New owner oil leak help

New to the Norton club, loving it so far. Wanted to ask for some help on a leak I can't get a grasp on. I was able to eliminate 2 oil leaks but one remains. Here are the symptoms. I have. 75 mk3. This leak only leaks while bike is running, from what I can see it is coming from a area near the front chain sprocket and the oil runs down the inner primary case and drops just behind the left center stand foot. At idle, the leak rate is approx 1 drop every minute, and stops when the bike is shut off. I have drained the crank case of oil and this did not change this leak. Thanks for any help. I am away from my bike for a week, wish I snapped a picture under there to share, hope my description makes it understandable. My bike doesn't leak a drop while sitting, but after 5 minutes of idle I get a few drops from this last remaining leak.
Ride safe

Only A Few Drops .? :? . :wink: :mrgreen:

Yes. About 5 drops in 5 minutes at idle power. Afraid it be worse under heavy power and all day riding. Again only leaks while running. Not a drop as it sits

This leak only leaks while bike is running, from what I can see it is coming from a area near the front chain sprocket and the oil runs down the inner primary case

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You have a classic case of crankshaft seal blow by. You can change those seals until you are dizzy and it will still leak. The problem is the crankcase itself is being pressurized. This can be caused by piston ring blow by or a crankcase that is not properly ventilated. If it doesn't have a proper PCV valve, then, by all means, install one. The XS 650 PCV valve (scroll down) works well and is cheap. The CNW breather modification] is a very sanitary installation. Those in the know say it's more effective. What ever you do you must eliminate the crankcase pressure in order to have an oil dry Commando.

Thanks Jim. I will give it a shit for sure. I must say for the price diff I am inclined to go with the 650. I assume this is just a in line hose install? Doesn't get any easier than that. Does this need to be secured to the bike? Requires drillIng. Thanks again for the intel

Here's one way.

If your leak is from around the front sprocket of the drive chain, it sounds like you've got oil dripping out the oil seal behind the clutch. Could be the seal is bad, or is leaking because of a pressurized crankcase. The Mk III has a different primary case than the earlier models, and has a seal around the main shaft, rather than the felt of earlier models. Check the level of the oil in the primary. Too much will encourage leaks. You want just enough to keep the primary chain and that MkIII tensioner lubed.

A trick I use is I run oil in the engine (Valvoline VR1 40W), ATF in the Primary (Type F which is supposed to be better for the bronze clutch plates) and gear oil in the tranny. This way, you can tell where the oil is coming from. If its thick and smelly, the transmission has a leak; if its red, the primary is the source; otherwise its the engine. Since you have a MkIII, you may want to keep regular oil in the primary, because of the tensioner, or you could use a mix of oil and ATF.

As others have posted, the crank seal is susceptible to a pressurized crankcase. This pressure can cause air to escape into the primary, pressurizing the primary, and cause a leak at that rear seal. Either the XS 650 breather valve or the Motormite #80190 brake booster check valve will eliminate this problem. The motormite unit runs around $6 and is found at many local auto parts stores in the US. Mine is in my breather line, replacing the adapter from the large hose to the smaller hose, right near the top of the oil tank.

Either the XS 650 breather valve or the Motormite #80190 brake booster check valve will eliminate this problem.

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I've tried the Motormite check valve. Many, in fact. They are a placebo, at best. If you have a belt drive primary you'll find the Motormite valve won't do the job.

Xs650 on the way. Any install info or gotchas to look out for? If anyone has pics of what hoses to mount up to for a mkiii I'd appriciate. Look forward to giving this a try when it arrives

Jeffmack, just to be sure your not just the victim of the typical over full primary do to the bike sitting and having oil seep in from the crank case after wetsumping open the "level" plug on your primary & see if it's not a bit to full. Doesn't take much. My bike sat when I first got it, When I road it I had a leak from the same spot as yours & the guys here told me to check the primary. It was to full so I drained it, cleaned the oil that had come out & all is fine.. Your bike like they told you may be differant and not leak like us with the "antique" kick start only but I'de try it. Good luck.

Hi

I have in order such valve to a 650 xs
I wonder where I should mount it. Want to mount it directly in the crankcase, (between the crankcase and starter, if there is enough space).
Will such placement be a problem for the valve, then I think of the vibrations from the engine? Viewing the valve to the CNV, is mounted in the crankcase.
If I mount the valve here, I may let the tubing go down below the engine, in order to get a cleaner look.
Assumes that, with such valve, it is mostly air that comes out of the hose?

