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Help B & S 18 model 31D777 won't turn over


localboy's Avatar
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07-09-12, 06:10 PM   #1  
Help B & S 18 model 31D777 won't turn over

Engine won't turn over. Swap starter. No difference. Bypassed bat cables. No change. How can I verify that timing gear position has't changed or that camshaft is ok?
It is my 80 year old father-in-law Yard Machine mower.

Bill

 
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cheese's Avatar
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07-09-12, 06:48 PM   #2  
Adjust the valves, they are loose.


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07-09-12, 08:17 PM   #3  
Huh? First let me clear something up. When someone says the engine won't turn over, I always took that to mean that when the key is turned to start, the engine will not spin. Not "won't start". Have I been wrong?
Now, if I'm not wrong, how do loose valves cause the engine to not spin when the key is turned? I'm not being smart, I'm asking.

 
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07-10-12, 01:06 AM   #4  
Correct, it won't turn over because there is too much compression. The engine has a compression release because the starter is not strong enough to spin it without it. The compression release is a centrifugal device on the camshaft that bumps open a valve just a hair during cranking to release a little compression so the engine can turn. When the valves are too loose, the compression release bumps the lifter and pushrod, but what do they do? The valve is too loose, so the pushrod just moves a little, taking up some of the loose slack instead of actually bumping the vale open. This is a very common problem on these engines. The manual states that this should be done periodically, however, hardly anyone adjusts their valves until they experience this problem.

There is a chance that there is gas in the cylinder causing this problem, but I prefer to start with adjusting the valves, since it probably needs doing anyway. Usually when gas in the cylinder is the cause, the complaint will also include dripping gas, engine full of gas, gas coming out of muffler, etc...


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07-10-12, 09:54 PM   #5  
In my opinion that compression problem is not exactly 'no crank'. To me no crank means nothing moves. In the compression problem it usually cranks to the compression point and then no further.

 
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07-11-12, 12:57 AM   #6  
In any case, the original poster says it "won't turn over", so it's irrelevant. If it won't turn over, or won't crank, it means the engine does not rotate. A compression problem can and often does cause this. When one is completely dead, as in nothing moves, the complaint is usually that "nothing happens when I turn the key", or "it only clicks".


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07-11-12, 08:36 AM   #7  
the complaint is usually that "nothing happens when I turn the key", or "it only clicks".

which could mean battery, switch, safeties , solenoid , not just valves

 
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07-11-12, 09:57 AM   #8  
Exactly... except that's not what this person said. This isn't something high on my "let's argue about it" list.


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07-11-12, 10:29 AM   #9  
Ahh, I see. Now that makes sense to me. I didn't know they had a device to release the compression.
I am one of the few that does adjust valves almost every year. Adjusting the valves has become the first step in a tune up for me. My "mechanic" friends ridicule that practice but I have a female friend who has one of my old mowers with a 14hp single cylinder that I maintain and it will idle as slow as you want it to and never misses a stroke.

 
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