Breather query

I know this subject has been done to death and believe me I have read most if not all of the threads over the last week.

My bike a 1971 Commando has two breathers, the timed breather off the Camshaft and the one out of the timing case at the rear.

After playing around with a few different options and ending up with pil all over my rear wheel on a few occasions I need to sort it before I go out again, or else I fear I may end up in an accident

When it came the timed breather attached to the top inlet of the oil tank as originally it would have, the breather from the timing case was blanked off.

Last night I plumbed the timed breather pipe into a HRC vented catch tank I had, once the bike warmed up it was putting about the same amount of oil into the catch tank as the oil return feed does :shock:

So this morning I put a small piece of pipe with a one way valve on each of the breathers and warmed the bike up.

If I put my finger over the timed breather pipe to block the air nothing happened there was little or no air coming out and no oil.

However if I put my finger over the breather from the timing case in the same manner oil immediately started to puke ou oil in pulses out of the timed breather pipe. having never owned a Norton before Is this normal ?

The question is do I run both breathers up to the oil tank or blank off the timed breather and only run the breather from the timing case to the oil tank.

Chris

Your problem seems to be more about your oil pump bypassing from the oil tank into the sump, where it then becomes a problem of too much oil in the crankcase that then gets pumped out by the breather(s).

It's kind of simple, but maybe the simplisity eludes some people. Breathing isn't what you want, so just having a breathing port drilled into your case just makes your bike push air back and forth. Instead, you want your breathing port (or ports) to have a reed valve or a disc valve on them, so when your pistons come down they push the air out, but when they go back up they close the port to keep air from moving back in and repressurizing the crankcase. Your timed breathing port has a disc on the end of the camshaft that NEEDS to be turning with the cam shaft in order to open and close. You should verify that the breather disc hasn't stripped the teeth that hold it in place on the camshaft and it turns with the camshaft.

The secondary port that was added needs to have a reed valve on it as close to the crankcase as possible to be most efficient.

Personally, I have both of those ports opperating on my 70 commando without a problem. I return both hoses to the oil tank by having a "T" in the line up by the oil tank. At start up, of course more oil returns to the tank via the oil return line and the breathers because of oil leaking down into the crankcase when the bike hasn't run for a week or more, but after it pumps the sump out, it should be mostly air, but not all..

If both breathers are working, you should be able to plug one breather and feel the other one pulsing as the engine runs. If you can't then maybe your timing disc is broken... as I said above.

It's a pretty simple thing when you look at it.

Edited to add: If your timing disc has failed in the open position, you can insert a reed valve on the return hose and get that port to operate again. If it's failed in the closed position then it could be more involved to open it and keep it open to use a reed valve inline as a substitute. Some people actually block the timed breather. (as you probably know) I didn't block mine for a few reasons. It doubles the engine's ability to drive air out of the crankcase, and it pulls an oily mist toward the camshaft galley and bushings when air is forced out the port...

You might also check your oil tank to make sure it's not cracked and leaking back on to your tire as well.

Could be the oil pump, I am certainly no expert on Norton engines having never owned one before. Bike does wet sump after while of being left however at present it is in use due to the Lovely summer weather so no or little sumping.

Is there anyway of checking if the timing disc is either installed or at least working without taking the engine to bits, not something I want to do over the summer.

I have valves on both breathers at present whilst testing and only the timing case breather allows air out during normal running, the timed breather does not allow any air out of the valve until I block the timing breather so at least something is working in there.

I run 2 breathers. The more active one goes to the oil tank and the other to atmosphere. Putting in a "Y" or a "T" seem self defeating to me.

If you unscrew the breather elbow, you should be able to peer in at the camshaft end and see if you see the timed disc rotate past as the engine is kicked through...

Thanks will try that tomorrow and see what I get

Spent the evening riggin up the timed breather back direct to the oil tank, and the timing case breather to a catch tank with its own vent leading to an air filter, only a temporary measure but will see how much oil ends up in the catch tank in the morning when i take her out for a ride.


