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MC How-To
Step by step: From general maintenance to complete restorations, we share tips and tricks for working on classic bikes.

DIY Norton Clutch Hub Compressor

Our homemade Norton Commando clutch hub compressor tool (at right) next to a factory tool. It may not be as sleek, but it works just as well.

If you’re servicing the clutch on your Norton Commando, a clutch hub compressor tool is a must. The Norton Commando clutch is a simple, robust design utilizing a single diaphragm spring to clamp the clutch plates together. Although factory-style clutch hub compressor tools are readily available and reasonably priced, (typically $25-$45), if you’re like us you get a certain kick out of making your own tools when you can, and this is one tool you can easily make, usually for less than $10 if you already have much of the hardware sitting around, as many of us do.

To make the compressor here, you’ll need:

• 1 x stick of fine-thread 1/2-inch all thread or a 5-inch 1/2-inch threaded bolt
• 1 x 1/2-inch bolt washer
• 1 x 1/2-inch fine-thread steel (not nylon insert-type) lock nut
• 2 x 1/2-inch fine-thread nuts
• 1 x 4-inch PCV pressure cap
• Medium (blue) thread-locking compound

Here’s all it takes to make the tool: a 5-inch OD PVC slip cap (shown here with center hole already drilled), a 5-inch bolt or piece of all-thread, and a few nuts and washers.

Making the compressor is simple.

• Take the PVC pressure cap and drill a 1/2-inch hole directly through the center of the cap. The pressure cap we used is rounded at the top instead of flat. You can use a standard slip cap, which is flat at the top, but we like this type better as it’s a little stronger. If necessary, trim the cap to an overall length of 3 inches. The cap we purchased was already at this dimension.
• Cut a 5-inch piece off the all-thread stick or use an existing 1/2-inch fine-thread bolt, making sure the threads are clean and serviceable.
• If using all-thread, thread the two standard nuts onto one end of the all-thread and then tighten them against each other to lock them in place. Clamp the end threaded with the two nuts in a vice to hold it firmly. Apply locking compound to the other end of the all-thread, then thread the steel lock nut onto the all thread until it’s fully on engaged on the all-thread and locked in place.
• Loosen the two nuts you jammed together. Remove the lower nut, then thread the upper one up to the lock nut. Install the washer under the nut then insert the threaded shaft through the top of the PVC cap. Thread the second regular nut onto the threaded shaft. That’s it; you’ve made your Norton clutch hub spring compressor.

Drill a 1/2-inch hole through the center of the PVC pressure cap. If necessary, trim the cap to an overall length of 3 inches.

Cut a 5-inch piece of 1/2-inch fine-threaded all-thread (or use a 5-inch bolt if you have one). Clean the threads and apply locking compound to one end.

Lock two regular nuts to one end of the all-thread, lock the piece in a vice, then thread the steel lock nut onto the all-thread until it’s fully engaged and locked in place.

Release the two regular nuts. Remove the lower one, then thread the upper one up to the lock nut and install the 1/2-inch washer.

Insert the center bolt through the PVC cap and thread the second regular nut onto the center bolt.

The homemade spring compressor assembled and ready to work.

Using the clutch hub compressor

To use the tool, remove the center adjuster screw from the clutch diaphragm spring hub. Place the clutch hub compressor loosely over the diaphragm spring. Thread the clutch hub compressor center bolt into the diaphragm spring hub, making sure at least five of the bolt threads are engaged in the hub. Jam the nut on the clutch tool center bolt tight to the spring hub. Next, hold the clutch hub compressor bolt while tightening the standard nut against the washer and PVC cap. As the nut is screwed tighter the clutch diaphragm spring will be pulled flat. Tighten slowly until the diaphragm spring releases and spins in the clutch hub. Remove the diaphragm retaining circlip, followed by the diaphragm spring.

To use the tool, remove the clutch hub adjuster screw then screw the clutch hub tool into place making sure at least five threads are engaged in the diaphragm spring hub.

Jam the lower nut against the diaphragm spring hub to lock the center bolt in place.

