I don't recall who wrote this but I saved it because it sounded like the truth. The 6mm center gives a good idea of how reduced in load the Super Blend became. norbsa
WAS LOOKING AT OLD POSTS AND SAW ONE ON THIS SUBJECT.
A FEW FACTS.
THE ORIGINAL COMMANDO USED THE SAME BALL AND ROLLER RACE BEARINGS AS THE ATLAS /650 MOTORS. THE ROLLER WAS A SKF 8MRJA30. NOTE THE 8. THIS DENOTED A BRASS CAGE. THE 11 ROLLER ELEMENTS WERE APPROX 11.12MM O.D. AND 11.12MM WIDE WITH A SLIGHT RADIUS ON THE ENDS LEAVING A PARALLEL WIDTH OF 10 MM. THE DYNAMIC LOAD CAPACITY WAS 41,000N AND THE STATIC WAS 35000N.
CRANKSHAFTS BROKE( THANKS TO TRHE STRESS RAISERS NORTONS INTRODUCED INTO THE CRANKS...PLUS OF COURSE THE HIGHER CRS AND OWNERS SCREWING THE BALLS OUT OF THE MOTORS) AND THE MAINS COULD USUALLY BE HEARD RUMBLING AT ABOUT 4000 MILES. THE CRANK FLEX WAS CAUSING THE EDGES OF THE ROLLERS TO DIG INTO THE INNER AND OUTER RACEWAYS, STARTING THE QUICK ROAD TO DESTRUCTION.. VARIOUS PEOPLE WERE CONSULTED AND BARRAL SHAPED ROLLER BEARINGS WERE DRAWN UP ON THE BACKS OF FAG PACKETS. THE END RESULT WAS THAT SKF MADE A FEW SUCH BEARINGS BUT THEY HAD STEEL CAGES AND NORTONS ENDED UP ADOPTING A RAMSOM AND MARLES BEAING DESIGNATED 6MRJA30. NOTE THE 6. THIS DENOTED A SPECIAL, IN THIS CASE BRASS CAGE AND 13 SPECIAL SHAPED ROLLING ELEMENTS. THE ROLLING ELEMENTS WERE APPROX 9.53MM WIDE AND 9.53MM OD. THERE WAS STILL A RADIUS ON THE OUTER EDGES BUT THE PARALLEL SECTION OF THE ROLLERS WAS ONLY APPROX 6MM (9.53MM DIA) WHICH THEN BARRAL SHAPED DOWN TO APPRODX 9.46MM AT THE POINT THE RADIUS STARTED. BOTH THE DYNAMIC AND STATIC LOADS WERE LOWER THAN THOSE OF THE OLDER BEARING AT, DYNAMIC 35,500N AND STATIC 31,000N.
NOW OF THE SKF BEARING I FOUND, EX NORTON STOCK, ONE WAS MARKED NJ306 (1972)AND THE OTHER NJ306E (1972). THE NJ306 HAD 11 ROILLERS OF APPROX 10MM WIDTH AND DIA BUT HAD A PARALLEL SECTION OF APPROX 7MM FROM WHICH IT TAPERED TO APPROX 9.97MM BY THE START OF THE RADIUS ON THE ENDS. THE LOAD CAPACITIES WERE GIVEN TO ME BY SKF AS DYNAMIC 36900N AND STATIC 20000N. THE NJ306E BEARING HAD 12 ROLLERS APPROX 12MM WIDE AND 11MM OD WITH A CENTERPARALLEL SECTION OF APPROX 8MM AND THEN TAPERING DOWN TO APPROX 9.97MM BY THE START OF THE RADIUS AT THE ENDS.ITS LOAD VALUES WERE GIVEN TO ME AS DYNAMIC 51200N AND STATIC 30000N.
SO THE ORIGINAL AND ONLY SUPERBLEND BEARING EVER USED IN PRODUCTION BY NORTONS WAS THE 6MRJA30 WHICH WORKED WONDERFULLY WELL EVEN THOUGH IT HAD LOWER DYNAMIC AND STATIC LOAD VALUES THAN THE OLDE BEARING THAT GAVE THE ORIGINAL PROBLEMS.
IN THE DAYS WHEN THE OLDE 8MRJA30 BEARING WAS PRODUCED WITH ITS BOG PARALLEL ROLLING ELEMENT AS FAR AS I AM AWARE, NOT HAVING RESEARCHED IT, ALL MANUFACTURS ROLLERS WERE SIMILAR. IF YOU BUY ANY MANUFACTURERS BEARING NOW I SUSPECT YOU WILL FIND THEY ALL HAVE A VERY SLIGHT BARRAL SHAPE TO THE ROLLERS BUT IT IS NOT AS GREAT AS ON THE 6MRJA30 BEARING. ALSO YOU WILL FIND THAT THE ROLLERS ARE WIDER TRHAN USED ON THE 6MRJA30 BEARING SO, ASSIMING THE SAME INTERNAL CLEARANCE WITHIN A FEW DIFFERENT BEARINGS THE 6MRJA30 WILL ALLOW A TAD MORE FLEX THAN THE OTHERS AND WHEN CHECKING USED MAINS IT IS INTERESTING TO NOTE THAT THE WEAR PATTERN ON A 6MRJA30 BEARINGS ROLLERS DOES NOT QUITE REACH THE START OF THE END RADIUS BUT IT DOES ON ALL THE OTHERS I HAVE LOOKED AT INCLUDING THE FAG ONES.I WAS TOLD THAT THE ONLY REASON FOR THE CHANGE TO FAG BEARINGS WAS THAT THEY WERE DOWN THE ROAD FROM THE FACTORY AND THEY WERE CHEAPER. OR WAS IT THAT RHP DIDNT WANT TO MAKE A FEW SPECIALS IN SMALL QUANTITIES?
