Resurrection Road: 1973 Honda CL350 Scrambler
Flushing the engine with kerosene to remove leftover metal debris.
Maybe few people know that in 1966, the instrumental group The Sandals created The Endless Summer surf movie theme song and threw it into an album stuffed with more surf songs as well as several cool bike instrumentals entitled, TR-6, Out Front, Good Greeves, and best of all, Scrambler.
And so it was, while putting the finishing touches on the 1973 Honda CL350 Scrambler rebuild seen here, the album would spring into mind. As well it might have, because while living in New York City in 1981, I found the LP record in a thrift shop and bought it for something like $1.50 — a heavy hit at the time of 25-cent albums. I still have it somewhere, and it’s a perfect match for this Honda, scratched and weathered as it is.
Ah yes, scratched and weathered records — and scramblers. If you read the July-August 2020 issue of Motorcycle Classics, you might have seen an article entitled Big Bang Theory, in which this author adopted a CL350 with a seriously hurt engine for the mechanical challenge it presented, but also as a way to encourage readers to adopt and nurse back to health broken bikes. Doing so will “make us feel good,” I suggested. The process would create “rolling art,” I promised. It would build friendship and community. And it might even, eventually, turn a buck.
When we left off the previous article, friends Amanda and Napper and son Derek had helped pinpoint the engine troubles as a complete lack of compression in the right-hand cylinder. With one rocker arm loose, I hoped to find only a bent valve, or at worst a broken one. And so, I set out to find out, and to make it right.
Tearing into it
The first step was removing everything attached to the engine — or more completely everything attached to everything attached to the engine — including side covers, air cleaners and housings, carburetors, fuel lines, fuel tank and seat, exhaust system, footpeg assembly, and all wiring running from the under-seat area along the frame to the engine. That was a pretty enjoyable and straightforward hour, and I made sure to stash take-off parts and fasteners in separate boxes and Ziploc bags, labeled with a marker, to simplify and quicken reassembly. Parts lost in the garage is a bad thing!
Removing a Honda 350 twin cylinder head requires first removing the engine from the frame. Which is not nearly so much fun as, say, removing a Yamaha Enduro or Hodaka engine, in that the Honda mill is a big, heavy lump that surely was installed in the frame using witchcraft and levitation during the Nixon era. It’s a peculiar dance — the motor has to rock backwards and then swing right, navigating through the frame opening like Robert Ballard guiding an ROV into the Titanic on a video screen. You don’t want to get it stuck, nor scratch the frame nor engine cases. But like grizzly claw marks on a pine, the Honda front downtube scratches bore evidence that this motor had been out before. But why, and when? I’d never know.
Who knows how Honda put the motors in so successfully, but watching YouTube videos showed how privateers remove them now. One method is to drop the bike on its right side, remove the last engine bolt or two, and then wiggle it until it falls out of the frame. That seemed very un-Soichiro Honda like, so I rigged up a makeshift lift using two aluminum ladders, an aluminum loading ramp, some tie-downs and a ratchet hoist. And I have to say, it worked great in taking the stress off the engine bolts, allowing their easy removal, and then finessing the engine — now safely hanging from the steel cable and tie-downs — out of the frame. A few steps later, the engine was on a car engine dolly repurposed to securely hold the Honda unit. I moved the rolling chassis to a corner of the garage for later cleaning. Cost so far: Zero. Satisfaction: 100.
To easily facilitate the removal of the engine, a makeshift lift was rigged up using two ladders, a ramp, tie-downs and a ratchet hoist.
Truth be told, removing the cylinder head was the one of the most fun moments of this entire CL rescue. And it was a quick process: remove eight 8mm acorn nuts, and the cylinder head cover and breather plate came off, revealing the camshaft and rocker arms.. From here, four 6mm bolts released the cam-chain tensioner and eight 6mm screws allowed removing the two cam holders (one on each side), and then the rocker shafts and rockers, and two 6mm bolts set the camshaft free. Which held puzzle number two: figuring out how to slide the camshaft out of the head. But gently turning the camshaft (and cam chain and crankshaft) finally allowed it to slide out. More concern here, as the left-hand lobes looked good and the right-hand lobes looked abused. All the parts were individually bagged and labeled to avoid unnecessary parts mix-ups and drama later in the project.
The grand finale at a fine meal of course is flaming crème brûlée. Brought to your table with great fanfare and perhaps the entire staff singing a cringeworthy Happy Birthday to Great Auntie Edna. There was no crème brûlée here, but it was plenty exciting to wiggle and lift the head off the wounded CL engine. Would I find the bent valve I was hoping to see, or worse? That’s the thing about moto-archeology; you never know for sure.