Hold the center bolt and tighten the outer nut until the diaphragm spring pulls flat and spins in the clutch hub. Remove the diaphragm spring circlip.

The Norton clutch diaphragm spring removed.

Honda Redux

Shane Powers with his Honda CB350

A curiously grinning Shane Powers with the 1970 Honda CB350 K2 he bought for the princely sum of $94 at the 2016 Barber Vintage Festival. Some would say he paid too much. Photos by Richard Backus.

Apparently, we have a thing for Honda CB350 twins. In 2016, we took a tired 1970 CB350 K2, stripped it to the frame, then slowly brought it back to life. Along the way, we learned what literally hundreds of thousands of buyers discovered back in the CB350’s heyday; that it’s a great, seemingly indestructible little bike.

We also discovered there’s a great community of CB350 fans, from owners to suppliers, all willing and happy to supply tips and information to help you keep your CB350 on the road – or, in our case, get it back on the road in the first place.

We gave a pretty exhausting accounting of our 1970 CB350 project bike, details of which you can find starting here or by typing “Project Honda CB350” into the search bar at the top of the page. And the paint was barely dry on that bike before ad man Shane Powers launched into reviving the 1970 CB350 K2 he bought at Barber last October and I launched into a father-son project on a 1972 Honda CB350 K4 that’s been languishing in the back of my garage for some 10-plus years.

1972 Honda CB350

Son Charlie’s 1972 CB350 not long after we started into it. The exhaust was a mixture of parts, with stock headers and funky aftermarket mufflers.

1972 Honda CB350

Charlie’s CB350 a little further along, now with the Mac 2-into-1 exhaust we picked up from Dime City Cycles. The fit is excellent and the sound fantastic.

Powers’ bike could win an award for Best Rusted Honda, its condition perversely motivating him to embark on a complete and total tear-down and rebuild just to prove it can be done, while Charlie and I are taking a more mellow approach, giving the ’72 a mild café overhaul and limiting our work to subtle upgrades and maintenance because, frankly, Charlie’s bike’s in pretty good shape. So far we’ve overhauled the carbs and rebuilt the front forks, plus installed a kick-ass 2-into-1 Mac exhaust system that we picked up from Dime City Cycles. The dry-rotted wiring system still needs some major love, but we’ll get to that. We’ve also been getting more use out of the Skat Cat 40 blast cabinet we picked up from TP Tools and we’re constantly awed by how much time it saves us cleaning parts and the options it gives us in reconditioning rusted bits, cleaning and painting parts instead of replacing or rechroming them.

CB350 swingarm

A shot of the swingarm on Shane’s Honda before treating it to media blasting in our TP Tools Skat Cat 40 blast cabinet (left), and a shot of Shane’s Honda CB350 swingarm after blasting in our Skat Cat 40, which took it down to bare metal in minutes.

CB350 cam block in Skat Cat blast cabinet

We used the Skat Cat to clean up bits of Shane’s CB350 engine including the cam block.

CB350 cam block

A close-up of the cam block after media blasting. Beats the hell out of using solvents.

Here’s a cool trick we did with our blast cabinet. The upper part of the fork legs on Charlie’s CB were badly pitted thanks to moisture that got locked in by the stock metal fork covers. The lower portion was still in excellent shape, and since Charlie’s going to run without the fork covers we decided to try bead blasting the legs. It worked beautifully, leaving us a clean metal finish that we plan to paint the same color as the upper and lower triple trees, which we also blasted before painting.

CB350 carb tops

Here’s another experiment we did using the blast cabinet. The chrome carb tops on Charlie’s 72 CB350 were pitted, so we thought we’d see if we could salvage them by bead blasting them and then painting them black. Took minutes and worked a treat!

So we’ve proven that Charlie’s bike runs great. Shane’s? Well, time will tell. Moving forward, we’ll post updates on our progress with both or either bike, showing the stuff we’re doing and learning as we move along. Stay tuned! — Richard Backus

Rebuild Norton Commando Roadholder Forks

Top to bottom: new fork tube and components; pitted fork tube and old bushings and seal, fork spring and damper assembly. Photo by Motorcycle Classics staff.

