can bet your sweet S90 that it will be a surprise along the way. 1965 Domestic Honda S90
you stay in one place for a long time and work on a lot of local
bikes, at some point in time one of them will come back around again.
So, when the “Honda S90” listing on Craigslist showed up I was
intrigued but not triggered to remember the bike from my past. A
quick message to the owner yielded a response that went, “You
worked on this bike 10 years ago.” Hmmmm???
made an appointment to meet up about 15 minutes away and the bike was
in a pretty sad state once you got close to it. Both tires were flat
and off the rims, the engine appeared to be seized, very old gasoline
was still in the fuel tank, the battery was dead and it was obvious
that the bike was actually a JDM domestic version judging from the
tail light, solid passenger pegs, low handlebars and a side stand
that was factory attached to the footpeg bracket. The speedometer was
in MPH, but it didn’t have a neutral light function, just a high
beam indicator and a meter light. The headlight switch had only a H-L
setting with no on-off function, so there were many puzzling features
as the investigation continued.
struck a “reasonable” deal price and the owner’s husband helped
push the poor little dead S90 up the driveway, from behind the
apartment building and into the back of my Tacoma. The bike was
pretty complete, but the wheel hubs were all chalky from sitting
somewhere wet for a long time and the rims has rust pits in various
places. I was told that the bike had been run for a while, but judging
from the virtually unused front tire with a 2011 date code, it didn’t
go very far. The bike didn’t have a title anyway, nor a license
plate, as it was a project bike at the time, made from various parts
which became more apparent as time went on.
unloading the bike from the truck, the shift lever got bumped and the
engine engaged, turning backward, releasing whatever the stuck
piston was doing previously. I resolved to remove the engine and take
a close look at what had happened to it, while starting a parts order
for tires, tubes, and a battery to get things started.
the stock muffler removed and the intake manifold/carburetor taken
away, the engine drops out with just three bolts. I hauled it up on
my bench and proceeded to dismantle the top end fearing the worst.
But as it came apart, the piston crown was mostly shiny from low
hours, but signs of water intrusion were present. The cylinder had
some staining, but the piston wasn’t seized, although the top
compression ring was kind of stuck in the ring land. A little
penetrating oil and some careful movement freed the ring and it
appeared to be good enough to reuse again. A quick hone of the
cylinder was done to rough up the surfaces just a little bit.
cylinder head was more of a mess. Old valves were cupped and water
had gone down in the intake port where it etched away at the metal
just behind the valve seat. New valves were ordered and the seats
were re cut with my ancient set of OEM valve seat cutters.
Fortunately, the seats had enough material left to allow for valve
seating, so the head was reassembled and installed back on the
new clutch cover was ordered from DavidSilverSpares.com as the
original was broken where the clutch cable is secured. There are two
different clutch covers, depending upon the serial number of the
engine, which was harder to determine as there were no serial numbers
on the engine apart from the cast in S90E and the space below was
wheels required some cleaning and the brake drums scraped clean with
a screwdriver blade then wire wheeled and finished with a Scotchbrite
pad. A set of inexpensive scooter tires, tubes and rim bands were
ordered from an eBay seller, so they were spooned on after de-rusting
the rims as much as possible. New brake shoes were ordered from an
eBay seller for very little money, having come from China.
fork seal appeared to be leaking so the forks were removed when the
wheel was taken off for tire replacement. The right side fork had a
screw-on fork seal holder, but the left side had a conventional fork
slider with the seal retained with a snap-ring. When they were
reinstalled, it turned out that they were different lengths! I
wondered why the axle came out with some difficulty, but now it was
apparent what that was the case. The difference was probably about
an inch with the forks uncompressed, but pulling down on the front
end finally matched them up enough to insert the axle once again. I
have to say that I haven’t run across that problem before! Either
the long fork is from a later version or perhaps from a CL90 bike
instead. Finally, the front brake cable was excessively long. The
early low handlebars take a shorter cable, of course and someone just
ordered a high bar US version. The clutch cable was the correct
length, however, as was the throttle cable
ignition coil was replaced due to a cracked spark plug wire and
general age-related damage. Once everything was correct, the little
engine was wrestled back into the frame. The fuel system was next on
the list so the Chinese copy of the original angled base carburetor was cleaned, which was a type that Honda used on the early
engines connected to the head with a twisted intake manifold. The
early carb setup requires a unique air filter and connector to put it
all together. All the parts were connected originally, so it is
puzzling how water had worked its way down into the intake port.
