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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 17592
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a John Deere STX38 mower that doesnt like to start.

Customer Question

I have a John Deere STX38 mower that doesn't like to start. I replaced the five-year-old battery with a new one and when it still didn't start, I called the John Deere store where they let me talk to someone in service. She (yes, she) suggested that I turn the engine until it rotated smoothly. After two or three turns, the engine rotated fine and the mower started. Today, I have been trying the same technique to no avail. When I was on the phone with the service gal, she said that there was a "compression lock". I've never heard of this before and am interested in knowing how to fix it. Thanks for any help you can provide.
Submitted: 3 years ago.
Category: Small Engine
Expert:  Curtis B. replied 3 years ago.

curtis b :

Welcome to JUST ANSWER small engines, let me try to help you !! Some engine have a compression release made into the cam and is activated by the valves. Yours is a Kohler engine and has hydraulic lifters, so there is no need to adjust the valves. Have you removed the spark plug and checked to see if the engine rotates freely? Replaced the spark plug to aid in starting? Your compression release is part of the camshaft and if it fails, the camshaft has to be changed.! It does have one, and when it doesn't function, the engine can be hard to turn over and start.

Customer:

Thank you for your input. In reply to your question, I have removed the spark plug and found that the engine rotates freely. After replacing the spark plug, the engine will not rotate freely, nor does it start.

curtis b :

Ok. before we come to the conclusion that the camshaft compression release has broken, do you have a voltmeter to check the battery voltage? With just battery, not on, it should read 12.5 volts or more, then when trying the starter , does it drop below 9 volts. If it drops below 9 volts the battery needs to be charged or is too small amp wise for engine. If voltage stays around 9 volts, the compression release is not working.

Customer:

Thanks for the reply. I get 12.53 volts from the battery terminals with the key in the off position. There is no drop in current when I turn the key. However, I did check the starter (I think it's the starter) and it registers 12.34 volts when I turn the key. To test the starter I had one lead on the hot wire supplying the starter and the negative lead grounded to the engine.

curtis b :

Just put the leads across the battery and see if the voltage drops below 9 volts, when trying to crank engine.

Customer:

Sorry to not be clear in my earlier post, when I measure the voltage of the battery, it reads 12.53. When I turn the key, the voltage didn't drop earlier. I just tested it again and the voltage dropped to 12.40. I'm pretty sure that I had the tester leads on pretty securely. Thanks for your help.

curtis b :

With such a high reading, I am not sure that you have a compression release problem. If the engine was hard to turn, the voltage should have pulled down more. Lets go back and check the starter solenoid. Deere is not clear on what starter and solenoid it has on this unit. Is your solenoid part of the starter or a separate relay? If it is the separate unit, take an old screwdriver and short across the two large post and see if the engine will crank over. This bypasses the solenoid. If you have the solenoid on the starter, it is going to be harder to test. Let me know. Thank you.

Customer:

When I think of all the chatter on my question, I feel gratitude that you have stuck with me through this. I appreciate it a lot and value the knowledge you have. I can't get schematics for the engine, so I'm not sure how to tell where the solenoid is. It has a pretty good sized starter, though, if that helps any. I'm familiar with shorting the solenoid to see if the starter works, as I used to do that kind of thing on older model cars that I used to work on. Can I upload a digital photo of the starter to you? Should I remove the starter to find the solenoid? Thanks, XXXXX XXXXX lawn looks like chaos and I'd like to get it mowed before the weekend.

curtis b :

Just follow the positive battery cable and see if it goes direct to the starter. If it does, it has no separate solenoid. You could try jumping it at the starter to see what happens. It just seems that if the engine was hard cranking , the battery voltage would drop a lot more than tenths of a volt. I think you are going to have to pull the starter and have it checked and repaired or replaced.

Customer:

Thanks for the advice. I did try to jump the starter hot post to the engine block (the closest ground I could find) and the result was to produce sparks at the hot post of the starter where my screwdriver was. I'll take the starter off today and bring it to the John Deere store to see if they can bench test it. Any other suggestions beside that?

curtis b :

No, I think we are on the right track.

Customer:

The John Deere store says the starter's bad. So, I have invested in a new one. It will be here in a couple days. I'll let you know if it works. Thanks for all your suggestions.

Curtis B., Technician
Category: Small Engine
Satisfied Customers: 17592
Experience: have worked on and around most engine models for 35 yrs./Polaris ATV expert
Curtis B. and 4 other Small Engine Specialists are ready to help you
Expert:  Curtis B. replied 3 years ago.
Ok, thanks !!

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