Symptom

Condition (if any)

Possible Fault

Investigation

Remedy

Oil loss from gearbox

Oil leaking either from the kick-start housing / shaft or oil level in the primary chaincase increases.

Overfilling gearbox.

Put bike on center stand and remove the oil level plug to check if oil level is too high.

Not allowing time for oil to drain to the level mark after refilling. Put bike on center stand and do not replace the level plug until oil stops flowing.

Oil loss from gearbox

Oil level in gearbox needs constantly topping up and or the oil level in the primary chaincase increases.

Sleeve gear bush worn.

Strip gearbox and check wear on sleeve gear bush and or wear on the mainshaft.

New bush and possibly new mainshaft. There is a modification, which involves machining the sleeve gear and bush and fitting a lipped oil seal.

Oil loss from gearbox

Oil level in gearbox needs constantly topping up and / or the oil level in the primary chaincase increases.

Split, worn or non-centralised sleeve gear bearing shims B31/2. There are also some sleeve gear bearings B22 with inner races that protrude further than the outer race. The result is that the shims do not seal correctly.

Strip gearbox and check the condition and position of the shims.

Replace and correctly fit the sleeve gear bearing shims.

Oil loss from gearbox

Oil level in gearbox needs constantly topping up and / or the oil level in the primary chaincase increases.

Drain hole blocked in the sleeve gear bearing housing is blocked.

Remove clutch and clutch actuating mechanism to check that oil can drain back through the drain hole.

Felt from the primary chaincase can be shed and block the drain hole, clean out any debris and check oil flow using gearbox oil in an oilcan.

Oil loss from gearbox

Oil level in gearbox needs constantly topping up and / or the oil level in the primary chaincase increases.

Incorrect grade of oil used allowing the oil to pass through the bearing shims (Lower SAE) or it's too high a viscosity to drain back into the gearbox via the sleeve gear bearing housing drain hole.

Check grade of oil being used.

Check grade of oil and if incorrect replace with makers recommended oil either SAE40 or 50 in hot climates. SAE 20/50 is not recommended for gearbox due to low viscosity at gearbox running temperature and shear of polymers.

Oil loss from gearbox

Oil level in gearbox needs constantly topping up and or the oil level in the primary chaincase increases.

Drain slot in ring in wrong position on B39/26 sleeve gear retaining ring.

Remove clutch and clutch mechanism to check the slot in the gearbox bearing retaining ring B39/26 is near to the oil drain hole in the gearbox case.

Cut an extra slot with a 1/8" round Swiss file as close to the oil drain hole as possible when the retaining ring is in the secured position.

Oil loss from gearbox

Oil level in gearbox needs constantly topping up and or the oil level in the primary chaincase increases.

Oil loss from gearbox

Oil leaking from selector rod hole or from the lower chaincase pins F201/X.

Remove clutch to investigate.

Seal with a suitable sealant.

Oil loss from gearbox

Oil leaking from either the kick-start shaft or the gear shaft due to excessive wear of housing.

Obvious, but check that the gearbox has not been overfilled.

Fit oil seal or O ring to the kick start housing or replace gear change bush on Spring Framed models.

Jumping out of first gear

Gear moving along bush where a single bush BK75/4 is fitted to the mainshaft first gear BK9/X.

Remove gearbox cover and check that the flange of the bush is tight against the gear.

Either mark bush position, remove clean and fix with a suitable Loctite grade if the bush is in good condition or replace bush and rebore.

Jumping out of first gear

Due to an accumulation of tolerances, or incorrect assembly the mainshaft is allowed to move too far to the offside or the BK78 gearshaft sliding gear (twin gear) is located too far to the nearside, thereby reducing the engagement of the  twin gear BK78s dogs  with the mainshaft first gear BK9/X dogs.

Remove cover and using a strait edge and depth micrometer or vernier, measure the distance between the bearing and the gearbox cover gasket face with a compressed gasket in place. Then measure the distance of the splined shoulder of the mainshaft from the face of the gearbox shell. From this calculate the depth of engagement of the dogs ensuring that there is full engagement. Check that the gearbox bearing retaining ring BK39/26 is tight, that the sleeve gear oil thrower BK33 has not worn and that the selector fork which holds the gearshaft sliding gear BK78 is not excessively worn.

Investigate and identify cause of miss-alignment. If there is no obvious cause, some owners have adjusted the position of the gearwheel by lengthening the gearshaft first wheel bush BK75/5 on the outside of the gear and reducing the length of the inner bush to effectively move the gear dogs in closer engagement with one another.

