JD 105 with Briggs 17.5 HP Broken Rocker Arm


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Old 04-12-19, 12:42 PM
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JD 105 with Briggs 17.5 HP Broken Rocker Arm

A customer stopped by today and said he had a John Deere 105 with a Briggs 17.5 HP engine and the rocker arm broke in half and the push rod was bent. Now, I can certainly fix it however, i would like to know what possibly happened before I do. My guess is the piston hit the valve. It is on the Intake side. He said the engine was running normal when it happened. The engine had oil. The engine has about 100 hours on it. What are your thoughts on why it may have happened. Could the valve have got stuck in the closed position and that is when the piston may have hit it ?? I have never seen this happen in the 10+ years I have working on these units. The guide was not sticking out of the head.
 
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Old 04-12-19, 03:43 PM
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The valve may have gotten stuck and the rocker arm broke in trying to push it or the valve lash may have gotten too far out of adjustments and the rocker slipped off the push rod.

I don't know if that engine would be an interference type where the piston and valve occupy the same space at different times. Some automotive engines are.

The piston wouldn't hit the valve if closed, regardless.
 
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Old 04-12-19, 07:26 PM
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The valve had to stick. If the piston hit the valve, it would just push it back into place, no way for that to bend the push rod. The push rod can't push the valve open while the piston is approaching TDC unless the entire camshaft was out of time, and then it wouldn't have been running in the first place. I've seen this before and usually there is a varnish on the valve stem that washes off easily with carb cleaner, and the problem usually comes with running old gas at the time or recently before it happened.
 
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Old 04-13-19, 08:26 AM
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Thanks everyone for the responses
 
 

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