Four Tiny Cylinders of Fury - 73 Honda CB350F Build

So last Friday I hit up a vintage motorcycle swap meet. Those who know me well know my track record of coming home from such events without some derelict POS in tow is, to say the least, rather poor. Much to the chagrin of SWMBO, this time not one but two crusty old motorcycles ended up in the bed of my truck.

Behold, 8 cylinders and 694cc of pure Japanese fury, for the low low price of $450 between the both of them!

I spied the red bike first, looking relatively shiny and complete and advertised with a title. The CB350F has always intrigued me, being the smallest production 4 cylinder ever sold at the time and significantly less common than the contemporaneous CB350K twin cylinder (although still not all that rare,) and so this one immediately drew me in. Closer inspection though revealed that the motor was locked up solid, some key pieces were missing, and the frame had been hacked up a bit for a café racer build or something, so after giving it the hard look over for a few minutes I kept walking.

A short while later I came upon the “green” (well ok, “rust” might be more appropriate) bike sitting in the back of a truck. “That a 550?” I inquired. “350”. “Oh…” The gears immediately began to turn. The engine kicked over freely, and although in generally worse shape it was overall pretty complete. I rushed back over to the red bike to make sure it was still available (it was,) made the deal on that, then returned to the “green” bike and snagged that one as well. I figure I can pick and choose the best from each and end up with one decent bike between the two, and probably some spares to sell and help offset the cost.

 My initial thought was to do a straight up back to stock restoration, but the hackery on the titled frame poses some challenges in that regard as far as mounting a stock seat and rear fender. The “green” bike did come with a PA salvage certificate as well, but I  have my doubts as to whether it’s easily transferable (not super clear on the rules here, but it looks to be missing a portion and isn’t notarized or anything) and frankly I don’t want to deal with a paperwork mess when I have a more straightforward solution at hand.

Red bike frame hackery:

So I think the general direction I have in mind is something of a mild “brat style” build. I had a couple of early 70s Honda projects back in college, an MT125 and a CL175, and I want to build this one like I didn’t have the money or skills to do back then. Goal is a fun and functional local back road bomber with some style!

They sound great with a nice 4 Into 1 exhaust! Not very fast but fun.

Just graft frame section from green to the red....

I've got two and a half Honda's of similar vintage sitting in my basement (a CL175 and A CB360) I expect these take a bunch of the same parts. Good luck with them!

You had me at brat style. 

First order of business, before laying a wrench to anything, was getting the title transferred on the red bike. Especially with the Vermont loop hole out the window now, I wanted to be sure there would be no snags there - lesson learned from my old CL175 project. So Monday I loaded back up and went to the notary to deal with that, then it was game on for the teardown. 

A few leisurely hours of wrenching, bagging, tagging, documenting and labeling everything along the way...

...and we wind up with this. There really isn't much to these old things.

If you don't have a cheap label maker in your garage, I can't recommend one enough btw.

That's as far as I plan to go with the tear down right now. I have a seat, rear fender, and hoop for the rear of the frame on order, which are going to need to have mounting provisions fabricated, and I want to mock all that up with the rear wheel, bars, and tank in place. Once that's done, and any welding on the frame is finished, I'll start stripping and painting, and basically just build from the frame out until it's a roller again before moving on to the engine. 

Speaking of which, one thing I probably should have thought through a little better was trying to break the locked up motor loose before I removed it from the frame. Should have at least tried to throw a wrench on the crank nut, little harder to hold it still now that it's just sitting on a furniture dolly. I did shoot some PB Blaster in the cylinders at least. 

As for the other engine, I did a compression test and it's at 40-50 psi on all cylinders, so looks like it's going to need a dingle ball hone job and re-ring at the very least. I'll tear down the top end and take some measurements when we get to that point and go from there. It also has some sort of red overspray all over it, not that that's a big deal since I'll be refinishing it anyway, just a funny coincidence because my Buell also has bits of red overspray in random nooks and crannies. Would love to know what the story was on that.

TurboFource said:

They sound great with a nice 4 Into 1 exhaust! Not very fast but fun.

Just graft frame section from green to the red....

I thought about that, but going the custom route seemed like more fun.

I've spent way too much time listening to these little things sing on Youtube already, a 4 into 1 is definitely in the plans!

Today's project was polishing up one of the fork lowers. Hit it with some glass bead, then 400-800-1000 grit, and finally some Mother's Mag and Aluminum polish. Not 100% perfect, but a hell of a lot better than it started. 

Before:

After:

I love this! These are fantastic little bikes. I had a CB400F, which, as I'm sure that you already know, was the evolution of the 350.

Be very careful with the cam chain tension adjuster, as they are very fragile and easy to strip. 
 

These are also bikes that really benefit from a steering stabilizer. 
 

