The Technical Stuff

(Mr. Reynolds adds to the almost frightening amount of meat in this issue by doing up his front end!)

After I tested the 2nd Law of Thermodynamics with my 70 Commando this summer ( energy was converted to heat and chaos was increased ), loosened up the front end, twisted it back, bounced it a few times; and re-tightened everything, it worked better, but after realigning the bike, the headlight was still off. One of the headlight support arms was bent, but by the time I discovered that, the forks were out. It doesn't hurt to look at forks once every five years.

To get started on rebuilding the front end, put a 2x8 under the center stand and hoist the bike up onto it. Put a block or jack under the motor. Remove the front fender, wheel, and the handlebars. Remove the damper bolts and washers from the ends of the sliders. Take out the oil drain screw, unscrew the top nuts from the tubes. Hold the 9/16" nut and remove the top nuts (they are nuts, they have internal threads) from the damper rod. Remove the gauges and pull the damper rods, springs, and damper tubes out of the stanchions. Put the top nuts back in about half an inch, loosen the lower triple clamp pinch bolts, and whack the top nuts to break the taper on the fork tube. Remove the top nuts and the fork legs. Drain the rest of the oil out of the slider.

Remove the gaiter or wiper from the slider. Pull the tube all the way up and see how much you can rock it in the slider. The upper and lower bushings are the closest together at this point and any wear will show up most clearly. Ideally there wouldn't be any side play; if you can just barely tell that there is some, the bushings are probably OK for you to reuse. If there are any doubts, replace them. Unscrew the seal retainer. The factory method is to clamp the retainer in a vise, and use the front axle as a tommy bar to unscrew the slider. Other methods include holding the slider and turning the retainer with a pair of channel locks. Push the tube into the slider about half a foot and give it a hearty yank. You are using the tube and lower bushing like a slide hammer to get the upper bushing and seat out. A few good tugs and the tube will come out with the seat, this mysterious little paper washer, and a big oillite bushing. The lower bushing is held onto the bottom of the tube with a circilp. Slide the seal and upper bushing off the tube. Remove the circlip and lower bushing.

Is the plating worn off the tubes anywhere? If so, it's time for replacement tubes. Are there stone chips that will cut the new seals ? The dings can be smoothed out with a fine file and polished up with a hard Arkansas stone. Push a rag through the tube to clean up the inside.

Check the tubes for straightness by rolling them across a surface plate. If you don't have a surface plate, roil them on something reasonably flat, or hold the tubes side by side and rotate them one at a time. If they are slightly bent, it may be possible to straighten them. But if they are kinked, start looking for an other tube. Usually the bend or kink will be near the lower triple clamp. If a tube is bent, plan on straightening the triple clamps. It will usually be the lower yoke that is bent. Old fork tubes are great tools for this.

To check the triple clamps, install one straight tube, install the top nut and tighten the pinch boil Slide another straight tube into the other side, Just up to the bottom of the top yoke. Tighten the pinch boll. Look through the hole in the top yoke. Is the tube perfectly centered? If not, remove the good tube, insert a bent one, and tighten the pinch clamp. Pull on the tube to move the top in the correct direction. Remember, if you pull the bike forward, it will fall on you. Check your progress with the straight tube. Keep at it until the straight tube is a perfect fit. Then repeat the entire procedure with the other side. My lower right clamp was off about 1 inch.

Back to the forks. To take the damper rods and tubes apart, poke a #2 Phillips screwdriver with a round shaft through the holes at the bottom of the damper tube. Compress the spring a little and use a ½" wrench to unscrew the aluminum, fork damper tube top cap. Replace the cap (06-1347) if the forks top out. As the cap wears, the rebound damping fades. The parts on the end of the rod, inside the damper cap, make up the damper valve. It is a little cylindrical cup that seats against a thick flat washer that has four flats on the circumference. Check that the valve and seat are not pitted, and the pin is not worn. Wash the spooge out of the damper tube. Badly pitted damper rods and tubes will let oil leak by and affect the damping. News of Physics has reached England, new damper tubes are aluminum.

Sliders are pretty basic. There is a red fibre washer in the bottom that the damper tube seats against. You need it for re-assembly, unless you have a replacement. Clean all the grunge out of the bottom of the slider and polish up the outside.

I'm going to try a set of Progressive Suspension fork springs. I have used them in other bikes and like them a lot. They are part number 1119, and are about $70 from any local shop. Stock springs are about $28 a set out of England. Progressive makes some new guts for Triumph forks. but they said there was not much they could do with a Norton. Back in the days of yore (late '40's ?!) when the Roadholder front end was designed, and two way hydraulic damping was new, the Roadholder was the cat's pajamas, Racing tackle. Today, it is not the most sophisticated hardware on the street.

Actually, it is quite simple. The damper rod screws into the top nut (it is really a bolt, it has threads on the outside), goes through the damper tube top cap and holds the damper valve inside the damper body. The spring is held between the upper end of the rod and the damper tube top cap. When the forks compress, the stanchion end damper rod move into the slider. Oil in the damper body forces the damper valve off its seat. As the oil squeezes between the seat and the valve, it resists the compression of the spring, and slows the progress of the stanchion into the slider. On rebound the spring pushes the damper rod up, and reaction forces the damper valve against the seat. The oil is now trapped in the damper tube above the valve and has to squeeze out between rod and the damper tube top cap, wasting the energy stored in the spring.

