850 Commando smoking on left cylinder

Hi Stephen, I'm a novice to these engines, however if fitting new oil seal(I'm assuming to inlet only) semi cured the problem; does this not suggest that both valve guides are worn on that side and some oil is still going down the exhaust valve guide.

The left hand cylinder has the most to deal with if a bike has been standing on the side-stand but if there is oil coming from the head and it isn't between valve and guide then there is a good chance that the guide is loose in the head. This is not exactly unknown on Commando engines and the only cure is to remove the head and fit an oversize guide.

The gas flow past the exhaust valve will draw any oil out of the exhaust pipe but should not draw oil down the guide like it does on the inlet valve. Try running the bike with the valve covers off and see if there is an excess of oil through the rocker feed system. The rocker spindles need to have the flats pointing away from the push rod end of the rocker to avoid over oiling. You may have one or more the wrong way round.

The guide does not have to be loose to pass oil. Poor mechanics can score the head when replacing guides. Oil then runs down the outside of an apparently tight guide. The correct Loctite product (I forget the number) will quickly fix this and not prevent future easy removal of the guide.

There is no way to regulate the flow to the rockers unless you put a restrictor in the line. The valve spindles the correct way round effectively create that restriction.

Hi Stephen glad your sorted. A photo of the tools you used would be nice. I searched on google images for valve spring compressors the other week and I had no idea there were so many different ideas. Some of the photos of tools looked as though you might be able to do the job without the rope.