Modifications and Improvements

Modifications and Improvements
C Range Triumph Modifications and Improvements
There are a number of modifications that can be done to improve the reliability and performance of
the ‘C’ Range Triumphs without losing the general character of the bike. I have listed the
modifications in the order shown as I feel some are more useful than others. I cannot warrant the
success or failure of them. All modifications are of course a personal preference and should be done
only after some thought as to what you intend to achieve. It is all too easy to over-modify a machine
and reduce its value. Care should be taken not to dispose of or damage parts so that the machine
cannot be returned to standard in the future. We too easily forget that we are only temporary
custodians of the machines in our ownership. A machine or part can be restored many times but it is
only original once!
Generally the ‘C’ Range engine is reliable without modification as long as the state of the
components such as the main bearings and sludge trap within the crankshaft is known. Weak points
are Timing side oil feed which, can be improved by the Devimead conversion offered by several
companies. Dynamic balancing will smooth the crankshaft vibration inherent to parallel twins.
The T21 has a different crankshaft than all later machines this crankshaft will fit in later cases but
the later cases will not fit the early crankshaft. There are subtle crankcase variations year on year.
350 cc engines until 1968 feature steel con rods while 500 cc machines all have RR.56 Hiduminium
alloy rods. Later engines (1969) feature Ball bearing timing and roller drive bearings.
Look for the December 1967 Motor Cycle Mechanics as this details a Race Prepared Tiger 90 and
the work done. (8500 rpm and 120 MPH).
Converting 3TA and T90 engines to 500cc to improve performance may initially seem relatively
easy but involves replacing the pistons, con-rods, barrels, heads, carb and also the sometimes
exhausts, you should first consider fitting the correct sports camshafts and high compression pistons
to improve the performance. It is viable to fit the readily available lower compression 3TA pistons
(7.5 to 1) if you accept there will be a loss of performance. Please note there are; many variations of
cylinder head/valves/camshafts/gearing and only the correct combinations will improve
performance. The camshafts all feature three keys to allow some variation in valve timing.
Machines fitted with the distributor (pre 1963) can be converted to the points in the Timing cover if
all the suitable components are obtained. Technical Bulletin 13 details this along with other factory
approved modifications.
Barrels in original sizes are becoming rare, together with standard pistons. An option is to have the
barrels sleeved to standard and then bored to suit the pistons available. Unfortunately this will often
double the cost !
Lead Free ...You may need to invest in a lead free conversion if you are intending to use the bike
regularly. The Tiger 90 and 100ss having high compression ratios benefit from high-octane fuel and
so some octane booster added to standard unleaded does improve performance. The original
specification does indicate Austinitic Iron Valve Seats but I do not know the reliability of these with
modern fuels.
Filtration ... The standard filtration system relies on wire gauzes in both the sump and oil tank,
together with the action of the centrifugal sludge trap in the crankshaft. A modern cartridge type
filter will greatly improve filtration; increase oil capacity and oil cooling. Anglo Nihon and Paul
Goff do a filter kit; this with a suitably shaped bracket or modification can be fitted neatly under the
gearbox attached to the frame by the footrest bolt. I have found replacement spin on filters with less
depth, which make this mod very discreet. I have in the past seen magnetic sump traps to replace
the crankcase drain, alternatively pop a magnet into the oil tank on a length of copper wire so that it
can be removed and examined periodically.
For High Performance engines improving oil cooling should be investigated, this could be done
discreetly by fitting a small oil cooler across under the engine. Post 66 machines have greater oil
tank capacity.
The Morgo big bore oil pump is a direct replacement for the Triumph unit; this is easily fitted once
the timing cover has been removed.
The Oil feed to the rockers can be improved by enlarging the centre hole of the rocker shaft so that
the flow is not restricted to the ends (beware this is hardened and a pig to drill). Also be aware that
over tightening the oil pipe domed nuts can crush the upper copper washer against the bolt therefore
restricting flow. I ease the inside of washer with a triangular file. Access to the bolts becomes
restricted once the head steady’s are located; locktite is advised.
