Hi the nut on the crank shaft primary drive side of my 85  evo won’t undo with an impact driver or long handle on a 3/4'” drive socket any ideas would be appreciated  

They are right handed threads? So anticlockwise  to undo. If they are and you are doing it right then mate. A bigger length cheata bar is required and hope you don't shear it off.

AJ's onto it, but if still no joy, a 1" bar and longer handle,

(To acheive the same result as a 5:1 torque multiplier, you need a 5 foot cheata bar.)

I just tried heat and a 3 foot bar, then the rattle gun all that happened was the clutch slipped

all done thanks very much for the help, I went through the old posts and found this from a guy in texas
 just changed my stator,rotor,regulater. I used no power tools. I took all the slack out of the chain, used a piece of aluminum angle,stuck in the compensating nut teeth against the chain, 1 1/2 in socket and break o bar , regular right hand tread. the angle is 1in x1in 2 in long. the clutch is left handed tread. a puller, 5/16 in or 3/8 steel plate 4 1/4 dia. or 5 in sq. 1/2 hole in center for a 3/8 fine tread hvy duty nut welded in center. there are four holes evenly spaced about the center on 2 7/8 circle. there is no pressure in the clutch basket . hope this is some help. Im looking for the oem numbers for 1993 fxstc rear pulley,front sprocket, and belt numbers thanks
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Thanks dagasa101 the bit of aluminum works a treat
cheers
Peter

hi, i would maybe look @ replacing the chain ?

  Feed a length of nylon rope into the front spark plug hole and then turn the engine over (via turning the back wheel in top gear) until you force the rope up against the head. Obviously you need to leave the end of the rope hanging out for retrieval when finished. Make sure you get plenty in there. Also make sure you are on the compression stroke........don't want the rope getting jammed under valves.

This will lock the engine up firmly without putting any stress on the drivetrain. I have never had a problem undoing even the tightest of compensator nuts using this method with a strong bar.........rattle guns are not recommended!

The same can be used for the clutch hub nut, obviously in the opposite direction, however this IS straining the primary chain, but since the clutch nut is no where near as tight, it won't bother it much.

A length of nylon rope is a hell of a lot cheaper and easier than buying/making "chain sprocket jammers".

Burto.