Flathead oil gallery

[Jacques Reed]

Thought this might be of interest:

As discussed, the orifice size on a bypass filter, or the orifice size in a grub screw when used in a semi full-flow filter, has to be very small to maintain oil pressure within the system.

I head read somewhere what the orifice size was on the bypass filter but cannot find it again. Not even sure if the size was factory info or someone's best measurement.

Thought I would see what it was on a spare bypass filter body I had laying around.

I used a set of numbered drills to check the hole size and my best estimate is a No.56 drill size which is 0.0465" diameter.

Unfortunately my No.55 drill is missing but a No.54 drill shank is too large and does not enter the hole so it could also be a No.55 which is 0.0520".

The difference between a No.56 and a No.55 drill is only 0.0055 so No.56 could still be the size as there is almost no gap around the drill in the photo. Whether that small difference would be critical is another matter.

In simple metric terms the hole is between 1.2 mm and 1.3 mm so any enlargement of it is not good for oil pressure.

Cheers,

[m606paz]

Originally Posted by Jacques Reed

Thought this might be of interest:

In simple metric terms the hole is between 1.2 mm and 1.3 mm so any enlargement of it is not good for oil pressure.

Cheers,

Jacques, thanks for your help!
Great info to know the hole diameter!

[Lynn Eades]

On a finer point, from memory, the volume that flows through a jet is not only dictated by the diameter of the orifice, but by its length as well.
Good info though Jacques.
For example the flow from the end of a long garden hose does not equal that from the tap without the hose connected.

[m606paz]

This is the home made grub screw found in the oil gallery

[m606paz]

This engine had enlarged holes diameter to put full flow oil filter and oil radiator. Now have original oil filter and pipes.