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Commando Main Bearings Service Releases

J.B. Nicholson http://www1.kingston.net/~fortierg/mainb.htm

The following says all there is to say about main bearings.
Take the advice as failure in this area is predominantly unpleasant

Premature failure of the crankshaft main bearings occasionally occurs. This is sometimes difficult to identify in that excessive up and down play at the crankshaft is not always evident when the crankshaft ends are lifted up and down in the usual checking procedure. Deterioration of the bearing track on the inner race sometimes occurs, resulting in a howling noise at certain speeds.

When the crankcase is disassembled it is wise to check the main bearings carefully. On the drive side bearing one of the rollers should be pulled out. This can be done by gripping with suitable pliers, then the bearing cage can be rotated slowly while the condition of the inner bearing track can be examined all the way around. If there is noticeable pitting or roughness, the bearing should be replaced. The timing side ball bearing (early models only) cannot be inspected in the same manner but usually roughness can be detected by careful examination or feel of the bearing when rotated.

Main bearings that are doubtful should be replaced. It should be noted that the ball and roller bearings are supplied in three grades according to clearance. This is indicated by the number of dots or zeros on one of the bearing races. An average fit bearing has two dots or zeros, a close fit one dot or zero and a three dot or three zero bearing indicates plus tolerance. Norton recommends using the single dot close fit bearing or as an alternative, the double dot, to reduce the possibility of bearing hammering and premature failure that may occur under certain conditions.

Prior to 1971, crankshaft main bearings comprised a roller drive side bearing (R&M Part No. MRJA30) and a timing side ball bearing (Part No. MJ30). Later models are fitted with two new type roller bearings (Part No. 6MRJA30) that give improved durability. These bearings can be fitted to earlier models on both the drive and timing side. When roller bearings are used on both sides, the crankshaft should be shimmed to provide an end play of between 0.010" and 0.020". This is Norton shim (Part No. NMT2196A, later changed to 067569).
 

Norton Service Release Notes

A total of 3 was issued by Norton Motors:-

Service Release No. 68
 Nature of Release Revised main bearings
 Models Affected All years and models of Commando
 Distribution Worldwide  


Explanation
We are introducing a new roller main bearing arrangement in production almost immediately. The fitting of this bearing arrangement reduces overall width between the main bearings and increases timing side main bearing journal diameter.

For service purposes we shall in future supply only the crankshaft of the latest size, Part No. 063106. The main bearings, Part No. 063114, must be used in conjunction. The new bearings are 2 dot single lip roller bearings and should be assembled with the lip into the crankcase in both cases. Main bearing Part No. 063114 is of the Ransomes type (R&M) MRJ A30. Alternative bearings which may be used are listed below:-

 
Manufacturer Type
S.K.F. NJ306 or NJ306E
F.A.G. NJ306
N.T.N. NJ306
Hoffman R306L
R.H.P. NF306
All bearings to be 2 dot or C2


Note in fitting that NJ type bearings have the rollers and cage assembled to the outer race so that the outer can be pressed into the crankcase either way around. The inner race must be pressed onto the crankshaft with the lip leading. The NF type bearings have the rollers and cage assembled to the inner race. The outer race must be pressed into the heated crankcase with the lip leading. The inner race complete with the cage and rollers can be pressed either way around onto the crankshaft. 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).

(October 1971)

 
Service Release No. N2/6
Nature of Release Crankshaft main bearings
Models Affected 1972 Models commencing at Engine No. 200004
Distribution Worldwide  


Explanation
Field experience with the 1972 models (incorporating two single lipped roller main bearings) indicates a small but significant premature roller main bearing failure rate. Reported failures have been confined solely to the one type of bearing.

Action:- When replacing defective roller main bearings, ensure the replacement is a Skefco double lipped outer, single lipped inner spool type NJ306, with a specified nominal internal diameter clearance of 0.0008" - 0.0012" (0.02mm - 0.03mm) prior to fitting . Ensure the crankshaft journals are carefully cleaned up, removing all signs of butts or scoring before fitting the inner spool. Models subsequent to Engine No. 207197 incorporate a nominal increase in bearing housing diameter to overcome any significant tendency to excessive closure of the single lipped outer series of roller bearing.

(July 1972)

 

Service Release No. N2/9
 Nature of Release Crankshaft main (roller) bearings
 Models Affected 1972 Commando (all models)
 Distribution Worldwide  


Explanation
In order to extend main bearing life, a change of roller main bearing specification has now been authorized and fitted on production engines from Engine No. 211891. The new roller bearing is designated 'Superblend' with an increased load carrying capacity and is supplied under Part No. 063906 (manufacturers part number R&M 6/MRJA30).

