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Compression release quandry

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sdsherer
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2020/03/23 17:26:05 (permalink)
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Compression release quandry

Hey. I have a Craftsman LT2000 with Briggs 18.5 OHV Intek. Engine has all the symptoms of a failed compression relief mechanism. I've set the valves properly. Turns over until compression stroke, then can't continue. Then I can actually turn the engine backward by hand, hearing it release the compression. New battery, starter. Spins great without spark plug in.
 
Took engine out and sump off. Camshaft with compression release seem fine.  Spring intact. No flat lobes. I'm at a loss.  What else can it be?
 
Thanks,
 
Steve
 

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    AVB
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    Re: Compression release quandry 2020/03/24 07:46:52 (permalink)
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    Was you getting the decompression bump on the intake valve (lower rocker)? If not it is the ACR that is the problem.Even if the spring and arm is intact the activation pin could be worn to a point where it stick out to bump the valve.
     
    Also make sure intake is set at .003-.004 and the exhaust .005-.006. If you got the decompression bump and the valve are set right then it is a starter problem (ie voltage drop problem or worn out). Voltage across the starter (measure at the starter need to be at 9.5-10 vdc for good cranking speed)
     
     
    sdsherer
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    Re: Compression release quandry 2020/03/24 10:49:18 (permalink)
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    Thanks, AVB. I will put it back together and check for the bump again after I reset valves.  Thanks for your input. It helps a lot.
    sdsherer
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    Re: Compression release quandry 2020/03/24 18:38:05 (permalink)
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    While I had the sump off so I could look at the cam and the ACR, and after resetting the valves, it became apparent that the intake valve truly does need to be with specs, if not tighter. The valve did get a little bump, but it was very small even with .003 on intake. Is that all it needs, just enough valve opening to let a tiny bit of air out? It doesn't appear that the ACR peg is flattened at all. I guess I'll put it back together and see what happens!
    AVB
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    Re: Compression release quandry 2020/03/24 18:46:27 (permalink)
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    It should be more pronounce once the camshaft is stable as without the cover it is only supported on one end when the cover is off.
    sdsherer
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    Re: Compression release quandry 2020/03/24 20:46:14 (permalink)
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    I thought of that. Thanks for the confirmation. We'll see if it's better when the gasket and seal get here and I can button it up.  Thanks.
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