Smokin... and I don't mean in a good way

It sounds like oil in the intake to me too. If some rebuilder (not familiar with Nortons) has just "knocked the guides out" then the oil may be coming around the outside of the guides. You might be able to look in the inlet valve cover and see if the seals have come off.
Have someone ride behind you and see if it smokes on deceleration also (engine braking). The vacuum on the intake side is highest when the throttle is closed. This would be a good clue.
Russ

Hi Chris:

I am working on a not dissimilar problem with my 1974 850. When I first purchased it and when it was wet sumped, my Commando would always produce voluminous quantities of white smoke at startup. Through trouble shooting and varied attempts at fixing the problem, (rebuilt head with new valves and seals, bore honed and replaced piston rings) I have learned quite a lot of relevant information, (primarily from this forum, an excellent local bike mechanic and youtube videos).

For me what it finally came down to was a previous owners poorly executed re-bore to .020 (.002" too wide), incorrectly installed oil control rings and otherwise generally poor quality piston rings. My other Norton, (650 twin) starts (even when wet sumped) with no smoke at all, ever! The big difference I attribute this to is that it was re-bored by a an expert and has high quality pistons with Japanese rings from Jim Schmidt. I am in the process of doing the same for my 850 in the confident expectation it will resolve my smoking issues.

Removing and refitting the head and barrels is relatively straight forward. The only thing I found a bit interesting were the valve pushrods. Rather fiddly and pretty much impossible if you do not use the correct technique. A decent shop manual is a must. Access to someone who has done it before even better.

Cheers,

James

concours said:

There is SO MUCH MORE than YouTube videos.

I would respectfully suggest you need a talented mechanic to help you.

50 years repairing engines, including fixing work the "pro shops" porked.

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I 100% agree a skilled mechanic should look it over, but alas there are none in my region (San Diego, CA), and I dont possess the resources needed to ship it elswhere.

Britstuff said:

Hi Chris:

I am working on a not dissimilar problem with my 1974 850. When I first purchased it and when it was wet sumped, my Commando would always produce voluminous quantities of white smoke at startup. Through trouble shooting and varied attempts at fixing the problem, (rebuilt head with new valves and seals, bore honed and replaced piston rings) I have learned quite a lot of relevant information, (primarily from this forum and youtube videos).

For me what it finally came down to was a previous owners poorly executed re-bore to .020 (.002" too wide), incorrectly installed oil control rings and otherwise generally poor quality piston rings. My other Norton, (650 twin) starts (even when wet sumped) with no smoke at all, ever! The big difference I attribute this to is that it was re-bored by a an expert and has high quality pistons with Japanese rings from Jim Schmidt. I am in the process of doing the same for my 850 in the confident expectation it will resolve my smoking issues.

Removing and refitting the head and barrels is relatively straight forward. The only thing I found a bit interesting were the valve pushrods. Rather fiddly and pretty much impossible if you do not use the correct technique. A decent shop manual is a must. Access to someone who has done it before even better.

Cheers,

James

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Sounds similar indeed. But mine is only on one side... would that be odd? I mentioned I have the tools and capability, yet I also possess a fear of opening the head and having it jack-in-the-box all over my garage. I'd rather have a pro-mech do it... if one was here. Just like when I replaced all my isolastics,,, its gotta start somewhare.

Thanks for the tips.

The only way you will get to know your bike is to do the work yourself, the head pull is not a hard job at all, but remove the valve covers first and inspect, even the pros gets things wrong and if it's only done low miles then something wasn't done right, maybe too much oil around the rings and pistons when rebuilt and the rings haven't bedded in, but look at the simple things first, do what the workshop manual say when pulling the head and reinstalling and can't go wrong, a lot of people do tricks to hold the push rods when installing but all I do is use my fingers to hold in place while installing the head and when the head is on make sure the push rods are sitting in place on the rocker arms before tightening the head down, hard to see sometimes and a small screw driver helps.

Ashley

In my humble opinion, (because there are many people who frequent this site who are way more experienced than me): If you can replace the rear iso's on your Commando, then you clearly already have the necessary lateral thinking skills. If it was me I would first torque down the head, check valve clearance. Then ride it some more and see what happens. Give it the old italian tune up (within reason of course), maybe the rings hav'nt quite bedded in yet. Then if no improvement, sounds like you are going to have to down a few and work yourself up to do a bit of a tear down. Start with checking the inlet valve seals and then follow the trail as far as needed. Hope you don't have to get into it too deep. That said you know you will be a much more knowledgeable owner once the job is done.

P.S. My Commando also liked to smoke mostly on the left. Although the the right had its moments. Plugs were nasty and oily.

My Commando is my first classic bike and only my second bike ever. I was able to R&R the head, in frame following the manual, the tips & suggestions on this forum and by watching a few of the videos I posted earlier. The rear iso was a much greater challenge...virtually no videos of that operation in frame exist, book says to remove engine; but got it done after much research here. Definitely more work than the head as I recall. Only thing worse would be the horn R&R ;-)

concours said:

Not always blue.