Fork oil is not supposed to be gray, but this kind of contamination is pretty common. Photo by the Motorcycle Classics staff.

Positioned as they are at the front of the bike, forks end up by default with heavy exposure to road debris and moisture. Dirt and moisture take a toll on fork seals, which help keep fork tubes clean, wiping them with every pass. And while keeping the fork tubes clean helps, once the tubes become pitted there’s nothing left to do but replace both the fork tubes and the seals.

This How-To centers on rebuilding Roadholder forks on a 1974 Norton Commando. First introduced in 1946 and then modified in 1953, Roadholder fork construction stayed relatively constant until the end of Norton production in the mid-1970s. A robust design — a fact echoed by their long production life — they’re generally easy to service, with the typical overhaul involving a full strip, followed by a thorough cleaning and seal replacement. There can be other issues, such as fork tube bushing wear and fork tube wear from years of use.

The tubes on our Norton were badly pitted, so we bought new fork tubes, as well as new bushings. That turned out to be a good call, as the upper bronze bushings were in poor shape. The lower bushings are hardened steel and tend to last much longer, although we replaced those, as well.

A project bike purchased by managing editor Landon Hall, our subject Norton hasn’t turned a wheel in 20-odd years, and with zero history on the bike, it was anybody’s guess what we’d find once we started.

What we did find was a high degree of moisture contamination and resultant sludge, the damper valve and damper tube cap on one fork being particularly grungy. Fortunately, they cleaned up fine and are perfectly serviceable.

BikeMaster

We also found worn steering head bearings, and with the front end already torn down it was time to replace them. Commando steering yokes turn on two sealed bearings press fit at the top and bottom of the steering head tube, with a spacer tube in between. Replacement is typically straightforward, but moisture contamination reared again as we discovered the steering stem was practically rusted to the inner bearing races. It took patience, but with a combination of penetrating solvent, a heat gun and a good hammer, we finally convinced the steering stem to break loose. Note: Never hammer on the stem without first threading the securing nut until it’s just flush with the end of the stem to prevent thread damage. Further, never hammer on the nut and stem directly; use a block of wood.

This isn’t an expensive proposition. Excepting fork tubes (not always necessary), expect to spend around $75-$100 on parts, with everything readily available from your favorite British parts supplier. If you do need fork tubes, add $110-$200 (prices vary depending on the maker and supplier) to the bill. Head bearings, purchased locally, cost us a further $23 for the pair.

This is an easy weekend job, but as usual we suggest taking your time. Budget four to eight hours total including initial teardown and final reassembly. As always, we recommend having a good shop manual on hand for parts identification and proper torque specs.

 

1. Support the front of the bike. Remove the front wheel, brake caliper and fender. Unbolt the headlamp shell from the locating ears. Disconnect speedometer and tach drive cables and instrument lights. With a 1-5/16in socket, unscrew the top chrome-plated fork caps.

2. Lift the fork leg enough to expose the top of the spring. Hold the nut securing the spring to the damper rod with a 1/2in open-end wrench. Loosen and remove the fork cap.

3. Loosen the pinch bolt on the lower steering yoke. You can drain the fork oil now by removing the drain screw at the bottom of the fork leg or pour it out once the fork has been removed.

4. The top of the fork tube is a taper fit to the upper yoke. Screw the fork cap back into the tube at least 5 turns. Hold a block of wood on top of the cap. Strike the wood with a hammer to break the taper. Remove the fork assembly.

5. Clamp the bottom of the fork leg in a vise and remove the threaded fork leg collar. Ours was seized. We heated the fork leg with a heat gun and finally broke it loose with a pair of C-shaped pliers. A strap wrench is preferred to avoid damage, but our collar was stuck fast. Fortunately, it came off clean.

6. Remove the fork leg from the vice and using a 1/2in socket, remove the damper rod-securing bolt.

7. Pull the damper rod assembly out of the fork. Note the fiber sealing washer at the bottom where it joins the fork leg. This must be renewed. Remove the nut holding the spring to the damper rod. Remove the spring. Clean all parts thoroughly in solvent and dry.

