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Ok, I have a craftsman riding mower, model 917.258523. It ran fine a week ago. I had to replace the flywheel because the plastic one that came on the motor started cracking and messing up the starter gear. I replaced the flywheel and now when I turn the key the motor turns over a full turn and then stops. If I hold the key it will continue to make a full turn and stop. the motor pauses for about 5 seconds then rotates again. I can spin the motor both ways by hand fine. I checked the spark plug and there is plenty of spark. I also thought it might have been the battery but used jumper cables and hooked it up to my car and it did the same thing. I checked the key on the crankshaft and it is still entaced. What am I missing or what can I try. Thanks

I am certain that the flywheel is NOT plastic. Perhaps the fan or fins are plastic. If you removed the entire flywheel, did you remember the flywheel key? This is what times the ignition

What engine is fitted?
Is there any model type or code numbers?

The key that you are talking about is the one that holds the flywheel assembly to the crankshaft, correct. If this is the one your talking about I did put it in and just checked it to see if it was sheared and it isn't.

The engine model number is 28N707. It is a 15.5hp briggs and stratton

What happens if you take the spark plug out and turn the key to engage starter?

If I take the spark plug out then the motor spins just fine.

Check your valve clearances.
Valve Clearance | Briggs & Stratton

If ok then the decompressor on the camshaft could be broken and not allowing engine to turn past conpression stroke.
A decompressor lets excess pressure out of engine to allow starting.

Inlet should be 0.003"-0.005"
Ex should be 0.005"-0.007".

I will check the valves. I need to buy a gauge for it. In the mean time. Where is the decompresser and is there any way to test it.

William2146 said:

I will check the valves. I need to buy a gauge for it. In the mean time. Where is the decompresser and is there any way to test it.

Click to expand...

The decomp is on the end of the camshaft which is in the engine.
The only way to test it is checking valve clearances.
With the rocker cover off and turning the engine by hand the valves should go up and down.
Looking closely 1 valve should open then close and then it should open/close ever so slightly like a small bump.
Thats the decomp working.
If it doesnt bump then the decomp may be broken and you would need to replace the camshaft.
Read the attachment i posted about setting valve clearances carefully.
You only need feeler guage.

Ok, I checked the valves and they are good. The decompressor seems to be working. I saw the valve move slightly but not 100% sure it was that or me twisting the motor to far and starting on the intake or exhaust stroke. Any other ideas. I seem lost since it started fine before I put the new flywheel on.

Did you loosen the ign coil at all? I ask because sometimes the OD of the flywheel gear, you "must" loosen the coil to remove the FW. If so, loosen the 2 bolts that secure it and move the coil the FURTHEST "away" from the flywheel and slightly tighten them. Then rotate the flywheel so that the magnets are centered just under the coil. Take any business card and place it between the flywheel magnet and the coil. Loosen the 2 coil bolts, and the magnetic force will draw the coil to the flywheel magnet. Then tighten the 2 coil bolts, rotate the flywheel and the business card will fall out giving you your coil to flywheel clearence. It's not totaly accurate, but I have been doing it this way since the 60's with never a problem.

I would check the size of the positive battery cables. Companies have been putting larger gauge (smaller diameter) wires on to save money. This creates a high resistance which means less power available to the starter. I recommend 6gauge wire for both battery to solenoid and solenoid to starter cables.

I didn't have to move the solinoid to replace the flywheel but checked the spacing with a buisness card just to rule it out and it didn't change the problem. Also, not sure exactly what gauge wire there is on the battery and starter, however I had no problem starting the mower untill after I replaced the flywheel.

William2146 said:

I didn't have to move the solinoid to replace the flywheel.

Click to expand...

I assume yopu meant "the ign coil"

Something to do with this flywheel.
What happens if you remove the coil, keep the plug in and turn engine over on the starter?

Could the alternator under the FW be dragging?

Is there 2 much oil in the engine?

pugaltitude said:

Something to do with this flywheel.
What happens if you remove the coil, keep the plug in and turn engine over on the starter?

Could the alternator under the FW be dragging?

Is there 2 much oil in the engine?

Click to expand...

Just a thought but do you have the correct flywheel? One that is slightly different could cause the intake, compression, firing, exhaust cycles to occur at the wrong time. The flywheel will fit but it won't work. Hope this helps. Dave

pugaltitude said:

Check your valve clearances.
Valve Clearance | Briggs & Stratton

If ok then the decompressor on the camshaft could be broken and not allowing engine to turn past conpression stroke.
A decompressor lets excess pressure out of engine to allow starting.

Inlet should be 0.003"-0.005"
Ex should be 0.005"-0.007".

Click to expand...

So here's the kicker for me. I have a similar issue with my Craftsman B&G 21HP motor. It won't turn past 1/2 but if I have my Dad manually hand turn it past while I'm turning it over it will start. Could this be the decompressor too? I've already replaced both intake / exhast valves and rods thinking that was the problem.