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Donald
Donald, Small Engine Technician
Category: Small Engine
Satisfied Customers: 2186
Experience:  I have 25+ years of experience repairing 2 & 4 cycle engines
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I have a craftsman 21 hp lawn tractor that will not start. I

Customer Question

I have a craftsman 21 hp lawn tractor that will not start. I replaced the starter thinking that was the problem and that didn't work. I used a meter on the solenoid and get 12v on the battery side and o on the starter side with the key off. with the key turned i get 12v on the abttery side and about 6v on the starter side. I had the battery jumped to another vehicle while testing, thinking the battery may have been the problem. The starter engages but will only spin the flywheel slightly.
Submitted: 1 year ago.
Category: Small Engine
Expert:  Donald replied 1 year ago.

Hello. Thank you for choosing Just Answer. My name is***** will be happy to assist you.

Expert:  Donald replied 1 year ago.

Remove your spark plug, then check to see if your engine will spin freely. If your engine will spin freely after you remove your spark plug, then it is likely that your valves are out of adjustment.

Expert:  Donald replied 1 year ago.

We can continue from here.

Customer: replied 1 year ago.
I removed the spark plug and the flywheel only spun about 1/4 turn in each direction.
Customer: replied 1 year ago.
Id rather go through email
Expert:  Donald replied 1 year ago.

I am back with you. Sorry for the delay. What brand is your engine? Single cylinder, or twin cylinder?

Customer: replied 1 year ago.
It is a single cylinder Briggs and Stratton #(###) ###-####G1
Expert:  Donald replied 1 year ago.

Thanks for this information. Have you check your oil level to see if it is too low? Many times if your engine will not spin freely after you remove your spark plug, our problem could be caused by a broken connecting piston rod, or a loose magnet under your flywheel, that is wedging between your flywheel and the stator/alternator underneath your flywheel.

Customer: replied 1 year ago.
the oil level was slightly low but not too bad. Should the flywheel spin freely all the way around?
Expert:  Donald replied 1 year ago.

Yes, your flywheel should spin freely all the way around, when your engine is working properly.

Expert:  Donald replied 1 year ago.

Have you tried spinning your flywheel by hand, after you have removed your spark plug?

Customer: replied 1 year ago.
it would just go about 1/4 turn or less in each direction and then stop I could not force it any further
Expert:  Donald replied 1 year ago.

Here are three things you can check:

  • check for a broken connecting rod
  • check for loose magnets underneath your flywheel
  • remove your valve cover, to see if something is binding
Expert:  Donald replied 1 year ago.

You can remove your spark plug, and insert a screwdriver into your spark plug hole, to feel for movement of your piston, as you rotate your flywheel.

Expert:  Donald replied 1 year ago.

You can also look for a crack in your engine block, near your electric starter.

Expert:  Donald replied 1 year ago.

Let's hope our problem is a loose magnet, rather than something internal.

Customer: replied 1 year ago.
I will check tomorrow and let you know Thanks
Expert:  Donald replied 1 year ago.

You are very welcome! I look forward to knowing your results.

Customer: replied 1 year ago.
I removed the spark plug and put a screwdriver in the opening. I could feel the cylinder head move slightly when rotating the flywheel the 1/4 that it would turn. after doing that if i pushed hard on the screwdriver i could feel the the cylinder move in about 1/4" or so
Expert:  Donald replied 1 year ago.

Thank you for checking. Are you familiar with removing your flywheel?

Customer: replied 1 year ago.
I'm sure I can remove it. what should I look for after removing it?
Expert:  Donald replied 1 year ago.

Look for loose magnets under your flywheel, after you remove it. If all of your magnets are intact, then you likely have internal damage inside your engine.

Customer: replied 1 year ago.
Ok Ill get back to you tomorrow.Thanks
Expert:  Donald replied 1 year ago.

You are very welcome!

Customer: replied 1 year ago.
i pulled the flywheel off and nothing was loose below it. I put the flywheel bolt back in and tried to spin the motor but it only turned 1/4 turn or so. Same as before.
Expert:  Donald replied 1 year ago.

Thank you for checking.

Expert:  Donald replied 1 year ago.

This leads me to believe that our problem is internal.