What size is the bolt used to push the clutch off of the engine shaft on a JX85 mower?

car and trucks section not mower section

motor seized?

The PTO clutch has a bolt that goes through it and into the vertical shaft of the engine. MANY of the PTO clutches have a large spacing washer that goes on before the PTO clutch is slipped onto the shaft. If the washer was lost when the clutch was changed, the bolt might be bottoming out in the shaft rather than tightening on the threads like it should. I'd get a diagram for your model and make sure all parts are in place.

Use a impact wrench.

it is a 9/16 head so it should be a 7/16 bolt

I am going to presume that this clutch actually installs on the lower end of the engine crankshaft. There should be a bolt that goes up thru the center of the clutch into the shaft. There's probably a spring or rod that will hold the outside of the clutch solid. Part of the clutch will be turning with the engine when it's running and when you throw the switch to engage the clutch, the other portion is activated by the current to connect to the turning portion.

To get the old one off, you'll need to get under the mower with a socket wrench. These can be quite stubborn to break loose, as the engine will want to turn over as you turn the bolt. If you have a gear drive machine you may be able to let the transmission help hold the engine from turning, but that, too, is run by a belt, so it may slip. Worse case is to use an air impact wrench, which will apply pressure so fast that it will make the bolt turn without turning the engine. Good Luck.

REMOVAL:

1. Lift clutch pedal to uppermost position to disengage clutch and brake pedal pivot shaft.
2. Push clutch and brake pedal pivot shaft forward and unhook clutch release lever cable from clutch and brake pedal pivot shaft and allow it to slowly swing rearward.
3. Raise and support vehicle.
4. Remove clutch release lever dust shield.
5. Disconnect clutch release lever cable from clutch release shaft.
6. Remove retaining clip, then clutch release lever cable from flywheel housing.
7. Remove starter motor from flywheel housing, then engine rear plate to front lower flywheel housing bolts.
8. Remove transmission.
9. Remove flywheel housing back just far enough to clear clutch pressure plate, then remove housing.
10. Remove clutch release shaft from flywheel housing by pulling it through window in flywheel housing until retainer spring disengages from pivot.
11. Remove clutch release hub and bearing from clutch release shaft.
12. Loosen six clutch pressure plate bolts evenly to release spring tension gradually and avoid distorting clutch pressure plate. If same clutch pressure plate is to be installed, mark plate and flywheel so pressure plate can be installed in its original position.
13. Remove clutch pressure plate and clutch disc from flywheel.

INSTALLATION:

1. Position clutch disc and pressure plate assembly on flywheel, noting following:
   1. Three flywheel housing to block dowels on flywheel must be properly aligned with clutch pressure plate.
   2. Bent, damaged or missing flywheel housing to block dowels must be replaced.
   3. tart clutch pressure plate bolts but do not tighten.
   4. Avoid touching clutch disc face, dropping parts or contaminating parts with oil or grease.
   5. Align clutch disc using suitable alignment tool inserted in pilot bearing.
   6. To avoid clutch pressure plate distortion, alternately tighten bolts a few turns at a time, until they are all tight, then tighten to specifications.
   
   
2. Install transmission to flywheel housing.
3. Install engine rear plate to flywheel front lower housing bolts, then connect clutch release cable to flywheel housing and connect retaining clip.
4. Connect clutch release lever cable to clutch release shaft, then install clutch release lever dust shield.
5. Install starter motor.
6. Lower vehicle, then install clutch release lever cable as follows:
   1. Lift clutch pedal to disengage clutch and brake pedal pivot shaft.
   2. Push clutch and brake pedal pivot shaft forward and hook end of clutch release lever cable over rear of clutch and brake pedal pivot shaft.
   
   
7. Cycle clutch pedal several times to adjust clutch release lever cable

take cover off flywheel so you can hold it from turning.or use a air compressor on clutch bolt

Sounds like you lost the drive key out of the crankshaft, it's usually half-moon shaped and keeps the blade hub and the crankshaft turning together, the bolt just holds it all on the end of the crankshaft.
Hope this helps!

my jx85 when cutting grass with my jx85 the power to the blade dies if i lift it up the power will come back put it back into grass it dies again any ideas please