Jumping out of first gear

Worn dogs on mainshaft first gear BK8/X or BK78 mainshaft sliding gear.

Remove gearbox cover and check that the dogs on the first gear and gearshaft sliding gear are not worn.

If gears are rounded greater than one third of the depth of the dogs replacement gears may be required.

Jumping out of first gear

Worn lower selector fork MAS43 BK76 due to clutch dragging or heavy gear changing when selecting gears.

Strip gearbox and check the wear on the selector forks as per the specification table.

Fit replacement selector fork, or try swapping the top and bottom selector forks around.

Jumping out of first gear

Gearbox end cover circlip B100 on Spring Frame or retaining end cap BK3 or B3 on Rigid Framed gearboxes have come loose allowing the mainshaft and first gear on the mainshaft move to the offside.

On Spring Framed models remove gearbox cover plate B97 and check that the circlip and gear is correctly located. On rigid framed models check that the retaining end cap is tight.

Refit circlip or if groove is damaged repair groove of turn up a spacing bush, which is held in place by the gearbox cover plate B97. Ensure that if you make up a spacer that the oil can still drain from the small hole in the top of the bearing housing into the bearing.

Jumping out or difficulty engaging first gear with rearset gear change

Gear pedal MAS169 GC4/26 making contact with the gear change rod SL31/21 SL30/40 or worn gear lever pivots on MAS169 GC4/26 and GC41/7 GC41/8.

Check that the gear lever does not touch either the rod on upward movement or foul the exhaust pipe when moved down.

Adjust the rod and clevis joints to give clearance in either direction.  Either rebush or replace the clevis joints if significantly worn.

Jumping out of or difficulty engaging first gear

Worn first gear bush(s) BK75/ resulting in first gear BK9/X not meshing fully with the gearshaft sliding gear (twin gear) due to excess end float

Remove cover and check that the first gear does not have excessive clearance on the mainshaft (ideal c 0.005 - 0.010")

Replace both bushes in the first gear, if excess clearance is present. Bushes with longer shoulders are now available to correct excessive clearance. Replace and machine as required.

“Graunching” on changing into third gear

Layshaft first gear wheel loose on its spines allowing the layshaft third gear to move further to the left.

Remove cover and check that the layshaft first gear is not loose on the layshaft splines

Fit new layshaft first gear or layshaft, or try fixing first gear on layshaft with high strength Loctite

Jumping out of fourth gear

Clutch constantly requires adjustment.

The sleeve gear BK8/X is not fully engaging in the dogs of the gearshaft sliding gear (twin gear) BK78, caused by the gearbox bearing retaining ring BK39/26 becoming loose.

Remove clutch and clutch actuating mechanism to check that the sleeve gear retaining ring is tight in the housing. Also strip the gearbox to check if there is any damage to the sleeve gear BK8/X or the fourth gear on the layshaft BK86/X

Tighten the retaining ring (right hand thread) and carefully burr over the gearbox shell into one or more of the slots in the ring. If the thread is damaged either get it repaired or source a new gearbox shell. Some owners have fitted a circlip in place of the threaded ring, but there are no reports on whether this has proved to be a robust repair. Alternatively get a left hand threaded retaining ring made and a matching thread cut in the gearbox shell.

Jumping out of fourth gear

The sleeve gear BK8/X is not fully engaging in the dogs of the gearshaft sliding gear (twin gear) BK78, caused by wear or omission of the sleeve gear oil thrower BK33.

Strip gearbox and check wear of the oil thrower where it contacts the sleeve gear - original thickness is 0.031".

Replace the oil thrower

Jumping out of fourth gear

The selector fork pin BK32 is worn and does not allow the  gearshaft sliding gear (twin gear) BK78 to move to the fully engaged position.

Strip gearbox and check wear on the selector pins BK32.

Replace selector pins in the selector fork. If new pins are not available the existing pins can be removed and rotated through 90 degrees and refitted.

Jumping out of fourth gear

Excessive axial clearance on the layshaft, check that the correct pins K191 (3/16" X 9/16") and kick-start layshaft thrust washer BK82 and layshaft washer "Wedding Ring" BK95 are in place.

Strip gearbox and check.

Fit the correct pins / layshaft thrust washer -either BK82 which is 0.187" thick or BK82/4 which is 0.176" thick, so that layshaft end float is between 0.005” – 0.010”.

