wheels
the CT90 uses the standard 1.40 x 17" wheel rims fitted originally to the very first 50cc super cubs and many other small capacity bikes made by Honda over the years.
The earliest rims were made by D.I.D - who still produce this size rim for Honda today - but other manufacturers were also used in later years, including Araya and Futaba.
front brake panel
The front hub was redesigned with the introduction of the K1 with the brake arm and speedo cable now fitted to the left, rather than on the right as was the case with the earlier leading-link suspension equipped K0 model.
The original front brake panel was a flush fit to the edge of the hub with a lip covered half of the exposed join to the rim.
old style brake plate (note that the early axles did not have a hole for a split pin to secure the wheel nut).
This design was changed around 1975 and the new version has a lip that fully encloses the edge of the hub, presumably to provide better protection from the ingress of rain and road dirt.
new style front brake panels
The hub was changed at the same time and the brake panels are not interchangeable. The slightly larger hub also meant the front spoke dimensions needed to be changed (see the next section).
spokes
Four types of spokes are used and there are subtle differences between each one: the heads that lay on the outside of the hub are right angled, whereas the spokes that fit on the inside need a wider angle to allow them to fit properly. The rear spokes are thicker than those on the front wheel and are also “butted” (thicker near the head).
72 spokes are needed.
Old style hub spoke sizes:
* butted spokes
New style:
The original Honda spoke nipples need a 5.1mm spanner, but this is not a standard size. I bought a cheap multi-size spoke spanner and slightly widened the no 11 slot with a file.
rear sprocket
The standard sprocket has 45 teeth (you can read more about the gear ratios here)
The rear sprocket carrier bearing is bigger on the Ct90 (6303) compared to the the c90 cubs of the same era (6203) , presumably a reflection of the extra abuse the CT was expected to receive.
sprocket installed on the sprocket carrier
wheel bearings
Both wheels are fitted with 2x 6301 bearings: 12mm (inside diameter) x 37mm (outside) x12mm (width). The wheel bearings originally supplied were sealed on one side, but you can install bearings with seals on both sides if you prefer.
wheel bearing removal
The bearings in each wheel are separated by a spacer and, once the axle is removed and the tension is off the bearings, there is just enough wiggle room to insert a metal drift from one side and get it onto the edge of the inner race on the opposite side. After that, with a bit of judicious tapping, you can knock out the bearing.
Note that when doing this all the pressure is applied to the unsupported inner race and - because this can damage the bearing - it should be replaced.
wheel bearing installation
There is a proper driver for reinstalling the replacement bearings but if you haven't got one you can improvise with a suitable sized socket (you need a socket that will align exactly to the outer race of the bearing, or an upturned socket that will contact both the inner and outer race at the same time - pressing on the inner race or the rubber seal will damage the bearing).
Bearings are installed with the manufactures's name and size code facing out (so they are visible from the side the bearing is installed from).
rear brake
An unusual feature of the earlier CT90s is that the rear brake can be hand or foot operated. Quite useful if, for instance, you are paddling down a steep hill and would like to use your rear brake to control the descent.
This is the elaborate mechanism they used to achieve this:
The bean counters soon got wind of this expensive solution and the last model to use it was the K5 (1974).
front brake
The 1969 K1 used a rather heath robinson solution to turn on the brake light when the front brake is applied: there is a mechanical switch included into the hand brake cable that - when the lever is pulled - closes a circuit so the brake light turns on (this was replaced by a simpler/cheaper mechanism soon after - the same solution as on the later C90s where the light is turned on by a switch installed in the brake lever bracket)
replacement cables
If you need new cables for your CT then search for Mel Bashor on the Facebook Honda CT90 owners group - he is an expert in all things CT and has arranged for manufacture of complete cable sets for many CT models - including the unique K1 model - and he sells them for a very reasonable price. For UK folks, Although Mel lives in America, he is also happy to deliver here (mine were delivered in less than a week!)
refurbishment
If you are sorting out an old bike it is generally a good idea to replace the wheel and drive sprocket bearings - the bearings are inexpensive, so just think of it as cheap insurance. The originals were from Nachi but any decent brand - NTN, SFK, FAG etc - will do instead. Ditto the brake shoes, and seals should be replaced as a matter of course.
If there are signs of wear on the drive sprocket, rear (driven) sprocket or the drive chain it is good practice to replace all three as a set.
If the cush drive rubbers are cracked or damaged they will need replacing (try and get the genuine Honda if you can find them). If the bike has been neglected the rubbers can disintegrate and the webs in the hub damaged as a result, as can be seen in my hub below.
Damaged webs (left) / replacement cush rubbers (right)
If you are feeling adventurous you can respoke the wheels - Honda spokes are still available but expensive.
In the case of my bike, which spent its earlier life in California, the spokes and rims were in good nick with very little rust, so all I needed to do was to tighten the spokes and true the wheels.
I fitted the heavy duty dunlop 70/100-17 inner tubes and the tyres are Heidenau K46 2.75-17. Not cheap but it is hard to find knobbly tires this size, and the tread pattern is similar to the early tyres Honda used.
Incidentally, the 1969 model originally came with a 2.50 tyre on the front - mine was still fitted with the original Yokahama from the factory - but from 1970 onwards 2.75 was specified for both wheels.
