Gearbox Dismantling
Experienced members can ignore this, although any comments to improve the
procedures would he welcome.
Many faced with a BSA box to dismantle for the
first time may have difficulty, unlike a modern you can't nip down to Halfords and
buy a Haynes Manual to help.
When the box is old, perhaps unused for many
years and rusted solid, it can be even more of a problem, so I'll try to take you
through the simplest dismantling procedure step by step.
Assuming you have the box out of the car and off the engine, the oil drained out
and the outside cleaned up a bit, you are ready to start.
Remove the side cover if it's not already off, also the front speed drive housing.
The speedo worm gear is a hit vulnerable when things get violent later on, so
remove it if it will come, by taking out the split pin on the front of the layshaft,
and pulling the worm gear out. If it's stuck you could wrap the whole thing with
tape to protect it.
Try to remove the starting handle dog, this has spanner flats on it and is right-hand
thread, it's easier to take it off now when there is some resistance in the box. Put
the box in gear and tap the spanner to loosen the dog. If it's really stuck, warm
it up with a butane torch or carefully with a welding torch.
The selector shafts can be removed by taking out the two l/4" grub screws and
driving the shafts forwards, watch the balls as the selectors come off the shaft as
they will fly out into your eye, or become lost in the darkest corner of the
workshop. Note the position of the selectors and do yourself a sketch, it's
surprising how what seems obvious when you dismantle something, is a total
mystery when you try to re-assemble it. The shafts are different, as are the forks.
Next thing is to strip the differential. Begin by taking off the brake drum retaining
nut, you should use a C spanner but as you probably haven't got one that will fit,
use the hodger technique of hashing it round with an old screwdriver and hammer.
I know that's terrible engineering but we all do it, don't we? It's a right-hand
thread! Once the nut and old felt seal is off you can pull off the brake drum.
Remove the brake side steel bearing housing, this may need careful levering with
said screwdriver after removing the 5/16" nuts. Try not to damage the case or break
off the lugs on the bearing housing. This is cast iron and quite brittle.
turning your attention to the other side, unscrew the shaft seal and nut, remove
the bearing housing complete by taking off the nuts and inserting two 5/16" BSF
screws in the tapped holes and using these to jack the housing complete out of the
alloy cover. Alloy side plate off next, again a bit of levering but don't damage the
case, if you do create a burr don't forget to file it flat before re-assembly. The
whole diff assembly will then lift out for subsequent attention.
Take off the nut holding the clutch centre, this will require a large socket or box
spanner. Sizes of this nut may vary7, so I'm not going to quote mine, you will have
to check this yourselves, again right-hand thread. The usual problem is how to
stop the centre from turning. Jamming something in the gears is risky and you
could chip them, a better way would he to fix a handle on an old clutch plate, but
how many of us have one?
I knocked up a locking tool from a bit of 1/16" plate (see sketch), it's pretty self
explanatory, just a series of W holes on an appropriate p.c.d. (pitch circle
diameter) and jigsaw or turn the centre out, the handle has to be spaced out to
clear the clutch housing. Armed with the locking tool it will be much easier to
remove the nut and pull off the clutch centre.
The 3 5/16 nuts holding the bearing cover and clutch operating lever are now
removed and the cover complete with lever pulled off.
You can now remove the main shaft, this will come out complete through the front
where the speedo drive was. The simplest way is to drift it out with a "1/4" rod
through the centre of the primary gear (the hole in the middle of the bit the clutch
centre was on). A few hard smacks on this drift should knock the whole shaft
forward and eventually you should be able to pull it out forwards.
In the event that the shaft is too tight to move this way, a good puller can he
hooked around the clutch centre and pushing on something like a 1/4" cap screw in
place of the drift (they don't bend too easily) you should be able to move things.
