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By Huey
#88438
Hi , I'm new here ...old to Enfields . Having worked on quiet s few other bikes Nortons BSAs Triumphs and others the most striking difference is the oil pressure at the crank . The Bullet 350cc that I checked had around 3 to 5 pounds / inch at the timing cover nut . Seeing that this is a white metal floating bush type big end it has double the clearance and double the start up contact heat to handle . My question is simple ' what are the two extra holes in the pump body for ?' Now I've gone through the manuals so would request less quotes from them 😁Thank you
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By stinkwheel
#88444
You think that's bad, wait 'till it gets hot, the pressure drops to near zero.

Consensus seems to be that bullets operate on oil volume rather than oil pressure.

It's actually over-opressure that causes problems, then you strip pump drive gears and you're in trouble.
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By Wheaters
#88448
Once you understand how the oil pumps work you will understand why the pressure is so low! ;)

I think the floating bush big end is quite a clever design. The rotational contact speed is, in effect, halved over that of a normal plain bearing.
By vince
#88466
Hi, the pump works on the up stroke and on the down stroke, hence the extra two holes . Think of it like a two stroke engine. Compression at top of piston and in the crankcase at the bottom of the stroke. Vince
By Huey
#88468
Ok ....here's what I think ( not an engineer)..... After a lot of trial and error I came to the conclusion that the two holes in the pump body act as a relief valve allowing more oil to seep back to the suction side when the Piston is vertical no matter in or out .....that's the time discharge and suction ports are joined just for a couple of micro seconds . So depending on the temperature of the oil the discharge and suction pressures are different ..... Triumphs have around 40 lb/ at about 18° C oil temp ....so while mucking around on a friend's bike I shut off the discharge side hole in the pump body and volla had around 60 lb/in which incidentally started braking through the gaskets . So a 1.5 mm hole was drilled through the solder bringing it down to around 40 lb/in . Now remember that this bike is running in India and the climate has mild changes in temp so it's working but for running around the Himalayas I'm not sure if switching to a thinner oil will work . Oh and that thing about the Piston making more pressure on the outward stroke is a load of BS as If the low pressure ( suction ) and high pressure ( discharge ) were open at the same time where would u think the pressure caused by the extention of the Piston go ??? Duh 😜😂 Peace Out
By Huey
#88469
Ok ....here's what I think ( not an engineer)..... After a lot of trial and error I came to the conclusion that the two holes in the pump body act as a relief valve allowing more oil to seep back to the suction side when the Piston is vertical no matter in or out .....that's the time discharge and suction ports are joined just for a couple of micro seconds . So depending on the temperature of the oil the discharge and suction pressures are different ..... Triumphs have around 40 lb/ at about 18° C oil temp ....so while mucking around on a friend's bike I shut off the discharge side hole in the pump body and volla had around 60 lb/in which incidentally started braking through the gaskets . So a 1.5 mm hole was drilled through the solder bringing it down to around 40 lb/in . Now remember that this bike is running in India and the climate has mild changes in temp so it's working but for running around the Himalayas I'm not sure if switching to a thinner oil will work . Oh and that thing about the Piston making more pressure on the outward stroke is a load of BS as If the low pressure ( suction ) and high pressure ( discharge ) were open at the same time where would u think the pressure caused by the extention of the Piston go ??? Duh 😜😂 Peace Out
By Huey
#88470
Regarding the floating bush absorbing the heat .you may be right but the principle of white metal bearings is oil pressure to keep the contact apart at all times which will need twice the amount of pressure as normal shell bearing . And as regards to quantity of oil the oil pump rotates 1/12 the times of the crank that means if ur crank rotates 12 times the oil pump pushes one plunger of oil into it .....Quantity u say ? Triumph pumps have it 1 in 2 rotations ABD they have a non return ball and spring valve . Quantity supplying oil pumps were designed mostly for roller big ends which needed the rollers to be cooled as there was no way to maintain pressure in these type of cranks ....Gear pumps are fail proof and are the best in my book ... ..The pumps on the AVL engines are huge gear pumps as compared to BSA B31s reason being the difference in rpm of the pump compared to da crank but would definately be a good modefication with the floating bush crank . Sadly the timing covers don't match up . Oh ....and don't forget to add a relief valve if any of you do ....Peace Out
By Bullet Whisperer
#88471
The oil pressure in a Bullet engine is low because there is little resistance to the flow and many [not all] have relief valves in the timing side mainshafts, which lift at fairly low pressures in any case, but when they open, the escaping oil still gets flung around the inside of the engine and does some good. The oil pumps themselves could probably raise a much greater pressure than that inside the engine, but as long as the flow [under a reasonable pressure] gets to where it is needed, the system is doing its job as intended. I have worked on a couple of old Ariel singles, with roller big ends and oil pressure gauges, which have shown around 35 psi hot - you know why? - Because before the oil gets to the big end, it has to get past an adjustable, spring loaded ball control valve, whose sole purpose is to create some resistance to the oil flow in order that the gauge gives a respectable reading. Running with this valve slacked off reduces the reading to about 5 psi, because the oil goes straight into the roller big end, but it is exactly the same amount of oil getting pumped around the engine, as before.
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By stinkwheel
#88472
"new" model enfields have hydraulic tappets no? So they need a higher oil pressure.

The fact is, regardless of any measurements or theoretical considerations, the piston pumps on pre-unit enfields obviously produce sufficient oil pressure for a floating bush big-end. Time has confirmed that. Despite the horriffic abuse I've given it, the big end on my 350 bullet had zero play on it after an estimated 90k miles. The rest of the crank wasn't in great shape with heavily peened main bearings and a loose drive shaft. I think it was on its 4th or 5th piston but the big end was fine.

As has been noted, what kills them is pressure spikes. I have a pressure relief fitted to mine and I'm also careful not to "blip" the throttle. I either rev it up or don't rev it up.
By Bullet Whisperer
#88473
Hydraulic tappets are self charging, they don't rely on oil pressure to work, but they need a good presence of oil so they can 'pump themselves up'.

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