My 1970 K2 Restoration
In 1973, my father went out one day and returned with a small, red Honda motorcycle. It was the first Honda CT-90 I had ever seen.

A 1970 CT-90 K2, freshly liberated from the shrubs

A 1970 CT-90 K2, freshly liberated from the shrubs

This is it. The same machine, over 25 years later. This is a 1970 Honda CT-90, what's called the "K2" after Honda's peculiar way of naming the sub-versions of this bike. After years of neglect, literally sitting in some shrubs behind my parents' barn for more than 10 years, and maybe 15, I retrieved this Honda, and spent the winter of 1999-2000 finding replacement parts for it. I learned to ride on this bike, developed an affection for these things as a result of being around it, and the existence of this site can be traced directly back to this specific motorcycle.
There's a 1970 Honda CT-90 in there

This is what it looked like after all the years behind the barn, with small trees growing up through the frame and spiders and worms taking up residence in any place that offered shelter. To be sure, it also suffered at the hands of my two younger half-brothers, who, with their friends, liberated various parts from it over the years. It was a wonder anything was left. If you can't pick it out of this picture, click the image to get some help tracing the outline of it.

In a fit of wanting a CT-series a few years ago, I found this bike's later sister, a 1981 Honda CT-110. A nice bike, a good deal, but I never gave up the idea of restoring this one. It took enough abuse over the years and still performed well that it deserves to shine again. Since then I've acquired two other CT-110s, and have pretty much run out of space to put any more until I actually finish this restoration and some car projects I have.

My parents still had the twin to this, an even-sorrier 1971 CT-90. I later went up in the summer of 2000 to retrieve it, and did, but likely will not restore it, partly because finding enough parts to restore this one was a real chore and a huge expense (over $500 so far, for a bike that cost about that much in 1970) and partly because the 1971 has serious frame corrosion and would require replacement of almost every major part. If this restoration on the 1970 goes well, though, I'll consider dealing with the 1971. There are still a lot of great mechanical parts available, but the trim is extremely hard to find in good shape. Both these bikes need almost everything. For now, the 1971 is sitting next to the barn, preserved against further degeneration but otherwise not being touched.

The start - April 6, 2000
Starting teardown

This is where I started. April 6, 2000. I realized I had to tear the entire bike down to the bare frame, have it painted or powder-coated, polish and replace everything, refit all the mechanical parts, and bolt it back together. Dismantling was the first step, and I documented it in the spring of 2000 with the following images. Note that the seat is destroyed, the taillight is pretty much gone (the bulb and reflector, not the frame). The air cleaner and side covers are gone. The footpegs are gone. The frame cover is gone. The wheels are locked, because the brake shoes corroded and expanded in place, locking the wheels and keeping them from rolling. There's corrosion inside the frame, and there are bugs and webs and dirt everywhere.

Right side, at start of disassembly Another view, showing the messy shape the thing is in. Realistically, if you were lying on your side in the woods since the Reagan Administration, you'd look worse than this.

At least the engine is complete, and while the carburetor is in difficult shape, I might be able to bring it back to usable shape. That rubber intake is actually quite difficult to find, and I was pleased that it's still there. The engine is also fairly solid and the metal isn't pitted. It doesn't really turn over, but that doesn't surprise me much. All of the chrome has come off the rear shocks. I have replacements.

Start: 3:00 in the afternoon.

Two hours later, the tank, seat, rear rack and the engine are out. The rear swing arm is next, then the bars and headlight as well as the front wheel.

The engine is amazingly complete. The gearbox will need some work... the thing doesn't feel right and the clutch is probably corroded or something. All the wiring was in decent shape. With new rings, new oil and a new plug, this engine will probably start within a minute or two.

5:45 the same afternoon, and the bike has been atomized. The nice thing about the CT90 is that once you tear it down, there's no component you can't just pick up in your arms, including the engine, which weighs barely 50 pounds. After some study, it appears that the wheels and tires are unusable. I couldn't get the hubs out of the rims, they were locked solidly. I sprayed lube in there and set them aside for a year to think about their sins. The headlight bucket may have to be replaced. The front fender is straight but corroded and faded. The tank is pretty much the same. Front fork is still good. The oil is clean.

