My primary focus on vintage Hondas has been the variations
of the 250-305cc models for more than a decade.
Having owned, repaired and overhauled numerous vintage big twins, I am
perfectly at home with those models.
Honda’s CB92 Super Sport machines are extremely rare in the
US, having only received about 1,000 machines in the 1960-62 era and many of
those were supposedly the racing versions. I owned CB92 #24 about 30 years ago,
which was a bike originally sold here in San Diego. In the years since about
half a dozen more have come my way and were resold without taking on full
restorations. Obviously, after 58 years, the parts sources are very thin.
Additionally, the changes made during production, complicates the picture even
further.
Honda began production in 1959 with both a 125cc CB92 and a
companion 150cc version CB95. Bear in mind that these were newly designed OHC
twins which revved to 10k rpms, but only carried a little over one quart of oil
in the crankcases. Early bikes suffered crankshaft failures and left side
piston seizures when run hard, especially of the oil level dropped below the
safe mark.
From 1959 through 1962, there were three different
crankshafts and a matching number of crankcase changes to follow. The first
generation crankshafts had a 1mm larger center main bearing than the end
bearings, all located in the cases with split half ring retainers. At high rpms
the bearings could actually rotate in the cases and not enough oil was passing
through the crankshaft to feed the left side crankpin. Honda did an unusual stopgap modification by
machining an oil passage in the base of the cylinder block that lead from the
oil feed stud hole across the back and into a window that was machined in the
rear of the left side cylinder bore. A
special gasket was created to match the oil channel work. The early cases featured a “rear breather”
design that collected and separated the oil solids from the crankcase vapors at
high speeds and allowed just the separated air to escape.
The second generation featured main bearings of all the same
diameter, but the center main was locked in place with a locating pin to ensure
that it was getting a constant oil feed from above. The end bearings continued
to be of the split ring design. The
crankcases were changed to make the breather system function back inside the
top cylinder head cover with a vent/drain line coming off of a fitting.
Finally, in 1962, they pinned all three bearings, so the
cases were changed again to reflect those modifications. Obviously, the
crankshafts and crankcases all have different part numbers and design features
which preclude mixing and matching parts from other years.
A good friend in AZ had purchased a couple of less than
perfect CB92s and dropped off an engine for me to rebuild. It had suffered a
severe piston seizure early in its life and was parked for decades. The engine
required a full cleaning and vapor blasting to recover the original finish,
plus all the fasteners needed to be re-zinc plated. Fresh pistons and rings
were installed back into the original STD bores which were not damaged. All the
rocker arms were replaced, but the camshaft appeared to be in serviceable
condition. All new valves were installed due to cupping of the seats and valve
faces. After a few weeks of running parts back and forth to machine shops, the
engine was reassembled and stood waiting for pickup.
As time went on, the VJMC West Coast Rally was announced in
Prescott, AZ, so I saved John a 600 mile round trip by dropping off the rebuilt
engine at his house. During the interim he pulled another CB92 engine apart for
rebuild and had already cleaned and re-plated all the parts. The engine cases
had suffered a bizarre damage situation to one of the carburetor cover mounting
posts. Apparently one of the mounting screws was seized into the mount and
probable use of an impact driver had broken the whole mount off of the case,
taking a large chunk of the top case with it.
John sent the case off to Colorado where a skilled welder
had managed to re-weld the chunk back into the case, blending the repairs so
well that it was almost invisible on the outside. Good save as that is the half that contains
the serial numbers.
When the parts were unpacked, I noticed that the 1960 engine
cases had a non-matching 1961 crankshaft installed! Apparently the engine was
run like this with the center main bearing free to spin around inside the cases
as there was no contact with the crankcase bores. So, the hunt was on for a new crankshaft with
the larger center main bearing. After almost 60 years, finding NOS CB92 parts
has become problematical, but within a week, I managed to flush out three
different correct crankshafts for sale. Two were out of the country (Thailand
and the UK), but the last one came from a stash in WA state, where a long time
owner/racer of CB92s had some leftovers buried in his garage.
