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Achtung Baby!...

This time we started with a bare frame and swingarm from a German market ST70. It was a bargain swap meet find but it wouldn't have made much difference to the bottom line if it had been free!

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The headlight shell was no jewel, unless you consider it a diamond in the rough. It was intact, however.

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 The frame was remarkably straight as-received. Restoration would have been a simple matter of media-blasting it then repainting. Since this is going to be a full-on custom build, we opted to smooth & straighten every square inch of it. We began by dressing-down all of the factory seam welds and filling-in the spot welds. Notice that there are no spot welds visible in the rear wheel arch or motor mount area as there normally are on a stock frame, yet the headstock welds were painstakingly smoothed instead of  being completely leaded-in and blended. Filling & smoothing all of the welds would have been easier, but easy is not what this project is about, attention to detail is. This is the type of subtle detail that balances OEM and custom appearance. In all, the frame  received four coats of high-build epoxy primer/surfacer with thorough block sanding between coats, leaving the frame completely straight and ripple-free. The swingarm was finished on all sides and the sharp edges were all radiused. Unfortunately, the photo disc was fatally flawed and the photo record of the swingarm in-process lost.

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In keeping with the smooth look of the frame, the headlight/speedo shell was treated to a thorough block sanding. All of the parting lines, as well as scratches, were completely removed. The headlight ears were hand-fabricated from sheet steel and blended-into the main body of the upper fork tubes with body lead. Even the back sides were smoothed for a molded-in appearance. Note that the headlight retaining bosses are blind-threaded, continuing the smoothed theme of the build. Capping it all off is an NOS 80MPH Honda speedometer that we sourced from Singapore.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 This is where all of the meticulous metalfinishing work really paid off. As can be seen in these shots, the highlight reflections are virtually mirror-straight throughout the frame, even in spots that will not be visible once the bike is assembled.  The headlight shell and swingarm have had all of the rough edges, casting marks and welds smoothed to the point where the pieces take on the look of sculpture and that's the idea... to allow the purity of the original design show through. Paint is three-stage candy urethane. Both the midcoat and base were custom tinted in-house for a true one-of-a-kind, hotrod-inspired, color that looks different in nearly every lighting condition.

 With the body and paintwork completed, the real work begins. Normally, mock-ups & fabrication are done prior to the body finishing. Having the luxury of a spare frame, for purposes of fitment, allowed us to turn the process inside out. Step-by-step details of the build will be added as the project continues.

 

 

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Our new engine is wider than the original powerplant and the shifter is unique to this series of new gen Honda motors.  New footrest assemblies fit with the addition of spacers beneath the engine and of course Honda supplies a very nice rubber-isolated unit specifically designed for this engine series, unfortunately, the footpegs don't fold...what to do? Getting a tailor-made fit was going to involve cutting & welding no matter which footrest assembly was chosen. We had a few old cast-offs from vintage Hondas that we had been saving for a rainy day...time to take out the umbrella. One was in nicer condition, but the kickstand bracket was tiny. The other had the necessary kickstand bracket, but was in really rough shape; it had been broken and "booger welded", plus, the hollow tube construction didn't inspire much confidence.  Neither unit was wide enough and the mounting holes of both were incompatible with our engine. We decided to cut & splice the two, discarding the bits that were not needed and fabricating anything that was missing.

First, the RH mounting ears and  entire LH mount were removed from the base we were going to use. The RH mount was relocated to the LH side, in the proper position. This provided the necessary point from which we could reference the new RH mount. The kickstand bracket, along with a good-sized chunk of the hollow unit was sectioned, then fillet-welded into place and used as a brace for the LH footpeg.  A new RH mounting flange was fabricated from .125" plate steel.  The completed custom assembly now accommodated the heel/toe shifter and brake pedal in their ideal locations. Once the kickstand was cut to length, the whole unit was disassembled, metalfinished & painted; the hardware was prepped & sent out for plating. Upon final assembly, the freshly plated hardware and new Honda footpeg rubber were installed. The end result is a perfect fit and OEM appearance.

 

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 The brake pedal was too short and the bends did not line up with the footrest. We cut and spliced-in a 3" section, then heated & bent the arm to fit. The shifter and kickstarter were roughly finished, then powdercoated black right from Honda. While we're glad that Honda limited their cost-reduction to cosmetic aspects, this build demanded better. All four pieces were metalfinished and polished for chroming. The photo on the far right shows what parts look like just before they are ready for plating. Unlike softer metals, polishing steel is definitely not for the inexperienced.

 

 

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The engine guard presented another challenge. The stainless steel exhaust we had selected interfered with the RH tube, plus we are going to fit a large capacity oil cooler to the engine. The solution was to modify the engine guard. Starting with a really rough OE engine guard, we removed the bottom plate, heated & bent the RH tube to clear the exhaust, removed the sparkplug guard mounting tabs, then welded the assembly back together. The bottom plate was fabricated from .125" plate steel which should hold up much better to bike lifts as well as rocks. The heavier gauge metal also adds some structural stiffness to the lower frame. We fabricated a torque brace (an MCM exclusive) to supplement the engine guard, further reinforcing the lower frame. The sparkplug guard will not be used on this bike.  It was felt that it impeded airflow around the engine and would interfere with cooling, and at 20hp, this engine will generate considerably more heat than a stock tune.

