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busted puah rod

T

The JD Workmen

Member
hello, this past weekend I had my oliver 77 at a tractor pull and it started popping threw the carb. So we loaded it up and brought it home. Upon disassembly we found an exhaust push rod had busted in half and the intake push rod to that cylinder got bent. We tore the engine further down to inspect the lifters and found that the exhaust lifter had a crack in it. There is no other damage that i can find the cam looks good the valves and lifters all move freely in there bore. Has any one else seen anything like this or have any idea what caused it?
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very -- very rare,I went thru several dozen lifters,some out of 8000 hr tractors with little maintenance,few oil changes,found very little to no wear on any even from engines with cam lobes worn completely off.
 
If you consider the failure sequence;

1) Exhaust lifter seizes in block.
2) Exhaust valve is stuck in the open state.
3) Piston contact valve and closes it (depends on head recess depth, valve lift, piston dome etc.).
4) Pushrod bends/breaks (they are surprisingly weak).
5) Intake valve attempts to open against internal pressure, bends pushrod (the internal pressure is because the exhaust valve couldn't open)

If you haven't already, I would look at the top of the piston for damage and pull the valves to see if they are bent.

Regards
Rich
 
One other thing, the back fire through the crab is because the exhaust valve didn't open and the pressure is going out through the intake manifold when the intake valve does open.
 
If pushrods are bent, the valves are bent, maybe not visibly crooked, but they are tweeked and a leak-down test will show it. A valve job would be required.
 
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