850 valve removal

thanks for all the replies so far, much appreciated. i think a little history about me and the bike would be helpful now. this is my first norton and it has been a massive learning curve. i was a teenager in the 80's and all my previous bikes have been japanese and german tourer's. i had always yearned for anorton as a project and one weekend thiscommando popped up in the local paper. the bike was a non runner and had been stood for over a decade. i had never kick started a bike before, but eventually after changing oils, and giving it a good service i got it running. smoke was belching out of one exhaust so i removed head and found bores were badly corroded. that is when i had it rebored so referring to david evans post i had never ridden bike before this so dont know if it ever had this oil issue. i reassembled the engine post rebore so maybe that is another issue. i have been riding the bike a couple of years now since the rebore and it runs lovely,but getting frustrated with the plug oiling up. if ime riding on traffic free roads its fine but in traffic the plug fouls and it will drop onto 1 cylinder. the bike will then not start the next day unless i remove plug and clean it

since my original post i have removed barrels andpistons/rings areintact and the bores look good with no obvious issues. i am going to take the barrels into work on friday and check them for ovality and parrallel. the rebore is +.020" so looking in my manual the original bores are 75mm so they should be 75.51mm dia, will check this with internal mic.

have taken the top ring off one piston and checked ring gap and it does seem a bit big, measures 0.017", manual says 0.012" max. is this an issue.

will post after friday with my findings, anything else i should check down there before i attack head please advise, as i said earlier this is my first top end rebuild so appreciate any help

thanks, paul

Previously john_holmes wrote:

Large ring gaps are not an issue, the 12 thou is for new rings, bedding in always increases it. Could be the rings not seating properly on the oily side, running in at low revs will not get the rings bedded in quickly enough as will using too slippy an oil for running in. Lots for you to look at but don't go jumping in for a rebore until you have more info. Is it the timing side or drive side plug that is fouling. The plug fouling says the oil is either coming from the inlet or from the rings so you can rule out the exhaust for the moment. As oil drains through the head gasket on its return to the sump look for any signs the gasket has blown between the combustion chamber and one of the oilways or the pushrod holes allowing the engine to suck in oil.

thanks john, its the drive side plug

checked barrels and they are fine. ovality is within 0.0003" and both bores are parallel within 0.0005" so i am happy there's no problems with the re-bore.

have removed the valves and found the inlet seal on the cylinder which was oiling the plug up had come off the guide. the other side was in place so hopefully that will be my problem there. the valve guides and valves themselves look in pretty good order to me, have measured the valves and they are showing no wear and they all feel to have the same clearance on their relative guides. got to admit the cylinder head face looks a bit tatty in particular the small land area between the pushrod tunnels and the combustion chambers. the head gasket looks like there may have been some oil getting across in that area, is that possible, orit could just be oil thats dripped out of head onto and underthe gasket while i was wrestling with the pushrods on head removal. anyway ime going to give mick hemmings a call tomorrow and see if he will skim the head for me.

as for removing the rockers to get the valves out, as was my original question, as the replies said, not necessary and a std car valve compressor did the job.

thanks for all the help