I believe light alloy tappet push rod tubes are available that reduce the oil leaks at the seals. Only
regular seal changes here will cure the leak. Triumph tried several tube/seal combinations over the
years so were aware of the inherent weakness of the design.
Tappets. Mushroom headed; light alloy Allen-key tappets are sometimes available, these ease tappet
adjustment. You will need to remove the rocker boxes to fit these. I have found the light alloy
nuts strip easily, but can be replaced without removing the rocker boxes. The Tappet Covers are
easily lost, ensure that the retaining clip (fitted from 1963) is actually in contact with the cap and
indenting the serrations, examine the cap edge and file to suit.
Clutch ... The clutch fitted to the ‘C’ range is under stressed and reliable Several changes were
made over the years and so clutch hubs and main shafts may not be compatible. The Clutch benefits
from careful assembly and a rigid cast domed plate (SRM), sometimes available. Belt drive clutches
are available for all Triumph models.
Clutch problems are usually the result of wear within the shock absorber and the engagement slots
on the clutch hub and basket. Additional problems stem from wear in the release mechanism. Once
wear has occurred very little can be done. Replacement is the only solution.
Gearing ... It is possible to increase the gearing by fitting a larger gearbox sprocket but at some loss
of acceleration, Ideally you should increase by two teeth to avoid using a chain with a cranked link.
This will mean the gearing will increase by 12%, which will be too high for the smaller engines in
standard tune. The post 66 bikes have the removable rear sprocket, which could be increased in size
(its too small to decrease the size without the chain fouling the fastenings). Combined with a larger
gearbox sprocket this would to give a smaller leap in overall gearing. I have found the standard
gearing excellent for general use with only prolonged motorway use exposing the low top
gear. Alternative gear ratios were supplied in standard, close or wide ratios but the final gearing is
the same. I have copy of a technical bulletin; which details the variations.
Early 3 and 5TA’s feature plain bushes on the layshaft, consider replacing these with the needle
roller bearings as fitted to the Tiger 90 and Tiger 100.
Gaining access to the gearbox sprocket involves removing both the alternator, primary drive and
dismantling the clutch. Six small screws often punched and requiring drilling retain the access plate.
Special tools are needed for three/four of the operations.
Engine tools are a sometimes available to loan from the TOMCC Branches but I have identified a
number of methods of succeeding without these tools.
For Parts advice I recommend Oliver at Tri-Supply.
Improving Electrics
Pre 1966 C Range Triumphs will benefit from changing to a 12 Volt System. This can be achieved
in several ways. Either by using the 1966 or later wiring scheme, fitting the Zener diode in a
suitable location. A heat sink hidden behind the left hand panel neatly re-creates the 1966 location.
While the later Zener heat sink is effective it is also visible in its location between the forks. You
can replace the Lucas plate rectifier with a modern encapsulated unit. Ideally you can retain the
original rectifier for show using dummy wiring to complete the deception.
Alternatively the excellent Boyer Bransden Power Box or alternative unit can be fitted; there is
sufficient space on the back of the battery carrier for this to fit. I have had great success using the
Boyer power box without a battery but it only really suitable for a machine used solely during
daylight. With the power box it is possible to simplify the wiring, eliminating the ammeter, fuse,
ignition switch, Rectifier and Zener, though you will need to arrange an ignition kill switch. If rewiring later machines consider dummy wiring the Zener diode and other components to retain the
appearance of originality.
When re-wiring I recommend using modern 2mm cable and running dedicated earth wires to the
headlamp, tail lamp, engine and coils. Carefully crimped, soldered and finished with a little heat
shrink tubing the standard British bullet connector is reliable, especially if filled with Vaseline or
silicone grease before pressing together, the correct tool is essential. Try to keep to the wiring
colours used in the appropriate diagram for the year, as this will help you to trace problems you or
the next owner may have later. Generally there is a wiring convention for British Machines and you
will soon learn the primary colours.