Jumping out of gears or not fully engaging gears

Striking plate assembly BK81/X MAS45 contacting the camplate pivot BK64/X before the camplate has indexed.

Strip the gearbox and check

Grind a small amount from the 'hole' in the striking plate assembly to allow full movement.

Jumping out of neutral into gear when idling

The neutral notch in the camplate BK80/X is worn and or wear on the indexing pawl BK66.

Check condition of both the camplate and the indexing pawl.

Grind a little metal from the camplate to indexing notch. Carefully reprofile the indexing pawl, being careful not to significantly alter either shape or position.

Jumping out of fourth gear with rearset gear change

Only when rearset gear change linkage is used.

Gear pedal MAS169 GC4/26 making contact with the exhaust pipe SL31/21 SL30/40 or worn gear lever pivots on MAS169 GC4/26 and GC41/7 GC41/8

Check that the gear lever does not touch either the rod on upwards changes or foul the exhaust pipe when moved down.

Adjust the rod and clevis joints to give clearance in either direction. Either rebush or replace the clevis joints if necessary.

Gearbox locks in third gear after being rebuilt

Only on heavyweight gearboxes

Layshaft third gear BK89AS is fouling the web on the lower selector fork BK26 MAS43.

Strip gearbox and check that the lower selector fork has had its web partly machined away.

File, grind or mill to relieve the web of the selector fork.

Gearbox locks after being rebuilt

Problem only occurs when manually testing newly assembled gearbox without clutch being fitted.

Sleeve gear BK8/X being pulled into gearbox if clutch not fitted.

Either manually pull out the sleeve gear or fit the clutch to check if the condition still exists

Gearbox locks after being rebuilt

Layshaft BK11/X not properly located in layshaft housing bearing B22/2.

Strip and check layshaft bearing is correctly fitted in housing and that the layshaft is fully home in the bearing.

Gearbox stiff to rotate after being rebuilt

Too little end float on mainshaft or layshaft

Strip gearbox and remove mainshaft, mainshaft gears and selector forks and rods. Reassemble and check layshaft is free to rotate without excessive clearance.

Investigate cause of binding.

Gearbox stiff to rotate after being rebuilt

Bent selector fork rod BK90/X.

Strip gearbox and check wear and straightness of the selector rods.

Replace selector rod.

Gearbox stiff to rotate after being rebuilt

Gearbox gasket BK43/X not fitted or too thin a gasket used.

Fit the gasket and chick if the problem still exists.

Difficulty in selecting first gear

Excessive clearance on mainshaft first gear bush(s)  BK75/X or gearbox end cover circlip B100 on Spring Frame or retaining end cap BK3 or B3 on Rigid Framed gearboxes have come loose

Remove gearbox cover and investigate

Difficulty in finding neutral between first and second or finding a false neutral between fourth and third

An alternative camplate BK80/X has been fitted which either has no neutral indent or a neutral indent between the incorrect gear selection indents.

Strip gearbox and check the camplate.

Replace camplate if necessary or if no neutral notch, grind a neutral notch using another camplate as a template.

Difficulty in selecting gears

Difficulty in selecting gears or stiff gear change.

Selector pins BK32 protruding too far out of the selector forks BK26.

Strip gearbox and check that the pins are not protruding through the forks.

Press pins in so that they are marginally below the level of the cam plate face and peen the fork over the pins.

Difficulty in selecting gears

Only a problem when the engine is running and tends to be more f a problem when changing down rather than up.

Clutch dragging.

Check the adjustment of the clutch to ensure it is not dragging. In particular check that the plain plates are not warped or the clutch outer plate is binding on the chaincase or felt seal F285/X.

Adjust clutch or replace components as necessary.

Difficulty in selecting gears

Gears are selected in one direction of movement, but not in the opposite direction.

Centralising Lever BK99/X not making even contact between the two flats, which stops the camplate BK80/X from centralising, thereby not allowing it to rotate far enough to enable the indexing pawl BK66 to engage in its indent. Alternatively check that the 'hole' in the  striking plate assembly MAS45 is not fouling the camplate pivot BK64/X.

Strip the gearbox and assemble the camplate BK80/X, indexing pawl BK66 and springs on the pivot and check that the pawl fully engages in the camplate slot when the camplate is rotated.

Grind a small amount off either side of the centralising lever so that the striking pawl can centralise and move fully in either direction. Alternatively grind a small amount from the sides of the hole in the centre of MAS45 striking plate assembly, so that they do not make contact with the camplate pivot BK64/X.

