TThe "D" Comet.

                           At the 1954 Motorcycle Show Vincent displayed their new range of Series "D" motorcycles.  
              These new models incorporated fully sprung mono shock rear ends and the new Princes and 
              Knights were fully enclosed in fibreglass fairings.   It would appear that the enclosed 500cc Victors,
              of which there were two or three on display at the show,   never went into production.   When the 
              factory subsequently had trouble getting good enough quality fairings,  they produced open Series 
              "D" Shadows and Rapides,  but the "D" Comet did not go into production.   At least one Victor 
              was sold and some time after motorcycle production had ceased a "D" Comet,  which had been 
              used as a factory hack was also sold.   Luckily there are photographs in books and I had earlier 
              taken some pictures of this bike.

                      I had a number of "D" pieces in my garage and not being able to afford a twin engine I decided
              I would have to make a "D" Comet.   I did not want to construct a highly tuned sports bike,  nor a 
              concours machine.   I just wanted a pleasantly mannered road bike that was a rider's machine and 
              bult to last with minimum attention.   I knew that as there was only the one prototype Comet of this 
              type,   I would have to make all parts peculiar to that particular model.   Having owned a Comet many
              years before  and worked on other peoples bikes,  I knew the failings of this bike.   The only trouble 
              I ever had was with the clutch basket cracking and allowing the ears to open out like the petals on a 
              flower.   The Burman gearbox itself seldom gave trouble but the gear change was very slow and 
              ponderous.   I decided that as I was starting with a blank sheet I would fit an AMC box and clutch 
              and get rid of both my former problems in one go.

                            First I had to get together the necessary parts to build the engine.   Luckily I had a front head 
               and a cylinder muff,   which I fitted with a new liner and had rebored to fit a standard 7.3 : 1 piston.   
               I had the head rocker tunnels bored and lined and fitted new valves,  guides and springs.   I made 
               special rocker feed bolts to lock the rocker bushes to the roof of the reconditioned rocker tunnels.  
               The rockers I lightened, balanced and polished.    I also drilled and tapped a second plug hole to 
               take the compression release device I made ot of stainless steel.   I did not intend to use a timed
               breather,  so I removed the surplus section of the steady plate and left out the breather pinion.   I 
               replaced all the timing gear spindles.    I had a set of cams and followers stellited and I had the 
               necessary gear,  which I turned and drilled to lighten it.   I initially set up the timing side with a large 
               alloy idler,  as seen in the photograph above,  but I have subsequently fitted a steel item.  I obtained 
               a crankshaft complete with con rod from Ted Davis.   I machined the flywheels and fitted a new 
               timing side mainshaft before truing and balancing.   I fitted an oilseal between the timing side 
               crankcase and primary chain case,  as I always run my primary chains in automatic transmission 
               fluid and did not want this contaminated with engine oil.   The big end was replaced,  as were all the 
               main bearings.   I remade all the crankcase studs,  bolts and nuts in stainless steel.   The engine I 
               then carefully assembled using all new gaskets and sealing washer where necessary.   I must say the 
               time spent has proved successful for I have an oiltight engine.   At first I assembled it with just an 
               atmospheric breather from the inlet valve cap.   I did relieve the top valve as in the original twins to 
               allow the engine to breathe.

                        I then did measurements with an old central alloy frame member (F106) to get dimensions for 
               mounting the AMC box,   I wanted to mount it in the standard fashion with it pivoting from the top 
               and having a primary chain adjuster underneath.   To do this I acquired a new unmachined F106 
               casting from Ron Kemp and had the two ears at the bottom,   on which the gearbox hangs,

                                                                   

                lengthened with weald about 3/4 inch.   I then completely machined the casting with the gearbox 
                mounting holes lower than on the original.   I had also had both sides of the top strengthened with
                extra weld and this allowed me to mill a slot in the centre to take the lug of the upper frame member.  
                It all worked out very well,  as you can see in the photo.   Using a Norton Commando cranked 
                kickstart to clear the exhaust pipe it all fitted in very nicely.   As you can also see I made up a new 
                right side gearbox plate from dural,  which runs down the front of the box and allows the oil pipes 
                to be hidden behind it.   I made a new plate to take the place of the right footrest mount on a 
                standard Comet,  which incorporated the silencer mount and right centre stand mount.   This plate 
                would normally be bolted onto the gearbox plate with spacer bushes between them.   I left these 
                bushes out as my measurements showed that I could then get the silencer closer into the side of the 
                bike;  it in fact clears the swinging arm by less than 1/4 inch.   I also made a new left side mounting 
                plate to incorporate the centre stand mounts,  which I sized by scaling up measurements taken from 
                photographs.

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