750 Commando LH cylinder smoking at idle (warm?)

StephenP said:

I had a 73 MK1A

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In the USA? That would be a rare beast indeed as none were officially exported to the US as far as I know as it was a European model unless perhaps it was a personal export machine.

As mentioned, incorrectly installed spindles will cause oil to overwhelm the seals/guides. Seems unlikely if the bike has never been apart...assuming the Norton engine builder that day wasn't asleep/drunk.

IF the bike has original seals, they are probably ineffective due to age. They become brittle over the years. Note that nowadays, many (most? all?) current engines have seals on both intake and exhaust valves. Contrary to earlier belief, oil CAN be pulled into the exhaust stream via the exhaust valve guides. I don't know if exhaust valve seals are offered by AN (or anybody else) for these bikes but I'd install them if they are and I was doing valve work.

There is an old J. Giles song " First I look at the Purse" , But on my bikes , "First I look at the Plugs" ( Spark Plugs can tell the whole lot.) And then I look at the Ports and the Piston tops after I do the normal compression checks and a leak down test.

In the old days it was common to decarbonize the top end and check valve clearances and replace worn parts.

StephenP said:

I am wondering maybe an oil drain back issue on that side? Pooling above valve guide at idle?

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You have the pushrod tunnels for the exhaust valves and the other drain for the inlet valves is on the timing side that runs down into the timing chamber leaving the driveside inlet a bit lacking in draining if parked on the side stand.

Carl H said:

There is an old J. Giles song " First I look at the Purse" , But on my bikes , "First I look at the Plugs" ( Spark Plugs can tell the whole lot.) And then I look at the Ports and the Piston tops after I do the normal compression checks and a leak down test.

In the old days it was common to decarbonize the top end and check valve clearances and replace worn parts.

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"why waste time looking at the waist line… First, I look at the purse!"


Oh Waba goober made some valid points.

The J Giles band live full house album was playing on the tape deck in my 68 Ford LSD lot of the time back in high school

Back on topic, any motorcycle running modern pump gas will color plugs with OIL only

I've read Peter Wolf's Book "Waiting on the Moon", and heard several radio interviews on the book and his life with the band and his marriage and some of the fascinating people he met. He is a great frontman and rock n roller.

J. Geils was a " Hard Driving Band." And like I once did "Driving just as fast as I can." WBCN Boston, until Video Killed the Radio Star.

Try blocking the oil feed to the head to see if the smoking stops
If it does it's something to do with the head over oiling or a loose valve guide etc and not the rings
This is a standard test so don't worry about lack of oil
If you suspect the rocker spindles are fitted wrong you can easily check by removing the oval spindle covers and using a bit of wire with a small bend on the end and have a feel which way the drilling faces

Carl H said:

I've read Peter Wolf's Book "Waiting on the Moon", and heard several radio interviews on the book and his life with the band and his marriage and some of the fascinating people he met. He is a great frontman and rock n roller.

J. Geils was a " Hard Driving Band." And like I once did "Driving just as fast as I can." WBCN Boston, until Video Killed the Radio Star.

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Peter Wolfe would come on and promote WBCN, 104.1 where you got to have all the fun

Got to see them when they were on the Full House tour. 1973 I think.

Whammer Jammer comes to mind ... I heard it first on 8 Track!