Group - Norton Commando 1969 Service Notes

GROUP 1.- Crank assembly inc. pistons, camshaft and timing gear
CON RODS: Con rods don't usually give trouble -- the unbushed little-end never wears and trouble at the big end can
usually be traced to a fault elsewhere, particularly running out of oil. Rods should be free from nicks and deep scratches
especially up the sides from the bolt holes. Fatigue life can be improved by shot-peening, but this is only important for
racing where stresses are much increased.
John Hudson: I have never seen dural rods shot-peened at the work:. For racing they were polished all over and if the
steel caps did not match the contour of the outside of the rod they were filed to shape before polishing.
Everyone misses a very important point in Norton con rod bolts -as supplied they have a razor sharp edge on the
underside of the head and this should be carefully filed off and the bolt rotated in lathe chuck or drilling machine and
the head polished with emery tape. Otherwise, the turning torque of the Phillidas nut causes this sharp edge to scrape a
shaving of dural off the side of the eccentric recess in the rod as the bolt is pulled down which, of course, then remains
under the head of the bolt and prevents its seating and tightening properly. This can have happened on original
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assembly at the works, so whenever bolts are removed from the rods, check that there is not already a shaving in the
bottom of the recess. > >
BIG ENDS: Big ends wear very slowly if oil is cared for. After a main bearing job the shells should be changed
because the hard bits of bearing circulating with the oil become embedded in the soft shells and can score the crank. At
the same time, of course. the crank should be dismantled and all the sludge scraped out.
CRANKSHAFTS: When having a crank reground specify in writing the size you want and the radius between the
crank pins and the webs (0.090in Rad, 2.25mm) then check that the work has been carried out properly before
reassembling.
Crank breakages can generally be placed to a radius too small-and not necessarily on a reground crank. New cranks
have broken at fairly low mileages because of tight radii - particularly around the drive-side main bearing. Even cracks
across the webs can start at the junction of the crankpin and web. Be careful too, when removing main bearing inners
by the traditional chisel method - nicks in the crank are just as bad as tight radii. Rig end bolts need not be replaced,
unless you are going racing; a tried and tested bolt is better than new one which might fail.
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Nuts should be used once only and not over tightened (or under tightened) If a nut comes off or a bolt breaks, it is
usually due to lack of lubrication - - you will see that the rod around the big end eye is brown in color if this is the case,
because -the hem generated when the oil supply ceased burns oil mist into the rod. The hammering after the big end
has gone will break bolts or loosen nuts very quickly, so -if you should have a motor nip up, always check the oil
supply before re-starting--there must be oil both in the tank and returning properly. Oil can be there but the pump
seized or an oilway blocked, and to continue would soon result in your own exploded view.
Before reassembling check the fit of the small timing pinion on the crank -the crank can be eased with emery cloth until
this is an easy push fit. The oil pump worm will hold it tight and it will make the next rebuild much quicker, as you
won't have to remember to whom you last lent your extractor (or where you borrowed one . . .).
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