6.9l - Bent Pushrods
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6.9l - Bent Pushrods
I have a 1985 F250 with an ATS Turbo Package. I've benn running this setup for 7 years with no problems. Lately, I took my truck into the shop for some mimor repairs. When they had finished, they noticed that the engine was missing. After chacking all the injectors, they found that the rear cylinder, drivers side, had bent both pushrods. The pushrods were replaced and the motor promptly started missing again, after another inspection the pushrods on the same cyclinder and the number 2 cylinder on the drivers side both bent pushrods. The head was removed, no problems found. The valves were leak tested and the head re-installed. And again, the pushrods on the drivers side rear cylinder only this time were bent. A compression test of all cylinders showed that the compression was good. The rear cylinder had bent the exhaust valve and could not be tested. Please, Some one, Anyone, who's been trough this - Why is the engine bending pushrods??????
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Joined: Nov 2004
Posts: 5,638
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From: Manitoba
First what were the minor repairs.
Pushrods usually only bend if the valve hits the piston top, usually caused by the lifter rocker assy being torqued down when the engine is not at TDC. The other reason is the lifter not being bled off correctly before starting by rotating the engine by hand several rotations to ensure the lifters/valves/pushrods/cylinders do not conflict with each other. This usually only happens if the rockers and or heads are removed which allows the lifter to expand. When the lifter expands it makes the stroke of the pushrod longer on the first strokes and holds the valve open which contacts the piston and bends the push rod. There is only 35 thou between piston top and head, with about 50 thou plus 35 thou = 85 thou from the valve seated to the piston face at TDC.
Pushrods usually only bend if the valve hits the piston top, usually caused by the lifter rocker assy being torqued down when the engine is not at TDC. The other reason is the lifter not being bled off correctly before starting by rotating the engine by hand several rotations to ensure the lifters/valves/pushrods/cylinders do not conflict with each other. This usually only happens if the rockers and or heads are removed which allows the lifter to expand. When the lifter expands it makes the stroke of the pushrod longer on the first strokes and holds the valve open which contacts the piston and bends the push rod. There is only 35 thou between piston top and head, with about 50 thou plus 35 thou = 85 thou from the valve seated to the piston face at TDC.
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