Hanna the Grader (my '68 12F grader) is running well and earning her keep with all the snow we've been needing to clear this month. But there is an issue with the circle control in the power control system. Circle turns fine clockwise. But counter clockwise intermittently results in an unhealthy clattering noise. And on Friday, there was the noise and then sheared the shear pin. After 3 more shear pins, I turned the circle clockwise without issue and did a bit of plowing before needing to turn counter clockwise again. But this time it moved counter clockwise with no issue.n

I'm very much a newbie in all this and the maintenance manual does not have much to say beyond a general description of the Power Control box. If I had to guess, it would strike me as a gear with a bad tooth that gets caught in the bad spot sometimes...)

Any wisdom out there about something like this?  Thanks!

Hi, Onfoot.
Your issue may well be in the circle guide adjustment and/or wear therein. The easiest way I know of to check is to set the blade square and centered under the machine, blade resting ON the ground without downward pressure, and drive forward slowly and watchfully until the circle appears to be fully back against the front set of circle guides. This should only take a couple of inches of forward travel.

Then check the meshing of the circle drive teeth with the circle and all the guides for adjustment. I don't have the exact specs but there should be pretty minimal spacing between the circle and the guides and the teeth should be fully meshed without bottoming out.

Also. I have never heard of it happening on a Cat grader but it might be worth looking across the top of the circle from several directions to check for warping. You need to place equal height blocks on top of the circle high enough to be seen over the draught frame. It could also be worth measuring the inside diameter in several places to check for 'out-of-round'.

Shady tree workshop stuff. Hope it helps.

Just my 0.02.

Heaps of grease on the circle and dig the corner of the blade in the ground and creep forward to persuade it to co-operate

Thanks, Deas. Shady tree shop stuff for sure--but the snow's got to all melt first... Really useful tips and suggestions. Much appreciated as always!

Hi Team,
found this Service Magazine from April 10 1969 that covers Grader Circle adjustment.

www.acmoc.org/bb/discussion-d72/27767-mo...er-circle-adjustment

Hope it helps.
Cheers,
Eddie B.