Cranks seals on IT 490??

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Oct 14, 2003
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#1
Hi, I'm new here, maybe you guys can help me out. The bike is an 83 Yamaha 490. I have the motor out for top end work and I'm thinking of replacing the crank seals. Are they outboard under the covers or do you have to split the case to get to them? The shop manual is lacking in detail. Thanks, -Noah
 
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#2
I'm allmost sure the clutch side seal can be removed without splitting the cases, but I'm not sure about the left one... i cant remember if there actually was a seal on the left side or if it was a z type c3 bearing with a built in seal on the external side.
 
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#3
I USED TO RACE A '83 YZ 490K WITH YZ 465H GEAR BOX (GIVES YOU ANOTHER GEAR BELOW 1ST- JUST GEAR UP TO SUIT) SIDECAR ENDURO OUTFIT IN THE UK, AND WE HAD TO CHANGE CRANK SEALS QUITE OFTEN DUE TO THE CRANK FLEXING/MOVING, CAUSED BY THE THRAPPING THE POOR OLD THING USED TO GET TRYING TO STAY IN FRONT OF MORE MODERN KIT.
YOU CAN GET TO BOTH SEALS FROM OUT SIDE THE CASES, THOUGH ARE YOU SURE THE SEALS HAVE GONE 'COS THESE ENGINES DO USE A LOT OF TRANSMISSION OIL DUE THE POOR/LACK OF SEAL IN THE PRIMARY GEAR. YOU CAN CURE THIS BY FITTING A PRIMARY DRIVE PINION SEAL FROM (I THINK, IT WAS SOME TIME AGO) AN RD/RZ 350, IT'S LIKE AN 'O' RING WITH A TAB ON IT THAT SITS IN THE KEY WAY ON THE CRANK BETWEEN THE RH MAIN BEARING AND THE PRIMARY DRIVE PINION, THERES' EVEN A SUITABLE CHAMFER IN THE BACK OF THE PINION SO WHY YAMAHA DIDN'T FIT THEM AS STANDARD I DON'T KNOW, PREHAPS THEY WERN'T EXPECTING THE ENGINES TO GET QUITE THE HARD USE AS THEY DO IN SIDECARS.
ANY WAY, DRIVE SIDE - TAKE OUT PRIMARY PINION AND REMOVE SEAL KEEPER PLATE AND EITHER GENTLY LEVER OUT SEAL WITH A BLUNT SCREW DRIVER OR USE SEAL PULLER (EXPENSIVE). OIL NEW SEAL AND USE PRIMARY PINION REVERSED TO GENTLY DRIVE SEAL HOME MAKE SURE IT'S THE CORRECT WAY ROUND, SEEM TO REMEMBER THAT SEAL IS MARKED WITH ORRIENTATION REPLACE KEEPER PLATE, PUT PINION SEALING JOBBIE ON CRANK AGAINST BEARING, OIL PINION O/D AND VERY CAREFULLY SLIDE INTO SEAL, IT'S THEN A CASE OF PUTTING EVERY THING BACK WHENCE IT CAME. IT'S ALSO A GOOD IDEA IF YOU ARE DOING A FULL REBUILD TO MAKE SURE THAT THE MAINS ARE TOP QUALITY ONES (OE YAMAHA OR BETTER, SADDLY THEY'RE CHEAP, BUT BEEN THERE GOT THE BROKEN CASES ETC).
IGNITION SIDE- REMOVE THE GENERATOR FLYWHEEL/ROTOR BEST DONE WITH THE MOTOR IN THE FRAME IT CAN BE QUITE TIGHT(BOTH NUT AND ROTOR ON TAPER) HAVE FOUND THE BEST METHOD TO BREAK THE TAPER IS TO USE THE PROPER LH THREADED PULLER, MAKE SURE IT'S SCREWED RIGHT HOME IN THE ROTOR,DO THE CENTRE BOLT UP GOOD AND TIGHT AND IF THAT DOES'NT SHIFT IT GIVE THE END OF THE BOLT A GOOD SHARP TAP WITH A HARD METAL HAMMER AND OF IT COMES. DON'T HIT THE ROTOR OR USE A 3 LEG PULLER OR HEAT IF YOU WANT TO USE THE IGNITION AGAIN 'COS THEY'RE DISTRESSINGLY DELICATE. MARK THE POSITION OF THE STATOR PLATE RELATIVE TO THE CASES AND REMOVE. PUNCH NOT DRILL 2 HOLES IN THE MIDDLE OF THE METAL BACKING OF THE SEAL AND SCREW IN 2 COARSE WOOD SCREWS, USE PLIERS/'MOLE' GRIPS TO EASE THE SEAL OUT. OIL NEW SEAL AND GENTLY EASE INTO PLACE TRYING TO KEEP IT SQUARE. REASSEMBLE, CHECK THE TIMING AND AWAY YOU GO.
SOUNDS EASY AND IT'S NOT BAD IF YOU TAKE YOUR TIME (ESPECIALLY AS I'VE PROBABLY FORGOTTEN SOMETHING IMPORTANT).
YOU CAN MAKE THESE OLD ENGINES RUN LOADS BETTER IF YOU DO THE FOLLOWING-( THEY PING AND RATTLE UNDER LOAD LIKE IT'S GOING OUT OF FASHION) MACHINE THE TOP OF THE CYLINDER (IF NECESSARY) SO THE PISTON COMES FLUSH WITH THE GASKET FACE, MACHINE THE HEAD SO THAT THE STRAIGHT/PARALLEL DIAMETER AROUND THE OUTSIDE OF THE SQUISH AREA IS TAKEN OFF (APPROX 0.75 TO 1.0MM) I.E. TIL THE CUT STARTS TO REMOVE THE SMALL CORNER RADIUS, AND USE AN IT/YZ 465 COPPER GASKET, IT'S 2MM SMALLER INSIDE DIA SO YOU HAVE TO CAREFULLY TRIM THE EXCESS OUT WITH A SHARP KNIFE. JETTING IS USUALLY FINE BUT CHECK, DOES TAKE SOME OF THE TOP END OVER-REV AWAY BUT YOU GET LOADS OF EXTRA, SMOOTH BOTTOM END PUNCH WITH NO DETONATION,WHICH MEANS YOU CAN THEN LEAN OUT THE BOTTOM END JETTING SO IT RUNS REALLY CLEAN,NO MORE PLUG FOULING AND THE ENGINE RESPONDS TO THE SLIGHTEST TURN OF THE THROTTLE INSTEAD OF LOADING UP AND THEN COMING CLEAN IN A BIG BANGOF POWER,I WOULD RECOMMEND A STEADY RIGHT HAND 'TIL YOU GET USED TO IT.
 