As the shaft is pushed out you will leave the two sliding gears inside the case, these
can then he lifted out, note which way round they go! The mainshaft will have
come out complete with two bearings and the main drive worm gear. Now is the
time to look to see what you have. The bronze worm wheel will probably look
second hand (after all it almost certainly will he, unless you've found the elusive
trike with one careful lady owner and 100 miles on the clock!). Providing the tooth
surfaces are not deeply rutted and, even if they come to a sharp point, appear to
he about the right depth to meet up with the worm, then it should he serviceable.
New ones may be available from Steve but talk to your bank manager first.
If you have an early gearbox the primary gears will he straight-cut and you could
remove the small primary gear by tapping it into the box from the clutch end, mind
the thread doesn't get chipped. Double helical gears will not come out yet so you
need to move on to removing the lay-shaft. Before this, however, take out the
reverse idler gear. It has a slot in the end and can be levered out with our faithful
old screwdriver.
Now for the worst part - getting the layshaft out! Remove the front cover by
taking off the two nuts and gently levering it out. It may pay to remove the studs
as well if they haven't come out with the nuts. If it's tight try warming the case
with a butane torch or simply pour a kettle of boiling water on it, the housing will
usually come out leaving the hearing behind. If the hearing comes off with the
housing so much the better.
Take off the rear layshaft hearing cover plate and start to drift the end of the shaft
through the centre of the hearing towards the front of the box. Take care because
after 1/2" or so the second gear will come up against the alloy lug which housed the
reverse idler. I'll bet more gearbox cases are broken by continued bashing at the
layshaft at this point than any other reason. Now the tricky part, you can't get
any further forward without sliding the second and large primary gear off the
layshaft. Special tools would help and may have been recommended, anyone
know? However, I've always resorted to a soft drift (mild steel) and gentle
tapping to try to drive the gears towards the end of the shaft. As the gears come
off, the shaft can be tapped further forward until eventually the front hearing is
pushed clear of the housing, and the rear bearing is either inside the box or still
in the case with the shaft clear of it, and in the box. If the gears will not budge,
try heating them with the butane torch. A drift rod or long 1/4" Whit screw can he
inserted through the front hearing housing stud hole to support the rear of the
gear while attempts are made to drift the shaft through it.
When the shaft is dislodged and the front hearing pulled off, it can he pivoted and
withdrawn through the side of the case. The large primary gear and the second
gear can make the same exit, again note which way round the gears were.
Now you can shift the small primary helical if still in position. That's the worst
hit over now, go and have a coffee or something stronger.
Gearbox Assembly
On later boxes with double helical primary drive gears, fit the large rear bearing,
its housing, and this gear first, with its spinner washer, dished side toward the gear.
Add the clutch operating fork and rear bearing retainer complete, this is required
to ensure that the bearing is in its correct position. Fit the clutch centre and
tighten with a socket and the clutch locking tool, ('Front Wheels', October). Loctite
in my view is better than tab washers, heating will destroy it when dismantling!
Insert the rear layshaft bearing into its housing, warm the case if necessary, don't
fit the cover plate yet. Hot water from the kettle is a good way to heat the case,
or alternatively a medium propane torch.
Fit second gear (the one with the key-way) on to the layshaft with the boss to the
back - see drawing. Do not slide fully on, leave about 3/8" from full home position.
This will ensure clearance on the reverse gear mounting lug. Note that this gear
can be very tight which makes it a struggle to get off. If you can spin the shaft in
a lathe or drill, polish the shaft down a bit so that the gear is not quite so tight.
Fit the main layshaft gear on to the layshaft - helical on later boxes - again check
the drawing for the right way round, the bosses are a different length.
(Longer
boss to the front).
Insert the layshaft, front end first, through the side of the gearbox, the end being
free to enter the front bearing housing that is empty at this stage. It will be
possible, given the correct positioning of the two loose gears on the layshaft, to
align the shaft with the rear bearing, helical gears in mesh and tap the shaft back
through the gears into the rear bearing.