Modern oils, and HOW HOT it gets determines the color of smoke. (Depends on where it is coming from) intake valve stem, rings, exhaust valve)

One poster here dumped white smoke for the last four seasons, saw it again & again.

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And here's why

Not saying these are your problem, but they did not require any major surgery, so worth checking: I had left side smoking on my 850, but only after it had been stòod for days on the sidestand. I also had a leaky head, which I could hear if it got close + oil leaks from the head and the rocker covers.

I cured it without taking the head off.
- I found a pool of oil in the head, visible through the rocker cover. I had a slight obstruction in the right side oil drain hole in the head, cleared with a bottom E guitar string (+ poking the hole with the string was how I found the obstruction);
- Some (most) of the head bolts were not tight. The engine had been rebuilt 4,000 miles earlier, so I suspect it had not been re-torqued;
- I also fitted a reed valve in the oil return line to help manage crankcase pressure;
- I put the reusable JS Motorsport gaskets on the rocker covers.
This sorted the leaks and smoking and the bike has run like a young puppy since (5,000 miles). I've checked and the bolts have remained tight.

As an aside, in my case, the read valve was transformational. It smoothed the engine and it generally felt very much happier.

You can go dizzy thinking of all the possible causes, so write a list and eliminate them one by one. But first list the causes and order them with the easiest to fix at the top and the hardest at the bottom. Then start at the top of the list. That way when you do find the problem you will have done the least amount of work.

So start with leaving the bike for 2 weeks, drain the sump and record the amount of oil and then start the bike. No smoke and its a wet sumping issue, still smokes then move on to the next on the list which will be the inlet area and oil pooling.

Way back in 1982 I rebuilt a 750 and it smoked like crazy on startup. Pulled the top end and had the machine shop check the bore, ring gap, guides and seals, etc.....all good. While in the shop, which shared space with an auto parts store, I overheard a conversation between some flat track (auto) racers about how one had built a motor that wouldn't break in and smoked like crazy. Turned out they had initially filled the engine with that new-fangled Mobile-1 synthetic oil and the rings wouldn't seal. Yep, me too. Put the 750 back together and filled with some thin Castrol...problem solved.

If your center stand is mounted, you could try leaving it parked vertically and see if it makes any difference. versus the sidestand. Obviously won't solve your problem but that would definitely point to the valve guide or drainage scenarios described above, with no need to remove the head to make repairs.

MikeG said:

And here's why

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Like MikeG, I had a circlip pop out of a piston too many years ago. My incident happened at 65mph with a loud "POP" and a puff of blue/white smoke showing in my side view mirror. I shut the bike off, and coasted to a stop. I got my friend to get my van and come to pick up the bike and me. There was no debate in my mind whether the engine was coming apart to find the issue or not. It wasn't fun tearing down an engine that I had just rebuilt recently, but I would have ruined every other part of that bike that was still good if I had rode it home with a dislodged circlip bouncing around... spewing metal through the whole engine.....

Don't be afraid, you can do it. Or pay someone to do it,.... but the answer has to be found before you can ride this bike...

Chris L.,
Try contacting some of the Members of the INOA in your area:
Look for contacts and vendors and go from there. They might be able to help.

Chris Larkin said:

Yes, I have the manual, and I use Andover's website to search parts. I've looked through the manual and can visuaize the work... yet hoping a "how to" videos is out there. My searches have been unsuccessful so far. Thanks for the reply Bert.

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Chris,
You can try Mighty Garage to see if they have anything on pulling the head off.Some of their videos are worth looking at but like the others have posted,you can’t go wrong with the manual.
Mike

YING said:

Chris,
You can try Mighty Garage to see if they have anything on pulling the head off.Some of their videos are worth looking at but like the others have posted,you can’t go wrong with the manual.
Mike

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The manual includes illustrations.

remove exhaust and look at valve guide, I suspect it's coming down between the stem and guide or down the side of the guide. You might see it dripping off the nose of the guide or running down the valve stem. As it clears the exhaust pressure prevents a constant supply of oil past the stem. Inlet side will smoke all the time.

I had a chronic smoking problem on my 850 which turned out to be oil running down the outside of the exhaust guides. The shop slammed them in too cold. It gave really weird symptoms: it would smoke on one cylinder on startup, and then it would smoke from both when sitting at a light for a minute. I "cured" it by putting high heat silicone under the heat washers, concentrating it at the guide and not getting carried away so it didn't puke out the sides. Has worked for years now.

hhh said:

I had a chronic smoking problem on my 850 which turned out to be oil running down the outside of the exhaust guides. The shop slammed them in too cold. It gave really weird symptoms: it would smoke on one cylinder on startup, and then it would smoke from both when sitting at a light for a minute. I "cured" it by putting high heat silicone under the heat washers, concentrating it at the guide and not getting carried away so it didn't puke out the sides. Has worked for years now.

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I love these success stories.
Sometimes a bodge works well, and saves a wheelbarrow full of cash.

Head removal video.