1206 camshaft key

IA1456 · Feb 17, 2019

About a month ago and I posted a problem of shearing the key on a 1206 camshaft upon startup if a overhaul causing the push rods to be bent on half the valves.i believe I figured out what happened. While over hauling I replaced the thrust plate on the camshaft I got one from a&I when it came it was to thick so I took it to work and had a toolmaker surface grind it down to the. Same thickness as the old one. Now this is where I don't understand what caused it to Gould up between the gear and the cam but I'm realtively sure what happened would explain why it almost started then it ran dry and the friction caused it to shear. Just looking for other thoughts if this is possible

Janicholson · Feb 17, 2019

Some thoughts that may apply. If the plate was too thick to work properly (possibly interfering with the cam gear) it needed to be discussed with A&I to assure the correct part was sent. The clearance for the cam to move forward and back is probably set by the thickness, and depends on how deep the cam gear can seat on the cam stub. If a new gear was used, and a new plate was ground, the clearance could have been zero. If the wear plate was hardened, and the surface hardness was removed by grinding, or an inadequate surface finish, it could add to that issue. My thinking is the plate was pinched between the cam and the gear. The plate controls the end play and absorbs axial thrust. Was engine assembly lube put on the components, and was the end play specification checked? Jim

IA1456 · Feb 17, 2019

I agree with all of your comments as far as dealing with a&i over the issue. You obviously never dealt with them in this type of thing. I'm thinking the moral of the story when in doubt stick with original parts and avoid aftermarket parts

caterpillar guy · Feb 17, 2019

How much difference in thickness was there. Unless there was an awful lot it don't think that was the problem. The old plate may have has some wear on it to show up as a difference if it was just a we bit.
I woudl more likely suspect the valve adjustment was to tight to not hit the piston as it came around. If you didn't get oil either it didn't get to run long enough for oil to get up there or the bearings are turned off the hole in the block for oil to flow.
The key could have been partly sheared from the last 45-50 years of use in the past, or worn some from those years.
I have derived these theories from past knowledge and looking at the CaseIH parts breakdown. It looks like there is a spot that was made slightly smaller for the the oil to flow around the plate for the gear to get oil.

dwag · Feb 17, 2019

agree

EP · Feb 18, 2019

Always check camshaft end play as well as backlash with the gear it meshes with. Agree with the idea of checking the oil passage to be sure it isn't plugged. If that thrust plate is too thick it's going to bind it up. There is a shoulder on the cam that the plate must not stick above. After the gear is installed on the cam the to thrust plate should spin freely.

1206 camshaft key

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