The reverse gear will now slip in behind the layshaft, do not forget the bronze
thrust washer to the rear of the gear. Slip in the reverse gear shaft and align the
flat to coincide with the flat on the front layshaft bearing housing - yet to be fitted.
The front bearing and felt seal, or lip seal if you prefer,
(the nearest size I could get
involved opening out the bore in the cast iron bearing housing, however this is one
place where the felt does seem sufficient) can now be fitted into the bearing housing.
Watch for shims behind the bearing or on the shaft, and refit them if they were
there previously. Now you can fit the front housing and bearing with joint
compound into the case. Bolt up with the studs and 5/16" nuts and spring washers.
Note to aid subsequent assembly this is another shaft which can stand a polish to
reduce the interference fit of the front bearing. Use bearing fit Loctite on the
outer race in the cast iron housing so that next time you strip the box the bearing
will lever out with the housing.
Ensure the rear bearing is now fully seated on to the layshaft and the shaft is as
far forward as it will go. Check the meshing of the primary gears and that the
mainshaft primary gear is fully seated against the bearing. If not correct, shimming
will be required which will involve taking everything out again. That is the reason
I have tried to ensure that the bearings are in the correct positions at this stage.
It is however better to get it right now than when everything else is in place.
The starter dog is next, a piece of wood or ally can be used to jam the gear to stop
shaft rotation while this is being screwed on. This will ensure the shaft is pulled
up against the bearing. The dog can be finally locked up tight when the mainshaft
and clutch centre are fitted, using the clutch centre locking tool.
When you are happy that there is little or no end float when tapped and that the
rear bearing is as far forward as possible you may find that this bearing is sub-flush
to the mounting face for the bearing cover plate. Check the sub-flush dimension
then lever out the front bearing housing complete with the bearing if you followed
the instructions earlier, and add sufficient shims/packing to push the rear bearing
up to the cover plate on reassembly. This will ensure that the bearing does not
work its way back.
At this stage the layshaft and primary gears should rotate freely and should not be
able to slide fore-aft. The reason this is critical is that end clearance on the gears
in their different positions is limited, incorrect positioning, especially with worn
parts, can allow the gears to rub against each other at times giving some pretty
unhealthy sounds.
Now take the mainshaft and fit the inner bearing spinner disc, bearing (sealed if
you wish), worm gear, front bearing seals not necessary, in any event this size is no
longer a standard, and its spinner together with any previously fitted shims. Fit the
nut and tighten but don't bother with the split pin yet. Now fit the whole main
shaft assembly through the front of the gearbox, slipping on the two loose gears
(see diagram) as you go, and tapping the shaft into place and checking for meshing
as you go.
Temporarily fit the speedo drive housing to ensure the front bearing is seated as
this controls the end position of the shaft. Try sliding the gears back and forth and
check tht you can get neutral to ensure that the primary is not jammed tight against the layshaft
Now we are ready for the selectors. If you noted which way they fitted when you
took them out it's easy, if like me you've forgotten see the photo. The selector
shafts are fitted from the front of the box, not forgetting the spring and detent ball
in each. The steel strip separator complete with its ball must be positioned before
the selector shafts are fitted.
Getting the detent balls in can be a bit of a game, often ending up with the ball
flying out into a distant part of the workshop, or back into the gearbox which
involves turning everything upside down to get it out. Two things help a lot.
Grind a bevel on the front of the selector shaft about 1/8" at 45 degrees, (see
diagram). This should be positioned so as to be in-line with the ball as the shaft
is inserted. Take an old 5/16" bolt, two or more inches long, and file/grind the end
to a 'D' shape.
Position everything as shown in the diagram, press the bolt down and the selector
shaft in as far as it will go, maintain pressure on the selector shaft as you lift the
bolt out, then give the end of the shaft a smart tap with a hammer and with a bit
of luck the shaft will have trapped the ball, the rest is fairly easy. Fully insert the
shafts and fit the grub screws to lock them in place.