just when you think you have it all sorted out, the unexpected
happens… The compression tested out about 130 psi, which is about
20 short of normal, owing to a less-than-ideal valve seat repair
attempt. Still, it should have at least started up, but when the
battery was checked, it was down to 3 volts from six. Given that the
only thing that can drain the battery down is the rectifier, it was
apparent that it would need to be changed. And to change the
rectifier, you have to remove the engine.
recharged the battery back to 6 volts and installed it without
hooking up the rectifier, just to see if the engine would start up. I
had compression, spark, and fuel in the carburetor, but it wouldn’t
even give any signs of life. The spark plug appeared to be dry
despite all the kicking, so the carb was removed again for a check of
the idle jet and passages. Everything seemed to be in order, but it
didn’t affect the starting routine at all. Kicking the engine over
with the spark plug out I noticed that the spark was erratic at the
plug. The spark plug cap tested normal, so all that was left was the
possibility that the condenser was failing. Apparently, the part that
was failing was my brain because when I assembled the coil on the top
of the engine case, somehow I failed to reinstall the condenser! Of
course, in order to check the coil and condenser, you have to remove
the engine again.
cure the compression issue, I removed the head again, stripped it of
all the valve train stuff and took it to my local machinist, who cut
nice fresh valve seats to match the new valves for $25. When the
engine was reassembled the compression jumped up to 150psi, which is
in the range of factory specs. Sometimes, the DIY efforts are better
left for the professionals.
the meantime, I ordered a cheap rectifier from an eBay seller who
modifies those little solid state cube bridge rectifiers like Radio
Shack used to sell for a couple of bucks. The unit was already made
up with long proper colored wires, but when I went to install it the
mounting bolt was just a round 6mm bolt and the hole in the chassis
is half-round! So, at that point, the options are to either drill out
the frame hole or grind a flat on the bolt. I put the bolt on the
grinder wheel to make it flat on one side, but when I tried to
install it, the bolt proved to be too short! Back to the shop to find
a longer bolt or screw, which I found in a 6mm Phillips screw from my
drawer of fasteners. I had to regrind a flat on the screw again and
finally got the little unit to fit back into the frame hole.
problem with these little S90 engines is that they are just kind of
egg-shaped and it is difficult to find a nice flat space to use to
raise it back into the frame without it wobbling all over the place
in the process. The engine harness plug is tucked up way inside the
frame, so you have to reach up and plug it in carefully while
balancing the engine on a stand or jack. Finally, with a condenser
installed and the new rectifier bolted up, the three mount bolts were
inserted and the rest of the fasteners were installed.
charged the battery once more, it was installed and hooked up to the
new rectifier and the bike was ready for another starting attempt.
Not surprisingly, once a proper condenser is installed, the bike lit
off on the second kick, as it should.
final challenge was the fuel tank and petcock. The tank had been
sealed with Kreem about 10 years ago and that product doesn’t
really hold up in the long term. Plus it looks like they just poured
it over the top of existing rust so the insides had been peeling away
from being exposed to old gasoline left behind the last time it ran.
The petcock brass tube was gone, eaten away by corrosion. I cleaned
out the passages and installed what I thought was a new 4-hole
petcock gasket, but apparently, it was used in the past and had
hardened enough to allow gasoline to slip past the surfaces of the
correct petcock for the early model S90s is difficult to find now, as
it has a crossover tube to connect the bottoms of both sides of the
fuel tank together. There are numerous Chinese copies of these
petcocks as they fit a number of models. There are variations with an
outlet that points down, points sideways, with and without the
crossover tube that also points in different directions. What seems
to be the problem is that most of the fuel line fittings for these
copies are for a 4mm hose instead of the 5.5 mm hose that is needed to
connect the carburetor to the petcock. These petcocks are dirt cheap,
so I ordered one similar to the one on the bike, which didn’t have
a crossover tube fitting, just to get something fitted up to allow
the fuel tank to be installed so the bike could be test-driven.