8. The damper rod assembly on the left fork was covered in sludge from moisture and dirt contamination. If necessary, remove the aluminum top cap on the damper rod tube. Separate the damper rod from the damper rod tube and clean all parts thoroughly. Reassemble the damper rod with spring.

9. Next, secure the fork leg in a vice. Push the fork tube in fully, then pull back sharply to knock the upper bushing complete with seal loose from the leg. Remove the fork tube. This photo shows the major fork components, with the fork leg in the background, followed by the fork tube and finally the damper rod assembly and spring. The lower fork tube bushing is steel, the upper bronze.

10. If replacing the lower fork tube bushing, remove the circlip at the bottom of the tube. Remove the bushing. Install new bushing with new circlip.

11. Clean fork leg thoroughly and blow dry with compressed air. Place new sealing washer on damper rod assembly. Install damper rod assembly, then the securing bolt. Torque to 10ft/lb.

12. Place the fork leg upright. Install the fork tube. Slide the new upper bushing down the tube and push into the fork leg. Next, slide the old bushing upside down over the fork tube. Use the old bushing as a slide hammer, rapping it against the new bush until it fully seats.

13. Next, place the thin paper gasket on top of the new bushing. Lightly coat the new fork seal with grease and slide it into place using hand pressure. Seat the seal using an old top bushing as per step 12.

14. Return the fork leg to the vice. Screw the fork leg collar back in place. Use a strap wrench to fully seat it. Install the rubber fork tube boots.

15. Slide the fork assembly back in place through the steering yokes. Lightly secure with lower pinch bolt. Make sure the drain screw is secure with new fiber washer. Slowly fill the fork leg with 150cc of fork oil.

16. Once the oil has settled, push the fork leg up far enough to place the instrument over the spring, followed by the fork cap washer. Thread the fork cap onto the exposed damper rod shaft until it seats on the spring retaining nut. Hold the nut with a 1/2in wrench and tighten the fork cap to lock it to the shaft.

17. Push the fork cap down. Slowly turn counterclockwise until you feel its threads engage, then turn clockwise and thread into the fork tube. Loosen the lower pinch bolt. Position instrument and tighten the fork cap.

18. Reinstall the front wheel and fender. With the bike off the stand, firmly push down on the front forks several times to center the steering yokes. Tighten the fork caps to 35ft/lb and the lower yoke pinch bolts to 10-15ft/lb.

Rebuild Ducati Mikuni BDST Flat Slide Carburetors

 

This How-To might seem a little out of sync with our mission, focusing as it does on a 1992 Ducati 750SS. The name of the magazine is Motorcycle Classics, we hear you say, so isn’t 1992 too new?

Believe it or not, it’s been 26 years since Ducati introduced the 750SS for the 1991 year, putting it just inside our general policy of only featuring bikes 25 years old or older. Hard as it is to accept, 1991 was, well, a long time ago. In the motorcycle marketplace, our project 1992 Ducati is just old. It’s at that awkward age where it’s neither fish nor fowl; somewhat ignored by lovers of more vintage machinery yet too outdated to be interesting to riders looking for modern hardware. It is in fact a potential bargain Ducati, perfect for riders who appreciate the brand and its heritage.

An updated version of the 750 Sport of 1988-1990, the 750SS featured improvements over the outgoing 750 Sport including a wet clutch — the first Ducati so equipped since the Cagiva Alazzura and Elefant — and a pair of 38mm flat slide Mikuni constant velocity carburetors in place of the 750 Sport’s troublesome single Weber. The Mikuni swap yielded improved performance, with none of the flat spots or hesitation experienced on the Weber-equipped 750 Sport. But with the youngest Mikuni-equipped bikes now 20 years old (fuel injection came in 1998), the likelihood of one of these bikes needing a carb rebuild is high. BikeMaster

Fortunately, Mikuni BDST flat slide carbs are easy to rebuild — even on a Ducati — and parts are readily available, if you know where to look. Surprisingly, the same sources that don’t list kits for the 750SS do list O-ring and float needle kits for 1992-1993 Yamaha TDM 850s, which used the same 38mm Mikuni as the Ducati 750SS. Going to eBay and typing in the search term “1992 Ducati 750SS carb kit,” we found a few vendors offering kits that included not just the O-rings and float needle, but all new jets, the slide needle and the atomizer tube. Those kits ran in the $52-$56 range (per carb). In the end, we opted for O-ring and float needle kits from Power Barn for $32 each.

