Identifying The Right Clutch Part By David Childs

This article (originally published in Fishtail 173), is the starting point from which everyone should check their clutch details if they find they have a problem. David Childs has kindly allowed its republication on this site. 

In recent years I have examined numerous Velocette clutches which have given trouble because they have been fitted with the wrong parts. Many Velo clutch parts appear the same but close examination shows small differences, and you fit the wrong part AT YOUR PERIL.

To assist in identifying the various clutch components of all single cylinder four stroke Velos, (except KTT) from 1930 to 1969 I have compiled the accompanying tables. These should be used in conjunction with the following notes, many of which are referred to in the tables.

The main table shows the part numbers of clutch components fitted to any machine. The clutch elements tables show how to identify these parts.

1 . The number of plates quoted is the total which share the drive e.g. the seven plate clutch consists of (in order) inner end plate, inserted plate, plain plate, chain wheel, plain plate, inserted plate and outer end plate.

2. The number of springs quoted is the total number which can be fitted. i.e. the number of holes in the spring holder. A lesser number of springs may have been fitted when the machine was new e.g. the spares list states that the pre-war MkII KSS and KTS has 12 springs although the spring holder will take 20. I suggest you fit as many springs as you can.

3. All dimensions are in inches. Most parts seem to vary by about +/- 1/32" but some have smaller or larger tolerances.

4. Spring C12/2 was used only on O.H.C. models from 1930 to about 1934 or 35 when it was superseded by C12/3, which is directly interchangeable, in sets.

5. The clutch insert thickness quoted are for inserts fitted as original equipment. In later years replacement MAC inserted plates (C23AS) were apparently fitted with C25/2 inserts instead of C25. Some pattern inserts are of different thickness again. See also note 8.

6. The three-plate cork clutch fitted to the two strokes (GTP and earlier models) is similar to that on the MAC but is smaller. The inner and outer end plates are both 5 31/32" outside dia., the chain wheel has only 62 Inserts and either 41 teeth (1/2" pitch) or 55 teeth (3/8" pitch). The other parts are the same as MOV/MAC

7. I believe the change from the one-piece spring holder to the two piece type was made in 1940, but it may have been a year or so later.

8. On occasions, Veloce altered the design or dimensions of parts without changing the part number, and this may be the case with the change in the inserts fitted to replacement C23AS plates. I have measured a large number of parts and have only given dimensions which I believe have not changed, but I could be wrong.

9. In early spares lists there is some confusion between bare components and assemblies of these components and other components (for example between a bare inserted clutch plate and one complete with inserts) but after the war all assemblies had the letters AS in the part number. Therefore an inserted clutch plate for a post-war MAC was C23AS (usually described as "C23 and C25" before the war), and that for a Venom was MAS 106.

10.The spares lists show that sometime in 1939 (probably for the 1940 season) chainwheel B3/3 was replaced (on MOV and MAC) by chainwheel B3/7AS. This contained a single row of 36 circular "Bullite" (leather?) inserts, part number C13/2. Post war the MOV reverted to chainwheel C3/3 and the MAC used the seven plate clutch. I doubt whether many B3/7AS chainwheels reached the public and have reason to believe some were converted to take the usual 66 cork inserts, i.e. were converted to C3/3 standard. The Thruxton had a spring holder which held 20 springs and, in the late sixties the chain wheel bearing was changed on all models (I believe to a plain type) and to accommodate it the chain wheel and inner end plate were also changed. Unfortunately I have no details of any of these parts so have not been able to put them in the tables. If anyone has any of these parts please let me know as David is keen to examine them.