JS26 Pushmower - Upon starting it sparks and runs extremely loud and rough

[Laker64]

Hey folks,

I have a John Deere JS26 Momentum push mower (here it is in a video

). It ran over something a metal sewer cover. It immediately stopped and did not start. I assumed it needed a flywheel key. I replaced the flywheel key today (it was indeed sheered) and put it back together. Upon starting it the mower exhibits the following behavior:

-the sound of the mower increases very rapidly (1-2 seconds)
-the mower runs stronger and stronger, you can feel the vibrations
-you can see visible sparks underneath the mower

Does anyone have any insights here as to the problem? Any advice would be appreciated! Please keep in mind I know very little about mowers but am willing to tackle something (with the help of youtube!).

 

[Scrubcadet10]

Remove your spark plug.
Tip the mower up, (handle down) or carb side up, and rotate the mower blade and see if it spins concentrically. If not, your crankshaft is probably bent and the blade may be impacting the deck slightly.

 

[Laker64]

Remove your spark plug.
Tip the mower up, (handle down) or carb side up, and rotate the mower blade and see if it spins concentrically. If not, your crankshaft is probably bent and the blade may be impacting the deck slightly.

So when I do that it spins, however, it does not spin completely freely. I can do like a 45 degree spin and then I receive some resistance. With a little force I can push it along and spin it another ~45 degrees or so until I feel more resistance. I tried to get a look at the crankshaft directly from underneath but there is a cover over it.

 

[Scrubcadet10]

So when I do that it spins, however, it does not spin completely freely. I can do like a 45 degree spin and then I receive some resistance. With a little force I can push it along and spin it another ~45 degrees or so until I feel more resistance. I tried to get a look at the crankshaft directly from underneath but there is a cover over it.

spark plug in or out?

 

[Laker64]

Looks like I didn't read your response carefully enough. Spark plug in I only took the spark plug cap off! I'll remove the spark plug and then let you know how it goes.

 

[Scrubcadet10]

The resistance you were feeling was compression created by the piston moving up in the cylinder when the intake and exhaust valves were closed

 

[Laker64]

So I ended up needing to grab some deep sockets (did not have any that fit the spark plug). I removed it tonight and spun the blade. Nothing seemed out of place. I took a video so that you could see what I saw.

lawnmower

Watch "lawnmower" on Streamable.

streamable.com

 

[bertsmobile1]

Your crankshaft is bent
In my workshop that mower is now spare parts
In the USA where you use bar blades so the cranks bend all the time apparently crankshafts get straitened which from an engineering & metallurgical stance is both dangerous & plain stupid .
However it seems that the USA philosophy is "If it is cheap enough to do then it is good enough to do "
Getting a crankshaft to run true to within 0.001" by bending it back outside the engine is hard enough let alone doing it inside the mower .