Information sheet

Technical Information - Instructions for KTT Models MkVII (Engine No. KTT700 onwards) and MkVIII (Engine No. KTT800 onwards)

*  Note : with modern low expansion valve material 21-4N and the bike being used for short circuit work, I have found that tappet clearances of .008" for the inlet and .012" for the exhaust are adequate.

Valve Timing(Checked with 020" tappet clearance)
K17/8 camInlet opens 55 BTDCInlet closes 65 ABDC
Exhaust opens 75 BBDCExhaust closes 45 ATDC
Tappet Clearances (running) inlet 0012" * exhaust 0025" *
Valve Timing(Checked with 0025" tappet clearance)
K17/11 camInlet opens 55BTDC Inlet closes 60 ABDC
Exhaust opens 75 BBDCExhaust closes 45 ATDC
Tappet Clearances (running) inlet 0012" *

exhaust .025" *


Valve SpringsThe installed length of valve springs is 27/32" centres. This can best be checked between the top of the bottom valve spring washer and the underside of the top valve spring loop. This dimension is 0562".
Ignition SettingMk VII engines32 advance for petrol-benzol and alcohol.
30 advance for 70-75 octane fuel (pool).
Mk VIII engines 30 advance for all fuels.*
* NB I have found 35-36 degrees to be more effective with modern fuels ( typically 50\50 Avgas and Super unleaded)
These figures should be checked with 0012" gap in the contact breaker points and with the back run of the magneto chain tight.
Sparking Plugs14m/m long reach
For warming up:KLG FE 220 or 718C LR
Lodge} can be warmed up on racing plug
Champion} use least heat resistance
For racing:KLG 689 LR, 646 LR or 690 LR
LodgeRL 51, RL 49, RL 47.
ChampionNA 14
The racing plugs are arranged in order of heat resistance. Highest resistance first.
The machines are supplied with a warming up plug fitted and a racing plug with the tool kit.
PistonsMk VII engines.K27-15 for petrol benzol. C Ratio 875-1
K27-15 for 70/75 octane fuel. C ratio 78-1
K27-16 for alcohol fuels. C ratio 115-1
Mk VIII enginesK27-15 for 70/75-octane fuel. C ratio 78-1
K27-16 for petrol benzol. C ratio 1094-1
Gear RatiosTop 505-1, 3rd 555-1, 2nd 73-1, and 1st 96-1 with 24-tooth sprocket
Lubrication SystemLubrication is carried out by means of a gear type oil pump situated in the bottom timing case which consists of two separate pumps in one body, the larger of the two being the extractor pump which returns the oil from the sump to the oil tank. From the feed pump the delivery is taken to a check valve situated in the top of the timing case. The object of this valve is to prevent oil draining into the engine when the machine is standing. Should it be found, therefore, that the crankcase shows a tendency to fill up when the machine is stationary, this valve should be examined. The oil is then taken by suitable passages to a filter situated at the rear of the magneto chain case.
This filter should be removed periodically and washed thoroughly in petrol or benzol bearing in mind that any particles of dirt will remain on the outside of the filter. From the filter, suitable passages and pipes deliver the oil to a jet leading to the centre of the crankshaft to the big end bearing, a jet directed on to the top bevel gears and a jet directed on to the cam and lastly to a spring loaded regulating bye pass valve situated in the bottom of the timing case. A screw and lock nut operating this valve will be observed at the rear of the timing case. To increase the pressure, and therefore the quantity of oil fed to the engine this screw should be turned CLOCKWISE and to decrease ANTI-CLOCKWISE. Do not alter more than turn at a time. The oil pressure is set correctly on all engines before leaving the Works. The minimum pressure should be 8lbs per square inch taken with hot oil at an engine speed of 6,000 RPM. Give as much oil as possible while still keeping exhaust reasonably smoke free. The maximum oil pressure should normally not exceed 12 lbs per square inch. Remove plug (" x 20 TPI) from bottom of magneto chain case and attach pressure gauge pipe to this hole to check pressure.
CarburettorAmal type 10 TT 13/32" choke size.
SettingFor petrol benzol.
Main jet(Mk VII engines)380
(Mk VIII engines)400
Needle jet109
Needle position2
Throttle valve4
Pilot adjusting screw1 to 1 turns open.
For 70/75 octane fuel.Main jet 400 on both types of engine.
All other adjustments unchanged.
For alcohol fuels(Mk VII engines only)
Needle jet113
Main jet (Discol RDI or JAP Racing Fuel)800 approx
(BP Racing Ethyl, methanol or pure alcohol)1000-1500
It is not necessary to use a double float-chamber, as the standard type fitted will pass enough fuel to keep main jet fed.
NoteIt should be emphasised that the main jet settings are only approximate as the jet required varies with the locality and atmospheric conditions and should always be finally settled on the site. With alcohol fuels it is advisable to err on the side of richness as little or no power is lost and cool running is obtained. The ignition settings given should not be altered whatever fuel is used.
Tyre Pressures19 lbs front, 20 lbs rear. These are normal and should not be varied by more than one or two lbs per square inch.
NoteWhen heating up crankcase or cylinder heads for bearing or valve guide replacement etc., the temperature of the casting must not be raised above 160 centigrade.
TimingWhen timing, one rocker only should be in position at a time with no return spring.
Alcohol fuel with a Mk VIIIIf an engine is set up for use with petrol/benzol 50/50, the compression space is 35cc, which gives a ratio of 1094:1. To one gallon of 50/50 mixture, add one pint of methanol. It would then be found that more power is provided. It is possible that it will be found necessary to increase the jet size by one or two.
Rear Oleomatic suspensionIf the legs should be removed, on replacing, the centres between the two bolts must be 12", before finally tightening the bolts. At the base of each leg will be seen a bolt running at right angles to the rear wheel spindle. On the head of each bolt is stamped an arrow.

The softest ride is obtained when the arrow on the head of the adjuster is pointing vertically up the strut. The average position for normal use will be found to be about 45 to one side of this position. It does not matter which way the valve is turned - either way will stiffen up the damping.

On no account should the adjuster bolt, viz. the one with the arrow on, be reversed in the unit, as this will blank off the oil passages, and the unit will become solid.

If at any time oil has been lost,top up with Mobiloil 'Arctic' through the inflation valve hole. A little more oil than is required should be introduced, then the unit should be carefully compressed, allowing the excess oil to be expelled. The inflation valve end of the unit is held uppermost during this operation. Refit the inflation valve and pump up with a good tyre pump.

Inflation pressures will vary slightly with different riders, but about 35psi will be found suitable for a rider of average weight. Both units should be adjusted to the same pressure. Pressure should be checked with both wheels of the machine on the ground and uder its own weight. Allowance should be made for loss of air when removing the pressure gauge.
Amal carburettor settings used for the TT 1938 Official 350cc
1 3/16 x 1 7/32in jet block
Special RN1 carburettor 15/2312
520 jet
Valve 3
Needle position 2 with special RN7 needle
Standard length air tube
This setting used by Woods
Official 350cc1 5/32 x 1 3/16in carburettor
510 jet
Valve 2
Standard length air tube
This setting used by Mellors