We should note that this was not a comprehensive rebuild. Rather, it was sort of quick and dirty, to see if we could get this 750SS running again. Which we did, and quite nicely, thank you. Although we did not soak the carb bodies, our subject carbs cleaned up well using spray carb cleaner followed by compressed air to chase the orifices. If you do soak them, make sure not to soak any plastic parts, cleaning them individually instead.

This is a fairly straightforward project and well within the reach of the average weekend warrior. If you don’t rush it and give yourself the weekend, you shouldn’t have any trouble pulling the carbs on Saturday and reinstalling them on Sunday. Outside of a synchronizer, this job doesn’t require any special tools, and if you have the experience it’s easy to sync the carbs by ear and feel. Twins are nice that way, readily betraying when one cylinder is firing smoother than another.

As always, we recommend having a good shop manual on hand for parts identification and proper torque specs.

 

1. Remove the gas tank and air filter, the throttle and choke cables, then loosen the carburetor to manifold clamps and remove the carbs as a unit. Next, remove the fours screws securing the float bowl and cable bracket. This photo also shows the mixture screw and spring.

 

2. The plastic float assembly hinges on a plastic needle housing. The housing is a press fit into the carb body. Grasp the housing firmly and pull it straight up and out, complete with the float. It should release easily.

 

3. Remove the pin securing the float to the needle housing and separate the two, exposing the float needle. Thoroughly clean but do not soak the housing and float.

 

4. The jet block is secured to the atomizer tube. Remove the screw and collar securing the jet block, then remove the jet block. This also releases the flat slide body, as we’ll see soon.

 

5. As its name implies, the jet block contains most of the carb’s jets. Left to right above the block is the block retaining screw and collar, the main jet, the pilot jet retainer and the pilot jet.

 

6. The starter jet screws into the jet block. Removing the main jet first releases the pilot jet retainer. Remove the pilot jet, then unscrew the starter jet.

 

7. As noted in Step 4, removing the jet block releases the flat slide body. Turn the carb over and remove the two screws securing the CV cover. Remove the cover, followed by the slide spring. Push the flat slide up from inside the carb throat, then remove the flat slide and diaphragm. Next, pull the plastic flat slide body straight up and out of the carb body, as shown. The slide is at upper right.

 

8. Repeat this process on the other carb body. Clean the bodies and passages thoroughly, then blow them dry with compressed air, making sure to blow air through all the orifices to ensure they’re clean. Do not soak any of the plastic parts. Next, start the reassembly process by installing the new O-ring on the float needle body.

 

9. Next, install the new O-ring on the slide body at the base of the atomizer tube. This photo shows the new O-ring installed, with the old O-ring held for reference.

 

10. Next, lightly coat the O-ring with grease and reinstall the flat slide body in the carb body, making sure it’s pushed fully home. Gently turn the carb over to prepare to install the jet block.

 

11. After cleaning the jet block, blow it dry with compressed air, making sure all the jet passages are clean. Install the new O-ring from the kit, as shown.

 

12. Slip the jet block over the atomizer tube and onto the carb body, followed by the sleeve and retaining screw. Secure the jet block to the carb body. This also locks the slide body.

 

13. With the jet block installed, install the new O-ring on the pilot jet. Lightly coat the O-ring with grease and push the pilot jet into its bore in the position shown.

 

14. Next, after ensuring it’s thoroughly clean, screw the starter jet into its bore next to the pilot jet.

 

15. Place the retainer into position around the pilot jet, then screw the main jet into place, securing the retainer and pilot jet. Note that the retainer partially blocks the starter jet.