The results didn’t disappoint, at least from a drama standpoint. Inside the right cylinder, where a normally pleasant looking piston crown would live, was a piston more savagely destroyed than anything I’d seen in decades. Words nearly fail to explain it, except to say that nearly the entire piston crown was gone — in other words, what was once a precise piston crown was now a hole — and stuffed inside the hole were the broken intake and exhaust valve heads, the forensic proof points of a horrendous mechanical failure. And this was no “I swear, she was just idling, dude!” failure, nor a “loping along the backroads at 45mph” failure. The violence and destruction seen inside this cylinder could only have come from a full-throttle, high-rpm blowup at the hands of a lunatic throttleman named Captain Destroyer.
Then I turned the cylinder head over. Inside the intake port, scattered like diamonds through the rubber carburetor mounting spigot, was a gleaming trail of aluminum bits, looking like the tail of the Kohoutek comet in a wintery sky. But there was much more. Turning the head over to view the combustion chamber took my breath away. Scarcely recognizable as a cylinder head, it contained horrific evidence of the tangled warfare between piston crown and valves, with gouges, implanted aluminum and steel, and destroyed valve seats and guides remaining, unfortunately like fallen soldiers in battle. It was sad. It was also toast. As Taylor Swift sang, “’Cause I knew you were trouble when you walked in.”
Strewn aluminum bits are evident in the right intake port (left). The battered cylinder head had definitely lost the war (right).
Supporting the cam-chain on a makeshift sling allowed turning the crankshaft by grasping and rotating the alternator rotor. (I’d removed both the alternator and clutch covers.) And surprisingly, the crank and gearbox all turned smoothly and quietly, as if nothing had ever happened down below decks, far beneath the fray of reciprocating parts and fiery explosions. Hell’s fury above, peace, love and 10w-30 in the depths below.
Wait, it gets worse!
From here, pulling off the cylinder block off was a cinch, and the gudgeon pins — thanks to Honda’s quality materials and manufacturing — somehow slid easily from the pistons, after removal of their little retaining clips. The destroyed piston with its embedded valves went into a box for a later surprise gift for previous owner Napper, and I conducted a cursory cleanup of the engine’s lower end cases. In doing so, I noticed something really disturbing: The right-hand connecting rod was bent right and down, like a Ronda Rousey opponent getting the armbar treatment in the octagon.
The piston crown is almost entirely a hole, filled with the valve heads (left). Note the bent connecting rod (right).
Crud. Like really, C-R-U-D! After sending pictures around to friends, it occurred to me: Connecting rods are forged from high-strength steel, right? The process involves heating the steel blanks, hammering them into shape in a die, and then quenching them with oil. (At least, that’s what I remember from high-school shop class, where we made chisels, hammers and the like that way.) Write letters to editor Hall all you want, but facing an entire engine teardown, days or weeks of delays to get the crankshaft rebuilt or replaced — or else straightening the rod, the choice was easy. Straighten the rod. That’s what Burt Munro could have done, so that is what I did.
When in doubt, nuke it
So this happened. I got out the oxyacetylene welding set I’d bought used for $150 several years ago, found the biggest tip available, and rotated the crankshaft until the rod was pointing sky-high. Then I installed the gudgeon pin, effectively lengthened by a steel drift, and secured the entire little assembly in place with some sockets to keep the rod from flopping front- or backwards. Burn baby, burn! Heating the rod until it glowed modestly, and then leveraging the drift, slowly straightened the rod, with no harm done to the nearby aluminum crankcase. Quenching the rod in oil, I hoped, would leave it sufficiently hardened, like my high-school chisel (which still works great!).
This “eyeball” method got the rod close to straight initially, but victory (relatively speaking) arrived courtesy of a machinist’s ruler, whose fine graduations allowed more precisely measuring the gudgeon pin’s position (or attitude?) compared to the left-hand crankpin. Another round with the torch, this time aimed by collegiate Derek Stein, and another oil bath, produced a rod that looked pretty close to new. Time and miles will be the jury on this. “Heating up the connecting rod with the torch was actually very fun,” said the student and willing helper. “It ended up being extremely easy, and enjoyable to do.”
Scavenging for parts
While the crankshaft was getting the backyard-mechanic treatment, I shopped eBay for pistons, a cylinder block and head, and a gasket kit. They were all easy to find, thanks to the hundreds of thousands of 350 twins Honda produced. An aftermarket gasket kit soon arrived, followed by a complete cylinder/piston/gudgeon pin combination and a complete cylinder head with valves, valve springs and keepers. Steam was building on the CL redemption train. There were still worries though, above and beyond feeling guilty over straightening the rod rather than replacing the crankshaft. For instance, the replacement parts I ordered were all from a 1972 Honda CB350, which I hoped — but wasn’t sure — would fit the CL bottom end, camshaft, rockers, rocker shafts, camshaft case and holders. Only trying would tell.
