Is the problem that the shaft doesn't rotate to the correct spot? The lever installed on the end of the shaft incorrectly? Take linkage loose and see if you can get it to work by hand.
Or is there wear on the contact parts? Not sure why this would ever occur.
Has this engine been running lately? I'm wondering if there's enough carbon underneath the valves to hold them open enough that the decompression cam cannot touch the rocker arms. Might need to spin it over for a while and spray the valve stems with some kind of penetrating oil to get them to seat properly.
Another possiblility is that the seats have been replaced and ground to a higher profile or the valves replaced with some with slightly larger heads so the valve stem height is no longer in a correct range. I cannot find an installed height spec on the valves in any of the information I have on any CAT engine, so I wonder if they ever published that number.
We have some old D318's that have pretty severe wear on the rocker surfaces where they contact the top of the valve stems, and they still decompress OK, so I'm wondering if wear is the problem.
We reinstalled the head on a IH RD450 when I was a teenager and forgot the rotators, Had to adjust the rocker studs a long way to set the valves! The next time I was at the machine shop, the guy handed me the set of rotators and it all began to make sense. But the parts book I have (D318 which should be similar) doesn't show any rotators, so that wouldn't be it.
Hi Team,
I think CCJ has nailed it with the valve stem heights/lengths above the upper head face are too short/low. This puts the rocker arm at an incorrect angle so as the button on the lower arm is too far away from the de-compression cam bar.
Maybe in the past, with pocketed in/worn valve seats, the stems were ground shorter to allow the valve to close onto it's seat in the full compression position.
If I recall correctly, some Cat Engines had hardened caps to fit on the ends of the valve stems, but, I do not think the D311 was one of them. These may or may not help here to reset the rocker into an operable range.
Only other Bodge would be to build up the de-compression buttons on the rocker arm and grind to get into range.
Hope this helps.
Cheers,
Eddie B.
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