[Fot] Cam Bearings expansion

[Scott Janzen]

Thanks, everyone for the feedback.  The first step will be to straighten the cam - the machinist I work with will use the same methods/tools he uses for crank straightening.  BTW, he says he rarely sees a new cam that is straight.

Next steps, if needed, vary.  Cleaning up high spots on the bearings with a sharp tool is one method, by looking for shiny spots after the cam is installed and rotated, then removed. The cam journals could also be polished down by 5/10,000, as they measure out at the high end of the factory spec.
Third alternative, and perhaps the one that addresses the other root cause, is to remove the cam bearings, check the block to see if the bores measure under the 1.969" spec, and if so, have the them line honed.  This would get everything in line and probably open up the bearing bores slightly to increase the very low installed bearing clearance.  However, it's the most expensive and most work, and trashes all the new cam bearings.

I'll report back.  I learn new things every time I tackle a new project - just wish I learned them in the right order!


On Jan 7, 2015, at 4:56 PM, Larry Young wrote:

It is not difficult to straighten cams yourself. You can do it with a blunt cold chisel and hammer, but I prefer to use an air hammer with a blunt rounded chisel.  Use V blocks and a dial indicator to check it and decide where it is bent. You hit the cam between the lobes, which relieves the stresses and causes it to curve up. It seems counter intuitive, but that is the way they bend. It has been a while since I've done it, but I believe that is how it's done with these cast iron blanks.  If it still doesn't fit, then have it ground to fit as Greg suggested.
 - Larry Young

On 1/5/2015 8:40 PM, Scott Janzen via Fot wrote:
> I've got a bit of cam bind in a new cam I'm installing in the GT6.  It appears to be a combination of slight run-out (i.e., the cam is slightly bent, 1/1000 of runout in the middle), journal size right at the factory maximum spec, and installed bearing I.D. that is at or below the factory minimum I.D.
> 
> It's also possible that the block is not bored perfectly straight as the binding is not consistent around the rotation, but another cam I have, with journal diameters 5/10,000 smaller, turns freely.  I have not checked that cam for run-out.
> 
> Question is, is there a tool to "expand" the bearings into the block and possibly gain a bit of clearance?  I'm told the factory manual for one of those Octagon cars calls for such a tool.  I'm using the typical Spitfire bearings.
> 
> Next stop is a machine shop with a crank straightening machine to see if they can use it to straighten a cam.
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