How to undo dt 125 front sprocket nut left or right turn ?

Its not that hard really , But its one of those things if you don't know you can really stuff things up bad , First remove the sprocket cover then WHILE THE WHEEL is on the ground Tap the lock plate and flatten it away from the nut face so as to be able to turn the nut that holds the sprocket on , Now with the rear brake held on use a socket and breaker bar to undo the nut , Now with the nut loose you need to rase the rear of the bike use the centre stand and loosen the axle nut then the rear wheel alignment adjusters , so the chain is loose ,,, then lift the chain off the rear socket and then the front sprocket then remove the nut and pull the socket off , done ,,put back together in reverse order.

Axle nut 145 Nm
rear sprocket nuts B and C models 74 Nm
rear sprocket but E and F models 59Nm
front sprocket nut 125 Nm
front caliper mounting bolts 34Nm
Hope this helps - if your wrench isn't in Nm you can get a conversion online.

There should be a bent washer over the nut to stop it from turning. Have a good look.
Flatten the bent washer with a flat cold chisel, gently, as you need it again! Put the bike in top gear to hold the sprocket and use a spanner 27mm to undo the nut. It is a clockwise thread.
When you put a sprocket back on, don't forget the bent washer and a drop of Loctite Threadlock will help to hold it on.

IF YOU MEAN THE FRONT SPROCKET UNDER THE LEFT HAND REAR CASE. THE ACTION REQUIRED.TO REMOVE THE NUT TURN TO THE LEFT ANTI CLOCKWISE.
TO REPLACE THE NUT TURN TO THE RIGHT IN A CLOCKWISE DIRECTION TOOLS REQUIRED FAIRLY SURE ITS A 32MM SOCKET, COULD BE A LOCKING NUT OR MAY HAVE A TAB WASHER WICH IS BENT OVER THE NUT TO SAVE IT COMING LOOSE.IF THE NUT IS VERY TIGHT PLACE THE BIKE IN GEAR AND GET SOME 1 TO HOLD ON THE REAR BRAKE WHILE YOU UNDO IT

If it is on the right hand side of the bike then yes. Remove the clutch cable by undoing the adjustment nuts on the engine side of the cable and unhooking from the lever. Remove the nut on the gearshift pedal and pull of the pedal. Remove the dipstick. Undo all the nuts on the cover, and remove it. Locate the new gasket on the engine. There are 2 locating dowels so it should not have diffyculty staying in place. Replace the cover and clutch cable and readjust the clutch cable.
On the left hand side of the engine is a bit more tricky as the oil is not leaking past the gasket on the cover itself. There are 2 places where it can leak from. One is behind the drive sprocket. Remove the cover. Undo the nut on the sprocket. Bend back the tabs on the locking plate and remove the sprocket. Drive a self tapping screw into the shaft seal and pull it out with a pair of pliers. Drive a new on back in place. Also see this : http://www.fixya.com/motorcycles/t5649906-1996_yamaha_yz250
If the leak is from behind the alternator you will have to remove the magneto. This is diffycult as you need a puller to get the flywheel off the crank. Then the alternator assembly and only then will you be able to reach the shaft seal. This can be removed as per the previous link.

No they are not left hand thead,normal r/h thread.
make sure chain is still on bike and front sproket and then try good rattle gun. if this does not work,put bike in gear and hold on rear brake and use long breaker bar, if still no good will need to heat front sproket nut with oxy set very carefully and rattle off with rattle gun while nut is hot

Did you try an impact driver? How about putting the bike in low gear? If not, just get a breaker bar on there an whack it with a brass hammer. I'm pretty sure it is a right hand thread. Hope this helps.

remove the left faring undo the water pump mounting bolts not all the bolts around the pump just the two that hold it to the engine case pull the pump out about one inch the undo the sprocket cover and remove put the engine in gear and get somone to hold the rear brake on loosen the sprocket bolt undo the rear wheel axle nut and loosen the chain adjusters to put some slack in the chain then remove the front sprocket and fit the new one on put some lock tite on the sprocket bolt and do up tite with the bike in gear and someone holding the brake on put the water pump on and make sure it is lined up properley when you push it back in it should sit flush to the engine with an easy push.adust your chain and titen all the bolts and nuts and refit your faring.hope the was helpfull please leave feedback.

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

The compensating sprocket nut is indeed right hand threads. It is torqued to 150-165 foot pounds of torque and usually has Locktite 271 (red) in it. A lot of mechanics go overboard with the Loctite. I've seen the entire inside of the nut "painted" with this stuff. The book calls for "two lines" of the stuff when putting the nut back on.

The easiest way to get the nut off is with a GOOD air wrench. I bought one of those Ingersol-Rand Titanium air wrenches. I've seen nuts on so tight that I've had to use a 3/4" air wrench to get them off. If you don't want to purchase an air wrench, load the bike on a trailer and take it to a tire store. Ask them to take the nut off for you. Usually they'll do it free but they may charge you a couple of dollars. It is worth a couple of dollars to get the nut off.

When putting the bike back together, the compensator sprocket torques to 150-165 ft lbs. of torque with two lines of 271 Loctite in it. The clutch hub nut torques 60-80 ft. lbs. left handed with one line of 271 Locktite. Make sure your torque wrench will torque in the left handed direction. Not all wrenches will.
Good Luck.