Unfortunately, the first try with an eBay seller yielded the wrong
version despite the fact that I had ordered the correct one to match
what was on the bike now.
the engine back in the chassis and the chain hooked up, I confirmed
that the transmission is a rotary gearbox design, which is great for
around-town traffic, but not if you were going to ride it in some
kind of competition. The gear pattern is N-1-2-3-4-N going down,
down, down, down. You can, of course back shift it to gear down, but
not paying attention to the transmission in 4th gear will
get you into neutral at a high speed and if you push down again, you
get 1st gear when you are going 50mph. So, you just have
to override your normal shift pattern in your mind to compensate for
once the bike was running and safe to ride around the block, the
first thing I notice is that the clutch is slipping! I thought it
felt a little off when I was kick-starting it so much, kind of not
catching the engine fully and the suspicions are confirmed! Another
order to DSS for some clutch plates and a few days of waiting to
install them. Ordinarily, these little clutch packs are pretty
bullet-proof, but not knowing the full history of the engine can lead
to more surprises when it comes down to getting the bike to go down
the clutch revealed that one of the friction plates deteriorated
so it looked like I had three steel plates and one friction plate.
All the friction material was gone from the plate and bits had lodged
around within the clutch hub. New parts were installed after cleaning
out the old debris and suddenly I had a bike that kicked over smartly
and didn’t slip when power was put to the motor. That one should
last for years to come.
the OHC 87cc engine had a 20-year run of production. It replaced the
pushrod C/CT200 engine in 1964 and wound up expanded in the CT110
models for the early 1980s. Going over the parts lists for the S90s
is a real head-scratcher. There are three sets of engine cases, two
clutch covers, different oil pump and filter screens, two series of
transmissions, different cylinder heads, intake manifolds, air filter
systems and carburetors. By the time the CL90 versions came out
in 1967, most of the major redesigns were completed, but the early
years of the Super 90 are full of modifications and parts that are
not interchangeable with later versions.
from the Chinese copy carburetor, which is unique for the early
models, the other modification to the engine was a “performance”
camshaft from DRATV.com which is a $40 investment. I have used this
cam in conjunction with a big bore piston kit on a couple of CT90s
and it really woke them up. The cams are a drop-in modification,
having extended cam timing but no changes in the base circle or valve
the light bulbs were all blown out from someone running the engine
without a good battery in place. Typically, the US bikes have a
headlight switch has an ON-OFF, LOW, HIGH function all built into a
single unit. The domestic bikes only have a HIGH-LOW switch on the
left side and no separate ON-OFF switch function. That is controlled
by the ignition switch which has OFF-ON-Lights settings instead. The
unique domestic tail light has its own mounting bracket, lens unit
and base not commonly found in the US. The original turn signals were
MIA. The low beam of the replaceable bulb was burned out so DRATV
came to the rescue once again.
order to get the bike registered in CA it has to have an engine
number, which is missing on this machine. California has its own
CA-assigned stickers that are applied to either the frames or engines when cases like this occur. That will require a separate trip to the
CHP office after the first go-round with the local DMV office.
but surely, the bike is coming back to life and full function once
again. Even tiny little bikes like this can consume a lot of time and
effort to revive. S90s require attention to detail and a close study
of the various superseded parts that were made as production
increased through 1969.
finally replaced the venerable, horizontal OHC 90 series machines
with new CB/CL100s with upright cylinders, followed by a 125cc
version, which also included the SL100-125, the one-year CT125 and
eventually XL100-125 singles, all fitted with a 5-speed transmission.
The basic design morphed into later XL185-200 and XR200 versions. The
90s did do extended service in the US90/ATC90-ATC125 three-wheeler
models until 1985, so the linage of the original design carried on
for more than 20 years.
Silver aka MrHonda