B737 FLIGHT CREW DEPARTING LGA ON LGA2 MASPETH CLIMB MAKE A RIGHT TURN TO 180 DEGREES THEN A LEFT TURN TO 340 DEGREES. TWO RIGHT TURNS ARE REQUIRED BY THE SID.

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CLRED VIA RWY 13; LGA 2 MASPETH CLB. MASPETH CLB CALLS FOR CLBING R TURN TO HDG 180 DEGS; AT LGA 4.1 DME; R TURN TO 340 DEGS. DURING PREFLT; WE TALKED ABOUT OUR CLRNC; INCLUDING THE MASPETH CLB. DURING THE GATE BRIEF I; AS THE PF; BRIEFED THE TURNS ON THE MASPETH CLB. AFTER TKOF AT 400 FT; I CALLED FOR 'HDG SET 180 DEGS;' THE PNF SET A R TURN TO 180 DEGS. I RESPONDED 'HDG SELECT 180 DEGS' AND TURNED TO FOLLOW THE FLT DIRECTOR. AT LGA 4.1 DME; I CALLED FOR 'HDG SET 340 DEGS;' THE PNF TURNED THE HDG SELECTOR ON THE MCP TO THE L TO HDG 340 DEGS. I VERIFIED THE HDG AND RESPONDED 'HDG SELECT 340 DEGS.' I TURNED THE ACFT TO FOLLOW THE FLT DIRECTOR TO THE L (THE DEP PROC CALLS FOR A R TURN TO 340 DEGS). PASSING THROUGH ABOUT 120 DEGS; I NOTICED THE MISTAKE THAT I HAD MADE AND STARTED TO REVERSE MY DIRECTION OF TURN JUST AS THE DEP CTLR SAID 'ACFT X; WHAT HDG ARE YOU TURNING TO?' THE PNF RESPONDED 340 DEGS. THE DEP CTLR SAID 'ACFT X; IT'S A R TURN TO HDG 340 DEGS...CONTINUE YOUR L TURN TO 320 DEGS.' I ROLLED THE ACFT BACK TO THE L TO FLY THE 320 DEG HDG. BECAUSE I HAD ALREADY ROLLED THE ACFT TO THE R; THE DEP CTLR; WHO WAS NOW WATCHING US LIKE A HAWK; NOTICED THE R TURN AND AGAIN SAID 'ACFT X; IT LOOKS LIKE YOU'RE IN A R TURN.' WE EXPLAINED THAT WE WERE INDEED TURNING L AND ROLLING THROUGH A 105 DEG HDG. WE ESTABLISHED OURSELVES ON THE 320 DEG HDG. CLBING THROUGH 8000 FT THE DEP CTLR GAVE US A PHONE NUMBER TO CALL ABOUT A POSSIBLE PLTDEV. AFTER LNDG; WE CALLED LGA DEP AND TALKED WITH THE SUPVR; WHO HAPPENED TO BE THE CTLR THAT WAS WORKING OUR FLT LEAVING LGA. HE COUNSELED ME ON THE IMPORTANCE OF FOLLOWING DEP RTES EXACTLY AS PUBLISHED AND THE HAZARDS OF DEVIATING FROM THE PUBLISHED DEP PROCS. THE CTLR ALSO ADVISED ME THAT NO OTHER ACTION WOULD BE TAKEN. THE EVENT OCCURRED BECAUSE BOTH THE PF AND THE PNF MADE MISTAKES. ALL STANDARD PROCS AND CALLS WERE FOLLOWED. THE CORRECT HDG WAS CALLED FOR; THE CORRECT VERIFICATION WAS MADE AFTER THE HDG WAS SELECTED. HOWEVER; THERE WERE 3 MISTAKES MADE DESPITE ALL STANDARD PROCS WERE FOLLOWED. THE FIRST ERROR WAS ME; AS THE PF; BECAUSE OF THE UNUSUALLY LARGE CHANGE IN HDG ASSOCIATED WITH THE DEP PROC; SHOULD HAVE SPECIFIED WHICH DIRECTION I WANTED THE TURN INITIATED. THE SECOND MISTAKE WAS THE PNF TURNING THE HDG BUG IN THE WRONG DIRECTION; RESULTING IN A TURN IN THE WRONG DIRECTION. THE THIRD MISTAKE WAS AGAIN MADE BY ME -- I VERIFIED THE CORRECT HDG WAS SELECTED; BUT I DID NOT NOTICE THAT THE TURN WAS SELECTED IN THE WRONG DIRECTION. I BELIEVE THAT THIS WHOLE EVENT COULD HAVE BEEN AVOIDED BY BETTER COM BTWN PLTS. ALSO; I THINK THAT AS A PROC IT MAY BE A GOOD IDEA TO INCLUDE THE DIRECTION OF THE TURN WHEN COMMANDING A HDG CHANGE. I DID HAVE THE DEP CHART OUT AND HAD REFERENCED IT DURING THE GATE BRIEF AND AFTER WE GOT OUR CLRNC; HOWEVER; IT WAS SITTING AT MY SIDE ON TOP OF MY FLT BAG. IT SHOULD HAVE BEEN ON MY YOKE CLIP IN MY DIRECT VIEW.