Vidar

I noticed that no one mentioned the simple fact that there could be too much oil in the crankcase. Depending on where and how the oil tank vent hose is routed, the oil may show up anywhere. If this person is new to Nortons, it is very common to overfill with oil.

donmeek said:

I noticed that no one mentioned the simple fact that there could be too much oil in the crankcase. Depending on where and how the oil tank vent hose is routed, the oil may show up anywhere. If this person is new to Nortons, it is very common to overfill with oil.

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Also, the primary is not a pressure vessel. The crank seal could be totally blown and the lower mounting bolt holes for the primary to crankcase could be loose and weeping like an American Idle looser. The primary cases themselves could be tweaked due to poor shimming of the inner primary case.

All these should be checked and secured. The breather valve is all well and good but thinking that it should cure general faults as stated above is like think that the valve would produce such a vacuum that crankcase would suck the primary dry back through the lower bolt hole and over fill the tank.

The unit should not drip, period.

The valve is meant to lessen the severity of the pressure. All cranking unit may produce a moment of vacuum and I believe the valve increases this moment and in this regard takes away from the moment of pressure thus equalizing the inner environment to be closer to ambient.

Don't fix the problem by adding a valve, fix the problem then add a valve.

Got it, will check the level when I get back in town. The inner primary was replaced last month, but the leak was there before as well. Does it make sense that is a overfill problem due to the leak only occurring while the bike is running? It never leaks just sitting in the garage. Thanks

Don't fix the problem by adding a valve, fix the problem then add a valve.

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If the problem was fixed by adding a PCV valve wasn't the lack of same the problem? How are you going to fix the problem if the only problem is crankcase pressure?

Granted, there may be other causes for oil leaks other than crankcase pressure. Why not eliminate the crankcase pressure first, then if you still have leaks further investigation is warranted. There may be multiple causes for leaks, but you got to get rid of the crankcase pressure regardless.

Jeffmack, ya got different schools of thought here. In the end it's your choice and comfort level.
I do not want argue with Jimc's logic, but for me, I feel that these bikes should not leak and crank seals and loose threads should not be exceptable breathing points. Granted, many Nortons, maybe most, leak. Mine does not with or without a valve.

I, myself, would exhaust all efforts to seal things proper. It's too damn cold to ride and what else would i have to do.
Quite frankly, I love doing shit like this and am anal about getting it right. After that let the valve do its thing.

But hell, that just me.

There are two types of Commandos, those that leak oil and those that will leak oil. To me, installing a proper reed-type PCV valve lastly is backasswards. Any vessel that is pressurized will more likely leak oil than a vessel that has a vacuum. Having all joints and seals properly sealed is a given with any competent engine builder. I am in no way advocating that a PCV valve should be used to compensate for poor craftsmanship. I, too, had a non PCV valve Norton, a 1969, that was a non leaker after I rebuilt it. I suspect it was the rotary breather of the 1969 Commando that made it so. The 1972 Combat I have now leaked and weeped in more than one place until I got rid of the crankcase pressure.

Jim, your posting history indicates a curtain passion for the Yamaha XS 650 PCV valve. Passion is good.

There is one thing we can agree for sure. Reduced crank pressure in good.

Just let me say this, although we seem to be at odds somewhat today, we are more alike than it would appear.

Jeff, you should still change out the crank seal. An hour of work and $3.

Hey Jeffmack, to answer your question about the combo of only leaking when running and posible over full fluids. Yes it makes scence both ways. I think your primary is differant then my 73 but when my primary was just to full it only leaked when running. And the same might happen if your crankcase is not venting well enough too. But try the simple things 1st & let us know please.

Jeff, you should still change out the crank seal. An hour of work and $3.

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I doubt the crankshaft seal is faulty. Changing it is a PITA. Why not get rid of the crankcase pressure first? You know the case is being pressurized. Why not eliminate it? I'm not trying to be contrary here, just logical. My personal experience of constantly changing crankshaft seals, finding an expensive "super" seal, only to find it still leaks oil. When I installed a reed type PCV valve not only did the crankcase stop leaking, so did the tach drive. Your advice of changing seais is akin to advising someone with an internal infection to use a topical ointment.

Maybe my bike was extraordinary, but I've seen a lot of posts here with the same problem. Leaking crankshaft seals. It's rather infuriating to see someone advise changing seals to correct the problem when I know better.