How do I remove the crankcase cover

[bengriffiths]

Hi,I have a 1988 honda trx 125,and am new to all this,I need to replace the engine casing,Its the left side.i took all the bolts out but there's one big one in the middle which I cant get out because Its on the engine (it keeps going round when i try and loosen it". I know this sounds stupid but how do i stop this going round? I tryed putting it in gear,no good.

Also any tips for me as how to put the new crankcase cover and gasket on?
many thanks for any help
ben

[timex69]

if the engine is still in the frame then put a screw driver through the top of the chain and push it down thru the bottom of the chain..thus stops the sproket and the engine from turning.

[everydaycajun01]

30mm socket,air impact,nut is left hand treds.tight the nut to loosn.if its the one im thinking aboutgive a little more information please