Oil pump quandary

Hello John - You don't specify what year your crankcases were from - the early and late ones had different oil way sizes and breather passages.  When you fit plain rocker spindles make sure that the flats on the spindles face away from each other.  Cheers, howard

John you're quite correct. Your crankcases are early ones and would have had the standard SS oil pump which had an S stamped on the front.  The oil feed (and scavenge) at the junction block would have been 15/64 inch and this hole size would be followed through the oil ways.  The later 650s (and Atlases) that had the pressure fed rockers also had the double-speed oil pump gears. The oil feed, at the much bigger junction block, has 5/16 inch feed (and return) holes, flexi-tube inner diameters and these sizes are carried through the oil-ways in the crankcases. So the feed and scavenge of these models was much greater than your model.  These measures alone meant that there were breathing difficulties so extra holes and larger holes were needed to stop over-oiling and many leaks.  Doing some of the modifications may improve the original design but ... there are risks associated with this approach.  Cam wear,  cam-follower wear , short-lived big-end shells, main bearing failures,  piston collapses, rocker failure, bad leaks, smoking running and even con-rods thrown through the cases are some of the failures that have beset me tuning and racing  650SS and 750 Atlas engines.  Good luck, Howard 

When I was young and innocent and putting in big mileages on my 99 I fitted 6 start worm gears to the oil pump. What problems did this throw up? None whatsoever. Later on I fitted a 650SS head with the pressure feed to the rockers. No problems there either.

You can over-think things. 

Hi John,

My 650 is a bit of a mongrel in that all the engine is Norton, but most bits left the factory at different times. 

When I first got it, I was led to believe that it was necessary to 'upgrade' to the positive lubrication of the valvegear and so did that. The result was that you couldn't do more than about 5-8 miles before it looked like a 2-stroke from behind.

As Howard said,  the pressure feed mod isn't just a 'plain spindles and positive feed' thing, the oil drains were changed too.

Moving on, I reverted to the original set up of oil feed from the return line and it has been fine since.

Best mod I have done was to delete the 'Maltese cross' from the end of the cam and put a reed valve on the crankcase vent line. Well worth considering as crankcase breathing is marginal at best on a 650.

Regards, 

George

Sorry if I've thrown a spanner in your plans John.   On a road steed it is often better to stick to the design that Norton' s engineers developed for years before releasing the bike to the market.  After al,  if they were good enough to compete and win 500 Mile races at Thruxton etc then there was not too much to worry about.   The problem comes when embodying later modifications. Sometimes a part embodiment does not function as if the whole mod was completed.  When Paul Dunstall started selling the six start oil pump gears it was seen as a must-have item for many Dominator owners.  He had developed these items on his Domiracers and believe me there was much more to it than a pair of gears to speed up the pump rate.  Depending on what other tuning areas you have inherited and any wear on the other components may give you issues.  Over-oiling with pressure fed rockers is a common problem even with plain rocker spindles.  Oil lurks at the back of the head around the inlet valve and if it doesn't drain quickly enough has a habit of going down the guide. Larger oilways were required to assist with draining away the excess oil. Con rods with the oil bleed holes are stronger than the originals if you use the shells with the holes to suit but remember this mod puts a lot of oil on one side of the piston to stop seizures when running very hot and if your rings are not up to it some of the excess oil will by-pass the ring and burn.  Nortons introduced this mod with Wellworthy "Duaflex" piston rings to stop this problem.   Remember the holes in the rods need to face inwards so that they face each other.  At the least you should consider opening up some of the scavenge holes and fitting larger internal diameter tube to the return side of the oil flows to help with pressure problems that cause leaks and oil burning.  On a road bike i would agree with George and not have the high pressure feed to the rockers.   Early Commandos had to fit top-hats to the valve guides to help cure over-oiling and that was chaotic when they disintegrated.  Good luck, Howard  

Check out these words of wisdom from a Haynes Manual. Personally I am with Howard in that by facing the oil holes at each other the oil sprays cross and lubricate both sides of both cylinders. Rather than just the exhaust sides.

Adding a little more information from my own records.  The Slimline frame is probably pre-1965 as it shows the bolt that holds the upper gearbox cross-tube in place. This was welded in position from 65 onwards.

John's 650 engine is more interesting.  The number indicating a spring 1963 motor which would make it from the first batch of Plumstead produced 650 engines. The AMC factory was plagued with machining problems resulting in skip loads of rejected heads and crankcases.

This engine would have left the factory with scrolled rocker spindles fed by a 3 start oil pump and  low pressure oil return feed. The draw back of this set-up, in the early 650 motors, was the time it took to get oil properly circulating along the spindles. With the inside ends remaining dry for quite a time while the scrolls grounds away at the rocker innards.  Any owner going down the conversion to plain spindles and high pressure feed must check the clearance between respective parts otherwise oil will have an easy route straight to the rocker boxes and valve guides.

