For lightweight classic bikes is there a year resriction?

Is it only piston port or reed valve allowed?

air cooled or water cooled?

again thanks for the help.

Weirdly enough I have a copy of the Manx regs sitting in a window on my computer right now so heres the classic rules copied and pasted from last years regs

APPENDIX II - APPLICABLE TO CLASSIC MACHINES ONLY
In formulating the Classic Regulations, the Club has endeavoured to produce races for machines built using
components available in the eligibility periods.
When looking at entries consideration will be given to the period appearance of the machine as well as
adherence to the letter of these regulations.
All components fitted must be of a type available and fitted to machines of the relevant classes within the
relevant classic period, defined in paragraph 1 below. This includes all major components such as frame, forks,
wheels etc. No modifications (other than those specifically authorised in these regulations) will be permitted
unless used during the period. Where components are of later manufacture, they must exactly resemble the
original period components. No machines with more than 2 cylinders will be permitted, except by special
arrangement with the Club. The onus is on the rider or entrant to prove eligibility if required.

ELIGIBILITY SPECIFICATION
1 The MGP Classic races cater primarily for thoroughbred Grand Prix racing motorcycles constructed during
(i) the period 1 January 1945 to 31 December 1972 inclusive, for all 4 strokes; and
(ii) the period 1 January 1945 to 31 December 1967 inclusive, for all 2 strokes (with the addition of Greeves
Oulton and Bultaco TSS built before 31 December 1968)
for the specific purpose of participation in competition during that era.
In addition, short circuit specials, of a type which can be shown to have a connection with the Isle of Man TT
and MGP racing, will be considered on their merits. Such specials shall have a maximum of 2 cylinders and
must have an appearance of a typical racing machine of the era.
Entries will not be accepted without a specification sheet for each machine entered and with photographs, with
and without fairing, if applicable. Standard production machines will not be accepted. Riders who are in any
doubt about eligible components or modifications are invited to contact the Chief Technical Officer via the Race
Office for a ruling.
2 Seat, tank & fairing
Motorcycles must be presented in period condition. Seats, tanks and fairings (if fitted) must be of a pattern and
type manufactured and used in the period, ie pre-1968 for 2 strokes and pre-1973 for 4 strokes. Fuel tanks are
subject to the capacity of 24 litres (Reg 10h)
3 Wheels
Must be of a wire-spoked construction with a maximum rim width of WM3. Cast wheels will not be permitted,
except for the Arter Matchless.
4 Tyres
No hand cut slicks or wet weather tyres will be permitted and maximum tyre width, as stated on the
manufacturer’s specification sheet, shall be 4.00” for 250/350 cc machines and 4.50” for 500 cc machines.
Tyres must be fitted with inner tubes.
Approved rear tyres for 500 cc machines are Avon AM22, Dunlop KR 124, KR124A and KR108. Other makes of
tyre are acceptable providing the maximum width does not exceed 4.50” (114mm)
5 Brakes
May be drum or disc for 4 strokes. Only drum brakes may be used for 2 strokes. All disc brake components
must be pre-1973 for 4 strokes. Floating discs, 4 piston callipers and adjustable master cylinders will not be
permitted. Discs must be solid and may be drilled only parallel to the wheel spindles. An unmodified out-ofperiod
AP front brake master cylinder, part no CP3179-2 (plastic reservoir) is eligible.
For 2008 the AP Racing variable ratio front brake master cylinder parts no CP 3125-2 or CP 3125-4 may be
used for the 2008 Classic Races.
Where a rider has a genuine reason for not being able to operate a conventional brake lever, a thumb operated
brake lever will be permitted. Due to space constraints, this may mean that an out of period master cylinder will
be required. The use of such a device must be stated on the eligibility form and will be subject to prior approval
by the Chief Technical Official.
6 Swinging arm, suspension & front forks
Must be of a pattern, type and material manufactured and used in the period.
7 Carburettors
Shall be of a type available in the era, ie pre-1973 for 4 strokes and pre-1968 for 2 strokes, except that Amal Mk
II concentric carburettors, including smooth bore derivatives may be used. Pumper carburettors of any type are
not permitted even if the pumper is blocked off or disabled. Power jet carburettors are not permitted.
Fuel injection is not permitted. Keihin carburettors must be of "Tickler" type - the later mechanically operated
choke type is not approved.
8 Engine and gearbox
May be modified internally and/or fitted with components of modern manufacture. All engine and gearbox
casings must be unmodified externally, except modifications carried out in the period or to permit the
repositioning of controls. All primary drives (belt and chain) must be totally concealed from view. Multi-valve
heads are not permitted, unless available and used in the era, are not permitted. Non-period components, eg
engine castings, oil filter castings, cylinder barrels and expansion chambers will not be permitted. External oil
pumps are not permitted.
9 Clutch
Slipper clutches are not permitted. Dry clutches are not permitted unless originally fitted in the period.
10 Electric starters
Machines are not permitted to have an electric starter fitted.
11 Replica frames
Will be permitted provided they are dimensionally accurate copies of known period chassis. For chassis without
known pedigree, entries must be supported by documentary evidence proving eligibility.
12 Sound
For classic machines entered in the Classic races, the ACU has granted a waiver of the sound level permitted
under Standing Regulations.
13 Exhausts
Must comply with ACU Standing Regulations