Chris

Yes,it's easy to see the timing disk when you remove the elbow from the crank case, remove your plugs to make it easy to turn the engine over. There's another breather maybe you don't know about, it's the tube from inside the oil tank 'top hat' that runs through the oil and out the front of the oil tank, in the air intake area. That one, I threaded with a close nipple and ran a hose to it through the chrome air box cover and into a catch bottle. There is a certain amount of oil that comes out of that hole, but not much, mostly vapor, but mine for some reason put out a lot of oil and it was always dripping down from the air cleaner onto the top of the gearbox. The catch bottle fixed that. The breather you have off the timing chest is not original, someone added it, and like others have said, you need some sort of reed valve on that line, you can run that one back to the oil tank or catch bottle. There are instructions on drilling holes from the timing chest into the crankcase, but I've never done that and am also not clear on how that works. Jim Comstock makes a nice valve that fits on the crankcase drain, but it won't fit in 71 and earlier bikes because of the tube between the frame down there.

DogT said:

Jim Comstock makes a nice valve that fits on the crankcase drain, but it won't fit in 71 and earlier bikes because of the tube between the frame down there.

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It fit on my 71 roadster just fine, and works a treat! In addition to more efficent breathing, if your bike does wet sump while sitting four or five kicks with the key off is usually enough to return sufficient oil to the tank so you can start it.

Well looks like problem is sort of solved, test run this morning and a spoonful of oil in the temporary catch tank from the timing case, no other major leaks other than the slight weap from around the sprocket area which has always been there and I can live ( when it stops leaking I will get more concerned ).

I saw your mod with the drain through the front of the airbox and it looks great> If I can get a suitable permanent catch tank I will fit it below the airbox in the space, your right I cant fit the Comstock one due the cross member, I have seen a few old style VW campervan ones though that look really cool so they might fit.

For now though the concerne about oil on the rear tyre has subsided and I can enjoy the ride

Thanks for the help so far

MikeG said:

DogT said:

Jim Comstock makes a nice valve that fits on the crankcase drain, but it won't fit in 71 and earlier bikes because of the tube between the frame down there.

Click to expand...

It fit on my 71 roadster just fine, and works a treat! In addition to more efficent breathing, if your bike does wet sump while sitting four or five kicks with the key off is usually enough to return sufficient oil to the tank so you can start it.

Click to expand...

I'm running Jim's crank plug breather on my 71 as well, the lower frame tube was on 70 and earlier bikes I believe. Jim's breather works well, and clears the sump of oil within a few seconds. I'm still considering adding the second breather to the back of the timing chest, though I've been told the effect will be negligible without the inner case drilling.

OK about the 71 and the brace tube. I wonder if that tube changed when they changed from the central to the side oil tank, I think it may have something to do with the prop stand, that changed about the same time too.

As far as a catch bottle, I found a nice aluminum one that should be easy to mount somewhere, and it was less than $20, I forget where I found it. The tube out of the front of the air cleaner is a pain, but I've always just taken off the carbs to change the air filter anyhow, so I've gotten used to it.

DogT said:

OK about the 71 and the brace tube. I wonder if that tube changed when they changed from the central to the side oil tank, I think it may have something to do with the prop stand, that changed about the same time too.

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You were a year out that's all. You should've said '70 and earlier.

Just a quick update really.

The timed breather now runs by itself to the top of the oil tank, the breather from the rear of the timing case (non return valve inserted in the line) runs upto a seperate catch tank held in the right hand side cover with the drain running alongside the battery drain tube to the bottom of the bike via a clear tube. From the catch tank runs another line to a final air filter located at the rear of the bike behind my small pannier bag.

After a few decent runs the oil leaks have almost stopped completely with no drips to speak of, the catch tank is almost empty and at this rate will only require emptying very infrequently.

Farmboy said:

Just a quick update really.

The timed breather now runs by itself to the top of the oil tank, the breather from the rear of the timing case (non return valve inserted in the line) runs upto a seperate catch tank held in the right hand side cover with the drain running alongside the battery drain tube to the bottom of the bike via a clear tube. From the catch tank runs another line to a final air filter located at the rear of the bike behind my small pannier bag.

After a few decent runs the oil leaks have almost stopped completely with no drips to speak of, the catch tank is almost empty and at this rate will only require emptying very infrequently.

Click to expand...

I think your experience and mods show the timed breather is ineffective as a one-way valve, as I have long thought.

