density, viscosity, tube diameter and length, and frequency. I am certain "high" is within the range of a Norton engine. PM me if anyone wants a more detailed explanation.

Slick