My
friend Don brought me another one-off bike to bring back to life last
week. When he sent a photo of the engine, I knew that I was in
trouble. The bike was clearly a one-year-only 1969 Honda SL90
MotoSport machine but had oversized tires, a wide alloy rear rim and
the swing arm had been extended a couple of inches with some awful
slugs and scabby welds. The extension work was probably to clear the
over-sized rear tire.
It
was the engine photos that caused me concern. The stock SL90 engine
has a 4-speed transmission and manual clutch, pretty much borrowed
from the S90/CL90 models, but in a new heavy-duty tube frame. The
engine shot showed the SL90 engine serial numbers, but the left side
cover had a Hi-Low transmission grafted onto the otherwise stock-looking engine! Very puzzling…
I
did check the compression first and the readings were in the 125 psi
range, which should have been closer to 150 normally. The engine is
bolted down with 9 bolts. Two long ones at the rear, which are
normally used, then three more on the top case where the frame side
plates bolt in, plus four that came up through the solid frame pan
and into the bottom of the engine case.
I
nudged it out of the chassis and rolled it over to the workbench. It
was a nice change from the 100+ lb 250-305 engines to be able to lift
the little 90 engine up and into a snug place for screw extraction.
Obviously, the whole engine had been apart and a CT90 Trail 90
transmission was installed which includes a long output shaft. All the
screws were very tight and it took a lot of whacking with the 3lb
hammer on the impact driver to loosen them all up.
Next, the top end was removed and more surprises were discovered. The piston was
51mm vs about 49 for a stock engine. The valves looked stock and
there were no signs of engine porting. Even the stock carburetor was
still in place. With the cylinder removed there were signs of water
down in the cylinders for a while, etching the cylinder walls,
especially near the top. As I removed the piston from the rod, I
noticed a bump in the connecting rod that was not normal. My best guess
is that it was treated to a Powroll stroker kit and the process to
keep the top end height correct was to heat up the connecting rod in
the middle section and put it in a press, shortening the rod a few
millimeters.
The
camshaft was an odd piece, as well. One end looked as if it had been
hard-chromed, the lobes looked bigger than stock and the flange for
the camsprocket was a full circle instead of just a couple of ends
big enough to bolt the sprocket to normally.
So,
the little engine turned out to be a big-bore, stroker, cammed-up,
8-speed, manual-clutch dirt machine, but still sporting the original
carburetor and exhaust system. It’s not anything that you would
normally find out in the wild these days.
Meanwhile….
Don
hauled the chassis home and dismantled it for a silver powdercoat
finish. He tracked down a replacement stock swing arm and rear wheel
assembly. The plan was to make it as stock as possible, which
included a $800 paint job for all the bodywork. The hybrid motor
will be the only big departure from stock, overall.
I
shipped the cylinder to DrATV in Nebraska, who has pistons in an
oversize to clean up the cylinder and give it new life. Along with
that, I ordered new gaskets, seals, screw kits, and a new dipstick.
The carb will get a good ultrasonic bath, but it wasn’t in terrible
condition, surprisingly.
The
engine was covered in clay dirt, which was resistant to paint
thinner, so it required an hour of scraping and scrubbing with wire
brushes and screwdrivers to get all the grit out of the myriad of
little casting corners.
The
cylinder head was similarly gummed up, but the valves may be
reusable. The previous mechanic put the exhaust valve stem seal
holder on the valve guide first, then jammed the inner valve spring
seat over the top of it. Both parts were damaged in the removal
process, so more bits were added to the parts list. I seem to find
the oddest situations of previous repair attempts on just about
everything I have seen lately.
I
did pull the clutch cover off and everything inside looked nice and
well-oiled. The little wedge-shaped oil screen was clean, as well.
The cover was sealed with Gasgacinch sealer without a gasket! The
cylinder camchain tunnel seal was loaded with red RTV and the formed
seal was damaged somehow during installation. At least the left side
of the engine cover area was sealed with a proper gasket. Instead of
an SL90 gasket kit, the CT90 Trail 90 kit will be the one of choice
to reassemble this hybrid engine.
Next
up will be fork seals/boots, drive chain, new cables and switches.
Digging
deeper:
After
a lot of cleaning of the outside dirt and grime, the assembly process
began, but not without more problems. I received a box of parts from
DrATV including the rebored cylinder. I had set aside the old piston
and began to assemble the new one only to discover that I had
overlooked the fact that the piston skirt on the old piston was about
an 1” shorter because of the combination of the stroker crank and
shrunken connecting rod. So, I disassembled the top end again and
whittled down the piston using a combination of hacksaw and a little
belt sander I have in the corner of the shop.
The
head went together with the old valves and new valve stem seal and
holder. The new piston crown was somewhat different than the old one,
but the combusion chamber had been scooped out somewhat to lower the
compression generated by the increased bore and stroke.
The
carburetor was the early version with a horizontal float valve setup
which doesn’t seem to be available in a carb kit that I could find.
It cleaned up pretty well in the ultrasonic cleaner, so I left the
original parts inside. I am concerned that it had been running a
stock #85 main jet despite all the other mods including the lumpy
Harmon Collins camshaft. We’ll see how it turns out in a few weeks.
