Adding Front Drainbacks. Adding
front drainback holes in the lifter valley is a great mod for a v-drive boat (since the motor sits backwards) or for a drag
car (sudden decelleration with parachute deployment) or any max effort oil return situation.
The first photo shows
the front of a lifter valley on a block with the added drainback holes:
The passenger side drainback is a no-brainer and easy mod...just eyeball the starting point from the OUTSIDE of the block
and keep stepping up drill bits until you're at about 1/2-inch drill and on plane with the oil channel in the valley, then
use the carbide bit to smooth it out:
View from the outside:
Notice in the above photo how the lifter bosses are visible through the new front drainback hole...this side is easy
and can be very effective for oil drainback in the above noted applications.
The driver's side will also be effective
but positioning the drainbback hole is critical
. We are working very much near water jackets and oil
galleries when doing the driver's side.
Must be angled downward and a pointed a little toward the center of the block.
In the photo below, study the angle of the driver's side drainback hole (left) compared to the passenger side hole
Note (above) that the hole on the driver's side is very close to the cylinder bank's water jacket and lifter's oil gallery.
The drainback hole is a little offset from the drainback channel, but it is still on the same level as the channel,
so oil will drain, no problem. This hole does not need to be 1/2-inch to work (1/2-inch increases risk of breaking
though into the wrong place). Look at the photo below:
You can use your finger in the waterpump hole as a guide/help you feel how much wall you have to work with and also help to angle
the drill accurately. Additionally, a flashlight in the cylinder deck's waterjacket holes can be helpful too. Note
the proximity of head's oil drainback hole next to our new 1/2-inch hole. There is certainly enough material to do this, but
be careful because of the several walls where you may break through and really open a can of worms.