A review of correspondence from NOC-L
I noticed that down inside the threaded hole that receives the banjo bolt holding the rocker feed pipe, after the point at which the threads stop the bore of the hole, reduces by roughly half. I'm concerned that this restriction will impede the flow of oil to the rocker box. Is this a casting imperfection that I should drill out or is it designed this way to control the amount of oil in the head at any given time?
I have a 1962 600SS engine which I converted to pressure feed to the head, using all the advice given about the plain spindles etc.; but it always over oiled the head. I did not want to return to the hit or miss oil supply provided by a pipe of the return feed connection at the tank, but I needed to get the oil away from the head quicker than it was.
I machined the area around the valve springs to give a better flow to the cam tunnels but she still over oiled, which was good for keeping the inside of my silencers from rusting but that's about all. I eventually cured the problem by drilling and tapping the big banjo bolt on the timing cover to take a small grub screw which could be tuned in or out, restricting the oil flow from the pump to the head in a controlled fashion. By running the bike with the rocker covers off, I was able to see the flow to the rockers and adjust the grub screw to give a steady but controlled flow rate, to the rockers and also for the oiling of the cam followers etc.
That was five years ago, since then the Dommi has run as happy as Larry with no over or under oiling problems to the head, and it beats me why Norton bothered mucking about with restricting the flow at the spindles, which would in time wear and provide a increased flow, when they should have tackled the problem at the source i.e. the pump end.
Eddie Stephenson (firstname.lastname@example.org) on NOC-L 7th. Jan 1998
Separate oil restriction advised for inlet and exhaust sides
Eddie has come up with a good solution for reducing the oil flow! Norton's solution was strange indeed, especially considering that years back, the old AJS/Matchless singles, as well as some BSA singles had a needle valve system designed into the iron head casting.
Top end flooding was also an unexpected problem with the Lotus twin cam when they up-rated the oil pump for racing. Whereas the stock pump did the job for most uses, it could not keep up when engine clearances increased. The later high capacity pump caused havoc in the top end since it could pump madly away no matter how much the clearances opened up! Lotus solved it by putting restrictors in the oil feed to the top end.
You may want to consider that the exhaust side components benefit more from oil flow because of their higher temperatures, thus it may not be too wise to choke off the oil equally. With this in mind, BSA used to 'steer' more flow to the exhaust spindles on the Gold Star by using banjo bolts with a larger cross drilling on the exhaust spindle feed.
Greg Kricorissian (email@example.com) on NOC-L 8th. Jan 1998
No problems with the original setup
Various subscribers are making reference to the subject of top end over oiling. One of the various modifications made by AMC to the basic Norton twin design was to alter the method of oiling the top end. Originally, low pressure oil was taken from the oil return at the point where it reentered the oil tank, using a tee off a banjo. This was fed into the head via two drillings in the top of the cylinder head one left and one right. The rocker shafts were scrolled instead of plain, to encourage oil flow through each rocker. Although I heard some comments that the oil flow may be inadequate, I have never seen any evidence that a problem occurred. My brother still rides his 1965 Atlas, owned since 1968. It has been ridden everywhere, modified for production racing, put back in road trim and ridden hard all of the time. It has always had the original low pressure oil feed and the rocker shafts and rockers have never been changed.
If there were any concern about the amount of oil available, it could easily be increased by a slight reduction in the size of the oil return outlet into the oil tank, and this could be done simply by fitting a Jubilee or Navigator oil return junction into the oil tank. However, I have never heard of a case where it was necessary.
Apart from meaning that the top end never over oiled, oil pressure was not taken from the main bearing feed and valve guides did not need oil seals. It has been said that because a small amount of oil could get down the valve guide, it was anyway better for valve wear and cooling. Some of the changes made by AMC to the original engine design were beneficial, but I am not convinced that this one was. It should not be difficult to alter a later engine back to the earlier system and I doubt if it would cause any problems. Obviously, it is up to each individual to weigh up the risk.
Colin Leighfield (firstname.lastname@example.org) on NOC-L 10th. Jan 1998