Cam Bearings




Cam bearings can be frustrating, as most all will require some work to get them, first to fit into the block bore, and second, fit the camshaft.

What 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 happens.

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.

The 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:

  1. Eliminate the distortion in the OD of the front and middle bearings

  2. Ream the ID of the front and middle bearings to size

  3. Install the rear bushing and ream it in alignment with the front and middle bearings.

     Most 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.

I 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.

Set 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.

After 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. 

To finish 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 bearings. 

The boring bar pictured below was made using a 0.750 inch shell mill cutter, attached to 1 inch drill 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.

A final note: the rear cam bushing should be notched and grooved, allowing better oiling.

Respectfully submitted: