Oil Pressure

[nevhunter]

You shouldn't run your 35 or any other oil gauge equipped ARIEL with no pressure indicating as the gauge confirms the oil is going through the pump. The pressure indicated is a function of the ball valve (2 types earlier one is adjustable). Increasing the pressure does not increase oil quantity to the big end. The oil pumps are positive displacement dependent on revs . A low reading only exists as a result of the spring setting in a normally functioning engine. It's not performing the function of a relief valve in a normal oil system, like the twins and Sq4's. having plain bearings are equipped with. Nev

[paul.jameson]

Ian,

Perhaps I can clarify why both you and Nev are correct but in this instance, Nev is the one whose post is relevant.

The oil gauge on an Ariel single is fed from a chamber in the timing chest. The various forms of pressure relief valve govern the pressure in that chamber (which is pretty tiny). When the pressure exceeds that which the pressure relief valve can take the oil escapes - into the big end !!!

Hence the fact that the oil pressure merely indicates the pump is working and the fact that an increased pressure makes no difference to the volume of oil which goes to the big end. As has been said, a higher pressure merely means the pump is working harder.

My RH500 still runs on the small bore pump which came with the bike. If the small bore pump was good enough to race at Brooklands, it is good enough for me (and my frame and oil pump at least, have probably been raced at Booklands). One thing nobody can argue with is that the oil pump is the best lubricated part of the engine and so, if the ball valves are ok, it will keep going for a very long time.

[nevhunter]

reference Paul's post re pump size. Generally the only ARIELS that I've seen with problems with oil pumps have had "oversize" pumps fitted that often run hotter and leak oil everywhere. MY VCH which I used to ride hard is like that and is the only ARIEL single I've had any trouble with. It was fairly common knowledge that putting a lot of oil through an ariel has problems of scavenging it back into the oil tank. This is a fairly common problem with dry sump singles and Vee Twins at high revs. Gravity doesn't do enough when oil is going everywhere.
The "original" small pumps work fine on most bikes. Some pumps that have come into my hands over the years are quite worn when you inspect them in the areas that matter. Ie the ends of the plungers and the bore of the body near the porting where all the work happens, so they probably need reconditioning which done properly will need fits similar to a model aeroplane engine. To check them I use auto trans fluid with a bit of kerosene added and if the ball valves will "POP" the pump will work when the engine is very hot.
Most of the issues are with the ball valves and springs. Use the correct ball size and have the RIGHT springs. Some reconditioned pumps I've seen won't work reliably with the springs supplied. They are too long and have too much pressure. Dirt is to be avoided too. Nev

[david.anderson]

Paul
In practical terms you are correct in stating “an increased pressure makes no difference to the volume of oil which goes to the big end”, but theory dictates otherwise.
First I will expand a little on what you have already stated. In the case of oil pressure fed rockers, the oil pump directs all the oil to the rockers, but when the pressure builds up to the preset figure, a valve opens and lets the excess oil feed the bigend. The rockers are still fed the same volume of oil at the preset pressure. As engine revs increase the rockers will still be fed the same volume of oil because the pressure is constant, but the bigend will receive an ever increasing flow volume with the increase in revs.
The oil pressure gauge only ever reads the oil pressure to the rockers.
Now to the theory, if we remember back to high school physics and Bernoulli’s principle, we remember that flow is directly proportional to pressure. If we increase pressure, we increase flow. But to double the flow (the volume of oil delivered) we need 4 times the pressure. So, in effect to double the flow of oil to the rockers we would have to increase oil pressure from say 15psi up to 60psi. And because the oil pump delivery capacity is limited at any given revs, if we have more oil going to the rockers, then there will be less oil going to the bigend. (Of course, Bernoulli's principal only applies if the flow remains laminar with the increase in oil pressure). But in practical terms if we increase oil pressure from 15 to say 25psi then the increase in flow to the rockers is nominal (as is the reduction in flow to the bigend), but the pump is loaded up for no reason which is the point being made. Remember that the post 52 singles rockers are fed from the return line at minimal oil pressure.
David

[paul.jameson]

David,

I have long understood that the difference between theory and practice is that, in theory, there is no difference but in practice, there is !

Paul

[satchison]

So where would one find a smaller bore oil pump? Draganfly does not carry them, rather they offer to rebuild and supply the larger bore pump.

[pete.collings]

If you look at the top listing in the spares available/wanted section, you will see I have some early single oil pumps available.
If interested, email me using the listed address.

Pete

[nevhunter]

The fitting of oil rings coincided with bigger delivery pumps, and according to factory records was mainly to quieten the piston slap that the poor quality alloys caused by requiring a lot of clearance to prevent them seizing. Up till then pistons had 3 compression rings relieved under the bottom one with small oil drain holes. Most pistons available today may well have oil control rings and the engine may be a little oil starved especially if modern 3 piece oil rings are used. Not only do they remove oil too well from the cylinder bores, they contribute a relatively high amount of friction to the equation. Some oil helps ring sealing too for compression retention. They ran good as they were supplied in their day for normal work, so if you modify have a reason. They were "experts" in their own way with the technology of the time. Nev

[Ian.Taylor]

My NOS piston from Drags back in the 80's has just 2 compression rings and no drain holes .I thought the drain holes were for pistons with oil control ring.
The 2 ring system works well ( rings from Cox & Turner ) on the 31

[satchison]

This is a profile pic of my 350 piston, which utilizes 3 compression rings. It is the reason I am switching my later model oil pump for an earlier one. The later model pump seems to overload the oil system..