John Hudson and various authors from NOC-L Identification codes for the several types of Commando cylinder head
The Commando cylinder head can be distinguished from the earlier Heavy Twin head by its larger hemisphere which is offset to the cylinder bore and its 1½" inlet valves instead of the 1.406" valves on the 500cc and 650cc machines.
The rocker oil feeds go in at the sides of the rocker boxes, midway between the rocker shaft retaining plates, as the holes on top of the boxes are used to attach the head steady instead of the oil feeds.
The Commando head also has slightly different centres for the four bolts adjacent to the spark plugs, so that it is necessary to 'pull' the holes to fit on a 500cc or 650cc barrel. I have seen this done once, but it can only be described as a bodge.
Commando cylinder heads were not stamped RH1 from the beginning, and it would have been after 1972 when they started to make so many variants, which were as follows:-
| NORTON COMMANDO CYLINDER HEADS | |||||
| Identification Number |
Part Number |
Capacity | Compression Ratio |
Inlet Port | Remarks |
| RH1 | 060988 | 750cc | 9.0 : 1 | 30mm | Standard up to 1972 |
| RH2 | 061427 | 750cc | 10.25 : 1 | 32mm | AMA racer |
| RH3 | 063327 | 750cc | 10 : 1 | 32mm | 1972 Combat |
| RH4 | 064038 | 850cc | 8.5 : 1 | 32mm | 1973 |
| RH5 | 064048 | 750cc | 8.9 : 1 | 32mm | 1973 low compression |
| RH6 | 064097 | 750cc | 9.3 : 1 | 32mm | 1973 |
| RH7 | 064845 | 750cc | 10 : 1 | 32mm | 1973 short stroke |
| RH8 | 064884 | 750cc | - | 32mm | 1973 short stroke race kit |
| RH9 | 065013 | 850cc | 10:5 : 1 | 32mm | 1974 high performance |
| RH10 | 065062 | 850cc | 8.5 : 1 | 30mm | 1974 |
| A suffix S, e.g. RH6S, indicates a 750cc head fitted with 850cc guides | |||||
| Will a 750 head fit onto an 850 motor? Has anybody ever tried it? Also, the identifier code over the exhaust rocker is absent, but I believe the head in question is a 1972 Combat. Has anybody else run into heads with no identifier before? |
750 and 850 heads are different
The 750 and 850 heads are not easily interchangeable; they have different bolt patterns.
Eric Lamberts (ewl@med.unr.edu) on NOC-L 22nd. Apr 1998
Fitting a 750 head to an 850
|
The 750s and 850s have a different bolt pattern, the four outer ones being spread more on the 850. Dwaine Williams says "you can just drill the holes over on a 750 to fit an 850". Others have filled the holes with 'dowels' and redrilled the holes, but then there's the problem of head gasket and squish bands to deal with. |
I, and other racers (Todd Henning #454 for one), like small port heads for their flexibility and flow speed. Perhaps the easiest way is to port the 850 head and manifolds to 32mm, making a nice smoooth taper from the manifold surface to the valve guide area, similar to a Combat design.
A Combat head is marked with a large 'C' on the top in the middle near the top engine steady (on the two I have) and has a milled 0.040" surface. Earlier 750s have very small ports and fairly rough casting. Both my 750 S and 850 Mk.lla (with small port heads) could turn 12.8 second ¼ miles; the S handicapped by small S head pipes, and the 850 by 8.5:1 compression.
Carl Hokanson (hokansonc@juno.com) on NOC-L 23rd. Apr 1998
Combat head with no identifier
My Combat head has no RH identifier at all, yet all the evidence points to it being original to the machine.
Ben English (dmvms.mailnet.state.ny.us) on NOC-L 23rd. Apr 1998
