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Camshafts and Bushes

Steve Jowett www1.kingston.net/~fortierg/mainb.htm

Commando camshafts and bushes
 

Camshafts

 Standard Combat Material  EN32B EN32B
 Maximum Lift  Inlet 0.332" - 0.390" : Exhaust 0.332" - 0.346"
 Base Circle Diameter  0.885" - 0.906"
 Bearing Journal Diameter  0.8735" - 0.8735"

Camshaft Bushes

  Fitted i.d. - Left Bush Fitted i.d. - Right Bush
 Pre-1972 0.8750" 0.8750"
 1972-on 0.8750" 0.8750"

 

The following is a listing of the camshafts available from the factory, provided via the service release notes from Norton Motors. There were several camshafts available from the factory itself and it should be noted that a multitude of cams were made during the Commando time period by other sources. Some of these cams are still available from dealer networks and Norton shops.

Inspection of the cam should be done in good light to check for wear on the lobes and where the cam rides in the bushes. Factory cams are long wearing and last for thousands of miles. I replaced mine after about 65,000 miles as the lobes were starting to wear. I believe this was due to neglect from the original owner on oil changes and maintenance. Cams can wear faster if the chain tension is not provided for properly as a loose chain can cause jerking motions on the cam. Also, too tight a chain can cause faster bushing wear and possible cam wear at the bushing area. I check my chain tension about every 3000 miles. It is simple to do and requires only the fitting of a new gasket if the old one tears upon removal of the cover. Another cure for this is the automatic tensioner which can be provided by certain shops: I don't know of anyone who has one but then I have never read anything bad about them either.

Camshaft changes were affected on the Norton motor during the 1972 time period with the introduction of the Combat. The factory made available three camshafts noted as the S, SS and SSS camshafts. The S camshaft was the original as fitted to all pre 1972 Commandos. The SS was as fitted to the Combat and the SSS was as fitted to the Production Racer model.

The fitting of the S camshaft only poses problems with the bushes being scrolled or not (see the Norton Motors Service Release for this information). The SS and SSS camshafts produce a multitude of problems with clearances and valve considerations. I have run an S camshaft through out my 750's life and found it to be quite acceptable in performance. Fitting of the other camshafts tends to always lead to problems, (mainly due to improper fitment practices), including broken and bent valves to case rupture due to improper cutaways. Although the increase in low and mid range power may be of a benefit to some owners (racing especially) careful installation is a key factor here. Check all things twice. Valve clearance is the most important.

The cam changed in the following years:- In1969 it was changed to accept the new rev counter location and the points on the end of the camshaft (the 'S' Type was the first to receive this change). In 1972, it was altered again with the introduction of the new breather assembly and in the same year the Combat received a new cam with different ramps and valve timing. Norton reverted back to the original cam for 1973 and the 1972 and 1973 cam are the same except for part numbers. This stayed in production machines until its demise in 1975. The cam valve lift and duration remained the same except for part number changes. It is interesting to note that the cam bushes were different for all years except 1972 and 1973 where the bushes were the same for both drive and timing side.

Norton Service Release Notes

 
Service Release No. N77
Nature of Release 1972 Camshafts and Bushes
Models Affected All Commandos
Distribution Worldwide (for general distribution)  


Explanation
New type camshaft bushes with oil grooves are introduced for 1972. To suit these, camshafts are being produced without the figure of eight oil groove which was a feature of previous camshafts. Whilst we will continue to stock the bushes and camshafts of the previous type for spares purposes, all concerned are alerted to the danger of using a 1972 non-grooved camshaft in pre-1972 non-grooved bushes, which could result in oil starvation and possible engine damage. 1972 camshaft bushes are of a smaller outside diameter than previous camshaft bushes and as a result, it is not possible to fit later bushes to an earlier crankcase. No harm would result from using a grooved bush if this should prove necessary at anytime.

Action
Ensure that the correct years parts are ordered when replacement camshafts or camshaft bushes are required and on fitting recheck that either the camshaft journals or bushes have lubrication grooves.

(February 1972)

 

Service Release No. N3/13
Nature of Release Camshaft interchangeability
 ( to be read in conjuction with Service Release N77)
Models Affected 1970 and 1971 Commando (all models)
Parts Affected Camshaft, crankcase, cylinder head and valves
Distribution Worldwide  


Explanation
Following the introduction of new crankcases with modified breathing together with the introduction of the Combat SS type camshaft, there are now several possible combinations of crankcases and camshafts. In addition, where it is desired to fit the high performance SS type camshaft to a pre-1972 engine there are problems with cam lobe clearance at the crankcase oil filling shroud.