Slick

The timed breather on the end of the Norton cam was designed for a 500cc twin. Actually it worked very well even on bigger motors providing the cases were not full of oil when starting the motor and as all gear oil pumpspass oil when not in use .....unless you have a Gentleman in Birmingham modify your timing cover to include the fail safe anti drain valve system ......! As the pistons come down the compression in the cases escapes through the open valve...pistons go up and valve is closed allowing no air back in...after a few cycles crank case pressure has reduced to a very low value and engine leaks have reduced..... Trouble was people later in the British bike industry knew little or sweet nothing about engine breathing along with other subjects and thus we ended up with those rediculous Combat crank cases and their joke of a breather system....Triumph totally lost the plot and removed the crank oil seal to allow engine oil into the chain case so as to maintain the oil level in the chaion case as the service dept had found the average owner ran their primary chains dry and rusty......but at least they included 3 small drain holes back into the crank cases to maintain the required oil level!!.... thus gave a nice big plenum chamber for the crankcase to breath into as the pistons went down and to suck it all back in again as the pistons went back up resulting in a pressurised crank case....Then some idiot, at Umberslade Hall?, went and on the B50 motors removed the crank oil seal BUT FAILED to include in the crank cases the 3 small drain holes that regulated the oil level in the oil bath chain case.....I have the maching drawing for the D.S. cases and the3 drain holes AINT included nor were they included on the very last batch of crank cases machined for Jeff Clews and his CCM motors...a friend machined them. (71-1412. Iss 17) This results in oil flooding the clutch and clutch slip problems.....clever eh....
Funny but no one I can see has quoted crank case pressures recorded with their various systems. It cannot be difficult to do because Bob Oswald did such testing on Triumphs as long ago as the 1970s. He told me a very early Triumph system worked very well and was so cheap and simple they did away with it....run the breathers back to the oil tank and on the threaded filler cap shove a tiny hole in it. Pistons come down and pressurise the tank..pressurised air gets shoved out of hole but very little air at atmospheric pressure outside gets pulled back in as the pistons go back up....after a few cycles crank case pressure settles down to the value Bob told me he recorded.....go do your own testing !! Best idea of all in my opinion that is to run ALL brather pipes back to the oil tank and shove a BMW reed valve assembly into the top of the tank. As the motor fires up you can hear the reed working but it soon stops as pressure is reduced to getting on for sweet nothing....Appararently BMW did a lot of research into motor cycle crank case breathig many decades ago.....And no I did not bother to measure oil tank pressures....did not have the time.
In my younger days people (exspurts?) would run large bore pipes from the crank cases to the rear of their race bikes breathing toatmospher using the crank cases as a compressor and wasting horse power........
Ever read the section on crank case breathing in the book 'Tuning BL's A Series Engine'? David Vizard ISBN ......0-85429-732-4. It is rather iteresting. Your local library should be able to obtain a copy for you..... ASSUMING you still have one........

BL's A series engine is a 4 cylinder engine, 2 pistons are raising as 2 are falling, not like a 360 vertical twin as all as it has virtually no change in volumes under the pistons whilst it's turning, the extra air comes from blowby etc.

J. M. Leadbeater said:

Triumph totally lost the plot and removed the crank oil seal to allow engine oil into the chain case so as to maintain the oil level in the chaion case as the service dept had found the average owner ran their primary chains dry and rusty......but at least they included 3 small drain holes back into the crank cases to maintain the required oil level!!....

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....Only, they don't! :roll:


If you had ever examined a 1970-on Triumph crankcase then it would (should) be fairly obvious that the three (extremely) small holes aren't going to maintain the primary oil at what you might consider to be "the required level" in fact they are hardly any distance below the level of the open case/bearing!

The green line in the picture below represents the previously recommended 350cc level prior to the deletion of the drive side oil seal ('70-on). The yellow line is level with the three oil holes (the height of which, as far as I'm aware, was never altered)!

It was the late Doug Helne, who in his post Norton days devised a way of curing the oil leaks on the unit construction Triumph 500 twin when making a 500 that later won the Daytona 200 miler beating and upsetting the H/D s
There was an article in the Motor Cycle weekly on the winning 500, ( which later was sold as the 500 Daytona) all he did was to fit a top engine from the rocker box breather tube and drill three holes into the inner crankcase to the adjoining chaincase and Hey Presto! No oil leaks
I cannot comment on this system as I have never had a post as I have never owned a post ‘70 Truimph.