Action:- Where engine units are stripped for examination, or the need for main bearing replacement, fit only roller main bearings Part No. 063906 in place of the previously specified 063114. The new bearings are fully interchangeable, and should be fitted in pairs for maximum reliability.

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 1.1807" - 1.1812") diameter, now 1.1812" - 1.1815" diameter. Also crankshaft fitted end float should be checked, and shimmed where necessary to provide 0.010" minimum, 0.020" maximum end float using shim Part No. NMT2196A as necessary.

(August 1972

 

Norton Owners Club


Main Bearings:- There are so far, only two types of bearing I would recommend to anyone to use in a Norton twin (500 up anyway). These bearings are both Superblend roller bearings; one is Ransome and Marles, Norton Part No. 063906, and one from F.A.G., Norton Part No. 064118. Either should be used in 500 - 750 engines; the factory reckoned only to use the F.A.G. bearings in the 850s.

There will be some end float with the double roller bearing setup which previously was controlled by the ball bearing in the timing side. This should be between 10 and 30 thou., but don't worry if it's not, as long as there is some float. The outer rings of the bearings are glued in at the factory by Loctite Bearing Fit, so there's no reason why you shouldn't use it too, as long as you make sure that the rings are hard home before the glue sets, not when you find you haven't got any end float! Only use bearings with one of the following numbers:- NJ306E (E is very important, NJ306 is weaker) or 6 MRJA30. The 6 may be hand engraved on the bearing. The timing side bearing need not be a tight fit on the crank. Again don't use just any roller bearings, these ones are barrelled to allow crankshaft whip. Another number is NJ306E M1 (harder).

1968 Commando
Fastback after Serial Number 126125 - Frame Number 126125
Part No. Description Quantity Models
 17822  Ball bearing timing side 1 All
 T-2008  Sealing/washer (timing side bearing) 1 All
 17824  Roller bearing drive side 1 All
 T-2187  Oil seal (drive side) 1 All
 T-2196A  Crankshaft bearing shim 1 All

 

1969 Commando
Fastback, S and R after Serial Number 131257 - Frame Number 131257
Part No. Description Quantity Models
 17822  Ball bearing timing side 1 All
 T-2008  Sealing/washer (timing side bearing) 1 All
 17824  Roller bearing drive side 1 All
 T-2187  Oil seal (drive side) 1 All
 T-2196A  Crankshaft bearing shim 1 All

 

1970 Commando
Fastback, S, R and Roadster after Serial Number 135140 - Frame Number 135140
Part No. Description Quantity Models
 17822  Ball bearing timing side 1 All
 T-2008  Sealing/washer (timing side bearing) 1 All
 17824  Roller bearing drive side 1 All
 T-2187  Oil seal (drive side) 1 All
 T-2196A  Crankshaft bearing shim 1 All

 

1971 Commando
Fastback, Roadster, Hi Rider and SS after Serial Number 141717 - Frame Number 141717
Part No. Description Quantity Models
 17822  Ball bearing timing side 1 All
 T-2008  Sealing/washer (timing side bearing) 1 All
 17824  Roller bearing drive side 1 All
 T-2187  Oil seal (drive side) 1 All
 T-2196A  Crankshaft bearing shim 1 All

[Editor's Note:- Main bearing amended in late 1971]

 

 

1972 Commando
Fastback, Roadster Roadster Combat, Interstate and Hi Rider
after Serial Number 200001 - Frame Number 200001
Part No. Description Quantity Models
 063114  Main bearing 2 All
 NMT2187  Main bearing oil seal 1 All
 NMT2196A  Main bearing shim 1 or A/R All

 

1973 Commando
Roadster, Hi Rider and Interstate
Part No. Description Quantity Models
 063114  Main bearing 2 All
 NMT2187  Main bearing oil seal 1 All
 NMT2196A  Main bearing shim 1 or A/R All
 064118  Main bearing 2 850 only

 

1974 Commando
Roadster, Hi Rider and Interstate
Part No. Description Quantity Models
 063114  Main bearing 2 All
 NMT2187  Main bearing oil seal 1 All
 NMT2196A  Main bearing shim 1 or A/R All

 

1975 Commando
Roadster, Hi Rider and Interstate
Part No. Description Quantity Models
 063118  Main bearing 2 All
 067567  Main bearing oil seal 1 All
 065245  Circlip (added in 1975) 1 All
 067569  Shim A/R All

 

 

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