What holds the front sprocket on the spline - 1991 kawasaki ZZR 250

Of course. The bolt is in the middle of the splined shaft and holds the sprocket as well. Some have a hole where you insert a rod to lock the sprocket, or you can put the bike in 1st Gear and give the breaker bar a sharp tap with a lump hammer. Or you can jam the chain somewhere back by the back sprocket, for instance putting a ratchet strap through the rear forks and the wheel, or you can get someone to apply the rear brake.

It Will Have An External Snap Ring. To Retain Sprocket On The Spline Shaft Or A Strap Clip Bolted To The Sprocket. The Strap Has A Slot That Engages The Spline Shaft Thereby Retaining The Sprocket To The Shaft. Of Course You Will Have To Loosen The Chain To Access The Sprocket

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You can loosen the chain tension from the adjusters at the end of the swing arm. Then remove the mud guard (If exists) covering the front sprocket. Remove the M10 X 18mm bolt holding the sprocket. Slide the sprocket and chain off the spline and change out. If unable to slide off the spline you can always open the master link on the chain and do same step.

Use reverse process to re-install new sprocket. Readjust chain tension and make sure to re-tighten axel nuts. Good idea to use Locktite on the 10 x 18 bolt and spring washer holding the front sprocket. Replace mud guard or leave off as to your preference.
Kind regards,
TF

My old XT 600 had a thicker side, and a flat side. If you put it on backwards it sits too close to the engine. (causing play)
Do you still have your old sprocket to compare the thickness?

check to see if the chain is on the sprocket to do this you will probably have to remove the side cover on the saw if chain is on sprocket and still will not move then you may have a sheared key in the key way if this saw has one, if it does you should be able to see the key way on the end of the shaft coming out of the motor. there should be a nut that holds the sprocket in place if that nut is loose and the shaft is splined instead of having a key way the the sprocket could slip while the motor is turning.

There should be a spline for the sprocket and do the nut up hand tight plus an 1/8th turn with loctite blue threadlock.

To replace the main drive chain,you need to remove the chain cover on the engine case which should have a couple of bolts or screws securing it. Loosen the back wheel by untightening the rear axle bolts and then loosen the rear adjusters either side. Make a note of their positions they need to be be the same position either side, although the new chain may need a different setting but as long as they are both the same tightness each side is what matters.Loosen the wheel and move it forward when the axle is loose and the pin holding the axle nut is removed.Unscrew the two 6mm bolts holding the front sprocket a the engine side of the chain.Turn the part on the front sprocket where the two bolts have just been removed so that it lines with the gearbox splines and pull it forward along with the front sprocket at the same time as you push the loosened rear wheel the chain should pull away from the teeth on both sprockets.
To put on the new chain just reverse the proceedure.the ajusters need to be tight but not too tight just enough play to move it up and down slightly remember both adjustes need to be the same position each side and check that the wheel is in line with the bike and straight as uneven adjustments will cause the wheel to be turned slightly off the required vertical position.

3.4L Engine Fig. 7: View of the timing chain and related components with the front cover removed — 3.4L engine
Fig. 8: Retract the timing chain tensioner
Fig. 9: The special tools must be used . . .
Fig. 10: . . . to remove the timing chain, crankshaft sprocket and intermediate shaft sprocket
Fig. 11: Slide the sprocket and chain on the shafts, maintaining the proper alignment
Fig. 12: The crankshaft sprocket must be pressed on to specifications using a special tool

1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle.
3. For 1991 vehicles, perform the following:
   1. Remove the starter motor and flywheel cover.
   2. Remove oil pan retaining nuts and bolts. Remove lower frame and powertrain onto transmission table.
4. Remove the front cover, as outlined earlier this section.
5. Matchmark the intermediate sprocket, chain link, front face of cylinder and crank sprocket for reference.
6. Retract the timing chain tensioner shoe by using J–33875 or equivalent, on both sides of the tensioner and pulling on the thru pin in the tensioner arm to retract the spring. While spring is retracted, insert a holding tool to hold it.
7. Remove the timing chain tensioner retaining bolts.
8. Raise and safely support the vehicle.
9. Remove the timing chain, crankshaft sprocket and intermediate sprocket using tools J 8433 and J 28611, as shown in the accompanying figure. If the intermediate gear does not slide off easily with the timing chain assembly, rotate the crankshaft back and forth to loosen the tight fit.
10. If necessary, remove the timing chain tensioner. To install:
    
11. Check to ensure that crankshaft key is installed and fully seated and the chain tensioner is fully installed and blade retracted.
12. Slip both sprockets and chain over the proper shaft and engage the slot in the key. The intermediate shaft may move against the rear cover. Slide the sprocket and chain on the shafts, maintaining the proper alignment shown in the accompanying figure. While installing note the following:
    1. Make sure the rubber and tension blade of the tensioner does not become caught, misaligned, or dislodged.
    2. The large chamfer and counterbore of the crankshaft sprocket are installed towards the crankshaft. The intermediate sprocket spline sockets are installed away from the case.
    3. The crankshaft sprocket must be pressed on for the final 0.31 in. (8mm) to the seated position using tool J38612 or equivalent, as shown in the accompanying figure.
    4. Check to make sure timing was maintained. Remove the retaining pin from tensioner.
13. For 1991 vehicles, install the oil pan retaining nuts and bolts, and the flywheel cover and starter.
14. Install the front cover, as outlined earlier in this section.
15. Connect the negative battery cable. Start the engine and check for leaks.

You simply have the wrong sprocket ,there should be no play at all ,allso carefully check the spline edges they should be sharp edged if rounded your shaft will need replacing.some times a very small play can be felt ,but should not be visual. is the sprocket of good quality ,cheap items can be a bit dodgy.

thing there usaualy a clip on the spline then turn cog and remoce or there may be 2 bolts to undo and turn as above