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Restoring the Honda S90

This page gives some information on the bike restoration.

The aim was to put the bike back into a usable condition, rather than restore every fine detail. It needed to be tidied up cosmetically and made safe. It would also need to pass the road-worthiness test at the garage.

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These photographs show the bike in its original condition.
The missing parts included, the silencer, the drive chain, front brake cable, battery, indicators and the ignition switch.
Parts which required work were the seat, the paint and the wiring. The wiring in particular was very incomplete and had been modified by previous owners. The indicator and light switches were damaged.

The bike was disassembled into component parts. The painted parts were sent for shot blasting to remove paint and any rust. Then they were repainted in a new shade of orange. All the parts came up well except for the rear swinging arm which revealed a bodged repair near the rear wheel. It looked like the swinging arm had been damaged by the sprocket bolts at some stage. Whatever the cause, a significant amount of metal in the swinging arm tube, had been worn away making it unsafe to use.

Restoration

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This image shows the tank after painting. The chrome polished up OK and 2 new tank badges were purchased from David Silver Spares. The badges were not to the original design but they looked appropriate.

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The head-stock bearings replaced with an alternative taper roller bearing set, shown here on the left

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This picture shows the frame, forks and wheel arches assembled.

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The foot brake had a new bush made up to reduce lateral movement at the pivot.

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This photograph shows a bit more progress.
The handlebars were fitted along with the headlight and clock. The airbox and rear number plate were also in place.
Some of the electrics had been installed including both handlebar switches, the lights and a new ignition switch.

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The bike was rewired using a new wiring loom, but the loom was for a different revision of bike. Originally the bike would have had a multi-position ignition switch to operate the headlights, but the new loom was for a (more simple) 2 position ignition switch. Therefore a different (3 position) headlight switch was needed to operate the lights. Click the image for the new wiring diagram.

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Both the indicator switch and headlight switch needed to use the handlebars as an earth connection. However the bars were insulated from the rest of the bike because they were clamped via shock absorbing rubber mounts. So an earth lead was added to one of the bar clamps by drilling and tapping the end of the clamp bolt and attaching a wire with a small brass screw.

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The head of the engine cleaned up well and the valves were reground to ensure a seal

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The cylinder bore looked in good order, as did the piston. The piston was marked as being 0.25mm oversized, so some work had already been done on the engine.
The bore measured 50.22mm diameter and the piston 50.12mm; a difference of 0.1mm which was at the limit of permissible wear.

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The valve stems were measured to check for wear.
The exhaust valve measured 5.41mm against a specification of 5.435mm - 5.445mm, to be replaced if under 5.415mm.
The inlet valve measured 5.43mm against a specification of 5.455mm - 5.465mm, to be replaced if under 5.435mm.
Both valve stems measured just undersize, so were replaced.

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The outer valve springs were checked for free length.
The Exhaust one was 30.89mm.
The inlet one was 30.65mm.
Specification 31.8mm replace if under 30.6mm
Both these were just about OK.

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The inner valve springs were also checked.
The exhaust one was 26.88mm.
The inlet was 26.92mm.
Specification 26.5mm replace if under 25.5mm
Both these were OK.

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An original silencer was purchased from EBay. However the clamp to join it to the down-pipe was not available, so a new one was machined from a piece of bright-mild steel bar. The bar was machined to be a tight fit on the silencer pipe and a block of steel was brazed to the side for the pinch bolt. This block was then sliced through to allow tightening. The part was finished in high temperature paint.

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A replica set replaced the old ripped one.

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An adaptor plate was needed to make the seat latch to the loop in on the frame.

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First running test

With the engine back in the bike a running test was performed although it still lacked wheels and a fuel tap, so a bottle was used to feed a small amount of petrol into the carb.

It ran very roughly and there was smoke blowing from the crankcase breather. The plug was also covered in oil despite a short running time. The carburetor leaked fuel.

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A repair kit was ordered for the leaking carb. The float bowl gasket didn't fit so, one was cut from a sheet of cork.

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The original fuel tap (centre) leaked badly and the new replacement one (left) didn't have the second input pipe from the tank. The tap body on the right was correct but had no lever. So one good tap was made from the bits.

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A new 6v horn was mounted on a homemade bracket under the headlight

With the carburetor rebuilt and the wheels fitted.  A road test was carried out.

The bike was hard to start, performance was poor and there was a lot of smoke.

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The piston was inspected closely and the oil control ring was damaged in places. In fact all of the rings had imperfections/scratches on the surface and they had lost their springiness.

The piston was taken to an auto engineer for a re-bore and an oversized piston with new rings was fitted to make things good again.

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