Difficulty in selecting gears

Indexing pawl GC23/X worn or weak or broken indexing spring GC 24/X.

Strip gearbox and check that the indexing pawl is in good condition with little rounding of the 'claws'. Also check that the indexing spring is strait and not compressed compared to a new spring.

Replace pawl and or spring if found to be worn or damaged. Also try an alternative pawl even if the original pawl looks OK. Minor dimensional differences are critical to the correct operation of this component.

Difficulty in selecting gears

Unable to select gear or 'clunky' gear change. It tends to be more of a problem selecting first and second gears when moving.

Outer clutch plate binding on primary chaincase felt seal F285/X or clutch not fully freeing

Check to see if the outer chaincase flexes when you pull in the clutch

Replace with softer or thinner felt ring. Some owners add a second cork gasket A179/X to increase clearance in bolt up chaincase.

Difficulty in selecting gears

Gearbox housing bush BK36/X fouling the centralising lever BK99/X.

Strip the gearbox and check if the centralising lever BK99/X is fouling gearbox housing bush BK36/X.

Check that the correct shims are in place on the centralising lever pivot BK100/X. If this is all in order, heat the gearbox in the area of the bush and gently tap out the bush, so that it JUST clears the centralising lever.

Difficulty in selecting gears

Difficulty in selecting neutral when changing from second gear, particularly on rigid gearboxes.

The pawl GC23/X is moving from the second gear indent to the first gear indent on BK98/2 without engaging the neutral indent.

Strip gearbox and check that BK98/2 has a small flat in the correct position.

Grind a small flat on BK98/2 to enable the pawl GC82/X to easily engage the neutral ratchet, rather than missing it and engaging the first gear slot.

Drive side mainshaft sprocket nut constantly coming undone

Check tightness of nut BK106 BK50 etc

Fit a new Nylock nut or castellated nut and split pin on earlier gearboxes. If trouble persists fit a two part 'Nord-Lock' or similar washer or locking tab washer.

Excessive gearbox sprocket and mainshaft end float.

Nut is tight on gearbox sprocket, but the sprocket and mainshaft moves significantly axially.

Remove the offside mainshaft nut end cover and check if either the nut(s) have come loose or that the bearing on spring framed gearbox is still retained by the bearing circlip

Tighten offside mainshaft nuts if loose or tighten cover on rigid gearbox to locate bearing. Ensure circlip is secured in its groove on spring framed Gearbox. If circlip grove is damaged make up an alloy spacer, so that the bearing is trapped by the bearing cover when the two bolts are tightened.

Stiff gear change on rigid gearbox

No axial clearance on external lever BK65/X.

Check that there is some play between the external lever and the gearbox housing or bush BK36/X

Investigate cause of binding and resolve the issue

Stiff gear change on rigid gearbox

External gearbox gear shifting mechanism has tight joints, pivots or is fouling other parts of the bike.

Check that all joints are free and that none of the gear change mechanism is fouling.

Stiff gear change on rigid gearbox

One of the gearbox cover bolts adjacent to the cam plate is too long and may be fouling the cam plate

Loosen the offending bolt to check if the gear change frees off.

Remove the bolt and check its length, replace the bolt with the correct bolt 5/8" ? long under the head.

Stiff gear change

Centralising lever spring BK101 in poor condition or is fouling the gearbox case.

Inspect spring and check it operation. Check the centralising spring washers / shims are correctly in place.

Replace spring if necessary.

Stiff gear change on rigid gearbox

BK81/X centralising lever is stiff, either through corrosion in its bearing or through being over tightened.

Loosen off the gear change lever BK65 and see if it frees. Additionally check either the lever or securing nut are not rubbing on the frame or any other assembly. Otherwise strip gearbox to check.

Clean pivot and or bush or replace the Centralising lever if necessary.

Stiff gear change on Spring Framed gearbox

Rocker shaft bush GC53 and GC54 is binding on the gear change rockers shaft MAS46/X 

Loosen the bushes one at a time to check if it frees the rocker shaft.

Carefully remove material from the end of the offending rocker shaft bush, testing as you go along.

Gear lever does not return to the mid position on Spring Framed gearbox

Normally affect the return of the standard gear lever from the returning from its lover position

Rocker Shaft Bush GC53 and GC54 is binding on the Gearchange Rocker Shaft MAS46/X which does not allow the gear lever to return to the central position.

