I’ll
be the first to admit that I HATE to clean old motor parts,
especially scraping baked-on asbestos gaskets on the old 250-305
engine series. I have spent about 10 hours of my life in those
pursuits just in the past few weeks and I am TIRED OF IT!
After
completing a CB77 engine recently, which was favored with a vapor
blasting job, I reluctantly agreed to do ONE MORE engine overhaul on
a 1964 CL72 engine. It was delivered on a homemade engine stand,
which was handy for initial tasks that included tear-down of the top
end and loosening some engine case bolts. The entire engine was
basically an abused mud-ball of clay dirt, baked and sealed into the
open aluminum pores which are so prevalent on the many sand-cast
engine pieces. This turned out to be one of the most challenging
engine rebuilds I have ever done, due to the outside grime and the
inside baked-on varnish, which only comes off with physical scraping.
It was awful….
At
least it turned over, but getting many of the screws out was a test
of patience and endurance. The engine task included a total of three
engines from which to choose the best parts for the rebuild. The
customer told me that it would need a good cylinder, due to fin
damage and probably a cylinder head, as well. Not until I got the
head off that the magnitude of a previous attempt to remove the head
made itself known.
The
owner’s “helper” attempted to remove the head without
disconnecting the camchain, apparently thinking that the engine was a
push-rod twin, perhaps. When the engine was viewed from the right
rear, it was obvious that someone had broken several of the fins in a
misguided effort to pull the head off. When I disconnected the
camchain and removed the head, I discovered huge gouges in the edges
of the cylinder head surface and the top of the cylinder block. That
damage was fresh, but it became obvious that the top end had been
rebuilt once before, as there were .25 over-sized pistons installed.
Apparently, the correct 54mm head gasket was not readily available at
the time of the engine build, so the previous mechanic just placed a
61mm 305cc head gasket on the cylinders and put it back together
again. The baked-on varnish, a result of years of sitting on the
internal parts after being severely overheated were so gummy that the
transmission shift forks wouldn’t move because of the varnish
build-up between the two forks on the shift drum.
A
reconstruction would require a good replacement head and cylinders
from another 250cc engine. Fortunately, my friend, Ron Smith,
happened to have a spare CL72 engine that had been an inhabitant in
his garage for the better part of 10 years. We arranged to have me
pick it up from Ron’s Pacific Beach home and the lump was deposited
in the rear of the shop area awaiting the needs of the customer
engine.
Both
of the CL72 engines were packed with mud, hardened old grease and
varnished innards due to lack of engine changes and/or engine
overheating of the oil back in its history. The customer engine’s
internals appeared to be fairly clean and unworn as far as the cams
and rocker arms were concerned. Once the head was disassembled, the cam sprocket showed signs of loosening rivets, however, so that would
either have to be welded or replaced with a known good part.
Ron’s
engine was pretty much fried inside, with well-worn camshaft lobes,
rockers and a lot of varnish inside. Apart from one cracked fin on
the cylinder head, the head and cylinder block were sound, but filthy
full of dirt and grease. Wouldn’t you know that the “last one”
would be the worst one to clean.
The
customer engine also had a chunk missing out of the bottom case, back
below where the countershaft sprocket is located. I still had the
remains of a 1962 CB77 bitsa engine, which had a good bottom case, so
that engine was cracked open to donate a few parts, including the bottom engine case half. Some ill-advised mechanic had put the engine
together with orange RTV silicon sealer, which adhered to everything,
requiring patient residue removal efforts.
The
customer engine showed signs of some bottom-end work, judging from
the condition and type of fasteners used. Careful inspection showed
that someone had swapped in an earlier model transmission gear, which
used straight-cut gear dogs instead of the later type, that used
back-cut, angled gear dogs. The whole low gear bushing had the
separating ring worn off and the kickstarter pawl was severely worn
down, where it contacts the inside of low gear.
The
gear dogs were worn on the drive side due to a lack of proper gear
dog overlap which caused the transmission to jump out of 2nd
gear. Signs of its struggle were also seen on the high point of the
shift drum where it engages the fork that drives 2nd gear.