 

16. Slip the new float needle into place on the float tang. Slide the float seat over the needle, then reinstall the float pin. Make sure the pin is installed from the outside in as the float bowl acts to retain it. Lightly coat the float seat O-ring with grease and reinstall the float assembly. Put the new float cover gasket in place and reinstall the cover and the throttle cable bracket.

 

17. Turn the carb over and reinstall the slide and diaphragm. The slide will only go in one way. Install the new O-ring for the CV airway, visible here at approximately the 1 o’clock position. Install the slide spring and the slide cover.

 

18. Install the spring followed by the washer and new O-ring on the fuel mixture screw. Lightly seat the screw, then turn back out 1.5 turns for an initial set. Reinstall the carburetor set, accelerator and choke cables, airbox and gas tank, then start the engine and make final adjustments to the running engine.

Rebuild BMW R75/5 Bing CV Carburetors

 

Bing constant velocity carburetors as used on BMW R75/5s and up are wonderful devices, generally trouble free and long wearing. Yet overhauls are still occasionally necessary, as we found with our subject 1973 BMW R75/5. Suffering from deteriorated jet and throttle shaft O-rings, the carbs were impossible to properly set and the only solution was a full overhaul.

For parts, we turned to the Bing Agency International. After describing our carburetors’ condition, Fay Laughridge suggested their #6 32mm CV rebuild kit, which comes complete with every gasket and O-ring needed, new throttle slide diaphragms, new slide needles and jets, new floats, float pins and float needles, new float needle seats, and new throttle plate screws.

A comprehensive Bing rebuild isn’t cheap. Our kit with optional needle seats came in at $261, and while you can source some of the bits cheaper the ease factor of picking one part number and knowing you’re getting everything you’ll need is huge. Further, as near as we can find, the Bing Agency is the only source for replacement float needle seats. The Bing Agency offers troubleshooting help and can also supply Bing manuals. BikeMaster

The Bing Agency also offers a float and bowl kit with alcohol-proof floats. The stock floats aren’t alcohol proof, but they seem to hold up reasonably well over time. Whether you want the upgrade — we went stock — is a judgment call you’ll have to make.

While this is a somewhat fiddly rebuild, it’s certainly within reach of the average mechanic. The trick, as always, is to take your time. When something doesn’t want to move, find out why before you force it. The only special tool required might be a carb synchronizer for tuning, but a good ear can do well on a twin. That said, for this project it’s essential to have a good manual on hand to help with parts identification and location, and final tuning.

 MC How-To

1. The #6 kit from the Bing Agency for 32mm constant velocity Bing carburetors includes gaskets, floats, float needles, CV diaphragms, slide needles and jets, throttle plate screws and every O-ring for both carburetors. Float needle seats are optional.

 

2. The first step is to remove the carburetors. We removed the gas tank, not strictly necessary as the carbs are so easy to access. Loosen the clamps at the intake elbow and the engine, then gently twist the carburetor free.

 

3. Once the carb is free, remove the throttle cable from the throttle plate and release the choke cable from the choke plate by loosening the holding nut.

 

4. Release the float bowl retaining bail and remove the bowl. Put the carburetor on its side and gently tap out the float retaining pin. Note: The pin has serrations on one end to lock it in place. Drive the pin out from the opposite end.

 

5. Remove the main jet with washer, needle jet assembly, idle jet and idle mixture screw, noting their locations. Also note the order of the needle jet assembly, which has three pieces: the venturi, the jet and the pre-atomizer.

 

6. Turn the carb over. Remove the four screws securing the throttle slide cover. Remove the cover and then the throttle slide complete with diaphragm. It will drop free easily.

 

7. Remove the four screws holding the choke cover and remove the cover. Remove the throttle spring and idle screw. Remove the nut securing the throttle cable lever to the throttle shaft and remove the lever. Remove the two screws holding the throttle shaft retaining plate and remove the plate.

 

8. To remove the throttle shaft you must first remove the throttle plate. The two screws securing it to the shaft are peened at the factory to prevent them loosening. The exposed threaded ends must be filed off before you try to remove the screws.