Loosen the bushes one at a time to check if it frees the rocker shaft. Do not assume just because the rocker shaft is free to rotate in the end cover when stripped that it will be free when the cover is fitted!

Carefully remove material from the end of the offending rocker shaft bush, testing as you go along.

Gear lever does not return to the mid position on Spring Framed gearbox

Reverse gear-lever is fouling BK97 gearbox end cover bolts.

Check clearance between the gear lever and the mainshaft cover or bolts.

Adjust position of gear lever on the shaft.

Kick starter not returning

Worn, broken, deformed or jammed kick starter return spring BK19.

Remove kick-start housing BK4and check spring.

Refit or replace spring as required

Kick starter not engaging or occasionally engaging

Weak or broken kick starter engagement spring BK19/2

Remove kick start housing BK4 and check spring tension

Refit or replace spring as required

Kick start appears to be slipping on ratchet

Engine shock absorber loose allowing the sprocket to ride over the cam.

Tighten shock absorber nut M92/3 and refit split pin. If problem persists, remove the shock absorber spring M90/X and check to see if the cams ride over each other.

Tighten nut or if tight check that the cams on the shock absorber have not work allowing the shock absorber to ride over each other.

Noisy gearbox

In all or just some gears

Oil level too low, or water has entered the gearbox.

Drain some or all or the oil to check quality. If OK refill to correct level with correct grade of oil.

Drain oil and refill with correct grade of oil

Noisy gearbox

"Rumbling" sound

Worn or corroded bearings, particularly the sleeve gear bearing.

Strip gearbox, clean bearings, lightly oil and check bearing for roughness.

Replace bearings unless in perfect condition

"Grinding or racheting" noise from the gearbox

Kick start not returning to fully withdrawn position due to weak spring, loose cotter pin or cotter pin not flush with kick-start crank. Alternately the riders foot is pressing on the kick-start and moving it down the ramp.

Check if the kick-start is fully disengaged. Check that the cotter pin LE242 B20 is not fouling the kick-start housing BK4, the ramp is worn or the kick-start return spring BK19 is tired. Manually check by pulling the kick-start crank out while the engine is running to see if the noise subsides.

Replace or repair kick start housing, grind or file cotter pin flat so that it does not foul the ramp of the kick start housing. Replace the kick-start return spring.

"Grinding  or racheting" noise from the gearbox

Noise may be accompanied by what may seem like clutch slip.

Engine shock absorber loose allowing the sprocket to ride over the cam

Tighten shock absorber nut M92/3 and refit split pin. If problem persists, remove the shock absorber spring M90/X and check to see if the cams ride over each other when fitted without spring.

Tighten nut or if tight check that the cams on the shock absorber have not work allowing the shock absorber to ride over each other.

Noise from gearbox area

Clutch engaged

Possible worn gearbox sleeve gear bearing B22 worn.

Strip gearbox and check condition of sleeve gear bearing B22.

Replace bearing of found to be worn or corroded.

Noise from gearbox area

Clutch disengaged

Possible severely worn clutch thrust bearing MAS57 and associated bearing rings or clutch ballrace assembly C26AS.

Strip gearbox and check condition of clutch thrust bearing or clutch ballrace assembly.

Replace bearing of found to be worn or corroded.

Aluminium flakes in oil

Mainly Spring Framed Gearboxes

Early first gear on mainshaft has moved to offside due to the gear BK9 (MAS122)  moving on its single piece bush BK75/4. Alternatively a first gear pinion on the mainshaft BK9 from a rigid heavyweight gearbox has been fitted to a spring frame gearbox and the gear is wearing the Gearbox end cover bearing housing.

Strip and inspect both the gearbox end cover for wear and the mainshaft first gear to check it has not moved

Replace the single gear wheel bush with twin bushes BK75/5. Also replace the first gear wheel if a rigid gear. Check, repair or replace the gearbox end cover if damaged.

Golden flakes in the gearbox oil

One or more of the gear bushes or selector forks are being abraded due to a problem in the gearbox

Strip gearbox to check

Investigate causes and replace components if necessary.

Golden colouring of the gearbox oil

Wrong oil used causing corrosion of the phosphor bronze bushes

Modern Hypoid oils can attack the bronze bushes. Strip gearbox to check for any damage.

Check grade of oil and if incorrect replace with makers recommended oil either SAE40 or 50 in hot climates. Replace any damaged bushes.