More about improving your A10.

Clutch

The clutch is the standard 4 spring item for 1961 but I use Surflex plates and make sure I remove all the burrs from the plain plates to stop them scraping away the friction material from the friction plates. The clutch pushrod is cut in half, a quarter of an inch removed, both ends hardened and a quarter inch ball bearing. suitably greased, placed in between both halves. This allows the rod to spin and stops it wearing away or heating up with friction at the pressure plate, this also allows easier gear changing. 

Rocker box. At the top end of the engine a major source of oil leaks is at the front part of the rocker boxes where they meet the cylinder head. There are three reasons for this. The rocker box is subjected to crankcase pressure through the pushrod tunnel, this tends to suck and blow the gasket in and out. The rocker box to the cylinder head joint does not overlap evenly but the major cause is probably because most of the gaskets available are too thin and not wide enough, also the stud clearance holes are too large which means that part of the mating faces are not covered by gasket. To allow the rocker box to breathe I have drilled the rear rocker box cover and fed a pipe from it through an in-line petrol filter to stop dust getting sucked up and then down to the rear chain. The studs should be removed from the rocker box and the faces smeared with lapping paste then lapped into the cylinder head mating faces checking for an even dull surface across all joint faces. The compound should then be completely cleaned off. The gaskets I make myself, from 10thou thick gasket paper, this is cut to overlap on either side of the joint faces by 1mm. The holes are cut with a tool similar to a paper hole punch I made with a cutter 5 thou oversize so the holes are located correctly and the gaskets cannot move about so much that they don't miss the joint faces. These are smeared both sides with Aero Grade Blue Hylomar. All securing screws are tightened up evenly. Allen screws are used to secure all engine covers as they are easier to tighten evenly and to remove.

Timing

The engine is timed at 13/32 before TDC. To ensure that the timing is always spot on I put some timing marks on the engine. This is done in the following way:- With the outer timing cover removed, bring the engine to its correct firing position before top dead centre. This varies for each model. Then with a centre punch, make corresponding marks on the timed breather which turns at engine speed and its surrounding boss in the inner timing cover. The breather is hardened so you will have to use a sharp punch. Now, when you want to time the ignition you just line up these two marks and set your magneto. 		How many times have you set the timing then tightened up the magneto nut and found when you recheck, that the timing is slightly out? My solution to this is to elongate the three fixing holes in an arc around the armature. This can be done by placing one leg of a set of spring dividers in the end of the armature and, using the other end scribe an arc on either side of each hole. Using a round file elongate each hole either side by about 1/16'' keeping between the scribed lines. You should then mount the magneto in position with the studs in the centre of the elongated holes. Time the bike as normal and if, when you check, the timing it is out, all you need to do is loosen the fixing nuts and rotate the magneto in whichever direction necessary, to give perfect timing, then retighten the fixing nuts, after checking that the magneto and timing pinions mesh correctly.

Lubrication

The A10/A7 motor relies on a crude system of gauze to filter particles from the oil, because of this I have fitted a spin on car type oil filter kit available from Fair Spares the Norton dealer. This is fitted in the return line feed from the engine. It also allows an extra pint of oil to circulate and if fitted in the right place also aids engine cooling. SAE 20/50 oil is used and changed every 3000 miles along with the oil filter. SRM recommend a straight grade oil though and failure to comply with this will invalidate your warranty. The later A65 type oil pressure relief valve is used on my bike as the ball bearing type fitted as standard has let me down with zero oil pressure on a couple of occasions when the ball has become dislodged on its seat. The later type relies on a piston passing by a hole in a cylinder which cannot become dislodged. The gauze inside the sump plate was removed and a magnet dropped in before a flat gauze plate was fitted along with a gasket either side. The magnet picks up most of the stray bits of ferrous material floating about in the engine. Since then a friend has machined a sump plate from Aluminium with a magnet fitted in it and a drain screw, which means the sump plate doesn't need to be taken off for an oil change. Another job I did while the cases were apart, was to make a tapping for an oil pressure gauge. On a converted engine this is tapped into the dowel hole in the timing side crankcase which carried the oil from the pump through the timing side covers. On a normally lubricated engine the tapping should be taken from the back of the oil pressure relief valve chamber, although if you are of a nervous disposition I would not recommend this, because when the engine gets hot the wear in the timing side bush allows the oil pressure to drop to around zero to 5 PSI when riding and zero at the tickover on a standard unconverted engine.
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