NOW FOR LATER BEARINGS I LOOKED AT A FEW YEARS BACK.
THE RHP NUP306ETN BEARING HAS 13 ROLLERS APPROX 12MM WIDE AND 11MM OD WITH A PARALLEL SECTION APPROX 9MM WIDE TAPERING TO APPROX 10.96MM BY THE START OF THE END RADIUS.DYNAMIC = 57000N. STATIC = 53000N.
A FAG NJ306E BEARING HAS 12 ROLLERS APPROX 12MM WIDE 11MM OD WITH A PARALLEL SECTION OF 8MM TAPERING TO 10.97MM BY THE START OF THE END RADIUS. DYNAMIC= 51000N AND STATIC =48000N.
OF COURSE THE MEASUREMENTS AND HAVING THE FRIENDLY GENT AT THE RHP OLD RANSOME AND MARLES FACTORY GO INTO THE CELLAR, FIND THE DRAWINGS AND CALCULATE THE LOAD VALUES FOR THE 8 AND 6 MRJA30 BEARINGS WAS A LONG TIME AGO NOW AND OTHER MANUFACTURERS BEARING MAY OF CHANGED SINCE THOSE DAYS BUT I WOULD SUGGEST THAT CONCENTRATING ON THE LOAD VALUES IS A RED HERRING AS THE BEARING THAT SORTED OUT THE PROBLEM ON THE 750S HAD LOWER LOAD VALUES THAN THE ONE IT REPLACED.......
WITH NOTHING SPECIAL IN THE SHAPES OF THE VARIOUS MANUFACTURERS BEARINGS THESE DAYS WHY DO PEOPLE INSIST ON CALLING THEM SUPERBLENDS???
OH YES.... AND GUESS WHO, MANY YEARS AGO, FOUND BEING FLOGGED AS SUPERLENDS A PILE OF FAGNJ
(OR WAS IT NU?) 306E BEARINGS THAT HAD STRAIGHT PARALLEL ROLLERS..... YES THATS HOW FAG USED TO PRODUCE THEM BEFORE CHANGING TO THE NEW SHAPED ROLLERS MANY YEARS AGO.......WONDER HOW MANY OWNERS BOUGHT THOSE BEARINGS AND BUGGERED THEIR ENGINES???
LUCKILY I FOUND HIDDEN, SOMEWHERE IN BIRMINGHAM, MANY YEARS AGO AMOUNG THE HUNDREDS OF BOXES EACH CONTAINING 8 X 8MRJA30 BEARING TWO BOXES MARKED 6MRJA30 AND BOUGHT THEM AT THE SAME 30 BOB EACH AS WAS BEING CHARGED FOR THE OLD CRAP (THE BALL RACE 6306S BALL BEARINGS WERE 20 BOB). ONES....THINK I HAVE TWO LEFT NOW.... THANKS TO FRIENDS NICKING THEM.
WONDER IF THE OLDE RANSOM AND MARLES FACTORY NOW ITS PART OF A JAPANESE GROUP STILL HAS ALL ITS ORIGINAL DRAWINGS SO PEOPLE CAN STILL PHONE UP AND FIND OUT THE SPEC OF THEIR WW1 FIGHTER AIRCRAFT MOTORS BEARINGS OR HAVE THEY ALL BEEN 'THROWN ON A BIG SKIP' AS I WAS TOLD WERE THE DRAWINGS AND CHANGE SHEETS FOR THE LAYCOCK ENGINEERING COMMANDO CLUTCH DIAPHRAGM SPRINGS BY GKN WHEN THEY CLOSED THEM DOWN?????.
SUGGESTED READING FOR ANYONE INTERESTED.IN FACT IT SHOULD BE COMPOLSORY READING FOR ALL NORTON OWNERS.
MOTOR CYCLE SPORT. JAN 77. PAGES 27 AND 28...''VICIOUS CIRCLE'' ' A CAUTIONARY TALE IN WHICH IT IS SHOWN THAT IN ENGINEERING, AT LEAST, NOTHING IS AS SIMPLE AS IT SEEMS. THE FOLLOWING STORY IS BASED ON A SERIES OF EVENTS WHICH TOOK PLACE NOT LONG AGO, AT A MOTORCYCLE MANUFACTURER SOMEWHERE IN EUROPE. ONLY THE NAMES HAVE BEEN OMITTED TO PROTECT THE GUILTY'.
READ IT AND CRY AT THE INCOMPETENCE THAT WAS NORTONS. ITS 100% FACT.
NO SPELL OR GRAMMER CHECKS APPLIED.