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First off I will let you know what the details of the mower are, It's a craftsmans 42" with a Briggs and Stratton 15.5HP turbo cool engine (28n707)

I bought the mower off my neighbor not knowing what it needed and took on the project of fixing it up.
Everything seemed to be in pretty good shape besides the ring gear was completely stripped so I replaced that and when re-installing the engine I forgot to put the flywheel key back on and tried to start it not realizing it was missing the flywheel key. It would backfire through the carb and stop turning over on the compression stroke. I adjusted the valve clearance as well. The spark plug is also new and there is fuel getting to the cylinder I can smell it on the plug not to mention I've poured it directly into the cylinder to see if it was a fuel issue. It would only backfire out of the carb..


Today I bought some key stock to use as a flywheel key, I couldn't seem to file it down to the right shape and every time I tried to crank the flywheel down it wouldn't seat properly on the shaft. Finally after trying everything I tried to crank the flywheel down on the shaft without the key and it still won't go all the way down! What could cause this?? I'm running out of ideas for solving this problem. I need someone with experience to give me their opinion on what I can do to get this thing cutting grass! Thank you in advance, Matt

Buy the right key from Briggs. Key stock is a good way to do a lot of damage.

reynoldston said:

Buy the right key from Briggs. Key stock is a good way to do a lot of damage.

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Correct although this does not answer why the flywheel will not go down without the key. There is no reason to "Crank Down" a flywheel. It should drop right on and seat. Check for a loose, dislodged magnet in the flywheel. I would also point out that a B&S key is ONLY to correctly position the flywheel to crankshaft until the flywheel nut/bolt is "properly" torqued. It is not to keep the flywheel from turning.

Walt Conner

Tinkerer200 said:

Correct although this does not answer why the flywheel will not go down without the key. There is no reason to "Crank Down" a flywheel. It should drop right on and seat. Check for a loose, dislodged magnet in the flywheel. I would also point out that a B&S key is ONLY to correctly position the flywheel to crankshaft until the flywheel nut/bolt is "properly" torqued. It is not to keep the flywheel from turning.

Walt Conner

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Go for it seeing the proper B&S key way is so much money. :thumbsup: Yes the flywheel should drop right on and seat so just maybe this should be telling you something?

Tinkerer200 said:

Correct although this does not answer why the flywheel will not go down without the key. There is no reason to "Crank Down" a flywheel. It should drop right on and seat. Check for a loose, dislodged magnet in the flywheel. I would also point out that a B&S key is ONLY to correctly position the flywheel to crankshaft until the flywheel nut/bolt is "properly" torqued. It is not to keep the flywheel from turning.

Walt Conner

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Usually it is because the magnets have picked up something,, like perhaps the flywheel key and that is stopping it from seating.
The magnets themselves can come loose and get out of position.
If the flywheel has been spinning on the crank you can get little lips on both the flywheel & crank key ways.
The tollerance on the tapper is +/- 0.0005" so you don't need much to stop it seating.
The crank is not hardened in this area and if you go hammering a key in that is the wrong shape oe size you can damage the crank.
Get some "bearing blue" , wipe a thin coat on the inside of the tapper then slip it strait down on the crank without any rotation the pull it back off.
The crank will hae some blue where it is high and some blue will have been wipped off the tapper hole where the damage is.