When I first bought by 1967 Norton 650SS it idled and ran perfectly with no signs of oil leaks. Once I had insured it and took it for a brief ride all of that changed. The bike spit oil from most engine joints and exhaust flanges as well as fowled spark plugs.
After an extensive rebuild that included machining the barrel and head surfaces flat I've cured the offending mating surfaces that leaked so badly and the bike no longer fowls plugs. I did a complete disassembly and made sure the camshaft breather timing valve was installed correctly and it was. While apart I also changed the crankshaft main roller bearings and shell bearings.
Because the bike is built in the classic cafe racer style I am not married to originality so have a bit of a free hand. It seemed to me there were two reasons the bike leaked oil.
1- poor mating surfaces and sealing of same (think I now have that in hand)
2-crankcase pressure build up at or above 3000RPM (there is nothing at idle as I've checked it with a pressure gauge). The other thing that makes me conclude this is it appears all the British bike builders that built 360 degree engines tried to improve crankcase ventilation in the early to mid 70's when oil leaks were no longer given a pass by the buying public that had turned to the Japanese manufacturers. A slightly positive crankcase is constantly looking for a leak source and in the end finds it.
With this in mind I've modified my bike as follows
-bought a 99 timing chest cover and modified it to include a venting device welded to its rear half aiming up slightly.
-a 12mm hose connects to the venting device on the timing chest and angles vertically up past the oil tank and contains a PCV valve as can be seen in the pictures and then exits the ride along the right side of the rear fender
-modified the 99 cover oil feed plug to allow for the pressure feed to the rocker spindles as found on 1967 650SS's rather than on the return line "T" splitter in the oil tank return line.
-I also installed a wet sump valve in the oil feed line that is interlocked with the ignition system to prevent starting if the valve is not open. This can be seen in the pictures attached
The final test will be when the bike goes back on the road in the spring. If there is a noticeable reduction in engine oil leaks I will report it here
If you still have scrolled…
- Log in to post comments
Robert, thank you for your…
Robert, thank you for your comments. The bike does have a 6 start pump and plain spindles
- Log in to post comments
Are your bores glazed? That…
Are your bores glazed? That's what used to cause my single to oil up plugs. You would see smoking exhaust as well.
Your description of problems seems a bit extreme relative to all the well behaved Dommies on the road. My only significant leak is the b****d chain case..sometimes well behaved but usually not.
- Log in to post comments
Funny that David, mine has…
Funny that David, mine has started to seep a bit after a run , May see you tuesday, we can compare leaks. After a change of pilot jet my 99 is now running the best it has in years ,can't believe something that simple -----------.
- Log in to post comments
David, my 650SS was extreme…
David, my 650SS was extreme when it came to engine oil leaks and only manifested itself when given a trip down the road. I did de-glaze the bores the first time I had the barrels off. Once both head and barrel were flat and annealed copper head gasket installed the leaks stopped but I am convinced that above an idle less than perfect crankcase ventilation is an issue. It's interesting to note that of all the topics on this forum the one with the most posts is the one about ventilation. I suspect that Triumph and BSA's that have the same engine design (360 degree engines) also suffer from the same issue. This seems to be supported by their efforts to improve the ventilation problems right up to their end of production. Still, only my opinion and thoughts. The other little twist,.......... my primary chain case cover leaked ever so slightly but was well masked by the prevelant engine leaks..
- Log in to post comments
If you still have scrolled spindles you are likely to find the valve area to be a bit overoiled. If you have the 3 start pump gearset you may find the big ends oil supply to be a bit compromised. You also may be lucky too and not have a problem.