 

9. Using a tight-fitting screwdriver, loosen the screws. If they fight you, turn them back in and file the ends again. Repeat until the screws will come out, then pull the throttle plate free.

 

10. Remove the throttle shaft. Note the orientation. The screw head recess is to the outside, as shown. The throttle plate has a small dimple at 12 o’clock that also faces to the outside.

 

11. Remove the four screws and plate securing the diaphragm to the slide and remove the diaphragm. The slide needle is held by an internal spring clip and has four stops. Remove it by twisting it 90 degrees then pulling it out. If it clicks and stops, twist another 90 degrees and continue. Repeat until it pulls free. Note the number of stops to remove; you’ll want to reinstall the new needle the same number of stops. 

 

12. Soak the carb body and all parts in solvent. Rinse and, if available, give them a final clean in an ultrasonic washer, rinsing when done. Blow out all ports with compressed air. To replace the float needle seat, thread a 7mm x 0.75mm pitch tap into the seat until it stops.

 

13. Next, clamp the end of the tap firmly in a vice. With an assistant holding the carb body, place a block of wood over the jet ports and hit the wood with a hammer until the body separates from the seat. We heated the body with a heat gun, making removal easier.

 

14. Make sure the seat bore is clean. Coat the outside of the new seat with anti-seize compound. Using a wooden dowel, drive the new seat into place until it bottoms out.

 

15. Put a new O-ring on the throttle shaft. Coat the O-ring with silicone lubricant and install the shaft into the body, noting its orientation. Install the throttle shaft retainer and screws.

 

16. Install the throttle plate in the shaft making sure the dimple on the plate is facing up (toward the top of the carb) and out. Coat the retaining screws with permanent-type thread-locking compound. Screw firmly in place.

 

17. Install the throttle cable plate on the throttle shaft. Reinstall the idle screw and spring. Place a new O-ring on the choke valve shaft and coat with silicone lube. Install the choke valve with index hole on choke plate aligned with oblong intake port on choke valve body. Using a new gasket, reinstall the choke assembly to the carb body.

 

18. Install new O-rings on the idle jet, main jet, needle valve venturi and idle mixture screw. The central needle valve jet has three pieces: Install the pre-atomizer followed by the jet and finally the jet venturi. Install the idle and main jets and the idle mixture screw.

 

19. Place new float needle into seat. Install new float and pivot pin. Seat the serrated end of the pin by lightly squeezing it into the float bowl post. Set the float so it’s parallel to the carb body when it touches the needle. Install new float gasket followed by the float bowl.

 

20. Install new diaphragm on slide. The diaphragm is “clocked” to the slide, with a molded, raised rubber edge that locks into a corresponding slot in the top of the slide. The outer edge of the diaphragm (just visible above thumb at left) has a similar molded edge that slots into the carb body when the slide is dropped in place. Replace slide cover and four screws.

 

21. Adjust the idle screw until it just touches its stop, then screw it in one turn. Lightly seat idle mixture screw, then turn out 1-1/2 turn. Attach throttle and choke cables and install carbs. Finally, start the engine and fine-tune the carbs.

BMW /5 Charging System Upgrade

 

As good as BMW’s classic /5 series is, there’s always room for improvement. One thing old /5s — and just about every airhead from 1970-1994 — can really benefit from is a charging system upgrade. While the stock system basically works fine, it can come up short in voltage delivery, especially in low-rpm urban situations where the engine doesn’t spin at high enough revolutions to maintain the necessary voltage to keep the battery up. 

Euro MotoElectrics in Denver, Colorado, specializes in electric system upgrades for BMW, Moto Guzzi and Ducati. Over the years, they’ve developed numerous starting and charging kits for vintage and contemporary BMWs, including the EnDuraLast III kit for 1970-1977 airheads. 

The comprehensive kit includes a new 4-wire stator plus a new rotor, diode board, diode board mounts, alternator brushes, an adjustable voltage regulator and wiring. The major benefits of the system are increased output (240 watts versus 180 watts stock), with charging voltage coming on at significantly lower rpms than the stock system.