John - Throw away the Haynes manual and get yourself a copy of the Dominator Service Notes from the NOC Shop or use the website to read it as required.  There are many errors in the Haynes manual so don't rely on it.  If you don't want to use the bleed holes in the con-rods reverse the top shell with the hole,  with the bottom shell without the bleed hole.   You'll get there eventually have no fear.  Keep using the Forum when you're unsure about things.   Howard

Hi John, With the higher flow and pressure that the gears give you will probably get enough oil to the rockers even with the low pressure feed.If you go back to the 3 start set you can always adapt the tank return hole size to increase oil to rockers  if they look dryish .

Several factors need to be considered when using the 3 start oil pump set-up. Even with the 'S' oil pump this must be in tip-top condition and not have a worn return feed as many older pumps tend to have. You definitely should not use conrods with bleed holes in them unless the holes are blanked off. As Howard points out above.

The Haynes Service books are often the butt of many jokes. Generally as a result of their poor photographs which are often nowhere near the text supporting them. However, even the Norton maintenance books have their faults. Check out the engine diagrams (650SS as below) which until 1966 never represented anything with a post 1961 cylinder head.  Also this same diagram has the crankshaft bolt heads on the Timing side.

Notes from Neill on design changes.

My 650SS has pressure fed rockers 6 start oil pump, the head comes from what the NOC calls a 650 standard (I have the crankcases but did not use them as they are not stamped SS) I fitted seals to the inlet valves to help stop smoking, plain rocker spindles and conrods with the oil hole facing outwards, with the PW3 cam supplied by the late great Mick Hemmings my bike goes really well and has covered thousands of miles.

It is not difficult to open out the oil feed drillings in the crankcase to 5/16”.  I did exactly that on my Atlas case.  Once thus modified it means you could use either 3 or 6 start gears.  the only thing to be careful about is to ensure that the drillings are thoroughly flushed, but that’s just common sense.

With the higher speed pump, there is nothing to stop you from utilising the lower pressure scavenge return for valve gear lubrication, and you would not have to dismantle your bottom end to block the con-rod drillings.

Another option for you at least.

Andy

My single carb 650SS engine has the big oil pump with six-start gears, plain rocker spindles and the pressure oil feed, it also has a needle valve in the rocker oil feed pipe, so that I can adjust the oil feed rate, without this it over-oiled dramatically and I got a lot of comments about popes and coal burners.

Regarding Phil's comment about the time taken for for oil to reach all the valve gear with the original, early, low pressure system, I always do what I was told to do with Norton singles, on the first start-up of the day, take off the oil-tank cap, and stick your (gloved) finger over the oil return for 20 seconds or so, this forces a good slug of oil up into the rocker gear, and once so primed it will manage very well on its own after that.

A useful addition to the low pressure rocker feed would be a one-way valve in the oil line to the rockers. When the oil pump gets worn Gravity will often beat the struggle the pump has of trying to get oil up to the cylinder head. Instead it takes the escape route of heading off to the oil tank which is only half the height.

On my 1962 Dominator 650, this rocker oil feed issue was very noticeable through the replacement plastic  tubing feed to the head. John Hudson's suggested cure was to put a washer shaped restrictor inside the oil tank return fitting. I found an easier option using a chunk of 1/4" internal bore rubber tubing that was split along one side. This was fitted inside the oil tank over the return pipe so that it covered the return hole. On cold starts this did the same job as Niall's finger and  helped to force oil to the rockers. Once the oil got hot, the rubber softened and allowed more oil back to the tank.

Dear Members,

I acquired my 1965 650SS in 1974 with a wrecked engine caused by a snapped drive side con rod. I restored the whole machine over the following eighteen months utilising the Haynes manual because I had no other reference material.

I bought two 650SS crankcase halves and two con rods on the second hand market. I followed implicitly the instructions written by Haynes. The replacement con rods did have the small holes in them.

I have ridden the bike ever since then with a mileage of about 800 miles per annum and have had the cylinder head off three times but never delved into the crankcase.

I ride fairly moderately and have hardly ever revved the engine over 4500rpm. I fairly occasionally put my finger over the oil tank return when finishing a ride out.

I have no intention of dismantling the engine to reverse the oil holes position. If it ain’t broke, don’t fix it.

Regards,

Anthony Bolton

What is the S oil pump? 

The S oil pump had more capacity than the standard pump. It was introduced to all he UK models wearing the SS derivative in 1960/61.  It was also fitted first to all Atlas, 650 Standard and De-Luxe models.  There is an S stamped into the front of the pump's casting to identify it.  The S disappeared when the standard pumps ceased production around 1964.  The scavenge gears in the pump are bigger than the standard pumps.     Cheers, Howard  

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