Tomas L

M42Racer,

If I remember my bearing theory correctly then your conclusions are wrong.

It's not the oil pump pressure that keeps the bearing and the crank separated. It's pressure in the oil film caused by the friction between the oil and surfaces. This pressure increases with speed difference (bearing rotational speed) and oil viscosity (and some other factors). If you multiply oil pressure with bearing area you will see that the oil pressure from the pump nowhere near gives enough force to keep the journal and bearing separated.
The oil pump pressure only serves to pump oil into the bearing. To get maximum amount of oil into the bearing you should put the hole in a low pressure area on the journal, you also want to fill the bearing with oil just before you place heavy load on the bearing. If you put the oil hole in a heavy loaded area then the oil pump pressure will not overcome the bearing pressure and no oil will enter the bearing. You will also drastically reduce the bearings load carrying capability of you reduce journal area by putting a hole in a loaded area.

Tomas

Laust Pedersen

“4. Where would you want the Oil supplied to give the best control? At the heaviest loaded part.”

You got to be kidding. Lets assume a conservative 100 bar combustion pressure. The connecting rod sees an effective WxD = 2.4x5.3 cm2 = 12.7 cm2 (W & D is the width and ID of the bearing cap) bearing area. With a 100 mm bore (= 78.5 cm2) you have a 78.5/12.7 * 100 bar = ~600 bar pressure on the oil film. Now try and pump that up with a 5 bar oil pump.

Laust

Edit: I now see that I am essentially quantifying Tomas’ post (same conclusions).

m42racer

Your correct and I was wrong in my first post and corrected it by my last post. This is why the oil hole is off center. It still is not at 90 degrees though. My understanding was the hole was not at 90 degrees and that it was in a straight line from the Main Journal. I have since been told that its off center for the exact reasons you both state. The Oil galley wants to be straight so the Oil does not have to change direction, and is drilled off center to place it in a the required place.

Tomas L

Thanks Laust, I was to lazy to do that calculation.

Bengt Sweden

No it works just like in any other hydraulic system, the turns make no difference, just like in your brake system. The only difference is that the outlet has a slightly shorter distance from the crank center and thereby a bit less centrifugal force but that is too little to make any real difference.

The oil travels "uphill" to the crank center and then "downhill" to the rod bearing, first loosing pressure then building pressure again. If the oil were a rope then it would be no problem but as is with too much negative tension in the center, the oil column can break. We did tests in school to simulate this condition, with degased oil compared to normal oil. Few cranks have as large main journals as ours and those who have are for cars which run lower rpms. In some cases racing cranks are built with center feed oiling to avoid this.
problem.
Bengt