Had the whole units not been discovered, the Plan B was to
buy one of the center main bearings and have a machine shop rebuild the
crankshaft with a new main bearing in the middle. These crankshafts are small
and difficult to press apart and back together again, so I am glad to have a
whole new correct unit to use as a replacement part.
In the meantime, my friend John Stein, in LA, wanted me to
revive a 1960 CB92 which he had owned for the past 30 years. I agreed to take
on the revival (not restoration) work, so that made three 1960 CB92 bikes or
engines that have come to the shop in the past month. That bike showed up dirty
and sad looking with a mismatched paint color on the headlight bucket,
incorrect tail light, wrong brake cable and other woes, but some restoration
work had been done to the hubs and wheels. The bike must have been raced at
sometime as there were some crash damage scuffs remaining, a racing rear tire
on the back and an all aluminum cylinder block installed. Plus there were no mufflers on the bike, just
a set of loud factory megaphones from the race kit. The bike featured a YB
racing seat, as well, plus a tachometer in place of the speedometer.
While all of this was happening, I received a message from a
CB92 owner in Los Angeles area who was moving to AZ soon and wanted to sell his
“project” 1960 CB92. At the moment, my bike inventory is pretty much at max
levels, including a 2013 CB1100, 1988 CBR250R (250 four cylinder), 1988 Hawk
NT650 with 1,000 original miles and a newly acquired 1990 NC30 VFR400R. With
one 1960 CB92 on the bike stand and another 1960 engine on the work bench,
things are in overflow status.
The LA bike was disassembled, had been repainted metallic
green, had a chopped off front fender and the kneepad was disintegrating. The
engine had 150 cylinders, but the head was still stock 125 parts. The bike had
been stored in poor conditions, so there is lots of rust and patina on the
parts visible in photos. The price was
at the upper level for what was there, but it had been the seller’s bike since
1964 and he was aware of the value of the bike, even as a parts source.
Reality check…
After much consideration and parts availability checking, I
decided not to pursue the LA CB92 project bike. The 1960 bikes seem to be prone
to needing new crankshafts and based upon recent searches, their availability
and cost are budget busters. Some of the rare chassis parts are available from
a source in Japan, but the seller doesn’t ship to the US, so they would need to
be relayed from one of my Japanese based contacts out here to California,
increasing costs dramatically.
The current 1960 CB92 engine was held up for a new crankshaft,
which arrived recently, but without end bearings or the special thrust washers.
I ordered the thrust washers from DSS in the UK, who has to nab them from their
partner resource in Holland, so delivery time can be a couple of weeks in the
end. I asked about the spare C92 engine
crankshaft still in AZ and they were intact. So, with a little persuasion, the
end of the crankshaft was cleaned off and washers shipped out with the set of
CA95 cylinders which need to be re-bored before assembly.
Once the cylinders were bored, much of the reassembly went
smoothly. The oil filter needed was the shorter version and not serviced. The
small 4mm screws tend to get stuck and often the heads are damaged when removal
is attempted. I did manage to get them loose and the unit cleaned. Some allen
head screws were supplied as replacements, but the thread pitch is slightly
different between JIS and ISO so the holes were rethreaded. Eventually, all the
bits fell into place and the engine was picked up in late Oct.
Top end tear down…
The 1960 #517 CB92 on the bike lift finally got to the point
where I could try the electric starter to spin the engine over in preparation
for a startup after 30 years. The starter solenoid just buzzed a little bit,
probably due to dirty internal contacts. After a stint on the battery charger,
finally the engine spun over with the electric starter, but not very briskly
even with the spark plugs removed. A compression check revealed 80 psi on the
right cylinder and about 85 psi on the right side, which is way under the
suggested 130 psi in the manuals.
The motor was eased down onto the work table and the top end
removed. Within the alloy YB racing cylinder block were two STD bore YB
pistons, both of which were carboned up on top, but showed little wear on the
piston skirts or within the bores. The top ring was removed and checked in the
bore for end gap width, but appeared to be on the minimum end of specs.
