rocker spindles

The flats acted as a channel to get oil quickly to the rocker bearing surface and the ball ends of each rocker. Plus as you suggested....the pushrod cups as well.

The scrolled spindles are not quite so efficient as the plain versions, especially if the return oil feed is poor. On a cold engine start-up, the oil tends to gather at the feed end and centre and not flow so quickly to the inner rocker ends. Consequently, more wear tends to occur at the inner end and it is not uncommon to find a ridge has formed on the spindles of engines that have done many miles. Plus the rockers may have slightly oval openings.

Check each of your rocker and spindle sets for a good, close but not binding fit. If there are wear ridges on the spindles then replace them. You can fit the later plain spindles to any of the cylinder heads.

Phil. I was under the impression that plain spindles should only be used with a 6-start pump, and high pressure rocker feed. The low pressure feed with 3-start pump doesn't provide enough pressure to force the oil through the minimal clearance between rocker arm and plain spindle...? My engine had been fitted with 2x plain and 2x scrolled spindles by the PO, unbeknown to me, the result being that the rockers with plain spindles picked up, turning the spindles sufficient to break off the locating tabs on the end plates, allowing them to turn more,with the result that the oil feed was then completely blocked, causing rapid wear, which manifested itself in ever increasing tappet clearances. Fortunately the wear was pretty well all on the spindles, not the rockers, which are mad money to replace. I invested in a set of RGM end plates which positively lock in position, doing away with the weak tabs.

Hi Ian.........until quite recently nobody appeared to be manufacturing scrolled spindles. I note that they are now being sold by Norvil. Apart from NOS I had not seen any on the market since the 1980s. John Hudson said that it was OK to use plain spindles in the earlier motors as long as the rocker feed was sufficient. Which generally implies an oil pump that is not knackered.

Reading through the Norton Twin Re-build Manual for 1964, they actually say that owners should dismantle and check the rockers during each major service, removing any build up of burnt oil or carbon and that any signs of seizure should be removed with abrasive strip. The suggestion here being that seizing rockerswas a known issue.

Another point.......about 25 years ago plain replacement spindles were available that did not have any flats at all. These relying, totally on a good oil pressure to provide lubrication to all 4 rockers. Mission Impossible!!!

Finally........ if the engine has a low pressure return oil feed to the rockers then there is not too much difference between using a 3 start or 6 start worm set on the pump.

What must not happen is either a 3 start oil pump trying to pressure feed the rockers. Or a 6 start oil pump pressure feeding scrolled spindles. Bad news either way.