This view is with the timing gear cover removed.  

The small crankshaft mounted gear is in the centre of picture, the large gear to your left drives the camshaft (to which it is keyed), the large magneto idler gear is to your right, and the magneto drive gear is at the top right. Missing in this view is the oil pump and oil-pump drive gear below the crankshaft gear - they are of the same size - the two bolt holes for mounting the oilpump are visible near the base of the enclosure.  

The cam gear and idler gear have twice the number of teeth as the crank drive gear, so as to to drive the camshaft at half-speed for correct valve operation. The small gear on the magneto driveshaft means that the  
magneto spins at crankshaft speed. The magneto has its own half-speed reduction drive internally, to give correct spark timing to the four spark plug wires.  

In this engine, the magneto drive gear is aluminium, a non-standard fitting (?). This engine has been fitted with an aircraft magneto, and automatic advance ignition timing unit. No DIY ignition timing on this Ace!!  

Note the traces of Indian Red over the almost black finish. The original color of the Ace for 1926 was listed as Rolls Royce Blue. Whether the engine of the 1926 Ace was blue or black is an interesting question - all the remaining traces of paint appear to be black - but is any of this the original paint ?? This particular 1926 timing gear cover has a warning stamped into it (picture 5). Whether this was factory-done is an  
interesting question. Comments anyone ? Note the paint cleaned off around the stamping - it is believed that this was someone cleaning around the area of writing for a better look.  No doubts about the order of dismantling on this engine !!!  (Back to main text on page 1)  
  
  

Inside the 1926 Ace gearbox.   
  
A complicated view...from underneath don't forget.  

This view is from behind and underneath the bike - the ONLY access to the gearbox is with the sump cover removed, and possibly with the complete engine removed from the bike. Partly visible in the top of this view is the large (and heavy) 10" clutch. This mounts automotive style on the rear of the crankshaft immediately behind the rear cylinder.  

The gearbox mainshaft and gears are clamped into the housing using bearing caps - note the lockwire or split pins on every nut. The labelled picture points out most interesting features. Second gear (the middle  
sliding set) appears a little thinner compared to the outer gear sets - it gets a lot of hard use, being between first and top.  
  
This small bevel gear behind the clutch transmits all the power, through a 90 degree turn, into the gearbox. Four keys appear to be the only method of location, with no evidence of a taper I can detect. Poor  
engineering ?? Or protection against crankshaft breakage ?? The latter, I think... hopefully the keys will shear before the crankshaft snaps. Be interesting when we examine an earlier Ace engine...  (Back to main text on page 1) 
  
  
Stay tuned for Part 2 next month!