Correcting Modified Oil Flow

[autotech2]

If there are any classic Japanese motorcycle enthusiast reading, this is a 1982 KZ1000 "J" engine.

The attached picture shows the cylinder block and head. This engine delivers oil to the camshaft bearings through the space between the 4 outer mounting studs, and the drilled holes in the block and head. The stud on the right is original equipment with an OD of 8mm. The stud on the left is heavy duty with an OD of 9.4mm. This is to strengthen the hold on the block and head in performance applications.

To me, the larger OD studs in the same ID hole obviously lessens the space for oil to travel, and therefore restricts the volume of oil delivered to the camshaft bearings.

Question #1: This is more geometry. The hole in the cylinder head is 10.8mm. Replacing the 8mm with 9.4mm studs, what ID should I enlarge the stud hole to accurately compensate for the reduced area for oil travel?

Question #2: The stud holes in the block are 11.8mm, while the holes in the head are 10.8mm. Will the larger space for oil travel in the block, stepped down to the smaller space in the head before reaching the cam bearings, have any effect on oil flow looking at the adjustment I'm trying to make?

[autotech2]

Here's a terrible sketch showing what I'm looking at: original oil passage, after installing oversized studs, and enlarging the head hole ID to 11.8mm equaling the block hole ID. Assuming 1mm increase in head hole ID is correct to compensate oil passage area lost with the installation of the 1.4mm larger OD studs.

Can anyone tell me the difference in flow from original to oversized studs, with enlarged head hole to equal original oil passage area through the head, but losing the effect of larger to smaller ID from the block to head? And if there is a difference, is there a way to compensate without enlarging the block hole ID? Possibly a little less enlargement of the head hole ID?

My amateur view shows me lost turbulence from eliminating the step-down, therefore the modification may overcompensate. And/or a loss of velocity in the head which may decrease flow, and the modification may undercompensate.

Thanks...

[Kelly_Bramble]

For an engineer this is not a simple question nor is there a straight answer. Fluid flow dynamics and design are dependant on pressure, viscosity, resistance to flow and other factors.. I'm going to give you an answer - but make it clear that I really don't know what the design parameters of this engine's hydrostatic lubrication system.

Whatever you do I would attempt to closely match the original designs fluid dynamics at this location.

The math I would consider it as follows:

Original design:

Hole area - Stud Area = Cross Section Area

then for the new modified design;

New Hole area - New Stud Area = Cross Section Area

or by algebra..

New Hole Area = Cross section area + New Stud Area

Area = pi r^2

Where:

pi = 3.14157
r = radius of hole or stud.

Be aware that the larger hole and stud changes the fluid dynamics along the length of the hole and stud.. The original step down was either a location feature for the head or a purposeful fluid restrictor.

Good luck

[Hudson]

The controlling aspect of the oil flow may well be the bearing. So multiply the circumference (pi x D) of the bearing(s) being fed by the average diametral clearance and compare this area to the area of the flow channel. If the oil escape area is much smaller than the oil feed area, you may not have a problem.

Note: the use of diametral clearance instead of radial clearance assumes that the bearing can leak from both sides of the journal.

[JAlberts]

The pressure loss through the body and the head is also a function of the length of the bores in those two components and, as a result, even though the head bore is smaller, if the length of the head hole bore is shorter than the length of the body hole bore then there may be either an equal or less pressure loss through the head hole bore than through the larger body hole bore.

Also, if you are using larger head studs, that would imply you have increased the engine's compression ratio and the connecting rod and main crankshaft bearings are the components that will most experience a load increase from that modification. As a result, you want to be careful not to make any oil flow changes that might reduce the oil pressure supply to those bearings.

[autotech2]

Also, if you are using larger head studs, that would imply you have increased the engine's compression ratio and the connecting rod and main crankshaft bearings are the components that will most experience a load increase from that modification. As a result, you want to be careful not to make any oil flow changes that might reduce the oil pressure supply to those bearings.

That's a very good point you made about more force at the crankshaft, and yes it's up from OEM 9.1:1 to 10.5:1. But I've learned a lot about aftermarket manufacturers over the years, as compared to OEM engineering. And when these HD studs came out I'm pretty sure they were not designed for both stronger clamping, and at the same time increased oil flow to the crank for higher compression. I think it was more like, the loss of oil volume up top shouldn't be enough to hurt anything.

By the way, this engine uses needle bearings at the crank with very low oil pressure (3psi hot/idle). So taking all the information I've gathered, and the fact that these HD studs have been out for years with no public hardcore failures, I'm going to split the difference. I'll drill out the head holes .5mm instead of 1. This way it should help any flow limitations up top, with a lower risk of overcompensation causing damage elsewhere.

What do you think of my conclusion?

Thanks to everybody for your help!!!