Cleanup on Aisle 2
Before starting the assembly process, another challenge presented itself — one that I honestly hadn’t thought that much about as the project got rolling: Like nuclear fallout from the Yucca Flat A-Bomb tests, the remnants of the torpedoed right piston and valves had clearly gotten into the bottom end. I thought long and hard about this (well, okay, I thought for several minutes, with reasonable focus) — what to do about the debris that might still be in the engine. Operative word might, because removing and examining the oil pickup screen and centrifugal filter inside the engine cases revealed little that was concerning.
“You’ve got to know when to hold ’em, know when to fold ’em,” sang Kenny Rogers in The Gambler. Isn’t that just life? So, in the spirit of straightening the rod with a torch, and buying random CB350 used parts on eBay, for Operation CL350 Rescue, I decided to go full Joe Dirt and flush the cases with kerosene. Like a clergyman exorcising demons from parishioners at the pulpit, your author, yes, in full admission of guilt here, poured a half-gallon of kerosene through the cases, adding it at the cylinder opening and letting it drain out the drain plug and side of the cases. After that he followed up with a half quart of motor oil to ensure that the crankshaft bearings, in particular, stayed coated. (You might want to save writing to editor Hall yet, because it gets better — or worse — later on.) When nothing evil came out in this flush, I became encouraged to put the engine back together.
Derek Stein uses a welding torch to heat the bent connecting rod (left), followed by quenching it in oil.
The replacement pistons went on easily, and after honing the replacement cylinder block, it did too. One of the cam tensioner rollers was chunking, and I found an NOS item on eBay that arrived in a few days and renewed the cam-chain adjuster to near-new status. All parts were pre-lubed before assembly.
Oh, I almost forgot: The eBay cylinder head looked okay, but with no indication how many miles it had gone, I thought it best to check the valve seats and guides. But how? I didn’t own a Honda 350 valve spring compressor, only one from a Ducati 250 with hairpin valve springs. Fortunately, a piece of square section steel tubing, cut, filed and sporting a 1/2-inch hole to allow removing the valve-stem keepers adapted the ancient Ducati tool (dating from perhaps 1965) to 2020 usability. “Go Burt!” Note: Protective eyewear on. With the cylinder head disassembled, I scraped carbon off the valves and head, and examined the seats and valves, which were a bit blemished. The last time I owned a tube of valve-grinding compound was before the Space Shuttle made its debut flight, and at 10 p.m. on a weeknight, I wasn’t likely to find any at the supermarket. So I made some. (Okay, now start writing Mr. Hall.)
The key to figuring life out, I feel, is to ask questions and determine real answers, and not pap. Valve-grinding compound is a paste with embedded abrasives. Think of a tube of toothpaste with more grit. And that’s what I made up, starting with a pickle jar top as a palette, I added Lucas oil, toothpaste, tile grout, Pro Honda Rust Penetrant and Griot’s paint compound to achieve a paste that stuck on the valve heads. Then, using a shop towel for grip, I was able to install each valve and turn it back and forth by hand, just like a real mechanic with a real valve-lapping kit. And guess what? This fly-by-night method lightly lapped the valves to create nice looking valve faces and seats.
I admit to all of this for a reason: This CL350 Rescue project is intended to empower MC readers to push past their known limitations, to experiment, and to learn to solve problems and get around roadblocks by trial and error. In other words, it’s giving you support and permission to try. Could I have afforded a new crankshaft? Yes. To split the cases to and have them ultrasonically cleaned? Surely. And to wait one lousy day to get some real valve-lapping compound and a valve-holding tool? Of course. But I didn’t want to. In my own stuck-on-a-desert-island self-sufficiency mindset, I wanted to do it myself, solve it myself — with friends’ help — and succeed. And in doing so, encourage you to try too.
Getting it together
Going back together, the barrels are slipped over the used piston and ring assemblies.
After everything was cleaned up with kerosene, Pro Honda contact cleaner and carburetor cleaner, and coated with oil, the top end went back together. The prior labeling of Ziploc bags with parts made reassembly amazingly easy, although I’ll admit to watching a few more YouTube videos concerning how to set the valve lash and adjust the cam chain, and printed out several Honda parts book images found on cmsnl.com. But Lordy, that’s the great thing about Hondas — they just about won’t go together any way but one. Torqueing the cylinder head nuts, and adjusting the cam-chain tension, valves and ignition timing was reasonably easy work. “Although this was not my first time using a toque wrench, I felt much more confident knowing the wrench was set to the correct specification,” said torque-meister Derek.