Chassis
build
Don
brought back the frame and suspension bits to start the reassembly. I
had to extract the old swing arm bushings and spacer from the
extended one to the powdercoated stock one. Using a slide-hammer
setup I was able to coax the old bushings out and reinstall them into
the good swing arm. There were new aftermarket shocks but the eye
ends were the same on both ends and the bottom one fits the swing arm
mount fine, but the top mount is an 8mm bolt, so requires a bushing.
I had one lying around, but will need to get another one before I am
finished.
The
steering stem was the next part to install, but the races were
somewhat pitted and the package of balls that was delivered had 18 in
it and the installation calls for 42! I tried Home Depot and called
ACE Hardware, but no luck. I told Don that I needed more 3/16”
balls and he came up with a package of them by the next morning! I
had used a small Dremel grinding wheel to work down the pits in the
races in hopes of them being good enough to use and they were. I had
already replaced the fork seals on the fork set, so they were slipped
into the stem, after some excess powdercoat was removed. With the
fork bridge in place the forks rotated side to side very smoothly.
The
rectifier bolts to the side of the battery box which had also been
powdercoated. I had to grind off some of the coating to get a nice
solid electrical ground for the box to the frame and the rectifier to
the batttery box.
More
cleaning time was spent on the front brake backing plate and shoes.
The worst problem was that someone had torqued down the axle when the
speedometer drive gear wasn’t registered into the two little slots
on the hub. The tabs were flattened out and it took some time to coax
it out of the drive cavity and then put it in a vise to bend the tabs
back to ninety degrees so they fit the hub once again. It’s amazing
how much time is spent on doing little steps to move forward in the
assembly process. I turned the frame upside down in order to feed
the front wheel and brake assembly into the ends of the forks, then
flipped it back over again.
I
tracked down new cables including one of the rare front brake cables,
which have a brake switch burid in the middle of the cable. This was
a 1969-only feature on most of the street bikes in that year and the
correct cables are very hard to find and can cost $100+ from some
sellers.
The
side stand was assembled and the spring installed with my brake
spring tool. Unfortunately, the SL90 only has a side stand, so the
frame was sitting wobbly on the work table until the rear hub and
sprocket holder were cleaned and installed with the new wheel and
tire. With new shocks and oversized tires, I hope that the bike will
sit on the sidestand correctly. I have to put a rear wheel stand
under the swing arm and feed the rear wheel into the back end of the
chassis. Once both wheels are in place, the engine can be installed
once again.
The
engine is certainly bolted firmly into the chassis. Normally, a
S/CL90 engine bolts in two places at the back of the engine case. On
the SL90, the rear bolts still are installed once the frame side
plates are assembled, but then 4 more long 8mm bolts come up from the
bottom of the frame’s skidplate and into the engine case. So, the
engine is secured with 8 bolts. It’s probably a good thing, as the
big bore, stroker engine isn’t balanced for those mods, so the bike
might be more than a little buzzy.
The
wiring harness was all crispy with heat/age damaged push connectors,
plus, like everything else, was coated in the fine dust seen on the
whole bike. I ordered some silver electrical tape to tape up the
forward section of the harness where it enters the back of the
headlight case. Reviewing the condition of the connectors and wiring
leads, I wound up buying a better quality used harness from eBay.
The
original handlebar was refitted with a new left side headlight
control/dimmer switch. The right side throttle housing has one
two-wire electrical lead that connects to the kill switch. Again the
wire sheath was crispy and flaked off with little effort. I snaked a
few pieces of heat shrink tubing together to clean up the appearance
of the bike. This is not designed to be a 100 point show bike, so
some corners can be cut in order to get the bike completed under a
reasonable budget.
The
rear fender is rubber-mounted and the rear mount wraps around the
back of the frame tube. A curved mount plate and insulating rubber
are unique pieces and NLA out in the world, for the most part. I ran
the part number and it came up in an old list for OhioCycle’s
inventory online. I sent a message to Nick and he posted it on eBay
where he is doing all of his sales now. Not cheap, but it is new and
will be just what we needed to mount the back of the fender. The
forward section of the rear fender mounts with a little set of
rubbers, spacers, bolts and washers for two spots. In the end, the
tab for rear fender rubbers came to nearly $100. You have to do what
you have to do when repairing a 56-year old, one-of- a-kind Honda
MotoSport 90.
The
speedometer packing had all flaked off, but fortunately it is a low
cost item that has been reproduced and fits a number of smaller Honda
models. As with all the other steps, you have to take time out to
research the part number of some small bit and then find one for
sale, ordering it up and adding it to the growing list. In projects
like this, several hours are spent in cleaning parts, evaluating the
project, researching the correct replacement parts, finding them and
ordering them, hopefully on a decent time frame.