Once again check all four gear positions by rotating the gears and smartly tapping
the selectors back and forth with your old screwdriver and hammer. You're
looking to check that the gears clear each other when in position and don't make
any rough noises.
If all is well now you can fit the speedo gear and split pin the nut on the
mainshaft. The front cover and speedo drive fitted with compound and all you
have left to fit is the differential and gear lever.
The gear change shaft and selector cover are best left until the box is in the car
and the differential I will cover in a future episode. If you can't wait watch the
position of any shims on the output shafts as these control the centring of the
worm and wheel.
A4 workshop size copies of the entire gearbox article are obtainable from me, see regalia address
inside front-cover. send large S.A.E please.
Second Gear Slippage
Trikes often suffer from second gear slipping out, especially when climbing steep hills.
Living in Bedfordshire I don't suffer the latter too often, however it can be annoying
whenever gears slip out. Having to hang on to the gear lever with the left hand while
steering, adjusting the control levers, and hand signalling with the right does not
represent the most relaxing form of motoring.
More seriously though, on steep hills, if
the gear slips out while you are pushing hard on the lever you risk breaking a gear, or
at the least badly chipping a gear tooth.
The problem, particularly in serious cases, is usually caused by worn gear teeth that
have become tapered and as a result push themselves apart.
The only answer where the problem is as bad as that shown in the 'photo
is to replace the pair of second gears, this is not cheap (about £160 per pair)
plus the work involved in a complete gearbox strip.
In a case where the the wear is not so advanced it is worth looking at an overhaul of the gear selector
mechanism before embarking on a complete rebuild.
The gears are intended to be held in engagement by the selector indent ball
and spring, this serves also to hold the gear lever in the upward position. When you
consider the length and weight of the lever and the leverage against the selector
mechanism one can see that the indent has to cope with much more than fore and aft
pressure from the gears. If the pivots and bushes or gear lever linkages are worn, any
vibration or jolting from road bumps can quite easily overcome the indent spring and
drop the gears out of mesh. Removal of wear on these points is worth while, and if not
entirely effective, will at least make gear changing a little less like stirring a jelly.
Start by removing the side cover of the gearbox, together with the gear change tube and
gear lever. The whole unit can usually be withdrawn forwards after removing the rear
support from the crankcase and any internal gaiter arrangement from around the lever.
The lever pivot hole will probably have worn oversize from its original Vs" diameter.
This could be re-bushed, however it is easier to drill oversize through both the lever
and the fork on the gear change rod, either 10mm or up to 7/l6". Replace with an
appropriate bolt, adding washers to take out any end float. If the fork has been strained
inwards and the sides are no longer parallel they can be gently levered apart before
packing with the washers. Tighten the nut until the lever moves easily but has
sufficient friction to hold its position against gravity. A Nyloc nut is a good idea as it
will enable you to adjust this point easily once the assembly has been replaced and
avoid it rattling loose again.
Now turn your attention to the ball and socket joint. If the ball is a loose fit you can
build it up with weld, either gas or MIG, then file down again to as near a sphere as
you can get so that it is a reasonable fit in the socket. Note some assemblies have a
spring in a pocket at the base of the socket, this should be replaced although I have
never found it much help. Any play between the gear change rod and the rear end of
the tube can be removed by re-bushing the tube. The front end is somewhat less
critical and does not usually need attention.
Reassemble everything and try again. If the slipping is still bad then it's worth looking
at the selector indent. Unfortunately this means a good deal more work, as you will
have to get the selector rod and fork out. This is not quite as simple as one might
imagine, as the front brake drum needs to come off to allow the rod to be removed.
To remove the drum you will need to free the top of the offside swivel assembly from
the springs and the damper if fitted. This will enable the unit to be swung out to free
the drive shaft from the spiders and flexy coupling. Now with a bit of fiddling you
should be able to remove the flexy coupling complete after loosening the grub screws.
