Saturday, January 20, 2024

 Fluid management... Rainy day musings…

                                              Smiley face, about to be erased on the fuel lever.

Honda kept from going with liquid-cooled engines until the GL1000 Gold Wing in 1975. Soichiro was so adamant about keeping engines air-cooled that he had his engineers design a air-cooled four-cylinder 1300cc car engine for the model called the Honda 7/77 or just the Honda 1300.      see: Beyond the Gold Wings and the following CX500-650 V-twins, liquid cooling slowly seeped into mainstream motorcycling with each model year. And with that, coolant leaks began to show their nasty selves.

Honda’s reputation for cleanliness in designs and functions is legendary. Vintage Honda motorcycles from the 1960s-70s are not supposed to be dripping fluids beneath the machine if normally maintained.

Apart from chain lube being flung off the chain at both sprockets, Honda machines should not be drooling anything else. Of course, these 50-60-year-old motorcycles have aging engine oil seals and gaskets which are typically the sources for any oil leaks. What are the fluid sources?

1. Engine oil, leaking from oil seals and gaskets and sometimes from breather tubes when the engine is tired. Honda used the stud channels in the cylinder and cylinder head to feed oil to the camshaft, rockers, and tach drive hardware. The gaskets generally have an o-ring placed inside the oil feed hole to prevent oil migration through the gasket material. What seems to be a good solution often fails as head gasket oil leaks are prevalent on almost all models of air-cooled engines. Heat cycles, hot oil, and expansion of the parts, sooner or later will reveal oil leaks that migrate past the sealing o-rings and laterally through the gasket material. Forgetting to use a new drain plug gasket often results in a small oil drip beneath the engine. BTW Honda 160 engines have TWO drain bolts.

2. Fork oil, from leaking fork seals, of course. This wasn’t a problem for most models with leading-link suspensions, but they did have small, ineffective dampers shoved up inside the pressed-steel fork housings that could eventually leak the small amount of fluid inside. Honda’s early design shocks had replaceable shaft seals, but later they just crimped the seal housing into the body, negating any service attempts.

3. Battery acid! It’s hard to find a nice clean vintage Honda that doesn’t have signs of battery acid leaks onto the frame or mufflers. Either the vent tubes fell off from vibration and age or people forgot to hook them up when the battery was removed for service or replacement. Today’s new AGM and Li-On batteries have no fluid openings to leak, unlike the classic lead-acid batteries that we all grew up with in the 1960s-70s.

4. Gasoline. Starting with the top… the gas cap. Early gas caps used a simple baffle system which featured a small vent hole to allow air to help vent the fuel tank properly. This prevents air locks in the fuel system, however, it also allows evaporating gasoline vapors to leave the tank, eventually causing a buildup inside the tiny 1/16” hole which creates a vacuum in the tank. The early gas cap gaskets were made from cork and degraded quickly due to the compression of the spring-loaded cap retainer mechanism and exposure to gasoline products. Bad gaskets, caused fuel leaks at the top of the fuel opening, especially with a full tank of gas. Honda replaced all the cork gaskets with modern rubber compounds that resist breakdown from fuel exposure and cap spring tension. Having a lap full of gasoline when you hit the throttle or brakes with a full tank is downright dangerous, if not very uncomfortable when it seeps into your crotch area.

Fuel leaks can occur in many places in vintage Honda bikes. Besides the gas cap, the next step down is the petcock/shut-off valve. Most of the early models used a rubber 4-hole gasket to seal against the fuel selection lever face. Either the 4-hole gasket degrades and starts to leak around the lever arm, or the back side of the lever has both warped and become etched with gasoline acids, causing fuel to bypass the lever setting, even when OFF.

The lever face can usually be smoothed out with a fine-cut file or piece of high-number grip wet/dry sandpaper. That step, coupled with a new 4-hole gasket, should fix any petcock leaks at that point. The other fuel leak source at the petcock is where it attaches to the fuel tank. CB72-77 and most of the 350-450 lineup used a large nut that has left-handed threads on one end and right-handed threads on the opposite end. There is a thin rubber flat gasket that is supposed to be squeezed down when the petcock is secured to the fuel tank nipple evenly with the threads on the petcock body. If one end bottoms out before the other, then the petcock will be loose and often leaking.

For petcocks that bolt to the bottom of the fuel tank, either with one or two screws, you MUST use the proper sealing washers on the screws to prevent fuel from seeping down past the threads into the fuel cup. Be sure that the screws are tightened securely to prevent leaks. Also, replace the o-ring that seals the body to the tank on these models. Otherwise, the same cautions are true for the fuel lever and 4-hole gasket.