Show us a picture of that glorious redline on the tach!

In reply to Woody (Forum Supportum) :

Well I would, but unfortunately I have precisely zero tachs and only one speedo between the two of them . Fortunately, I found one in my box of random motorcycle parts that IIRC originally came from a CB350 twin. I THINK pretty much all of these old Hondas use the same ratio and I found a place that sells replacement gauge faces with the glorious 10k redline, so I think I can make it work. 

Good tips on the cam chain tensioner and steering stabilizer.

Love the 400s, btw, the stock headers on those were just gorgeous. 

Some meager progress has been made. Now that I'm gainfully employed again, my free time for dicking around with motorcycles is unfortunately lacking.

My seat, rear fender, and frame hoop came in several weeks ago. Super impressed with the quality of the seat for the price, and shout out to 4into1.com for selling what seems to be the same part as a number of other retailers at 75% of the cost of everyone else. Going to be spending a lot of money there on this project. 

In the meantime, I started stripping the frame with a wire wheel, since it's much too large to fit in my blast cabinet. Got about as far as I could with that before needing to disassemble the swing arm and center stand, which I wanted to leave in place until mounting of the seat and fender is finalized. 
 

Had to rethink the plan for seat mounting and rear frame section, as the "cafe hoop" doesn't allow the fender to be mounted high enough for sufficient clearance to the tire. Wound up just welding in some straight pieces of 1" tube to extend the hacked off frame back to the mounting brackets that came with the seat, welded some tabs on for those that will get riv nuts, and another piece of bent flat stock between the tubes that provides support under some rubber pads on the underside of the seat and will also serve as one of the fender mounts. The front of the seat has an L shaped plastic tab that hooks under a piece of flat stock welded in just aft of the gas tank. Seems sturdy and should be quick and easy to remove.

Still have some cleanup/finishing on the welds to do but the overall profile with the seat mounted is pretty much what I was shooting for.

I'm going to order a tail light before I finalize mounting of the rear fender, just to be sure that all fits together the way I envision. Think im also going to mount the rear turn signals in the ends of the frame tubes, should be an unobtrusive spot and gives a more finished look to the tube ends. Have a few ideas how that might be accomplished.

Liking your build. 

For tiny and screaming the RC149 - 125, 5 cylinders, 30 hp @ 18k rpm

In for the brat as well. It's already looking awesome 

Furious_E (Forum Supporter) said:

First order of business, before laying a wrench to anything, was getting the title transferred on the red bike. Especially with the Vermont loop hole out the window now, I wanted to be sure there would be no snags there - lesson learned from my old CL175 project. So Monday I loaded back up and went to the notary to deal with that, then it was game on for the teardown. 

A few leisurely hours of wrenching, bagging, tagging, documenting and labeling everything along the way...

...and we wind up with this. There really isn't much to these old things.

If you don't have a cheap label maker in your garage, I can't recommend one enough btw.

That's as far as I plan to go with the tear down right now. I have a seat, rear fender, and hoop for the rear of the frame on order, which are going to need to have mounting provisions fabricated, and I want to mock all that up with the rear wheel, bars, and tank in place. Once that's done, and any welding on the frame is finished, I'll start stripping and painting, and basically just build from the frame out until it's a roller again before moving on to the engine. 

Speaking of which, one thing I probably should have thought through a little better was trying to break the locked up motor loose before I removed it from the frame. Should have at least tried to throw a wrench on the crank nut, little harder to hold it still now that it's just sitting on a furniture dolly. I did shoot some PB Blaster in the cylinders at least. 

As for the other engine, I did a compression test and it's at 40-50 psi on all cylinders, so looks like it's going to need a dingle ball hone job and re-ring at the very least. I'll tear down the top end and take some measurements when we get to that point and go from there. It also has some sort of red overspray all over it, not that that's a big deal since I'll be refinishing it anyway, just a funny coincidence because my Buell also has bits of red overspray in random nooks and crannies. Would love to know what the story was on that.

Nice car!  

This is making me miss my CB650. I've spent a lot of money at 4into1.com. 

I keep envisioning a 700cc V8....

Back in the day, Bassani had the best performing pipes for the four-cylinder bikes and it wasn't even close. Kerker had the name & market share (and aesthetics) but Bassanis were the pipe to have. Last I checked, they will still build one up special order, but it's been awhile....still worth it though.... :)

The last thing I need is to get involved with Honda CBs... again.

In reply to wvumtnbkr :

Look familiar? 

It needs a bit of love as well at some point this winter, just some nagging stuff like the driver's side window that's stuck down and a minor oil leak at the oil cooler adapter. Took a bit of a break from auto x this year, so the RX7 has been on the back burner for a while, but planning to jump back in again next spring.