My recent disaster

RknRusty wrote:

ian1954 wrote:I am not sure that the oil groove is necessary.

If bronze is used, doesn't it soak up and wick oil by itself? I remember that from my copy machine days.
Rusty

Almost correct but no cigar!

Bronze or phosphor bronze is ideal for bearing material but it is not porous and difficult to machine.

The best bearing material is Oilite bushes. These are made from bronze and are porous. Confused?????

Oilite is a porous bronze or iron alloy commonly impregnated with an oil lubricant and used in bearings. The original Oilite and Oilite Plus are bronze alloys, while Super Oilite and Super Oilite 16 are iron-based.

Oilite is formed using powder metallurgy so that tiny pores are present in the metal. The pores are then vacuum impregnated with an oil to improve the materials bearing ability.The material holds approximately 20% oil by volume.

Now here is the challenge with Oilite.

Due to the porous structure, machining Oilite poses a special situation. To machine Oilite, the cutting tool must be and stay sharp; therefore, tungsten carbide is often used. The sharp tool preserves the open-pore structure, because a dull tool would smear the material and close up the pores that are on the surface adjacent to the journal, which is where the lubrication needs to be.

Reaming is not recommended, but can be done with an extremely sharp tool.

Honing and grinding should not be performed on any surface that is in contact with the journal as these processes always smear the pores.

It is safer (easier) to buy preformed bushes.

Try finding an Oilite or even a ball raced bearing with an inner hole of .28175.

7/32 is available but the Oilite will need machining. Ever tried boring out a ball raced bearing? Almost impossible. The inner is rock hard and almost impossible to stop spinning.

The alternative is to reduce the crankshaft by .00025 (not easy to set up!) or attempt a press fit. This can ruin the bearing (I know!!!)

Ian; how much on a bushing fit are you going to allow for lubrication flow as the crank to bearing fit ? Eric

getback wrote:Ian; how much on a bushing fit are you going to allow for lubrication flow as the crank to bearing fit ? Eric

I aim for 0.0005–0.0008". Usually known as a sliding fit.

If you take the reamer that I use .21905 and subtract the hole .21875, you get .0003, But by using cutting fluid and other inaccuracies I think I end up in the above range.

I do not have the equipment to measure bores of that size accurately.