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#4
P.S. FORGOT TO ADD TO ABOVE, IT DOES MAKE THE MOTOR HARDER TO KICK OVER, BUT IT'LL FIRE UP SO MUCH EASIER WHEN YOU GET USED TO IT.
ALSO WE USED TO FIND THE CYLINDERS USED TO WEAR QUICKER THAN THE PISTONS SO WE WOULD HAVE THE CYLINDER BORED TO MATCH AN OLD PISTON WITH ONLY ABOUT .05 TO .08MM TOTAL CLEARANCE AND THEN RUN/BREAK IN CAREFULLY, THOUGH IT WAS EASY FOR US TO DO THAT 'COS YOU COULDN'T GIVE THEM AWAY OVER HERE.
 
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#5
I managed to remove both seals this afternoon. New ones are on order. I did notice that shaft/key set up on the gear and it does seem strange that there was no attempt to seal it. I've heard the rumors about detonation, the previous owner burned a piston with this motor. I may try a little head maching to improve the squish band. It does seem a bit far from the piston. I'll be in machine shop at the Motorcycle Mechanic's Institute in three weeks, so why not? I may just hold off until the cylinder needs boring though. It's still got a little life and at $125 a pop for a piston, I'll wait. I'll let you all know how it goes. Thanks for the help, -Noah
 
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#6
Hello Noah, I have a '82 490 and am looking for the procedure to make sure the timing is set correctly. Do you happen to have any tips? Thanks, Kevin