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[Dennis C]

Hi John J

I agree with you regarding the high volume pumps, but unless the big end has been converted to roller bearings then it does require oil pressure to keep the bearing faces in good order.

[trevorch]

My 2007 Bullet 535 at 6,000km, seized shortly after I had fitted an Amal and messed around with the timing. My dealer recommended larger capacity oil pumps in order to increase the flow of oil to the top end which would help with keeping it cooler. With correct main jet and proper timing, had no further problem over the next 10,000km. It does no harm and the worm drive was still like new after a total of 16,000km

[Les H]

In reply to Chris: "is it essential?” The answer is yes it is essential. As you know there are two pumps a feed and a scavenge pump. The front scavenge pump has to create a vacuum to lift the oil to the pump before it can send it back on its route to the tank. Due to the fact the scavenge pumps have to repeatedly restart to lift oil after the oil pick up runs dry caused by the scavenge pumps 2:1 size difference to the feed pump, a good seal is essential. Many owners experience a return flow problem after an oil change and this is the most likely cause. Any face leakage will make lifting oil back difficult, unlike the feed side which is under a head of oil from the tank. Secondly, regarding the feed side, we cannot always assume the pump is in a constant state of lift off and blowing off surplus oil. (The oil pressure relief valve on original engines was designed to lift off at around 60PSI). We should therefore aim for the pump to deliver all its content per stroke to the big end and the rest of the engine and not loose any unnecessarily. Any leakage before the pump lift-off pressure is reached, is less oil getting to the big end, so once again lapping in the pump face all but eradicates this wasteful leakage. The third benefit is wet sumping. I am sure that most wet sumping problems (if you have one) is due to oil leakage across the back of a badly seating pump face, in effect you will have a short-cut from the feed hole to the pump across the face to the feed hole to the crankshaft. Oil pumps with pistons are usually very good at preventing wet sumping due to their excellent sealing and fit of the piston in their bore. The later light pressure pump springs, which are fitted to help with lightening the load on the pump spindles certainly don’t help with pump face sealing so this is another reason to lap in the pumps. The original Royal Enfield factory states clearly that oil pumps should and must be lapped in...Now hopefully you know why. So what is the best abrasive? That will depend on the amount of unevenness or scoring. If bad use fine grinding paste and finish of with Solvol. Remember the face is only aluminium and relatively soft. The pumps are either bronze or steel but will cut more slowly which could be a problem if they are finished poorly but all scoring has to go to leave both surfaces mating perfectly.
The high capacity pumps have always been controversial. It does not matter what some people argue (and they often do) the floating bush big-end does require a good, decently high oil pressure delivery. . Some people think it just acts like a bronze bush spinning round, just avoiding metal to metal contact, but that is not so. The white metal bush should be set up with enough pressure to work hydro dynamically just like any ordinary white metal plain bush with enough pressure to ensure complete metal to metal separation at all times. At worst under high loads, the designer admits the inner surface of the bush can contact the pin but no wear should take place as the outer surface still has the layer of oil to maintain freedom of the outer big-end eye. However, this “occasional” contact is best avoided completely and can be by feeding enough oil in fast enough to maintain at least a half decent pressure, say 20PSI. The best way to know if high volume pumps are a benefit (and they can be) is to measure the oil feed pressure with the oil hot. The floating bush has two wear surfaces and thus two leakage areas to leak away pressure, so it can be seen to require roughly the same amount of oil flow as a twin cylinder engine. The weak point of the floating bush is the smallish diameter of the crankpin against the inner side of the floating bush which is on the limit, pressure wise, for it to work under a full 500cc worth of hammering against it, whereas the outer diameter of the bush is acceptable. With the correct clearance on the big-end and the correct grade of oil, the standard pumps should maintain the correct pressure. However the state of wear or original set up clearance is unknown so there can be a situation where the pressure created is too low for a plain bush to operate reliably especially the small diameter inner bush surface. If the pressure becomes too low, metal to metal contact on the small highly loaded inner side of the bush can start to wear even though the outer surface can still rotate. Once wear build up and is releasing too much oil, the pressure drops further and a rapid increase in wearing can take place and the life of the bearing is over. In my opinion (Only my opinion) the best way to choose whether you require bigger pumps is to measure the running oil pressure with hot oil of the correct recommended viscosity. If it appears very low, you can either choose a thicker grade oil but this is not recommended for various reasons or choose the hi cap pumps to boost the pressure and thus allow the plain bush bearing to maintain metal to metal separation and ensure a longish life. You could of course fit them especially if the bike has covered a few thousand miles and let either the OPR valve blow off surplus pressure or the oil pumps to lift off. The negative side is that you are loading the pumping system a bit more, but it is a balance of possibly extending big-end life against extra pump spindle wear, which is why measuring the oil pressures at least gives an insight to what is best. At the end of the day the engine can always be rebuilt simply enough and a roller bearing fitted so the choice is yours as far as fitting the bigger pumps.
PS...it is a pity that this message board removes paragaph spacing.

[another Allan]

Thanks Les H. Thanks for that. It all makes perfect sense to me. I agree about the inability to use paragraphs - it makes reading a chore. I would have thought out-of-synch-ordia or whoever could have fixed this; not exactly an unusual requirement.

[John J]

Hi Les H, Great posting, full of insight. Is there a ready made gauge to measure delivery pressure?

[Barry N]

Yes - thanks Les, for that informative post!

