With the last Tracy-bodied CB400F acquisition pretty much
done (as far as I am going to take it), another low-miles, all stock, red, 1975
CB400F turned up on the local Craigslist posts, although the bike was actually
in Temecula, CA. The photos looked promising and seller claimed to have had to
buy 3 different exhaust systems before he could cobble together an all-OEM
unit. Miles were in the 10k range, so it should be in decent shape overall, at
least mechanically.
A friend, Michael, who lives up in OC, had contacted me
looking for a nice vintage bike for his buddy to ride. He initially attached a
1969 CB450K2 listing from Craigslist, but it was up in Central CA. The bike
looked decent enough but parts for the 450s are getting scarce on the ground
and they aren’t my favorite model anyway. After imparting those thoughts,
Michael sent back a link to the red 1975 CB400, which had been posted up in OC,
after the one in San Diego had expired. Asking price was $4600, including a
bunch of spares, including a nice fuel tank. I opined that if the price was
closer to $4k, it would be a good deal, all things considered. Next thing I know the deal was done,
apparently at $4k and the bike was brought down to its new home in Mission Viejo.
A day or so later, after Michael had taken it out for a test run, he sent back
a message stating:
1. Most important, it has an oil leak, that
looks like from the head gasket just under were the pipe connects. Is this
simple fix… do we just need to torque the head bolts?
2. One of the 4 float bowl gas needle valves
leaks
3. The clutch slips a little when pulling
high RPMs.
Unfortunately, for many of the inline Fours from the 1970s,
the head gaskets tend to leak out around the o-ring seal, where the oil is
channeled up from the pump through the cylinders. This is common for
350-400-500-550 and 650 Fours and not unheard of on the SOHC 750s, starting
back in 1969. For a mechanic, the good news is that most all of the “small”
Fours have enough room around the frame to remove the cylinder head with the
engine still in the chassis.
A good webpage overview covering a restoration procedure is http://www.dotheton.com/forum/index.php?topic=59484.0
In this case, once the cylinder head is removed, then the
“fun” begins…
The valves must be removed and new valve stem seals
installed. The head needs to be checked for any high spots or warpage. All the
valves and combustion chambers need to be de-carboned and cleaned. Camchain
guides and end bumpers should be checked and replaced if needed. All the
cylinder head hardware and fasteners must be cleaned and inspected before
reuse. Securing the cylinders to the crankcase before any engine rotation has
begun can prevent the necessity of pulling the cylinders and scraping off a LOT
of factory gasket material from the base of the cylinders and the upper
crankcase. Once the cylinders break the gasket bond between the cylinder base
and crankcase, you are in for another couple of hours of labor.
After shedding the exhaust system, before mounting the bike
on my bike work rack, the rest of the task is just a slow and easy disassembly
of the top end components. ONE of the 8mm cylinder head nuts, which are one of
two that are exposed to the elements, needed a fork tube slid over the end of
my 3/8ths drive ratchet in order to break it loose. When the top cam
cover/cylinder head cover was lifted off, I could see remnants of a previous
attempt to seal up the cover to the head using some liquid gasket material,
instead of just replacing the elongated o-ring packing.
The cam and rocker arms all looked well lubricated, but the
tensioner blade on the back was getting some ridges in the face, so was
changed. The valves were taken out one
cylinder at a time, de-carboned and the stem seals changed on the inlet side.
The gasket kit came with 8 seals, so apparently these early engines only had
seals on the inlet side. Checking current parts lists show a different exhaust
valve guide part number, which can accept a stem seal, but the cylinder head
part number was a 377-000, the original part number to the bike, which takes
only 4 seals on the inlet sides.
There was a build-up of soft carbon on the back sides of the
intake valves, indicating worn stem seals. Soft carbon deposits covered the
combustion chambers and tops of the piston crowns, but the color on the exhaust
valves seemed to indicate pretty good burning even with stock jets.
The whole intake system was intact with all the proper
clamps and components in place, indicating that the carb rack might never have been
off the bike. The carbs came apart without drama and all of the o-rings that
seal the main jets and float valves showed definite signs of age. New carb kits
were ordered from my friends at 4into1.com, along with a couple of sets of over-sized
jets, fork seals, spark plug caps and other repair items needed for the bike.
The owner supplied a gasket kit, but it was one of the Athena aftermarket kits,
not a more desired OEM Honda kit. Hopefully, the head gasket will withstand the
heat and pressure of the engine for the immediate future.