Offset gear cotters were installed, along with new 14mm shaft
bushings on both ends of the layshaft. One end bushing was severely
worn where the kickstarter pawl was digging into the bushing for many
miles. The other end bushing which helps to contain the rollers had a
crack in the edge. That was a very unusual part to suffer damage from
my experience.
Fortunately,
I have a storage bin full of used transmission parts, so sifting
through the pile turned up just what I needed to put a good
transmission back together again. The last little trick was to X the
gears, which closes up the gear gap jump from 1st to 2nd
gear. The 250 engines respond to this modification well, as they
lack the grunt and power of the 305 models.
The
customer engine came without anything installed in the kickstarter
cover, so I had to dig out a kickstarter arm and pin from my stash, a
knuckle, clutch lifter/adjuster and return spring setup from Ron’s
engine. The remaining parts came from eBay which came to about $35
for just a handful of clips, springs and a ball bearing.
The
engine casings and top-end parts were repeatedly cleaned in various
solutions, including a pass with some oven cleaner, but much of the
embedded dirt needed direct removal using a combination of rifle
brushes, rotary brushes, stainless steel wire brushes and small
pointed metal tools to get down into the nooks and crannies of these
complex engine castings. I generally do not paint these engines,
apart from the clutch covers and kickstarter covers, but I am
probably going to make an exception to my usual practices, in order
to brighten up this grubby little motor.
Unfortunately, both of my
“cleaning” resources were unavailable, so I wound up spending
over an hour on each one, just to get them close to presentable. I
had to clean two different clutch covers before I was able to use one
with confidence, but that one needed some JB-Weld repairs for a small
dent just below the oil filter cover area. Even the outer filter
cover got a patch to cover some road damage. Every one of the filter
covers I had in stock was damaged almost exactly the same way and
place. The right side dyno covers are also NLA these days, but the solution was a $95 billet cover made on a CNC machine.
The
cylinder head from Ron’s spare engine received all new valves,
once the seats were cleaned and cut fresh to make a good valve seal.
I was surprised to discover one VERY loose fitting intake valve in
the head due to a worn valve guide. I have had valve guides floating
around in my spares for years, as they seldom go bad, but I really
needed one this time! Once I coaxed the new guide in, I had to clean
it up with a valve stem reamer, then re-cut the seats again to match
up with the new valves.
The
customer cams and rockers were reused and the best of a couple of
sets of valve springs put back into the engine. I have found that you
have to check the valve springs carefully, as one had the end broken
off. A near-new cam sprocket was discovered in the parts bins, which
had matching spline patterns which took care of the problem of the
loose rivets and floppy return springs.
All
new chains will be installed, including primary chain, oil filter
chain and camchain. I get the primary chains and oil filter chains
from a vendor in the UK, which is great because the OEM parts are NLA
and extremely expensive if you do happen upon any of them now. I
replaced the camchain guide roller with one from CMSNL, which
reproduced them recently.
The
most expensive part of the engine build would have been a $200 NOS camchain
tensioner, which seems to be one of the last remaining ones on the
planet. With some digging, I was able to purchase a usable camchain tensioner for $15 on eBay, so the new one will be resold or swapped for something else, perhaps. I had a NOS D.I.D. endless camchain in stock, so decided to
assemble the engine with that.
Ron’s
cylinder block was still on STD bore, but there was some rust in the
cylinders, which required a first overbore to match some pistons that
I had left in stock. Stock CB72 pistons, used in the CL72 engines
have a pretty high dome anyway, even in the lower 8.5:1 compression
versions. My spares are the 9.5:1 versions, which will give it a
little extra kick.
It
seems like my self-inflicted punishment for not stopping the rebuild
process, after the last CB77 completion, is being tethered to a
solvent bucket and scrub-brushes to clean the grime from all these
parts, one piece at a time by hand, which is a most unpleasant task
at my age. After this one is complete, I declare “Enough!”
Bill
“MrHonda” Silver 8/2019
DONE!
