The Chassis started out as a British Leyland proposal to form a replacement for the Leyland Atlantean and Bristol VR's that while modernised over the years were aging rapidly and had left the National Bus Company looking for more modern replacements.
Thus was born project B45, which was loosely based on the earlier project B15, which was the Workington-built Leyland Titan 'integral' double-decker for London Transport. The main differences of the 'Olympian' chassis being that the radiator was mounted on the front of the bus for better cooling, rather than transversely mounted above the engine as on the 'Titan' - which is the reason for the offset recessed square window on the rear of that bodywork - and also that the front and rear subframes were joined by bolted-on members, which permitted a variation in body lengths.
Initally, two power sources were offered - the Leyland TL11, which was a development of the proven 0.680 engine, with an 11-litre capacity, and turbocharged. (Turbo-Longitudinal-11l) - and also Gardner's 6LXB, a 10.45-litre 6-cylinder diesel engine, which offered lower engine revolutions but higher torque for the output. Both engines were coupled to the Leyland 'Hydracyclic' gearbox, which had both Automatic and Semi-Automatic options. Interestingly that is just a question of the selector and settings in the control box, the actual gearbox is identical.
One little known but interesting fact about Olympians, and certainly about 3603 in particular, is that they were first manufactured as a Bristol project in the Brislington works, and it was only after the first 500 chassis were constructed that the production was moved to Workington along with the Titan as part of a cost cutting measure. As Chassis number ON173, 3603 is taxed and registered as a Bristol, and is one of not many of that marque remaining. The Bristol chassis are sometimes jokingly referred to as Bristol VR series 4's because of the lineage!
Later Olympians introduced another engine option, and alternative gearbox options - the engine being the American Cummins Diesel L10, with various gearboxes available from Voith and ZF.
One Go-Ahead Northern Olympian, 3674 (C674 LJR) was unique in being fitted with a non-standard Gardner 5LXCT engine!
It is possible to deduce these engine and gearbox specifications from the chassis code, as explained below:
All codes started with an 'ON' to designate it was an Olympian chassis, which was then followed by a 3 or 4 letter/digit code to signify the engine choice, i.e.
ONLXB - Gardner 6LXB
ONTL11 - Leyland TL11
ONCL10 - Cummins L10
This was then followed by a '/', with another 2 letter code afterwards
/1R - Short wheelbase, R for Right-hand Drive
/2R - Long wheelbase
/1L - Short wheelbase, L for Left-hand Drive
/2L - Long wheelbase
Then a final letter was for the gear box:
'blank' - Leyland Hydracyclic
V - Voith
Z - ZF.
Hence, 3603 is an ONLXB/1R.
Bodywork was available from many coachbuilders from the very start, though most were fitted with Eastern Coach Works of Lowestoft's low-height bodywork and indeed to me they define what an Olympian looks like! However, Alexander of Falkirk offered the R-type bodywork, Northern Counties a development of their 'Standard' Atlantean/Fleetline bodywork, and less popularly East Lancs of Blackburn and Marshall of Cambridge bodied a small number for local municipals, though to a less stylish design.