Most early petcocks used a long brass tube to feed fuel to the carburetor when in the ON position. When the fuel level drops down below the tip of the fuel tube, then turning the fuel lever to RES is required and allows you to use the remaining fuel below the brass tube to help you make it to the nearest gas station. After 50-60 years, the brass tubes will suffer cracks or become plugged up. In years past, when petcocks were cheap, you just put a new one on. Petcocks for CB72-77 and CL72-77s are becoming very scarce, so the fix is to remove the old fuel tube and replace it with a section of 5mm brass tubing which can be purchased from hobby stores or online. Clean out any remaining debris from the tube hole and then just tap in the new section. Now you have the RESERVE function available, once again.

Often, when old fuel lines are left connected to either the petcock or the fuel fitting on the carburetor, the brass fitting pulls out of either part along with the fuel line. Carefully, cut the old fuel line off of the fitting piece and tap the brass fitting back into the hole. The end of the brass is somewhat tapered so usually will bottom out securely into the hole and stay secured.

Carburetors, of course, have the task of metering fuel in the correct amounts at various engine speeds and throttle openings are full of fuel and the potential for fuel leaks.

The early 250-305 Honda models used a banjo fitting and screen bolt to allow fuel lines to be attached to the carburetor bodies. The banjo fittings, not unlike those on the master cylinders of bikes with hydraulic disc brakes, need washers on both sides of the fitting. Fiber washers were used for many years, but then aftermarket makers started using punched-out aluminum washers which deform enough to seal fluid leaks. Most of the rest of the vintage Honda models used pressed-in brass fittings which generally give little cause for concern.

When carburetor float valves stick open due to dirt, wear, or the floats dragging up against the bowl gaskets, the fuel will leak out through the small brass overflow vents. When carburetor bowls begin to leak at the bottom of the overflow tube and all else has been replaced or cleaned, look carefully at the brass tube inside the float bowl. In many cases, the fuel tube has cracked down the side and is slowly draining the fuel bowl. You can often either use a good quality soldering iron and solder up the crack on the outside or slip a piece of 4mm tubing over the outside, secured with JB-Weld or a good epoxy adhesive sealer.

Most float bowls have small drain plugs at the bottom. Loosening the plugs can drain the bowls out without complete removal. Because water often works its way into the fuel system, the water sinks to the bottom of the bowl and often causes corrosion between the drain bolt and bowl threads. Also, the drain bolt requires either an o-ring or flat gasket to seal it to the bowl.

Carburetor float bowl gaskets are another source of fuel seepage. Once the bowl is in place, the fuel level is near the top of the bowl and will leak out the front side of the bowl/gasket area if the gasket is not correctly made, the bowl clip doesn’t have sufficient pressure to clamp the bowl securely or there is leftover gasket material in the body, itself. Honda used some kind of magical adhesive to glue the bowl gaskets in place originally. When the gasket is cracked and leaking, you have to clean the gasket channels very well to prevent any leftover stray bits to prevent proper gasket sealing between the bowl and gasket. Check the edges of the float bowl for any leftover debris or if there are irregularities to the edges of the bowl surfaces.

Honda’s bowl gaskets for 1960s models are about 2.5mm wide. Many of the aftermarket kit gaskets are 3+mm wide and do not lay flat on the front edge of the carburetor body. This has been a problem for many years, unfortunately. In some cases, use a small hand-held hole punch to notch the gasket where it contacts the two small posts in the carb body gasket channel.

Other places…

Leaving your bike out in the rain, or stored for long periods where the tire tubes deflate, allows moisture to seep in between the rim and the tire bead, causing rust and corrosion to build up on the inner rim surface and ends of the spoke nipples. Any tears in the seat upholstery will allow water to seep into the foam and eventually settle down into the metal seat pan causing rust and eventually holes in the steel seat pan material.

Early model instruments don’t really have a way to vent out moisture inside the unit. When bikes are left in the rain or even fog, after a ride, the moisture inside the meter will condense and a layer of moisture will form on the inside of the meter lens. In a worst-case scenario, the moisture will get into the speedometer mechanism itself, damaging the odometer number strips and the magnet and little gear train inside.

Stay alert for fluid leaks of any kind and mend them early to prevent mishaps or just an ugly motorcycle appearance.

Bill Silver

aka MrHonda


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