 

 

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We ordered a Kitaco stainless steel CT70-specific pipe. Although the Z50 pipe will fit, the lines don't match the CT70 and the muffler position is low. The biggest advantage of the CT profile is that the muffler position won't roast your passenger's right leg. Being made from 3-series stainless, we knew that the pipe could be polished to a chrome-like shine and stay that way for years to come. The welds, which were beautifully done by the factory, were dressed-down and polished. They almost disappear, lending a one-piece look. We had been advised that the race version of this pipe was very loud; using that advise, we ordered the road-spec pipe. It didn't take an engineer to figure out that the baffle was small enough to choke-off anything over 4hp. We fabbed our own baffle, reusing the fiberglass packing. The upper right photo shows the size of the factory-supplied baffle compared with the I.D. of the pipe. The new baffle is the same size as the pipe. We've not yet heard the exhaust note of the new engine, however, based upon other mufflers we've modded in the past is should have a nice throaty sound and still be below the legal db limit.

 

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Initially, we opted for current generation Honda fork legs along with custom trees and Honda Disc brake. The setup is of good quality (light-years ahead of the Chinese repro CT70 front ends currently on the market) and very reasonably priced. The only downside was the finishing of the lower sections. The metalwork is rough and covered-over with a thick layer of medium-gloss silver paint. As shown in the photos, even the paint had some scratches by the time they arrived here. We applied some serious metalfinishing to them and happily, the aluminum castings turned out to be of high quality.  We subsequently discovered a reasonably priced inverted fork which, it was felt, fit this project better than the conventional sweeper style, in both aesthetics and spring rate. Thus we applied the same metalworking to the lower sections of the upside down fork legs; they required a lot less smoothing and polishing. The fork in the above photos was outfitted with a disc brake and subsequently installed on the shop bike with excellent results.

 

 

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Something old, something new, something state-of-the-art, something...purple? Nowhere is the philosophy of this build better illustrated than in the wheels and hubs. The design of the original hubs fits the bike as well as anything we've seen and we consider them to be an integral part of the bike's overall look. We completely deburred, smoothed and polished the original castings to excellent effect. Next, a Honda/Nissin twin piston caliper and 220mm rotor were adapted to the front hub; the CT70 speedometer drive was retained. The finishing touch was the application of the body color to the caliper and rotor web areas; these are the kind of small details that can make of project stand out from the crowd without calling undue attention to themselves. The drum brake was retained for the rear wheel only the backing plate was polished to a mirror finish. Finally, we sourced a 28 tooth rear sprocket to match the engine's output. An offset plate was made to accommodate the wide rear tire.

 

 

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Back from the chrome shop, the kickstarter, heel/toe shifter and seat hinge have a subtle, yet vastly improved appearance. Of course these pieces all came from Honda with a crude black finish, but they still look as though they could be original equipment.

 

 

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Form follows function. This axiom of efficient design is in keeping with our design goals. The lefthand photo shows a length of 6061 aluminum rod, a piece of .1875" 6061 aluminum plate, a 30mm mandrel bend made from 304 stainless steel and a pair of 304 flanges. Eight hours later, we had completed fabrication and polished a new engine guard and custom intake manifold.  These were then sent out to be TIG welded. The lower two photos show the difference between a stock CT70 intake port and the intake on our 137cc modded motor, the reason why the hand-fabbed intake was needed.  The modified OE engine guard was substantially heavier than original. This, by itself wouldn't have been a big deal. However, once the added weight of the new engine, torque brace, etc. were totalled, we figured that the bike had gained about 10lbs over stock. That's not an unacceptable amount of added mass, but the substitution of a few key parts, such as the engine guard and wheels with aluminum replacements, made this a zero-sum proposition. In addition to the weight reduction, the new pieces have vastly superior finished appearance and the bike now has a completely flat surface that makes working with a portable bike lift a pleasure. The bottom plate is slightly wider than the original and slightly farther below the engine. Through experimentation, we have found that this improves airflow around the engine. At speed, the engine should run a few degrees cooler because of this. There is also just enough room to mount an oil cooler nearer the engine, yet out in the main airflow, should we ever decide to change its location. The modified OE guard would have looked fine on the bike, better than original. Sometimes, though, "fine" just isn't good enough, even when it means discarding one's own work in the process.

 

 

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Building a one-off is always a learning experience. In this case, we were about to get some hands-on lessons in front end design.  Aside from giving the bike a beefier look, this upside down unit had greater suspension travel and better spring rates for road riding. Unfortunately, that meant that the headlight mounts we had fabricated earlier in the project could not be used. With the project really starting to come into its own and a clear vision of how we wanted this bike, we weren't afraid to discard anything, no matter how much time we had invested into it, when something closer to our ideal became available. Since there wasn't much front-end real estate to work with in the first place, integrating the OEM triple clamp was a challenge; but, the folding bars were a non-negotiable item. We sourced some square 6061 aluminum bar stock. A day, vast quantities of MAP gas, tweaking, polishing, and obscene oaths, later we had our new headlight mounts. Off-the-shelf parts were readily available, just too run-of-the-mill for our tastes. The lower, aluminum sections of the fork legs were deburred and polished also. The headlight/speedo are just where we wanted them and there's enough room left to aim the headlight with the oil cooler in place. The dax frame has a large steering lock flange just below the triple clamp, unlike a CT70 frame. It is just visible between the headlight bucket and triple clamp in the RH photo. Fortunately, it wasn't a major obstacle. The headlight unit just seems to float in space...exactly the look we were after. Best of all, the fork tubes won't get the usual gouges from conventional headlight mounts.

 

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