This is not always as easy as those who write the books would have you believe and
you may finish by stripping the flexy coupling completely. After a great deal of time
and a few cross words you should be able to remove the central locknut which retains
the brake drum and pull the drum off.
Now to remove the selector shaft. Ideally start with the gears in top. After removing
the outer cover and gear linkage, as detailed above, take out the lower of the two
selector rods by removing the small grub screw, then tap the selector forward smartly
with a hammer and large screwdriver or other implement. You may have to rotate the
gears a little to allow them to mesh but the object is to move the whole selector
assembly, including the rod, forwards about 3/4" or sufficient to allow you to get the
screwdriver behind the rod and lever it to a point where you can pull it out from the
front of the box.
As the rod comes free the ball will probably fly out, so watch for it to ensure it doesn't
go in your eye, a dark and dingy part of the workshop or, worse still, fall back into the
gear box. If the worst occurs, one of those magnets on a stick is very handy. Be
careful also that the larger ball in the interlock bar does not fall out.
The obvious thing would seem to be to fit a stronger spring behind the ball. However,
there is little room for such a spring and other measures such as adding packing below
the spring will in all probability just make gear changing very difficult. A better
solution is to slightly deepen the indent groove in the selector rod, I say slightly
because even a few thou. can make a considerable difference, as can any change in the
angles of the vee or the radiuses. Overdo the deepening and you will not be able to get
out of second gear at all. As this mod. will in all probability involve some hand and
guess work as well as trial and error it is simpler to carry it out in a way that minimises
the number of times you have to strip things apart, and if all else fails in a way that you
can restore things back to normal easily.
Now to deepen the groove as shown on the drawing. The best way is to set it up in a
cylindrical grinder and modify the groove profile with a form wheel, however not
many members will have access to such equipment. You can achieve reasonable
results with an angle grinder, if you are careful. You can't file the rod as it is
hardened.
The object is to retain as far as possible the profile of the groove and simply deepen it
about 0.030" for about 25% of its circumference, blending this nicely with the original
so that no less than 30% of the original groove is left untouched. You will realise that
by rotating the rod it will now be possible to change from the original groove depth
gradually to an increase of O.030", this will in all probability be more than enough.
To rotate the rods, and to be able to tell which way to turn things during the inevitable
trial and error that will follow, we need a groove in the front end of the rod. Some rods
have these already, if not, use the angle grinder and a slitting wheel to produce
something similar to that shown on the drawing.
Now to re-assemble. Make sure the larger ball is in the interlock plate and the spring
and ball are in position in the selector. Push the rod back through the case and into the
selector fork until it comes up to the ball, which is visible through the drilled hole.
Using a tool similar to the
one shown in the sketch push
down on the spring and
apply pressure to the rod to
push it back hard against the
tool, then withdraw the tool
and give the rod a tap to push
it over the ball. Check the
position of the selector rod
by looking down through the
tapped hole in which the
grub screw fits and when the
groove is in line fit the grub
screw, tighten it, then back off half a turn. This will enable you to rotate the rod with
your screwdriver. Start with the unchanged side towards the ball. Reassemble the rest
of the linkage etc., making sure the operating lever enters the interlock slot as the cover
is replaced.
After replacing the brake and flexy coupling assemblies and the swivel unit you will be
ready for a road test.
Now you can try turning the rod to present the deepened side towards the ball, and try
changing gear. Continue to turn until you find difficulty in getting out of second, then
go back a bit. Having found the best position, remove the cover and tighten the grub
screw.
I hope this improves things. If not, you will either have to live with it, or do a
complete re-build and fit new second gears.
Mike Scott-Coomber
Gearbox/Differential Oil Retaining Washers and Flingers
by Peter Cook
I presented a question in one of my pieces for 'Front Wheels', published in 2002:
How many oil flingers are fitted to the BSA trike and Scout gearbox/diff case and
how many are serrated?
Those members who have rebuilt gearboxes should have known the answer, which
is six and three. That answer is partially correct because before 1934 the answer
would have been six and two.
