Ariel Owners Motorcycle Club

I needed 2 compression rings ( 1/8) and this firm supplied them
http://www.coxandturner.co.uk/holding.php

You will have to measure the diameter of the smallest of the plungers to identify the pump type accurately. This is the one that pumps oil into the engine (delivery). The scavenge is much bigger .3750 and the same size for a multitude of different models. The smallest delivery plunger is .1875" diameter used from 29 to 1949 in most bikes. Nev

Thank you for the reply. I feel like I might be getting to the route of my problem here. I initially disassembled the motor because my oil pressure gauge was reading at the maximum, fearing that the big end oil passage was blocked, or that the oil purifier plug was full of sludge. Neither seemed to be the case. Now it seems I may have the wrong oil pump for this piston/ring combination, causing the pump to overwork and giving me max oil pressure reading at the gauge? Does this seem plausible? It has been an education getting to this point, but I have enjoyed the mystery!
The oil delivery plunger measures .25" and the scavenger plunger .375"

Have you checked the pressure relief valve?

I have cleaned it and successfully blown air through it. It appears to be working properly. I'm assuming you mean the spring ball valve which feeds the the big end? I believe this engine does not have the oil pressure adjuster.

I'm wondering if someone has replaced the spring with one which is too stiff. A new one from Drags will show about 55 psi cold.

Piston ring types should make no difference to oil pressure. What oil are you using and does the pressure drop when the engine is hot? Assuming you do not have an oil pressure regulator (a photo of the timing side would enable us to confirm this) then the oil pressure gauge reading will simply be a function of the spring pressure. The reading on the pressure gauge on a single merely confirms that oil is circulating. If you get a reading, the oil will be circulating and a change in reading from say 10psi to 25psi will not alter the volume of oil circulating. All the pressure gauge tells you is how hard the pump is having to work. See Waller on this.

ALL the oil gauge does is tell you the pump is working. The pressure forces some oil to be supplied to the rockers on models where they are enclosed and only for those about pre 55 after when it's from the return line. A high oil pressure makes the pump work harder and if it's worn may actually reduce the amount of oil being pumped to the big end. A roller bearing applies no back pressure by it's design and needs none. The oil would centrifuge if just supplied to the end of the mainshaft. JAP fed their plain big ends from a slinger ring in the veteran models perfectly satisfactorily. Nev

satchison wrote: my oil pressure gauge was reading at the maximum

Have you checked the operation of your gauge by applying a known pressure to it?

nevhunter wrote:ALL the oil gauge does is tell you the pump is working. The pressure forces some oil to be supplied to the rockers on models where they are enclosed and only for those about pre 55 after when it's from the return line. A high oil pressure makes the pump work harder and if it's worn may actually reduce the amount of oil being pumped to the big end. A roller bearing applies no back pressure by it's design and needs none. The oil would centrifuge if just supplied to the end of the mainshaft. JAP fed their plain big ends from a slinger ring in the veteran models perfectly satisfactorily. Nev

I'm afraid I cannot agree with this. It may not be what you meant to say , but an oil pressure gauge only does one thing and that is show the pressure in the oil system. It works by feeding the oil into a coiled piece of copper tube which the oil pressure tries to straighten thus moving the needle . The oil is fed to the roller big end which does have resistance according to how great/small its clearences.
A later post 49 oil pump will pump too high a pressure for a correct 0-25 psi gauge especially at high tickover when cold.
Reading some of the earlier posts it would seem you have the correct 'open' valves and the rocker box is held by a pair of steel plates fixed to the head. These do not have any oil supply and are just lubed with a grease gun every few hundred miles.
Have you run the engine with the oil pipe dis-connected at the union to the crankcase ? That should indicate the sort of pressure in the system ?
I would not run my '35 with no oil pressure showing.


Ian