Project 1970 Honda CB350 — Part IV

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by Richard Backus
Rust, anyone? The original seat pan on our CB350.

The is the fourth in a series on our 1970 Honda CB350 build project. Read Part I, Part II and Part III for earlier stages of the project, and Part V, Part VI, Part VII and Part VIII for the later installments. You can also watch video of our Honda running for the first time.

Last issue, we told you about a broken mounting lug on the lower left of our 1970 Honda CB350’s engine. That broken lug was something of a mystery, as there wasn’t any indication how it might have happened. Thanks to a reader with experience in the matter, we’re pretty sure we now know what caused the break.

Former Honda CB350 owner Bob Sheehan wrote in to tell of us of his identical experience with his 1972 CB350, on which he’d mounted a set of crash bars. Bob told us that the left side crash bar mounted to the frame up top and the lower left engine mounting lug at the bottom. Following a left side crash, he discovered his engine mount was broken, even though at first it didn’t appear his bike had suffered any damage. “It looked exactly like the photograph of yours,” Bob wrote.

Looking through the pile of parts that came with our Honda (which, you might recall, was partially disassembled when we bought it), we found a set of crash bars, with evidence of road rash on the left crash bar. Mystery solved. Clearly, our Honda suffered the exact same fate as Bob’s. Who knows what kind of damage the Honda would have received in the absence of the crash bars in whatever fall it suffered, but it’s somehow ironic to think they played a role in its damage.

Moving forward

We were feeling pretty good about our progress up to last issue, but then I got laid out with a torn Achilles tendon. That slowed things down more than a little, and we’re still in a bit of a struggle to catch up thanks to the onset of winter and the craziness of the winter holidaze. It was something of a perfect storm, and all of those elements kept us out of the garage more than we’d expected, but we did make some important progress in some key areas.

A surprising issue — at least to us — was the difficulty in finding a new seat, something I touched on last issue. As the lead photo in this installment shows, our original seat was shot. We knew the cover and foam were shot, but apart from that it appeared reasonably sound on first look. Unfortunately, stripping it down revealed a mess, the seat pan terminally rusted and beyond repair. Well, beyond our capacity to repair, anyway. Someone more skilled could likely reconstruct the pan, either welding in new metal as needed or by using the pan as a form to make a replica out of fiberglass. I’ve seen plenty of people do both, but lacking those skills we were left to trolling the Internet and old bike junkyards in what was looking like a hopeless search for a reasonably priced replacement in good condition.

Hardcore CB350 fans will know that 1968-1970 CB350 seats hinge at the rear. Starting in 1971, Honda went to a more conventional side hinge. The early bikes weren’t made in near the numbers as the later 1971-1974 models, making certain parts — like seats — hard to find. We did find a close to perfect replacement, but at more than $400 it exceeded both our budget and our basic approach to this bike, which is a budget-minded classic. And given our desire to have this bike look mostly stock, we wanted to avoid going with a non-stock, aftermarket-type seat.

Fortunately for us, Honda specialist Don Stockett of Vintage Motorcycle Rescue took note of our predicament when we mentioned it in the last issue. Don contacted us about a used seat he had, and as an added bonus he also had a used headlight bucket to replace the broken one on our CB350. As it turns out, those are getting hard to find, as well. Don warned us that the used seat he had wasn’t perfect and would need work, but from my description he knew it was better than what we had. Actually, it was way better than what we had, and if we were just keeping an old rider on the road it could have been used straightaway. As Don warned us, it did have a few warts, chief among them two stress tears in the steel pan (one on either side), right in the middle, plus some minor rust along the lower edges and on the top of the pan.

To prepare it, we first stripped the pan using a soda blaster and then took it over to friend of the magazine Pat Slimmer, who quickly fixed the tears in the metal, welding them up and grinding them down smooth. With that done, we gave the pan a “final” prep before giving it a few coats of appliance-grade black epoxy paint. I say “final” because we didn’t knock ourselves out making the pan perfect. As the pictures show, the pan still shows plenty of defects from the rust that had attacked it. But that’s OK, because our goal was simply to remove any visible rust, followed by a thorough cleaning and prep so the paint would stick. With new foam and a new seat cover installed, it’ll look good as new.

Next step

We made a few other points of progress, as well. The hubs are polished — finally — and on their way to the folks at Buchanan’s Spoke & Rim, where they’ll get laced up with new chrome spokes, and we’ve made a bit more progress on cleaning the engine. Once we’d proved the engine runs, with good compression and no odd noises, we hoped we’d be able to clean it without any real tear down. Basically, we’re trying to be lazy, but we finally gave in and decided to strip it down as needed, as it’s proven surprisingly difficult to clean.

The funny thing is, it doesn’t look any worse than the engine on the 1973 Honda CB500 we café’d way back in 2009, but it sure doesn’t want to clean up as easily as that engine did. Go figure. Time will tell how far we’ll have to go pulling it apart, but just to be prepared we picked up a full gasket set from Honda engine specialist Bore Tech (, along with an oil filter and clutch hub spanner tool, which will come in handy when we install the new clutch plates we got from Barnett.

We’ve also started fitting the frame back together, so far mostly just to help us confirm what little bits we may be missing so we can get them sourced. We’ve torn down the front forks, and while we knew we’d need new fork tubes, we were happy to discover the sliders themselves are just fine. That wasn’t exactly a surprise given the bike’s apparently low miles, but it’s one of those things you just don’t know till you get there. The original drum brakes are fine, with plenty of material left on the brake shoes, so there’s nothing to do there but a thorough cleanup. New sprockets are on their way from Rebel Gears ( and we’ll need a new chain, but once the wheels come back from Buchanan’s we’ll actually get to start putting our Honda back together.

That’s going to be pretty exciting, but it underscores how much work we still have in front of us. With any luck, by next issue we’ll have something approaching a rolling chassis, with the bodywork sent off to Marbles Motors ( for prep and painting. MC

Project Honda CB350 Suppliers

Barnett Clutches & Cables: New clutch, brake, speedometer, tachometer and throttle cables, new clutch discs and springs
Bore Tech
: Full gasket set, oil filter/clutch spanner tool
Buchanan’s Spoke & Rim
: Relace wheels with new chrome spokes
Charlie’s Place
: Electronic ignition, ignition coils and mounts, voltage regulator/rectifier
Custom Coatings & Metal
: Media blasting and powder coating
Dime City Cycles
: Tapered steering head bearing kit, miscellaneous hardware
Forking by Frank
: New fork tubes
Hagon Shocks USA
: Classic I chrome shocks
Marbles Motors
: Paint prep and painting
Rebel Gears Motorcycle Sprockets USA
: Front and rear drive sprockets
Sirius Consolidated
: Master carb rebuild kit, seat foam, seat cover, seat strap and buckles
The Pit Stop: Aluminum engine welding — (785) 887-6626
Vintage Motorcycle Rescue: Used seat and headlight bucket, battery cover, magnetic switch cover

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