In the previous article I indicated than on more than one occasion I have had prob-
lems when rebuilding gearboxes and fitting the various oil retaining washers/flingers.
During the last rebuild I sought guidance from various Club members and in the
end resorted to obtaining the drawings from Tony Meade to resolve the issue.
Examining a 1 932 V-twin trike parts list and a Series 6 parts list shows that the six oil
retaining washers/flingers remained the same throughout the production life of the
cars, with one exception. That being the Primary Driving Gear Oil Flinger fitted to
the primary input shaft and located in the clutch chamber. This was changed from
what appears to be a non-serrated flinger to a serrated flinger. I am not absolutely
sure about the difference in the absence of the drawing for the earlier cars but
certainly the later cars were fitted with a serrated flinger. You may also find some
minor differences in the oil retaining washers/flingers reflecting amendments intro-
duced after the item entered production, however these are minor in nature includ-
ing changes in material specification.
The following provides the key details for the six oil retaining washers/flingers fitted
after May 1935:
| Item
| Part Number
| Date of Drawing
| Type
| Outside Diameter
| Notes |
| Primary drive gear oil flinger
| 35-4073
| 4/5/34
| serrated
| 2.4375"
| Clutch chamber |
| Primary driving gear oil flinger
| 35-4072
| 18/10/1929
| plain stepped (0.096")
| 2.73"
| gearbox |
| Mainshaft oil retaining washer
| 35-4106
| 20/1/31
| serrated
| 2.43"
| 1/16" hole drilled 7/8th" from the centre, gearbox |
| mainshaft oil retaining washer (front)
| 35-4105
| 17/10/29
| plain flat
| 2.43"
| 1/16" hole drilled 7/8" from the centre, gearbox |
| Oil retaining washer (mainshaft front bearing
| 35-4124
| 2/11/29
| plain stepped (0.008")
| 2.375"
| Diff Housing |
| layshaft oil retaining washer
| 35-4164
| 20/1/31
| serrated
| 2.25"
| gearbox |
The part number for the first oil flinger is given as 35-4084 in the 1932 parts list.
From the above list you should be able identify each of the oil retaining washers/
flingers. The 1/16" hole in the third and fourth oil retaining washers/flingers
make these relatively easy to identify. From the various boxes I have broken over the
years it has proved almost impossible to obtain a decent set of oil retaining wash-
ers/flingers. The oil retaining washers/flingers get damaged and the plain stepped
ones appear, in some cases, to have been assembled the wrong way round resulting
in the step being squashed.
The larger serrated retaining washer 35-41 06 appears
to suffer the most damage. This gets squeezed and is almost impossible to remove
from the mainshaft without being damaged. I am not sure if the damage is the
result of over tightening or excessive fore and aft movement on the mainshaft. I
have also noticed that the oil flinger fitted in the clutch chamber is often left out
during rebuilds and was certainly missing from the Series 4 box.
The pictures show examples of the flingers and the typical wear that you can expect
to find.
Following the rebuild I sent a drawing for 35-4105 (flat retaining washer) to John
Chadwick and 35-4124 (plain and slightly stepped) to Nick Bainbridge for quotation.
The result is that the Club now has for the first time two replacement oil
retaining washers/flingers and hopefully a third 35-4073 (plain and stepped) in due
course.
To complete the last rebuild I had to obtain a spare 4106 from Dave Howard.
Reproducing the serrated items may be more difficult but we will be looking at these
plus the differential pin retaining washers, which also appear to get damaged.
So if you are rebuilding your gearbox get the two new oil retaining washers/flingers
from Steve and make sure you assemble them the right way round. It is only possi-
ble to assembly one of the oil retaining washers/flingers without making a mistake
and that is 35-4105, which is flat. If the stepped or serrated oil retaining washers/
flingers are fitted the wrong way round they will lock up on the bearings so be
warned.
Peter Cook
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