In addition, problems can arise due to valve head diameter, valve stem and spring length discrepancies particularly where an earlier 'non-Combat' cylinder head is fitted. It is also essential to fit tappet locating plates Part No. 063092 to accommodate the increased lift on both the SS and SSS camshafts.

 
Cam Part No. ID Stamp Journal Type Use Part No. Comments
 061084 S  Scrolled  061084  Standard 1971 plain bushes
 062608 S  Plain  061084  Standard 1972 scrolled bushes
 062673 SS  Plain  063536  Combat 1972 scrolled bushes +
 062807 SS  Scrolled  063536  Combat 1972 plain bushes +
 063536* SS  Scrolled  063536  Combat 1972 plain bushes +
063537* SS  Plain  063536  Combat 1972 scrolled bushes +
TX0302 SSS  Scrolled  063761  Original NVPS camshaft plain bushes ++
063453 SSS  Plain  063761  Variant TX0302 scrolled bushes ++
063761* SSS  Scrolled  063761  Variant TX0302 plain bushes ++

Notes
Use scrolled journal camshafts prior to Engine No. 204048 with plain bushes Part Nos. NMT2036 and NMT2037. Use plain or scrolled journal camshafts subsequent to engine number 204049 with scrolled bushes Part No.062600. Scrolled condition camshafts only will be supplied against orders for all above camshafts.

 + Conversion from standard cams to Combat condition requires the following:-
  • a) cylinder head Part No. 063327 to provide a 10:1 compression ratio
  • b) solid skirt Combat pistons Part Nos. 063348 LH, 063349 RH, Std. (see service release N.2/4 for oversizes)
  • c) combat valves Part Nos. inlet 063283, exhaust 063282
  • d) standard valve springs Part Nos. NM22838 outer, NM22839 inner using spring seat spacers to provide 0.050"(1.27mm) clearance at full lift
  • e) Combat tappet locating plates Part No. 063092
 ++ Conversion to SSS specifications: as Combat from standard : no further action required for Combat.

(May 1972)

Crankcase Breather

1968 Commando
Fastback after Serial Number 126125 - Frame Number 126125
Part No. Description Quantity Models
 22729  Camshaft 1 All
 T-2036  Camshaft bush (timing side) 1 All
 T-2037  Camshaft bush (drive side) 1 All

 

1969 Commando
Fastback, S and R after Serial Number 131257 - Frame Number 131257
Part No. Description Quantity Models
 061084  Camshaft 1 All
 T-2036  Camshaft bush (timing side) 1 All
 T-2037  Camshaft bush (drive side) 1 All

 

1970 Commando
Fastback, S, R and Roadster after Serial Number 135140 - Frame Number 135140
Part No. Description Quantity Models
 061084  Camshaft 1 All
 T-2036  Camshaft bush (timing side) 1 All
 T-2037  Camshaft bush (drive side) 1 All

 

1971 Commando
Fastback, Roadster, Hi Rider and SS after Serial Number 141717 - Frame Number 141717
Part No. Description Quantity Models
 061084  Camshaft 1 All
 T-2036  Camshaft bush (timing side) 1 All
 T-2037  Camshaft bush (drive side) 1 All

 

1972 Commando
Fastback, Roadster Roadster Combat, Interstate and Hi Rider
after Serial Number 200001 - Frame Number 200001
Part No. Description Quantity Models
 061084  Camshaft (standard) 1 except Combat
 063536  Camshaft (Combat) 1 Combat only
 062600  Camshaft bush 2 All

 

1973 Commando
Roadster, Hi Rider and Interstate
Part No. Description Quantity Models
 061084  Camshaft (standard) 1 except Combat
 063536  Camshaft (Combat) 1 Combat only
 062600  Camshaft bush 2 All

 

1974 Commando
Roadster, Hi Rider and Interstate
Part No. Description Quantity Models
 062608  Camshaft 1 All
 065428  Camshaft bush (timing side) 1 All
 065425  Camshaft bush (drive side) 1 All

 

1975 Commando
Roadster, Hi Rider and Interstate
Part No. Description Quantity Models
 062608  Camshaft 1 All
 065428  Camshaft bush (timing side) 1 All
 065425  Camshaft bush (drive side) 1 All

 

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