Have you checked that the flywheel key is not partially sheared?

The position you describe would be at the beginning of the power stroke. It would be followed by the exhaust stroke as the piston comes up. Then the Intake will open in preparation for the downward intake stroke and the magnet will be in the relative position you describe. The magneto produces a spark each revolution, one wasted as the charge has not been drawn in and compressed. Don't see where you adjusted valves after assembling, Valve may not be seating completely?

Walt Conner

First of all thanks for your help tinkerer200

The flywheel key is ok.

I like the way you are getting into details.

The wasted spark actually happens with the intake valve being open & the exhaust valve being closed.

The exhaust valve should be open so the spark does not cause an explosion.

I have another engine just like it except with a different code #, on that one the exhaust valve is open when the wasted spark happens.

I hate to open the crankcase again to check but I even took a picture of the aligned dots on the camshaft and the timing gear.

Right now I see only two possible causes:

1. A sheared flywheel key

2. The dots on the camshaft and the timing gear not being aligned

You didn't accidentally align the cam gear to the key way in the crank gear? I dunno if it would even crank if it were that far off though. I assume that it doesn't run, but your description doesn't say either way. Do both valves have a similar lift?

I made sure that the timing dots were aligned, even made a pic of it.

Engine cranks over ok but it will misfire.

Both valves have a similar lift.

Tried everything I could think of: Proper valve adjustment, put 5 mL of gas into spark plug hole to rule out plugged carburetor, got spark, engine would not even make an attempt to run, compression 120 psi.

mikeliv82_yahoo_com has the exact same engine & problem as I have.

Why was the engine disassembled? What new was used? Was the coil removed and flipped?

Engine would not start so I used starter fluid, which was a big mistake.

When engine turned over I heard a loud knock, after that engine would not run at all.

Figuring that something broke inside engine I disassembled it but could not find anything broken or damaged.

I did find a lot of carbon build up on top of piston which I cleaned.

The coil was removed and reinstalled the same way it came off.

Thanks for your input, it makes me think.

You seem to be convincing that the valve timing is still off. Once you are certain the flywheel key is still intact, I would pull the sump and inspect again. Look for something not so obvious. Look for a broken cam boss in the block/ damaged cam. Slide the crank gear off to be certain the key is intact.

Flywheel key is ok

Opened up the sump again:

Turned crankshaft many times to see if anything is broken or worn, nothing obvious

Connecting rod ok

Camshaft gear and lobes ok, timing dots were aligned correctly.

Timing Woodruff key & timing gear on crankshaft are ok

I don't know where to go from here:

Trouble symptom after I reassembled engine the first time: Engine cranks over, does not even make an attempt to start, backfires.

Hmmm. Seeing as though you are thinking there is a physical problem, and you have 2 engines- run them both through the strokes and monitor valve positioning, location of magnet, piston travel etc. On the other hand, a coil can simply throw a spark at the wrong time is the cd gets wacky. I've seen it on a Kohler several times, not a Briggs though. Be a hoot if it was just a bad spark plug....

Actually I started out looking at the valve positions by turning both engines CW through the strokes, but that made me dizzy, so I started to compare the flywheel magnet positions.

That is when discovered that magnet position of the engine I am trying to repair is 180 Deg off from the engine with the cracked engine block

Engine to be repaired 31P777-0367E1 flywheel magnet position with piston at TDC at 2:30 o'clock position

Engine to be repaired 31P777-0367E1 flywheel magnet position with piston at bottom at 7:00 o'clock position

Engine comparing to 31P777-0237 G6 flywheel magnet position with piston at TDC at 6:30 o'clock position

Engine comparing to 31P777-0237 G6 flywheel magnet position with piston at bottom at 1:30 o'clock position

Valve cover being in the 6 o'clock position

Coil is in the 5:30 o'clock position

The 31P777-0237 G6 has a cracked engine block due to low oil.

I am now so paranoid that If I ever get the 31P777-0367E1 running, that I will check the oil level every time I am using the riding mower.

I interchanged spark plugs from both engines, checked the spark gap, no change.

I do regret that I did not engrave the position of the Crank shaft timing gear & Camshaft gear on both gears to rule out anything crazy going on.

You could compare parts lists.If i recall, there was a crank shaft change ~ 3 years ago with these. Flywheels can also be different. IE the ones that have the canister style air filters use a different one than the panel type. Maybe others. A few newer ones use a longer key in fact. Were parts swapped? Cams remained the same i believe. Though, should 1 have an oil pump and the other not- the drive end would be different of course.

I did check the parts lists of both engines. Both engines use the same crank shaft and flywheel.

When I really focused on the crank shaft and the flywheel magnet positions, not being sidetracked by the valve position, I discovered

that I did have a sheared flywheel key, which was not easy to see.

So I used the flywheel key from my other engine to reassemble 31P777-0367E1, added some gas to the carburetor & started the engine

The engine ran, not perfect, until the gas in carburetor ran out.

At this time I am trying to get the fuel line from the fuel tank to the gas filter primed, I must say the fuel pump could do a better job of

drawing & pushing gas from fuel tank to carburetor.

I probably have to get myself some kind of a hand pump to draw the gas to the carburetor.

After filling carburetor bowl three times with gas, one would think that a good flow would have been established.

For now I am so happy that I got the engine to run. Thanks tomplum