Incredibly off-putting as it was, I decided to try the YouTube trick of laying the engine on its right side, and then leaning the bike on top of it, for the install. Messy! I know the frame picked up a few more scratches, but it worked, and all engine-mounting bolts went in easily and cinched up to spec just fine.
Tip: Get one or two friends to help you install an engine, and protect the frame with tape, foam, towels or by some other means.
A few final fixes
Brazing patches onto a couple of rusty spots on the exhaust.
The rest of the reassembly was straightforward, but required brazing patches onto two different muffler spots that were rusting through — the exhaust system was clearly on its last lap around the sun. Then on went the engine side cases and carburetors, the wiring was connected, the battery recharged and installed, and the crankcase again flushed — twice with kerosene — five quarts at a time in fact, right up to the top of the filler hole. With each drain brought more glitter flecks, letting me know two things: I was getting rid of bad particles, and there were still more particles hiding. Then a fill with ATF (because there was plenty around), another drain, and then a fill with real Pro Honda 10w-30 convinced me that anything really big and evil was already exorcised.
One last test
Lewis Boslego retests compression after the rebuild.
And one afternoon after work, as suddenly as I’d said “Yes” to buying this bedraggled beast, I was ready to refill the pretty red-and-white tank, turn the key, and start it. But not before I took one more step: removing the spark plugs, running the starter for 10 cycles of 5-6 seconds each to pump fresh oil through all galleys, and then asking college economics major Lewis Boslego to re-test the compression using the same gauge that Amanda had used to start this adventure six weeks earlier. And hallelujah, it showed exactly 150psi on each cylinder — a huge, glorious, validating success. “Using the compression gauge seemed like it would be straightforward when I was learning how to use it, but it proved to be a bit more challenging than I had anticipated,” he said. “The gauge required a good bit of pressure from me to get an accurate readout, which took a couple tries to get right. After accomplishing this task, I feel more confident in my ability to take on future jobs like this one, as I had never used an analog gauge other than in checking tire pressures.” And ironically, Lewis’ own KTM 390 Duke had just grenaded on the freeway — also due to a broken valve.
Proof of pudding
And then it was time to start the Honda for the first time since its Very Bad Day earlier this year. Petcock on, chokes closed, throttle open 1/8, hit the button. Incredibly, the formerly blown-to-smithereens 1973 Honda CL350 started within seconds, and with a few carburetor adjustments warmed up and settled into a nice idle. Synchronizing the carb cables and idle screws made it run even better, and after five minutes of this — all performed on the centerstand — I drained the sump and refilled it with fresh Pro Honda 10w-30 oil (the engine holds just two quarts; cheap insurance).
And then it was ride time. It had been years — decades actually — since I’d been on a Honda 350. Or had I only imagined ever riding one? Regardless, I’d never ridden a CL350, which I always thought was one of the prettiest street scramblers extant. The motor is a gem — nice gentle vibration signature, plenty of torque right off idle and an energetic kick at higher revs. The 5-speed gearbox is light-shifting and the ratios are nicely spaced, although first is surprisingly low — perhaps in a nod to the bike’s scrambler pretensions.
But alas, an actual “scrambler” it’s not, I learned while plying a local trail. While the steering geometry is fair enough, the bike is extremely heavy for a dirt bike at 346 pounds dry (versus 213 pounds for a 1973 Honda Elsinore 250), and with streetbike suspension and only seven inches of ground clearance, no skid plate, and footpegs and a rear brake lever just begging to snag a stump or boulder, you’ll be wishing for that Yamaha Enduro or Hodaka if you’ve got far to go in real offroad conditions like sand, rocks and ravines.
So, instead of doing the Alligator Enduro on a CL350, look for two-lane roads and hard-packed dirt instead, such as at leisurely trip over California’s Senora Pass to the Bodie ghost town, perhaps a fall ride through Michigan’s Tunnel of Trees, or maybe on a warm Southern day, Brooks and Dunn’s very Red Dirt Road. Thanks to the determination to try, the resolve to do well, some creativity, a passel of good friends, and about $350 worth of parts and oil, this CL350 got saved from the wreckers — and is now ready for the road to redemption.
And we’ll all take turns riding it. MC
Back on the road and ready for more high jinks, donuts, wheelies and other moto-related fun.
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