E: Engine More Adventures with the Comet

manxman

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Non-VOC Member
The silver lining of the pandemic is that I finally have more time with the Comet, which was otherwise neglected in favor of a well-sorted (and faster...) Norton 750. I apologize.

I noticed it was smoking a fair amount from the exhaust at the end of the summer and made a note to check the plug and piston. Bottom of my list. It shouldn’t have been.

See the pictures below—fouled spark plug and sludge/carbon on the piston. (Using a cheap endoscope from Amazon.) Will need to keep going and have a look at the valves. The piston seems to have been enjoying an oil deluge. I expect I’m also running too rich but I’m focused on the oil for the moment.

I can’t tell if the cylinder wall scoring is exaggerated by the LEDs and the focal length of the scope. Will have to have a look at that too. My understanding is that there should be some intersected scoring, diagonally, on the cylinder wall as a result of the honing process, but I’m by no means an expert. Will try to get a few more pictures.

As a note, I never once had an issue starting (first or second kick) and the bike ran beautifully this summer, but for the smoke and some leaks from the Burman and primary (which I’m also addressing)... My error was not to check more regularly the spark plug, among others. I’m amazed a spark was coming through all that mess.

Anyway thought I would share. The downside is I have a lot of work to do; upside is I get to keep taking apart this lovely machine. Would welcome any thoughts.


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Martyn Goodwin

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Been there - done that! It may well be worn valve guides allowing oil into the combustion space. This means stripping down the head to check. It sounds like a daunting task but work slowly and methodically and its not that hard.

Remember to check the valve stems themselves for unusual wear on their sides - I had that and it was caused by misalignment between upper and lower valve guides.
 

Cyborg

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manxman

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Non-VOC Member
Thank you all. Yes the oil was certainly too light. 40 weight when I got the bike but I didn’t bother to replace it. Haven’t had it long, but this summer I gave it its first real going-through and I imagine the lighter oil exacerbated the issues.

Martyn yes I need to do some surgery on the head! I’d love to see the valve faces and seats so at least I can know the culprit. Need to finish up the work on the shaft seals in the primary first.

And Cyborg yes I had the same thought (just from what I can read online). The cross hatches look to be too shallow of an angle and quite deep. Will know better once I pop it open (and likely discover other issues). Thank you for the link. If I need honing done I’ll have to find someone good in New England. But I’m hoping I can avoid that step.
 

brian gains

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before you pull the top end check your ET49 is not loose. My Comet used to 'make smoke' and after I found the threads partially stripped I replaced retaining nut, punched and no more issues.
 

erik

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If you think the Valve guides are the reason for the oil consumption then dismount the inlet stub and have a look. And with your camera you can see where the oil is entering the inlet.Erik
 

Bill Thomas

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VOC Member
Maybe you could fit metering wires, If not already fitted ?,
In the rocker feed bolts ?
With the C/Head off, Check that oil could drain away from the valve guide area ,
Hold the head as it would be on the Bike and make sure it can't build a puddle of oil above the guide,
More so when Mk2 cams are fitted and the top of the guide has been shortened.
Some times we have to grind a bit of head where the guide is to allow drainage.
 
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