The bike apparently lived much of its life in Wisconsin or
somewhere in the Mid-West and there was a general sprinkling of corrosion on the
chrome and alloy parts that was consistent with its early days outside of California.
Michael wanted the outer engine covers repainted, as they showed signs of
corrosion that had worked beneath the original coatings. After the generator
side cover was removed, I was surprised to see signs of the rotor rubbing on
the inside of the field coil and a bit on the outside too. Given the fixed
nature of these components, which never should contact each other, one must
assume that the bike was crashed down on the left side and the case deformed
enough to allow contact between the rotor and field coil. When the cover was
stripped of all the components, it was clear that the cover had been impacted
enough to deform the outer edges of the cover casting. This could be a used
cover that was installed after the original crash had occurred.
I have been raiding the leftover parts of my friend Scott,
who restored a couple of CB400Fs back about 10 years ago. Of all the odd parts
that he still had was one NOS CB350-400F rotor! I made a quick 22 mile
round-trip on my newly-acquired 2002 Honda Reflex scooter and brought back the
prize for installation. The engine was spun over to check for any deformity on
the end of the crankshaft, but the rotor runs true with no wobble or run-out. The dented area of the cover was worked a bit
with a big brass drift and checked for any uneven heights of the screw
standoffs. The field coil checked in
with 4.5 ohms and the stator windings were all connected to each other, but not
to ground, so it should all work well, once the components are all reinstalled.
I did notice a different flange nut holding the rectifier onto the frame and
closer inspection revealed that the bracket had been re-welded at some point in
time.
Checking the forks for weeping seals, it appeared that they
had been replaced at least once before and they didn’t seem to be wet when the
dust boots were pried up for inspection. What did show up were some fine wear
lines on the fork tubes, equal on both sides.
A bit of test riding will be needed to confirm any leaks, but it may not
be the fault of the seals in this case.
Michael reported an oil leak beneath the engine on the right
side, as well. Apparently the galley plug cap was leaking slightly past the
o-ring, so that will be addressed when the clutch cover, on the same side is
removed for the clutch inspection and necessary repairs. Later a second galley
plug, just behind the oil filter housing was also weeping some oil passed the
o-ring. Both were replaced with the desired results.
The clutch cover was removed and the clutch disassembled to
check for signs of slipping. I have never had a CB400F that slipped its clutch,
even during racing conditions, so wasn’t surprised to find no signs of wear or
slipping on the plate sets. The bike came with a complete set of plates and
springs, so they were installed anyway. The springs were an optional 323 code
spring from the CB500 Fours, so the clutch lever has a bit more tension when
disengaging the clutch now. The cover was cleaned and painted, along with
installation of a new kickstarter shaft seal.
A new set of exhaust flanges were available from 4into1.com
so for a reasonable price, the exhaust system got a bit of extra bling. The
exhaust collars had been painted over the old rust, so were stripped again for
another coat of high-temperature engine silver.
The carbs were setup with #78 main jets, instead of the
stock #75 sized jets, in order to compensate for the alcohol-based fuels we
have to use in SoCal. The bike pulled strongly through the gears, once the
engine was running again, but the plugs came out on the white side, so a bump
up in the jetting to #80s might be in order. Speaking of spark plugs… the
original plug caps all showed between 9 and 10k ohms, which is out of spec for
resistor caps, which are set at 5k ohms of resistance.
The last stop in this journey was to re-seal the spare fuel
tank that came with the bike deal. The tank was straight and the paint in
decent condition, but a thin coating of surface rust was seen and felt in the
roof of the fuel tank. A flush with phosphoric acid, followed by a rinse and
dry preceded the installation of the 2-part Caswell epoxy sealer. A new OEM
fuel filter kit was installed after the petcock was disassembled and cleaned.
Riding the bike is a bit of a time travel, as it is about as
stock a bike as I have ridden for quite awhile. I bought one new in 1975 and
have the muscle memory of that bike still ingrained in my psyche. There is
still a bit of a lean stumble at part-throttle, consistent with just about
every 350-400 Four that I have ridden, but once it clears that little glitch
the engine winds out cleanly and with a pleasant roar from the intake and
exhaust muffler. The single piston brake requires a strong pull to haul the
bike down from speed, with an assist from the rear drum stopper. They are
pleasant bikes with classic café styling that has aged well over the past 44
years.
Wrapping up this revival project would seem to end the 2x2 of
the same bike combos that keep coming my way. Next up, not one but at least 2
CB72-77 engines for rebuilding…. One is very “stuck.”
Bill “MrHonda” Silver
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