[Les H]

Hi Allan and John. Thanks. It would be nice to have a ready to fit gauge to buy but I had to make one myself. My choice of engine position was the quill bolt on the engine cover. I bought a new quill bolt (cheap enough) drilled and tapped through the outer blank end to take a ready made male to female connector.(can't remember the thread size but I,m pretty sure I chose a metric thread possibly M8? The ready available pressure gauge 0-100PSI (also cheap enough and available with different threads to match) screwed into the connector, so quite a simple job if your are the inquisitive type and interested in knowing what the oil pressure is up to. As far as I remember, with cool oil, the pressure quickly reached around 30 psi (I have hi-cap pumps fitted) but then it seemed to stabilise with no further increase with higher revs. I assumed this was where the pump was lifting. I also noticed some odd pumping peaks which I theorised was the oil pump pumping into the outer cavity when the piston pulls out of the pump body (Twin action pumps on the Bullet) When the piston stroke is outwards, the pressure is created in the outer cavity (pump cover) so the pump body cannot lift away from the pump face as the delivery pressure is exactly the same both sides of the pump and is compelled to deliver it's full pressure (no crankshaft relief valve-Indian Bullets) Anyway with warm oil the pressure was still sufficiently high and not excessively so for me to be reassured about the bikes lubrication. I had all intentions to experiment more. I wanted to replace the feed pump pressure spring with an original heavier spring to see if the 30PSI cold figure would increase. I'm pretty sure it would have. As far as running pressure with hot oil, I cannot remember now if that dropped well below 30PSI. So I'll have to take the time to measure again and finish off the tests. It is just down to finding time...I have been very busy over the last couple of years. Yes the floating bush is a strange old bearing. There are so many variables in it's behaviour with different inner and outer clearances and knowing how the floating bush is performing and what speed it's spinning round at. Most experiments say it spins at anywhere between about 15% to 50% of the rotational speed of the shaft (big-end eye) If you want to set up the clearances it is normal to have the inner clearance set tighter perhaps around half the outer diameter. This will ensure the oil can sufficiently "grip" the floating bush and pull it round against the "stiction" of the bush against the con rod eye bush. If the F/Bush does not rotate or is pulled around only very slowly then all the relative spinning bearing action is taken by the small inner diameter of the F/bush leaving the outer surface doing nothing. By keeping the inner clearance tighter than the outer one, the oil can grip the bush a bit like a torque converter as it spin oils through the radial oil drillings in the f/bush. Ideally the floating bush is better suited to high speed/revs applications rather than slogging but it was used in ancient aero engines with some success. Whatever or however it works I reckon it still needs a decent pressure to ensure that the big end pin is kept away from the bushes inner surface, the outer surface has its load spread more since it has a larger area and has an easier life. The only problem is the relative slow surface speed difference at the outer surface of the f/bush where it probably has a struggle to get "aquaplanning" or utilising the hydrostatic principle of a plain bearing since the relative bearing speed probably never exceeds 500-1000 rpm at most at max revs as that's all the inner surface can drive it at. I've said this before but I've always thought a larger diameter crankpin (keeping the threaded ends the same to fit the flywheels with out modification) could be made quite simply so that either a con-rod from the twin engine could be fitted with its replaceable bearing shells (If its the same length) or even simpler, make the big-end pin a touch larger so it is a tight fit in the floating bush, so it cannot revolve, and thus forms a standard plain bearing where the outer surface of the white metal bush is guaranteed to take all the wear and tear rather than risk the inner, smaller diameter side of the bush seeing all the wear as it often can do. Some might say with total justification, just let the damn thing wear out and replace with a roller type, but if you have a low mileage bike it would seem sensible to make sure it lasts as long as possible, but then again maybe not. Rebuilding the engine is not too difficult as I said earlier. I've gone on a bit again..sorry...too cold and wet outside to do much at the moment. CU.

[Les H]

Just to ammend what I said about the floating bush's rotational speed. The range is likely to be between 500rpm up to around 2500 rpm at max revs (I said 1000rpm) All manner of things will determine this and it is virtually impossible to calculate.

[Les H]

Just found out another important fact regarding plain bearings. The highest pressure that the hydrodyanmic principle generates inside a plain bearing, and thus the highest load carrying ability it can generate, is at the centre of the bearing. This if you think about it seems sounds obvious as it is the furthest position from the edges of the bearing where the oil can escape from. However the floating bush is compromised severely in that the centre area is perforated all the way round with the radial oil drillings. Therefore at the centre of the bearing the load carrying ability depends soley on the feed oil pressure rather than the self created oil wedge pressure (which is far greater than the feed pressure) In contrast, a conventional crank delivers oil to its big end bearings from just one or two drillings at the centre that have been drilled at the position of least dynamic load, which is at 90 degrees from TDC & BDC. This positioning allows the dynamic oil wedge to build up at the highest loaded points in the big end which corresponds to TDC and BDC. The floating bush can only build up on two areas either side of the radial oil drillings and both these are far weaker as they are nearer the edges of the bearing and loose oil that much more quickly from the dynamic oil wedge. This failing emphasises the short comings of the floating bush and that it does require a good oil pressure to have even half a decent service life. My appologies if this sounds rather anorakish but I found it interesting.

[another Allan]

I lapped-in (with Autosol) my new high-capacity pumps yesterday, cleaned and oiled everything, then fitted them to the timing case with a new spindle. Everything turned easily with 'light thumb pressure' on the teeth of the spindle. However, fitting the end caps and springs was a different story. Even with the screws fitted by about two threads, it became almost impossible to turn the spindle. Tightening both end caps to the equivalent of two gaskets clearance made the spindle impossible to turn with my thumb. So, I tried one end at a time. With the return end cap fitted and tightened to the equivalent of two gaskets clearance, the spindle would turn, but it needed some effort. With just the feed end cap fitted, it was rather stiffer (so fitting just the feed end cap is creating more friction than fitting just the reurn end cap.) I've read in the technical notes on this site that weaker springs are available, so I'll order some, but I can't see that they're going to make that much difference if my pump will hardly turn manually with each end cap only just secured. What has anyone else found when doing this job? What am I missing?