idler pinion oil groove question

[chaz]

question, Im looking at machining various phosphor bronze  bushes for various uses. my problem has always been the figure of eight oil groove inside. my understanding is the fig 8 allows oil to lubricate only.
Ive just recieved a idler pinion bush from Draganfly which has a spiral groove all the way through.. I think this will allow oil to seep from front to back or oil will enter the oil hole in the middle then feed out both ends.
picture shows spiral groove through.
any thoughts? good or bad??

[DAVE BRADY]

Hi Chaz,

What bike is it for?  The outer one on the A10/A7 is spiralled to to take the oil back in to the timing case to keep it out of the dynamo drive part of the case.
I think the idea of open spirals is to allow fresh oil to flow through the bush.

Dave.

[ChrisG]

In my humble opinion, the groove is there to help distribute the oil across the whole surface. A figure of eight can be used when the feed in is through a central oil hole thereby distributing it both ways. The spiral shown will distribute from one end to the other as the oils drips down the side of the boss on the gear.
In your case this will do the job required.

[chaz]

Dave , its the idler pinon bush for a 1969 A50.
the normal figure of eight either ends with the ends not breaking out to the outsides or they end in a circular groove inside, but not exiting to the outside.
If the spiral exits both ends , wont that mean oil running into the outer cover?
there is another on ebay that is fig 8 grooved.

sat indoors at the moment so cant look at the casings.

[Calum]

The figure 8 style oil groove won't stop the oil exiting the bush as there's no seal, although it will likely retain it for a slightly longer length of time. The spiral groove is far far simpler to machine of course, hence why you probably see it so often. In a sealed environment, especially one that is fed with a pump, the oil leaving quicker probably won't be a problem. In a total loss bearing fed from an oil pot of a given size, you could well run into trouble as the oil pot empties in a short space of time and runs dry.

Scrolls to keep oil in a box are usually on the shaft rather than the bush in my experience, but I suppose the relative movement is the same regardless of which moves and which is stationary.
Of course you could also look at this spiral and work out which way the oil is likely to migrate.

[DAVE BRADY]

Hi Chaz,

The inner bush in the crank case will let oil in to the crank case and the other way in to the timing case which has oil in it anyway.  I do not know offhand if the spiral in the outer bush is directional but there is the seal behind the points to keep the oil in.

Dave.   

[DAVE BRADY]

Hi,

A bit of an add on re idler bushes.  Unlike the A10 which has the PRV squirt oil on to the timing gears when it blows off excess pressure the A65 depends on small drillings to catch splashed oil.  A modification carried out by a reputable engineer when doing end feed conversions is to increase the size of the 'funnel' effect so that it catches a bit more oil and drill a couple of oil ways through from above crank case.  A bit more oil will not only help with lubrication but may help to reduce the noisy timing side of the A65.

Dave