All connections will eventually become loose either due to corrosion, heat or metal fatigue, to
minimise these failures plan the wiring carefully to reduce the number of connections to an absolute
minimum and arrange the wiring to avoid hot spots and excessive flexing. Think of replacing the
bullet connectors after ten years and re-wiring after 20 years.
Pay attention to giving wires additional support or insulation where movement and abrasion occurs,
the wiring to the coils can short out on the sharp edges of petrol tank over time.
Any change to 12 Volts will need the Bulbs and Horn replaced. On no account feed the Lucas 6V
8H horn with 12 Volts as this will destroy it, with care and time a non working horn can be
dismantled, serviced and revived, Taff The Horn is helpful too, Retain the horn with dummy wiring
and place a modern version out of sight under the tank.
Alternator. The Lucas RM19; 3 wire alternator and the wiring scheme are not able to provide
sufficient charge when running with the dip beam on continually; as is required by European
Legislation, up rated alternators are available (approx £60) to improve the situation, an excellent
solution when combined with the Boyer power box. For long daylight runs alternate between
running with the lights on and then off in order to let the Zener and battery rest. Monitor the
ammeter to judge current flow.
Lighting. Improving the lighting is possible by fitting the halogen conversion from Paul Goff and
the LED tail light bulbs. Up rated pilot bulbs (21 watts) are also available. If touring on the
continent where daytime lights are mandatory I find the 21 watt Pilot a good option as the bulb is
small and easy to carry a spare of.
I have also had success with the Neolite headlamp unit supplied by Hitchcocks, this has an excellent
beam pattern and intense light provided by the modern Phillips bulb.
Electronic Ignition. Fitting the excellent Boyer Bransden Electronic Ignition is recommended. You
should already have changed to 12 Volts to get the best from the system and fitting will be easier if
you undertake the two jobs at the same time. The control box fits neatly under the tank between the
frame tubes, secured with a large cable tie or tape. The connections to the coils can then be kept
short while the location keeps the box and connections dry allowing some cooling air to reach the
unit. Setting up the ignition can be time consuming but once done is set for life. I use a little smear
of silicone on the adjustable plate to fix the location and loctite on the taper and thread of the
magnet holder. Problems with movement of the magnet plate are usually the result of a poor
interference fit with the exhaust camshaft.
I have found the crimp on bullets supplied with the ignition kit are distorted by heat and
recommend changing these to spade, British bullet or Japanese connectors, soldered in place and
carefully insulated. With care it is possible to re-solder the wiring directly to the PCB. Smear
silicone on the cover plate flange and fill the wiring entry point to weatherproof everything.
The only fault I have experienced is the unit WILL fail if the battery becomes disconnected or the
Zener fails allowing the voltage to rise to exceed the maximum. Regularly check these connections.
If the engine stops after a short period of erratic running, the main fuse and ignition box connections
are the first things to check. Misfiring at high revs is usually the result of a flat battery. Fitting the
power box described above is the best solution.
There is sufficient space within the headlamp shell to carry a complete spare ignition unit.
For Wiring, Tools and components try Vehicle Wiring Products.
Boyer Bransden are at
Hitchcocks (Royal Enfield) are at
Suspension ... Dual or Variable rate fork springs are available (L P Williams) or could be made for
you by a spring specialist. The grade of oil used in the standard pre 68 forks has little effect with no
shuttle damping, though Triumph do recommend experimenting with grades. Do not exceed the
recommended quantity. The oil has a dual role of lubrication and as a hydraulic stop. It is possible
to fit to post 64 machines the shuttle damping fitted as standard on the later machines. The works
manual details this modification.
It is not necessary to have the special fork assembly tool, I use a suitably sized jubilee clip to grip
the stancion while compressing the spring and then fit the complete unit. The Jubilee clip can then
be removed allowing the spring to extend to its normal position. A suitable ‘C’ spanner tool is
required to remove tighten the chromed oil seal spring/holder.
