Crankshaft Differences

marshg246

marshg246

VIP MEMBER
Joined
Jul 12, 2015
Messages
4,198
Country flag
The 68-70 complete assembled crankshaft has a different part number from the 72 complete assembled crankshaft but the flywheel, and both sides have the same numbers. Is a 69 crankshaft usable in a 72 engine? Are there any differences other than the bolts/studs that hold them together?
 
To add a question to your question - Were they balanced to a different %?
 
mean gene said:
To add a question to your question - Were they balanced to a different %?
Click to expand...
Everywhere I Iook says 58%. Also confusing is that the NOC says all are the same and lists the same individual part numbers for all pre-MK3 but that disagrees with the parts books, AN, and RGM. According to the NOC article, I can use it - found that after I asked here. Then, AN still lists the bolts but provides only studs in the kit that they say is good for 72-74; prior to that they list a kit with bolts. So, information on this is all over the place!

https://www.nortonownersclub.org/support/technical-support-commando/crankshaft
 
Greg, I believe the difference is probably due to the diameters of the timing side shafts. The earlier shafts, meant for a ball bearing, are ~.0005" smaller OD than those for the "Superblend" mains. Norton released a Service Note N.2/9 addressing this change, and stating that the later bearings could still be retrofitted to the earlier crankshafts with no issues.

Ken
 
Last edited:
Clip from the Service Release:

Note: The new bearings may also be fitted to advantage to 1971 and earlier Commando machines, provided care is taken fitting the inner spool to the right side crankshaft journal (was 1.1807in. 1.1812in.) diameter, now 1.1812in. 1.1815in. diameter. Also crankshaft fitted end float should be checked, and shimmed where necessary to provide O.OlOin. min. 0.020in. max. endfloat using shim part number NMT2196A as necessary.

Ken
 
lcrken said:
Greg, I believe the difference is probably due to the diameters of the timing side shafts. The earlier shafts, meant for a ball bearing, are ~.0005" smaller OD than those for the "Superblend" mains. Norton released a Service Note N.2/9 addressing this change, and stating that the later bearings could still be retrofitted to the earlier crankshafts with no issues.

Ken
Click to expand...
Thanks! I must be blind! I have a searchable database of the serivce releases on my web site, searched for crankshaft, and didn't see if before starting this thread. I see it now! I also see typos I need to fix in it.
 
lcrken said:
The earlier shafts, meant for a ball bearing, are ~.0005" smaller OD than those for the "Superblend" mains. Norton released a Service Note N.2/9 addressing this change,
Click to expand...

However, the change to two rollers occurred at 200004, before the Superblend so Service Release No.68 should also be noted.

Commando Main Bearings Service Releases | Norton Owners Club

www.nortonownersclub.org www.nortonownersclub.org

"The later crankshaft of reduced overall width is identified by the letter 'R' stamped into the timing side crankshaft cheek adjacent to the bearing location. The designed crankshaft fitted end float for the new arrangement is 0.010" to 0.024" (0.254mm - 0.609mm)."

lcrken said:
I believe the difference is probably due to the diameters of the timing side shafts.
Click to expand...

Although there appears to have been minor dimensional changes made to the crank, the three main crank components had the same part numbers from 1968 to 1973, therefore, logically the crankshaft assembly part number changed from '1972' when the fasteners changed to all (UNF) studs and nuts (so to 18 different UNF fastener parts from the previous BSC? Whit form? 14).
 
Last edited:
Which part of the 850 MK3 crank makes it wider, is it the flywheel or the cheeks?
 
Matchless said:
Which part of the 850 MK3 crank makes it wider, is it the flywheel or the cheeks?
Click to expand...

750 vs 850 Commando Crankshaft

Does anyone know the difference between the 1971 - 1972 750 & 1973-1974 850 Crankshafts ? Can the 750 crankshaft be used in 1973 850 cases without problem ? Another question is, Why does the 1972 Combat engine have the extra Tabbed Thrust Washer on the Camshaft ? Thanks in anticipation...
www.accessnorton.com www.accessnorton.com
dynodave said:
...both ES crank cheeks are WIDER than any earlier commando crank cheeks so they will NOT fit in NON ES cases.
Click to expand...
 
L.A.B. said:

750 vs 850 Commando Crankshaft

Does anyone know the difference between the 1971 - 1972 750 & 1973-1974 850 Crankshafts ? Can the 750 crankshaft be used in 1973 850 cases without problem ? Another question is, Why does the 1972 Combat engine have the extra Tabbed Thrust Washer on the Camshaft ? Thanks in anticipation...
www.accessnorton.com www.accessnorton.com
Click to expand...
Not that it matters to the mass inside the cases but isn't there a change to the crank output stub to accommodate the electric start mechanism? And a minor change from three fixings inner primary to the cases versus four on the E/S?
 
You must log in or register to reply here.
Back
Top