VJMC Tech Tip

By Gary E. Gadd

There are two distinctly different schools of thought concerning restorations. One is to replace all the marginal parts (those that don’t look showroom new) with NOS. The other is to refurbish those parts to acceptable (not so showroom new) condition. Both approaches have their own relative merit. The tradeoff is time and patience versus cash. There is nothing quite as striking as a 30-plus year old motorcycle which looks just as it did when it was the dealer’s responsibility. Motorcycles, however, were meant to be ridden. A well maintained machine touched with the patina age is just as appealing as a ‘zero time’ restoration.

We are rapidly approaching the point where we will have no option. New parts are no longer being manufactured and stocks are being depleted. They are already becoming more difficult to find and the cost of details (emblems, seats, sheet metal, etc.) is rising. Try to imagine performing a like-new restoration on a CB77, YDS-2, or H1…in another 30 years. What I am slowly coming around to is that we should not trash anything that, with any wild stretch of the imagination, can be refurbished and used. Take, for example, what my garage used to look like before I became somewhat organized.

Parts are arranged into categories of usefulness, much like the triage system at the site of a plane crash or natural disaster. Mental notes are made on which one can be used, which may be reworked and which are soon to be junk yard bound. One family of parts which usually makes it into the latter category is the air filter. Since they are still available and most are reasonably priced, we tend to throw them away and poke around for new replacements. This decision is usually based on the appearance of the filter element itself. After all, paper doesn’t age well.

Air filters come in an almost infinite variety of configurations, each designed to fit into unique spaces somewhere behind the carburetor and between the knees. In spite of that fact, all are basically the same. They consist of a paper element, a wire or sheet metal core which prevents deteriorated paper from entering the carb, and two end plates which are usually made from sheet metal. This collection of parts is held together with an adhesive of some description. That fact makes them easily restorable. Here is basically how to do it.

Measure the dimensions.

Note the length and girth (outside diameter) of the paper filter and depth of the accordion folds. Write them down. For example the filter from a CB77 has a length of 175mm and a girth of 265mm (That’s roughly six and seven eighths by ten and a half inches). The paper folds are 15mm (nine sixteenths) from top to bottom. Measurements are close but not exact as they were taken from an assembled filter.

Remove the paper element.

Cut away the paper, down to the core being careful not to damage it. Peel away the paper and save a sizable chunk of it for later reference. Now remove the remainder, which is glued to the end plates. Be careful to do no damage to the metal parts.

Disassemble.

Original ‘60’s filters were assembled with a pliable adhesive which can be peeled away with a little scraping. When enough adhesive has been removed, the end plates can be removed from the core. Once disassembly is complete, the metal parts can be cleaned of remaining adhesive. After market filters and OEM replacement parts sometimes use an adhesive which dries hard. Soak them, one end at a time, in thinner or MEK until the bond softens. In either case the idea is to disassemble the components without causing any damage to the metal parts. They are quite flimsy on some applications.

Clean up the metal parts.

Filter components were plated against corrosion and will usually be in good condition unless they have been exposed to moisture and allowed to rust. Clean them up as appropriate. Small dents and creases can be worked out easily since the metal is thin (it is not a structural member). Corrosion can be removed with a wire brush, acid bath or bead blast if necessary. The bare metal must then be protected from the formation of rust. Have the parts replated with cadmium or zinc or simply prime and paint them.

Fabricate a new element.

Take your measurements and element sample down the nearest auto parts bazaar and find an automotive filter which is the right size to sacrifice for your needs. The flat types come in all manner of dimensions and there will be one there which is just right for replacing elements on a rectangular bike filter. The large round filters can be used to refurbish smaller bike filters such as the CB450 down to the S65 (that is as small as my bikes go). Take it home (after you pay for it) and cut away the vinyl frame with scissors or a hobby knife. The auto filter is glued to the frame around its perimeter and most of the paper will be undamaged. Scrunch the paper up and cut it to the proper length. I use an X-acto miter box and a fine bladed razor saw. You will need to do a little trial and error work to get the proper fit around your particular filter core. Wrap the paper around your filter core and place on the end pieces just to see how it all fits. Small variations in filter depth can be adjusted by stretching the paper out a bit (makes it shorter) or by scrunching more folds around the core (makes it taller). The idea is to get the paper element to cover the wire core and fit into the flanges on both end caps at the same time. Simply cut along one of the accordion folds when everything looks right.

Glue it back together.

Use a clear silicone sealer to glue the paper element to the wire core. When dry, apply adhesive to one end of the paper and attach an end plate. Repeat for the next end plate. There is lots of slack in this procedure. Remember that the air should pass through the paper and not flow around the ends.

Make sure it fits.