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Please Help!! Briggs and Stratton 31P777 TOO Much Compression


Joseph1980's Avatar
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04-23-14, 08:21 AM   #1  
Please Help!! Briggs and Stratton 31P777 TOO Much Compression

I originally posted this in an older thread but figured it would do better in a new one.

I am having an issue. I adjusted the valve clearance a few weeks ago and it started and ran fine. About 2 days ago my daughter was riding the mower and instead of turning the ignition off she got up and the seat switch killed the motor. Every since then the mower will not start. I tried re-setting the valve clearance and still no luck. Here's a list of the symptoms and things I've checked so far.

New Ignition
New solenoid
Took starter off and tested just fine
charged battery
When I turn the key the motor turns about half and seems to get stuck? Like it has WAY too much compression, When I take the spark plug out it turns just fine. Like I said earlier this happened before and I adjusted the valves and it fixed the issue. I'm not sure why my daughter killing the mower that way would cause this issue? Any advice or help would be GREATLY appreciated. Bellow are the mower specs.

Craftsman DLT 3000
19.5 HP Briggs and Stratton
Model 31P777
Type 0296 E1
Code 050519ZD

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04-23-14, 10:37 AM   #2  
I can't shed too much light on why the kill switch would cause you a "stop on compression" situation later. Since the engine cranks at all, I would think that there is nothing wrong with the kill switch.

I would remove the valve cover and the spark plug. Now turn the flywheel very, very slowly and keep a close eye on the intake valve. It will eventually open and then close. Shortly after it closes, you should see a very small bump in that intake valve. This is the compression release working. If you do not see that and the valve lash is set right, I fear you may have a camshaft failure.

Others may have some better advise, but in the mean time take a look and see if you can observe that bump in the valve. Without that bump, your battery will never crank that motor past the compression stroke.

 
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04-23-14, 10:47 AM   #3  
I'll give that a try... Which one is the intake and outtake? top or bottom? I have watched a couple of videos on youtube and they are giving me conflicting info. Also I see some say that the piston needs to be TOC (top of center) how do I know if its TOC? without taking the block off, if I need to take the block off that's not a big deal just trying to stay away from that. Thanks for the reply

 
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04-23-14, 12:02 PM   #4  
The intake valve is usually the bottom one on B&S motors. To be sure, you know that a 4 stroke motor has an intake, compression, power and exhaust strokes. So when turning the flywheel, eventually you will see the exhaust open/close and then right away the intake will open and close. Then it will turn for a little while with nothing happening with the valves and then again the exhaust will open/close and then the intake will open/close. So when you see these two valves open and close together, you know the second one must be the intake valve.

So with that said, once the intake valve opens and then closes, very soon there after there should be a small bump in that valve. Without it you will not get any compression release and the motor will not crank over.

To set the valves, you turn the flywheel past the intake stroke and when the piston is coming up for the compression stroke, put a pencil with a soft eraser into the cylinder and rest the eraser part on the pistion. Keep turning the flywheel until you notice that the pencil stops rising. That is TDC. Now to set the valves, make a mark on that pencil relative to the cylinder hole and another, exactly 1/4" higher. Now keep turning the flywheel until the 1/4" mark is where the original mark was and now you have the piston 1/4" past TDC. You do not need to be exact here. All you are trying to do is ensure that both valves are fully closed and you are past the compression release bump on the camshaft.

At this point your intake valve lash should be 0.003" to 0.005". This is the critical valve lash for starting. The exhaust valve should be set at 0.005" to 0.007" but it has nothing to do with the start up of the motor.

If your valves are currently set right, check your feeler guage. I had a cheap one once from a dollar store where the 0.005" was actually 0.008". I spent a lot of time working on my valves before I figured that out. Lesson here. Don't buy precision tools at a dollar store. lol.

 
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04-23-14, 02:55 PM   #5  
I noticed earlier that the Bottom (Intake valve) doesn't go down nearly as far as the outtake vale does. Would this be a problem? and if so what could be causing it?

 
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04-24-14, 07:02 AM   #6  
That question is above my pay grade. If your valves are set right and you are seeing that ACR bump and it still does not start it may have something to do with it. What kind of difference in movement are you seeing?

 
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