I have found is the cast iron casings are out of round and in turn the babbitt
bearing surface as well. This happens after the bearing has been parted into
halves. Let me explain what I think
I am not sure of the process that the supplier
uses but just using some common sense makes me think that the shell is cast as a
whole. Then the ID and maybe the OD
are machined to size. The shell is
than poured with babbitt and bored to size with some additional
machining, grooving and chamfers.
bearing is parted into two halves, which distorts the casing, making it out of
round. I have found some bearings out of round by 0.020 inch.
The following is the simple and effective way I addressed the problem. The steps in this process are:
all of the engines I rebuild will have a new cam installed so it makes this much
easier, since the bearing surfaces are not worn.
However the same process will work with oversized bearings, using an
adjustable reamer, it just takes a little more time.
made a set of dies, to press the bearings back in to shape. It
is made from steel bar stock 1.5 X 3 inch.
Two pieces were cut to a length of 2.25 inch.
Locater pins of 0.375 inch diameter were installed and then it was bored to
1.375 inch ID.
cam bearing in the die and place die halves together with a thin strip of shim stock
to compensate for
spring back of the shell. Then
use a press to squeeze the halves together.
The left photo below shows the die with cam bearing and shims. The right
one shows the cam bearing being pressed.
The left photo below shows the die with cam bearing and shims. The right one shows the cam bearing being pressed.
pressing, the bearing will fit into the bore of the block.
All thatís left to do is ream the ID of the bearing to the correct
size. The photo below left shows a 0.750 inch spiral fluted reamer clamped in a vise.
Using a couple of hose clamps to apply pressure, the bearing is reamed to
size. For an oversize bearing, an
adjustable reamer would be used.
The finished result is a bearing that is round both OD and ID, and will slip into the bores of the block.
the installation, the rear bushing is pressed into the block and fitted
to the cam, but most importantly, it must be in alignment with the other two
boring bar pictured below was made using a 0.750 inch shell mill cutter, attached to 1
rod, with guides made for a slip fit into the front and middle cam bearing
bores. This tool slips into the
block, aligns, reams and lines up the rear bushing with the other two bearings,
allowing the cam to turn freely, with one finger.
final note: the rear cam bushing should be notched and grooved, allowing better