The
SL90 was about to start up some 10 weeks after arrival. It had a
fresh battery, 150 psi compression, new coil and condenser and
rebuilt carburetor. Kick, kick, kick.. check for spark and there
wasn't one. I jumped the points with a screwdriver and it was pretty
much non-existent. I cleaned the points carefully and the spark
improved slightly. The bike actually did start up and run for a
minute or so. I shut it down and it wouldn't start again. Same
minuscule spark issue. I removed the $15 eBay coil that was listed
for all 6v Honda singles and the primary side read 4.5 ohms. That's
great if you have a 12v system, but not for a 6v bike. I checked the
old original coil and it read 1.6 ohms. When I plugged the oil coil
back in, the spark at the plug was nice and crisp.
The bike fired up
on 2 kicks. This bike was powdercoated, so the frame needed some
places scraped off for engine grounding. What I discovered, was that
the coil, on most 90s, bolts to the engine crankcase and the
condenser rides on one end, so both are grounded, even though the
coil doesn't need to be grounded. On the SL90, the coil is mounted on
the backbone of the frame beneath the fuel tank on a split bracket
that clamps to the frame tube. It finally dawned on me that the new
condenser, mounted on the end of the coil wasn't getting grounded due
to the powdercoating on the frame tube. I ground of some of the
coating and made a secure ground for the coil bracket, thus also for
the condenser. Interestingly, the engine did run briefly without the
condenser functioning due to a lack of proper ground.
A
whole new disaster was discovered after the engine was fired up, when
a huge oil leak developed beneath the left side dyno cover and Hi-Lo
transmission unit. Once the cover was removed, the gasket was checked
as well as the oil seals. All were as expected, however there is a
cavity below the Hi-Lo transmission area that had a curious drilled
and threaded hole. Oil was gushing out from that spot and drooling
down into a partially blocked drain path. I initially used some red
Lock-Tite thread locker on a small 6mm screw, then covered it with
some GOOP to help seal the area. I didn’t give it all enough time
to set up and when it was restarted again, the leak returned.
Apparently, there is something in the transmission area just behind
the hole and the screw was dislodged and the leak continued.
Round
two was to cut down a shorter screw, use thread locker again and only
thread it in about a 1/8th of an inch. Then I mixed up a batch of
epoxy and filled the cavity, surrounding the screw. I made a little
dam to close off the cavity from leaking further and let it all set up overnight. That should fix the problem, permanently. This was another
example of spending extra hours discovering one-off customer mods
that were not expected or functional and having to find solutions for
effective repairs.
This
bike has been a nightmare since it arrived, packed with silt and dirt
in every square inch of the machine. I had to replace the wiring
harness as all of the connection insulators were fried to a crisp. I
could only find a better-used harness from eBay and piece it all back
together again. After the battery was installed, the ignition switch
failed to make the simple 2-wire connection internally. I removed the
switch and pried the back off only to find more of that silt and dirt
inside the contacts of the switch plate! I’m convinced that the
bike was submerged in a river of some kind, which can only explain
how much dirt got into so many places.
The
switch repair was successful and finally power was being distributed out to
all the lights and ignition system. Even the horn works!
Getting
close to the finish line…
Well,
the first test ride was around the block and down the street for an
initial checkover. The next one was further down my test ride course
and ended abruptly when the main jet fell out of the main jet holder.
Mechanic error! After a ¾ uphill hike back to the house and my
truck, I recovered the bike and reinstalled the main jet. I have been
very puzzled that this engine, with all of the modifications done to
the engine is running a stock exhaust and a stock carburetor with a
stock #85 main jet. I decided to play it safe and put in a little
bigger jet, but when I tried a #90 jet on my tapered jet reamers for
comparison, then I discovered that someone had drilled/reamed out the
stock #85 jet to just about #90 size. Well, that mystery was finally
solved.
The
next run, closer to home, was more at a fuller power setting and when
I returned, oil was puddling beneath the bike! First it was oil
coming from behind the right side cylinder head cover. I pulled the
cover, checked the surface of the head and cover and found a little
gouge in the head, near the screw hole. I added a bit of RTV to fill
in the gap and put a double gasket on, which fixed that leak.
Another
test ride and another leak from a different place. This time, oil was
seeping at the base gasket area where the camchain comes through. The
gasket set was not OEM and sometimes the replacement parts are not at
full specifications. I had to unhook the exhaust, pry up the intake
manifold and gently tease the cylinder head off just enough to access
the moulded camchain packing piece. It look absolutely fine, so I
gooped it up with some MotoSeal and reassembled it without disturbing
the cam timing, which was a small miracle. I had removed the camchain
tensioner spring to take the load off the tensioner so it wouldn’t
push on the camchain and disturb the timing.
Given
that the engine is springing oil leaks on new gaskets and seals leads
me to consider that perhaps the increase in displacement is
overwhelming the simple breather system and the excess pressure is
forcing oil past anywhere there is a weakness. Or, the gasket
material and seals are not of OEM quality.
The
last gasp repair attempt was a glob of RTV spooned up into the gasket
seam area. After hardening overnight, the initial test run looked
promising.
I needed more time to finish this bike in time for it to appear at the upcoming Steve McQueen car and bike
show. This was already Wednesday before the event, so it had to be
right, right now. Don called me on Monday... the bike didn't leak a drop and it went on the transport truck, headed for S. America.
Whew!
Bill Silver
aka MrHonda
www.vintagehonda.com
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