Fork Judder if present will be caused by worn sintered bronze bushes, replace these as a matter of
The rear shocks were factory fitted with 145lb Springs, these are suitable for pillion passengers,
changing to 90lb Springs as indicated in the Performance Bulletin will improve the handling for
solo riding/racing.
Frame ... The pre 67 C Range Frame has several issues, all early bikes benefit from the 65 frame
brace and tank if these can be sourced, or welding in a brace as in 1966, all the bikes up to 67 have
a tendency to shimmy when cornering especially when not on the throttle. This is because of the
lack of support for the swing arm. I have seen two early Tiger 90's modified to the 67 swing arm
arrangement by having additional plates welded to the frame with later swing arm parts. This is a
serious conversion which will be difficult to do well and difficult to undo later. Please don't do this
if the bike is in good condition buy a post 1968 bike instead where its all been sorted for you.
Tyres ... Unfortunately there is little Tyre choice in the 18 inch size (3.25 - 3.5) I have happily used
Dunlop K82's for several years. Replace any Tyre you suspect to be over 10 years old or obviously
cracked, your life is at stake! Always assess the rim for corrosion inside, check the spoke locations
before fitting a new tyre and use a new tape. Discard any tube that has been repaired, I don't want to
experience a blow out at any speed! I have found Michelin tubes if available hold their air better
than other makes. The factory recommended carefully balancing wheels for high-speed work.
Bearings ... Sealed bearings are usually available to replace the open wheel bearings, A good
bearing supplier will be able to advise if you can provide a sample. It is a good idea to have suitable
drifts made to drive the bearings in squarely and without damage. I pop the bearings in the freezer
overnight and heat the hub with a hot air gun to ease fitting. Bearing Locktite is a good idea if you
suspect there has been a problem.
Early C Range machines can be fitted with the fully floating brake shoes, part numbers W1406 and
W1407. Look carefully at the floating shoe slipper as this often becomes indented and ineffective.
A common modification is to fit the twin leading shoe brake from the later bikes, this will greatly
improve performance but at the loss of originality. It should be possible to modify the standard plate
to twin leading design internally as there is room within the hub. This could be done on a spare
plate and its components without committing.
The standard brake is quite adequate for normal riding if serviced and set up properly. Have the
drum skimmed, the linings replaced with modern compound and then machined to fit. Ask to have
the linings biased to improve the servo action and ensure the linings are chamfered on the leading
and trailing edges. Check the springs are in good condition and that the surface of the drum is not
contaminated with grease or oil.
After assembly, loosen the fixed anchor point and the spindle nut, apply the brake hard and while
maintaining pressure tighten the spindle nut and then the anchor. This procedure will position the
shoes at the optimum position. Try to ensure the operating arm is at right angles to the cable when
the brake is applied and the handlebar lever is not flexing on the bar.
This will all help to maximise the performance of the standard unit, but even I admit that at speeds
above 60 mph it can get a bit exciting !
New replacement units in both monoblock and concentric styles are available from various sources.
Plunger choke versions are available by request. Better still is to renew the jets and internals of the
original carb. Look up the manual to find the size and jet requirements you need. Please don’t throw
the original carb away as these are very difficult to find. Clean it and pack it away in an air-tight
container. Worn units can be re-sleeved and reconditioned to keep the authenticity.
Contact Hitchcocks Royal Enfield for Amal Carb Spares.
My bikes have been in my ownership for 20 years. I often tour on my 1966 Tiger 90 and recently
completed a 3000 mile trip in the USA. My enjoyment is in researching the machines, improving
them gradually, searching for and remaking the elusive parts that they have lost. Improving
reliability so that I enjoy riding them and letting others try them too. Important to me is retaining
the look and character of the Triumph, promoting old machines in general to a younger generation,
and preserving but not destroying our British motorcycling heritage.
Justin James The Tiger 90 Man.
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