Engine turns when starting but does not start

Sounds like your pinion/bendix gear is not reliably extending fully to engage the flywheel. There are three common causes of this: (most common) Dried up grease or dirt on the threads of the starter shaft and the pinion/bendix. Failing overrunning/one-way clutch in the bendix
replace starter.

Define won't turn over ? There are two different situations you could be trying to discribe . When you turn the key to the start position does the starter engage an spin the engine , but does not start an run ? Or when you turn the key to the start position it won't engage the starter an spin the engine . We have a engine cranks no start or a no crank no start . And what is this commutateur ????? commutator for what ? And it also makes a difference on what make , model and year vehicle it is .
and cyl ????? what cylinder ? Ignition ,key lock ????

Sounds like a timing chain problem, you could check compression but I think your going to have to take it to a shop regardless. Make sure that the engine is turning over and it's just not the starter spinning that your hearing.

very good post, few like it.
this is the starter free spinning
the solenoids job is the engage the teeth the fly wheel (ring gear)

the pinon shaft in starter is dirty, clean it (easy fix)
bad starter solenoid. get a new starter , most solenoids cost more.
your suspisons are dead on.

Hi without seeing (hearing) it sounds like the clutch in the bendix is faulty, as the solenoid will engage the bendix at the same time as connecting feed to the starter motor.
New starter required or a good strip down and rebuild on the solenoid and bendix.
What condition is the ring gear in by the way (Starter Motor removed). David

sounds like it.

Verify battery voltage should be approx 12.30V + give or take a few tenths with the engine off
When you turn over the car, the voltage should not drop below 10.5 volts at all

I would verify these voltages as it takes a lot of juice to turn over a starter and start a motor. I have seen batterys look fine but can't supply a voltage. I assume you have tried jumping your vehicle as well with the donor car running about 2k rpm? If the vehicle starts like this it is most likely a battery issue and not a starter.

Sorry I truly suspect 7 year old batteries a lot more than 7 year old starters. As for the click, the starter is made up of 2 parts, first, it pushes the gear out to engage the flywheel, when the gear is fully out, and engages, the starter starts turning to start the car. The click would be the gear either attempting to engage or engaging and the motor part of the starter failing. The starter will be located in the area of where the transmission and engine mate, usually in the front of the motor. Any autozone should be able to test your starter to ensure it's still good or tell you what failed on it.

The poster should first make sure new battery is fully charged.Be sure battery cables are very clean and tight,same with connectors on solenoid. Have an assistant turn on headlamps(high beam) and attempt to start vehicle.Do lights remain the same or do they dim excessively? If lights dim noticeably check for shorted starter cable or defective starter.also check engine for excessive turning effort using turning tool on engine crank bolt or screwdriver in flywheel with starter removed.If lights do not dim check for open circuit in starter or cable.Sometimes a few sharp raps on the starter body will get it to work temporarily.Defective starters will often have a burnt smell. IF engine is excessively hard to turn,mechanical problem,such as leaking coolant into cylinders or defective injector may exist.Always use extreme caution when working under vehicle or near electrical components,batteries can explode or burn you badly and starter can engage causing serious bodily harm.Most auto parts stores can test starter with component removed.Also be sure correct replacement part is installed.This vehicle has several solenoids that will fit,but will not necessarily work.

It is called the starter bendix or starter drive. It is not engaging the ring gear of the engine., thus you hear the whirrrrrr. (very good explanation)
You will need to replace the starter.
Please let me know if you wish to attempt this repair yourslef, I will give you step by step instructions.

SUBJECT:
Long Crank Time Due To Possible Contact Of Camshaft Sensor To Camshaft Gear
OVERVIEW:
This bulletin involves the replacement of the engine camshaft sensor.
MODELS:
2007 (JK) Wrangler
NOTE: This bulletin applies to vehicles equipped with a 3.8L engine (sales code
EGT).
SYMPTOM/CONDITION:
The customer may experience one of the following conditions:
a). Long engine crank time.
b). Two engine start attempts prior to engine starting.
c). Due to the “TIP Start Feature” on automatic transmission equipped vehicles, once the
ignition key / switch has been released from the “START” position, the starter may stay
engaged for up to 10 seconds while the engine attempts to start.
The above conditions may be due to the position of the camshaft sensor to the camshaft
gear. The sensor spacer gasket may have come loose during engine assembly and
caused the camshaft sensor to be adjusted too close or in contact with the camshaft gear.
DIAGNOSIS:
If the above condition is present perform the Repair Procedure.
PARTS REQUIRED:
Qty. Part No. Description
1 04686353 Sensor, Camshaft

Starter drive not engaging fully . Sticky or worn, but don't think changing thermostat had anything to do with it. Try having starter drive inspected & lubed if possible , but you may end up with new starter.