Next stage: electrolytic derusting (September, 2001)

I goofed off all the rest of the summer of 2000 and into 2001, working on tractor restoration and some other things, and came back to this in September, 2001.

CT90 forks I finished disassembly, including removing the forks and all the last of the components except for the rear shock towers, whose fasteners were corroded in place. Electro can often free rusted bolts, so I left them on. This is the top of the fork, and the red area is normally completely enclosed by the fork tube. This may be the only place on the entire bike you will find perfect, un-faded, original-color paint, so preserve it if you want an exact match to the original color. Note the bearing races at the top and bottom. They're loose ball bearings, so be sure you don't lose any.

The center stand and brake pedal come off as one unit. Keep it together, except while you derust and repaint the center stand, which should be black enamel. If you can get it powder-coated, so much the better, but don't coat the pivot surface.

Incredibly faded, this is the bike's last inspection sticker, in New York State. It expired in May, 1973. This bike was purchased used at Duryea Honda, in Brockport, New York. No idea who the original owner or dealer was, but could well have been originally purchased at Duryea and traded in.

This is the first shot of the electro bath. This is a large Rubbermaid tote filled with water. In the water, you mix about a cup of old-fashioned washing soda (you may not be able to get this in some states because it's kind of nasty and a pollutant)... I used the Arm & Hammer brand. Other substances may work to produce a decent electrolyte. At the upper right is an old piece of sheet metal to be used as the sacrificial electrode. The idea behind electro is that you put the rusted item and the sacrificial metal in an electrolyte solution, run a DC electric current across it all, and the sacrificial will gradually give up iron ions to derust the rusted item. The rust gets turned back into metal, and in addition ends up with a sort of a gunmetal bluing that resists corrosion. Among other things, it will strip all the paint off, often free up rusted or stuck parts, and produces free oxygen. Put the tank outside. I used a 12-volt battery charger set on 6 amps for current. The more current (not voltage) you can apply, the faster the process works, but I would not exceed 24 volts and would not exceed 10 amps. Note that the whole frame won't fit in the bath, so I put the back end in, and tomorrow, I'll flip it over and put the nose in, after coating the serial number plate with a heavy coat of grease so that it isn't harmed. I am somewhat concerned that the shock mounts will lose their chrome, but I can always rechrome or replace them.

A closer image of the sacrificial metal, the clips and the frame. The red clip (positive or +) goes on the sacrificial metal -- grind a shiny spot for good contact -- and the black clip (negative or -) goes on the item you're derusting. Do not permit the sacrificial metal to touch the item you're derusting, or it will short out and destroy your power source. Do not permit either alligator plug to touch the electrolyte solution and be sure to rinse them both thoroughly in clear water after doing this. If you do not, expect to replace the clips in a few months when they corrode -- I know, I already had to do it!

The solution will bubble immediately if you have a large enough piece of metal and enough current. Otherwise, you may have to wait an hour or so to see bubbles. After a few days or a number of hours (depending on the current and stuff) a layer of cruddy foam will appear on the surface of the solution. The solution will be usable for a long time, but be careful where you dump it out. It'll tend to kill the grass and weeds wherever you dump it.

After the part is derusted, you should go over it with a wire wheel and clean up any rough spots, then prime it immediately. Use a good quality primer or have it powder-coated, including the inside hidden areas Honda doesn't paint, like inside the battery box area. If you have it powder-coated, be sure that you mark all the threaded holes that must not be coated, or you will have to tap the threads back out!

Restoration parts

I've gone overboard obtaining restoration parts for this. I have no fewer than three spare engines, a rear swing arm, a NOS fender still in primer, handlebars, wheels, new tires and tubes, chain, a seat (newer than would have been correct on a 1970), a buddy seat, several racks, most of which are better than mine, headlights, mirrors, a stack of frame covers (only one is correct for a 1970) and lots of mechanical parts. I really went too far -- I nearly have enough parts to build another CT from scratch. Remember also that I have a 1971 K3 from which I can use many parts still. Stay tuned while I get the frame, fender, tank and headlight bolsters painted, have other parts rechromed, and start whatever mechanical work the thing needs.

Updated: 09/23/2001 03:03:30 PM

Last updated: 09/23/2001