In general the Sunbeam gearbox is built like the proverbial brick outhouse and will handle far more power than the engine is capable of producing , however due to age , wear and tear a few problems can occur .
If the two studs which secure the rear mounting rubber to the back of the gearbox are removed and replaced by bolts ( lock wiring the heads because they are coarse threads ) , it becomes possible to jack the gearbox up high enough to remove it to the rear without taking out the engine . This may save a great deal of effort in the future if you have problems with clutch , gearbox or the engine oil seal .
NOISE
If the gears are badly worn they can become very noisy , especially third , the only cure for this is some better gears .
JUMPING OUT OF GEAR
This normally only affects third gear and is caused by wear on the faces of the driving dogs , this in turn produces end thrust upon the shifter forks , which in the case of third gear can cause the gearchange cam to rotate allowing the gear to jump out , the cam spring then re-engages the gear with a jolt . In bad cases this cycle can keep on happening which makes for a pretty miserable ride .
The "Bedtime Book" recommends dismantling the layshaft and swapping the two sliding dogs over , since the 1st to 2nd one should be less worn than 3rd to 4th . It is also a good idea to turn each individual dog end for end so as to bring the less worn sides of the engaging teeth into play .Of course if someone has already done this you could end up worse off , so it pays to carefully inspect the teeth , your minds eye needs to be fully engaged when doing this as it is very easy to become confused as to which is thrusting on what .
KICKSTART CIRCLIP
As anyone who has had it happen can tell you , having the square section circlip ( No 28 Plate 2 ) that retains the kick-start ratchet onto the gearbox mainshaft come loose , is a real pain in the proverbial as the kick-start becomes completely non-operational . Also the only way to replace it properly is to remove the gearbox from the bike and strip it down completely which is one heck of a job for a 25p circlip . This problem has occured in two out of the four Beams that I have been closely associated with so it may be a fairly common fault .
The fix that I devised involves making a split ring which can easily assembled onto the shaft after removing the side cover from the gearbox and provides a 100%
positive cure .
The ring is easy enough to turn up on a lathe , the tricky bit is putting in the counter-bored holes , the best way if you have got the facilities is to turn the ring to size and then use a milling machine .
The other way is to initially turn the ring up to 40mm diameter and then cut a flat down to the finished 30mm diameter ( a hacksaw and a fine file are quite good enough ) this flat is wide enough for the holes to be marked out and drilled with a bench-drill . Be careful not to drill the counterbores too deep , you are not trying to bury the screw heads merely providing a flat seating . Finally the ring is turned to the finished 30mm diameter and then cut in half .
Assembly is easiest done lying beside the bike and someone passing you the parts , don't forget to Locktite the 3mm Allen screws .
You usually find the original circlip in two halves in the bottom of the gearbox and in it's passing it is quite likely to have damaged the bronze bush for the clutch release thrust bearing so check that this still moves freely before putting everything back together .
THE CLUTCH
This is pretty straighforward as covered in the "Bedside Book " the only real problem is the heavy pull at the handlebar lever , this can be completely cured by the " Richard Turner modification " , see the " Published articles ".
Locktite is a much better way of securing the clutch stud nuts than the barbaric method of centrepunching them .
REAR DRIVE
This is and always has been the Achilles Heel of all Sunbeams , as in any worm and wheel drive it is subject to wear and considerable power loss ( which is the last thing you need on a Sunbeam ) . However all is not lost as Stewarts are re-manufacturing the worm wheels and also sell a modern fully synthetic gear oil especially developed for this type of drive . I have personally tried this oil and it is Bloody Marvellous !!!!! . There is always a down side however , and in this case it is that the drive needs to be in reasonable condition with NEW OILSEALS as the oil is as thin as water ( Damned if I know how it works but it does ) and will piddle out of old ones .