The head was checked for compression losses and both exhaust
valves had odd pits on the valve seat faces, so will be replaced. The camshaft
was stamped YB in 2 places. All the cam lobes and rocker arms appeared to be
fully serviceable as-is. Intake valves
were de-carboned and re-installed as their seats were still nice and shiny thin
rings. Exhaust seats were lightly cleaned and should be a good match for new
valves. The ends of the valve stems appeared to be nearly unmarked, so the
engine run time must have been minimal on new parts.
The low compression was probably due to the exhaust valves
leaking, but the extended valve timing of the camshaft can actually reduce the
measured compression readings because of the YB cam timing. The combustion
chambers and piston crowns were pretty coked up with burned oil deposits, but
the exact cause of excess oil consumption is somewhat mysterious given the
condition of the parts inspected so far.
Once some fresh valves are installed, we’ll see what the
readings come up to afterwards. The old gaskets were very difficult to remove
and more than an hour and a half of labor was expended in just getting the
parts cleaned and free of leftover gasket residues. This is always the least
pleasant portion of engine rebuilds on vintage Hondas, as far as I am
concerned.
Progress…
Amazingly new correct 205-coded stainless exhaust valves are
still available from eBay sellers. The seats were cleaned up and new valves
lapped in. New head gasket, sealing rings and a few oil seals were installed
and the engine eventually reinstalled. The engine has to go back in with the
head first, which is awkward to do with a single jack. I eventually used 2
small floor jacks to get it stuffed back into place. I can do an engine swap on
a CB77 in half the time as these little Benly engines.
I managed to track down a new starter solenoid to replace the
one whose mounting ears had broken off and were replaced with strap metal. This
was another rare part that was found with an eBay seller who had several in
stock and took a “best offer” of about 30% less than “retail” for it. CB92
parts like that are probably slow movers in the US, as there were so few bikes
sold here and fewer remaining to repair or restore.
Start up and wrap up…
Initially, the bike engine didn’t want to fire up, but after
about 15 good kicks, it sputtered to life and kept running with little or no
choke, even when cold. The bike stutters just off-idle, then cleans up and
pulls through the gears. An open-megaphone CB92 is not something that you want
to spend a lot of time on, particularly in a residential neighborhood. I made a
couple of mid-day passes up and down the streets, right around home. It pulled
past redline going down a long hill, but struggled on the way back up. The 4
speed gearbox has somewhat wide ratios, so it falls off the powerband when you
upshift from 2nd to 3rd gears, under load.
I suspect that it needs a larger main jet for pulling high
speeds, but also needs a slide with a bigger cutaway or a needle with a fatter
taper to help lean out the low end. Despite the hi-dome YB pistons, the D8HA
spark plugs screw all the way down and haven’t had their electrodes hammered
shut yet. I think the longer duration YB
camshaft profile hurts the bottom end power, causing metering problems for the
carburetor, as well as lowering the compression readings at idle.
The clutch was initially “stuck” but leaving it in 3rd
gear at 30 mph with the clutch lever pulled in, finally released the pack and
the clutch began to work normally. A “best practice” would be to disassemble
the clutch pack and clean up the steel plates, but this is to be an occasional
bike for running around the block up in LA, so probably isn’t a significant
factor in the grand scheme of things.
The task was to get it up and running reliably and make sure
that nothing falls off of it during short jaunts. The steering is “twitchy”
when changing directions, as if the steering stem is a little bent. There were
some signs of at least one lay-down incident, but nothing significant was seen
as far as chassis damage. The tires are over 30 years old and the rear one is
an old Yokohama road race tire. The front is probably the original OEM 1960 rib
tire, so there is a lack of flexibility in the tire combo. The bikes ride like
buckboards anyway, with little suspension compliance on either end. A few quick
rides did nothing to endear these little Benly buzzers to me and more than in
the past. They are an iconic design, but with technology from the 1950s, it leaves
a lot to be desired.
