Honda CT90 - posi-torque sub transmission

Honda CT90 - posi-torque sub transmission

Honda invented the posi-torque system in 1967 and used it on the CT90 range of the same year. This ingenious device had the effect of providing the bike with 4 additional hillclimbing gears in addition to the standard 4 ratios for road-riding Earlier solutions The posi-torque system replaced the unwieldy dual rear sprocket arrangement used...

Honda invented the posi-torque system in 1967 and used it on the CT90 range of the same year. This ingenious...

Honda C90 - cam chain & cam chain tensioner

Honda C90 - cam chain & cam chain tensioner

Chains tend to 'stretch' in use because material wears away from the bushings and pins, increasing the clearance between the parts and causing the chain to elongate. So when Honda replaced the Super Cub push-rod engines with a new overhead cam model that used a chain to drive the mechanism they needed a...

Chains tend to 'stretch' in use because material wears away from the bushings and pins, increasing the clearance...

Honda CT90 - making a wiring harness

Honda CT90 - making a wiring harness

The CT90 has a simple wiring harness and making a replacement is pretty straightforward. Much of the wring on my 1969 K1 had been damaged, cut or patched so I decided to do a major overhaul, including making a brand new harness. Here are the before and after picture of the various repairs: making a...

The CT90 has a simple wiring harness and making a replacement is pretty straightforward. Much of the wring on my...

Honda CT90 - muffler and spark arrester

Honda CT90 - muffler and spark arrester

The CT90 exhaust system, although similar in appearance to the one used on the 6v C90, has different internals with fewer baffles and the addition of a Krizman spark arrester. Spark Arresters Spark arresters are designed to minimise the risk of fires being started by exhaust sparks and are required in the US when using...

The CT90 exhaust system, although similar in appearance to the one used on the 6v C90, has different internals with...

Honda CT90 - Front Suspension

Honda CT90 - Front Suspension

The earliest CT90s shared the same leading link suspension as the C90 Super Cubs. This is a great design, offering a comfortable ride and minimising maintenance issues by tucking the moving parts away from the elements. However, the forks were designed for road use and therefore only allowed a small amount of suspension travel; not...

The earliest CT90s shared the same leading link suspension as the C90 Super Cubs. This is a great design, offering...

Honda CT90 (k1) - wiring diagrams

Honda CT90 (k1) - wiring diagrams

I have just finished recommissioning a 1969 CT90 K1. The bike was originally sold in the US and was imported to the UK from California a few years ago. One of the many repairs that needed doing was to replace the damaged wiring harness, so I colourised the wiring diagram to help with the job....

I have just finished recommissioning a 1969 CT90 K1. The bike was originally sold in the US and was imported...

Honda C90 - crankshaft refurbishment

Honda C90 - crankshaft refurbishment

There are plenty of places that will rebuild your crankshaft for you, but it is also a job that can be done at home if you have the right equipment. tools You'll need a press (minimum 10 ton) to remove the pin and to reassemble the crankshaft and you’ll also need some...

There are plenty of places that will rebuild your crankshaft for you, but it is also a job that can...

Honda C90 - putting it back together

Honda C90 - putting it back together

Intro If you have dismantled your bike in order to refurbish it then, once you have finished reassembling the engine, you will be faced with a large pile of bits that need putting back together. In the immortal words of the old Honda manuals: "Perform the reassembly in the reverse procedure of disassembly."...

Intro If you have dismantled your bike in order to refurbish it then, once you have finished reassembling the engine,...

Honda C90 - air cleaner and exhaust

Honda C90 - air cleaner and exhaust

It hardly needs saying but the engine only works when air gets in one end and exhaust gasses exit the other. This article covers the two systems on either end of the engine, the air cleaner and the exhaust. Muffler and exhaust pipe Although in the UK we tend to refer generically to "exhaust...

It hardly needs saying but the engine only works when air gets in one end and exhaust gasses exit the...

Honda C90 - Crankshaft

Honda C90 - Crankshaft

The forces created by combustion pressure are transferred to the piston through to the connecting rod, causing the crankshaft to turn and thus converting the reciprocating motion of the piston to rotary motion. Here's what I learned about how it works. construction The connecting rod is located on the crankpin and the webs[...

The forces created by combustion pressure are transferred to the piston through to the connecting rod, causing the crankshaft to...

Honda C90 - transmission and performance

Honda C90 - transmission and performance

The transmission takes energy from combustion and transmits it to the rear wheel. The mechanism is shown below: The power is transmitted through a fairly convoluted path before it reaches the rear wheel: energy created by combustion forces the piston downwards causing the crank to rotate. The crank rotation is then transmitted through the clutch...

The transmission takes energy from combustion and transmits it to the rear wheel. The mechanism is shown below: The power...

Honda C90 - brakes

Honda C90 - brakes

The c90 uses a drum brake design that is essentially unchanged since it was first introduced over 120 years ago. Renault drum brake Drum brakes were first patented by Louis Renault in 1902 (see the patent diagram below left). Despite its apparent simplicity this invention was a huge improvement on the previous alternatives which had...

The c90 uses a drum brake design that is essentially unchanged since it was first introduced over 120 years ago....

Honda C90 - forks, suspension and steering

Honda C90 - forks, suspension and steering

This post explains the design of the Honda Super Cub suspension and steering. If you are interested in fitting tapered roller bearings instead of the standard ball bearing used in the steering head then see here. Leading Link Forks All the Honda Super cubs since their introduction in 1958 until relatively recently were fitted with...

This post explains the design of the Honda Super Cub suspension and steering. If you are interested in fitting tapered...

Honda C90 - piston, cylinder and combustion

Honda C90 - piston, cylinder and combustion

Internal combustion engines convert the chemical energy stored in fuel into the mechanical energy used to power machines when the fuel air mixture is compressed in the space between the piston and the cylinder head and ignited by the spark plug. The design of the piston, cylinder and cylinder head plays an important role in...

Internal combustion engines convert the chemical energy stored in fuel into the mechanical energy used to power machines when the...

Honda C90 - lubrication

Honda C90 - lubrication

The first Super Cubs did not have pumped lubrication, instead the crank, piston and cylinder were splashed by oil thrown up by a dipper on the big end of the connecting rod. A similar device can be seen in towards the end of this excellent video about engine lubrication: As shown in the diagram above,...

The first Super Cubs did not have pumped lubrication, instead the crank, piston and cylinder were splashed by oil thrown...

JIS screwdrivers, screws and fasteners from Japan

JIS screwdrivers, screws and fasteners from Japan

If you've ever worked on a vintage Japanese motorcycle you've almost certainly struggled with countless buggered-up cross head screws. The usual recommendation to avoid further screw mangling is to put aside your old Phillips screwdrivers and get some "JIS" ones instead. There is a lot of confusion about this...

If you've ever worked on a vintage Japanese motorcycle you've almost certainly struggled with countless buggered-up...