When all the fork parts are clean and straight, put 'em all back together. Assemble the damper valves, rods and springs, then put on the damper tubes. Put the red fibre washer on the end of the damper tube. Set the slider on top of the spring / damper assembly, look through the hole in the end of the slider to make sure the washer is still there, install the damper bolt and washer. You might not be able to tighten it with out installing the stanchion end top nut.

Put the lower bushing and clip back on the tube. Oil the bushing and insert the tube into the lower fork leg, Slide the upper bushing onto the tube, the flange towards the top. Use an old top bushing to tap the new bushing into the slider. Push the little paper washer in on top of the bushing. Oil the seal and install it. Once you get it past the first few threads, you can push it in the rest of the way with the seal retainer. I like the long gaiters, Triumph style look better than the Norton ones. US bikes came with hard plastic wipers. Install the drain screw and fibre washer.

While the tubes are out. this is a good time to check the steering head bearings. Early Commandos came with the same dopey system of cup, cone, and loose ball bearings that plagued all the Atlases and Dominators. This style bearing is susceptible to dirt, water and maladjustment. Later Commandos (after '71) came with sealed ball bearings. These bearings. although misapplied (the load is mostly axial), were sealed against dirt and water getting in, as well as grease getting out. and they had a spacer that eliminated possible misadjustment.

To get at the steering head bearings, on late model bikes, remove the nut under the lower triple clamp. On the older bikes, remove the top triple damp center nut, washer, and top triple clamp. Remove the bearing adjusting nut. As the stem sinks under the weight of the lower triple clamp, ball bearings will start to drop out. Don't worry about them, just don't drop the lower yoke. Collect the balls and check them for any signs of wear, pitting, spalling, galling, flaking, then throw them away. If any ball is damaged, they all must be replaced. The loose ball bearings have one thing going for them, the balls are about 10 cents a piece. Check the price on a box of 5/16 balls. The biggest problem will be damaged cups and cones. Replace them with tapered roller bearings. If the lower cone is stuck, try driving a cold chisel under it. Be careful not to nick the stem. Tapered roller bearings are easy to check for wear any frosting or wear marks on the cup: any pits, chips, spalls, galls, etc. on the rollers, and it is time for new bearings.

If you have sealed bearings, stick your finger in the hole and turn the inner race. Are the bearings perfectly smooth? No roughness, slack, or sticky Spots? They are probably fine to reuse. If not, just push the spacer tube out of the way, and beat on the inner race of the lower bearing until it falls out. It works the best if the bearing comes out fairly straight. Once the bearing and spacer are out, drive the upper bearing out too.

[Editor's note: A book on motorcycle electrics contends that the major cause of steering head bearing pitting is poor grounding. Since the only connection between the headlamp and controls (headlamp switch, horn, turn signals, etc.) and the rest of the bike is the steering head bearings, all the electricity flows back to earth (ground) through the greasy bearings causing spark erosion between the bearings and their races. This can be solved with a grounding strap. A grounding strap is simply a piece of wire that runs from the forks to the frame. Use flexible wire with plenty of slack for lock-to-lock movement of the fork routed so it won't get pinched. There are plenty of bolts on the triple clamps to tap into.]

Late model bikes use two standard sealed 6205 ball bearings. They are about $10 each. A Timken tapered roller set, 01097 cone and 07204 cup (the set is ISO part number 30205) cost about $15 each, do not come with seals, and are necessary if you have a bike without the spacer for the steering stem. Putting an axial pre-load on a radial ball bearing is begging for trouble, i.e. don't use the sealed ball bearings without a spacer.

Once you decide on bearings, clean the steering head, apply grease as needed, and carefully drive the outer race squarely into the head stock. Don't forget the spacer for the 6205s. Torque the stem nut to 15 ft-lbs, and stake the sheet metal washer to keep the nut from falling off. On the older bikes tighten the bearing adjusting nut until there is no end play, and the yokes turn smoothly, with out any effort. A little pre-load is okay, but too much will act like a steering damper. If you look under the steering head, you will see the bottom edge of the cup and cage. Push the original fell seals over the cones, they may be some help in keeping dirt and grit out. The bearings in my bike lasted about 25,000 miles, with out any kind of seals.

Put the tubes back in the triple clamps tighten the top nuts and pinch clamps. Remove the top nuts end dribble 150 ccs of 20 weight fork oil into each leg. Use 10-30 Duckhams if you must. Install the gauges and top nuts and loosen the pinch clamps a little. Loosely install the fender, wheel, handlebars, and tighten the axle nut enough to pull the axle almost home. Bounce the front end a few limes, make sure the tubes are parallel, and tighten everything, starting from the top. Tighten the axle clamp on the slider last. Bounce the front end again. It should not be any stiffer or stickier than it was with everything a little loose. If you have a drum brake, be sure to re-center the backing plate. It won't hurt to check the alignment of the bike while you are at it. Change the fork oil every year.

In the interest of increased technical content, Steve Gray asked me to drain the engine oil out of my bike and ride it to a meeting. in order to better observe the experiment, I drained the oil out of Steve Krenz's bike. Steve is out of the hospital and doing fine. He should actually start coming to meetings again, before too long. Full details next issue.

Greg Reynolds

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