For our BikeMasterinstall on a 1973 R75/5 we also had Euro MotoElectrics send us a new front crankshaft oil seal (easy to do while you’re there) along with a rotor removal bolt and an optional resistor lead for the charging light. The charging light excites the system, but if the light fails the system won’t charge. This simple modification is just a safeguard in the unlikely event the charge light does fail.

This is a high-quality, well-thought-out upgrade and everything goes together exactly as it should. That said, we suggest making this a weekend project to give yourself plenty of time, as it is fairly involved for the average weekend warrior. Required tools include a good soldering iron and solder/flux, a torque wrench, and, if you replace the crankshaft seal, a seal puller.

 

Depending on the exact year of your bike, you may or may not have to install an insulated Y-post connection for the upgraded 4-wire stator. The extra wire — added starting in 1974 — increases the efficiency of the AC to DC conversion. We forgot to order the available kit and came up with our own Y-post, a 4mm bolt with mylar for insulation. Simple enough, but the optional Y-bolt kit from Euro is only $2.75 and worth getting. That brings us to cost, which we consider very reasonable given the improvements gained (more on that in a second). The complete kit goes for $350, with the rotor tool adding $8.25, the seal $7.95 and the charging light circuit mod another $20, for an all-in of $388.95 if you also get the Y-post kit. By comparison, a replacement BMW rotor and stator alone will set you back almost $500.

As for performance, our system went from barely producing 13 volts at 4,000rpm to kicking out 14.25 volts as low as 1,500rpm. That’s an impressive improvement, ensuring full charging even if all you do is lope around town. As ever, we suggest having a good manual on hand for parts identification and proper torque specs.

 

1. First and most importantly, disconnect the battery by removing the ground cable. The alternator is under the front engine cover. Remove the three Allen-head bolts securing the front cover to the engine and remove the cover.

 

2. Next, disconnect the electrical connections at the alternator (five spades on our R75), then remove the three Allen-head bolts securing the alternator cover and stator to the engine.

 

3. With the Allen-head bolts removed the alternator cover and stator should remove easily as a unit to reveal the alternator rotor. The stator is pinned to the cover with a roll pin at the factory. The new stator is not.

 

4. Remove the Allen bolt securing the alternator rotor to the crankshaft. Install the long removal bolt. It threads into the rotor only, pushing against the inside of the crank to pull the rotor free.

 

5. Tighten the bolt, then tap the rotor with a brass or rubber mallet. It will usually pop off its taper. Be careful not to overtighten the bolt; it could break.

 

6. With the rotor off, we elected to replace the front crank seal. It wasn’t leaking, but it’s easy enough to do. After drilling a small pilot hole, we used a seal puller and it popped right out.

 

7. Installing the new seal is a simple matter of positioning it and pushing it evenly around its circumference with hand pressure to start, followed by seating with a flat driver such as a socket or small block of wood, working evenly around until it’s flush with the case.

 

8. Using a soldering iron, melt the solder securing the three wires from the stator to the junction block on the alternator cover and remove them from the block. The blue device is a “solder sucker” — a handy vacuum that sucks up the solder and gets it out of the way while you’re working.

 

9. With the three alternator wires pulled free from the junction block, remove the two screws securing the block to the cover and remove the block.

 how-to

10. Next, place the cover on the jaws of a vice with the stator clear and gently drive the stator out of the cover, working back and forth from one side to another. It usually comes out quite easily.

 

11. With the stator removed, flip the cover over and remove the two nuts securing the brush holder to the alternator cover, followed by the brush holder itself. Note the insulating collar on one of the locating posts.

 

12. With the brush holder removed, use a soldering iron to melt the solder at the brush lead connections and remove the brushes from the holder.

 

13. The kit comes with new brushes. The insulation on the leads from our old brushes was in good shape so we transferred it to the new brushes after first lightly soldering the wire ends to keep them closed.

 

14. Next, install and solder the new brushes to the holder, making sure that once installed the brush wires will be under the holder and the solder joint at the top for proper clearance to the cover. Reinstall the brush holder, noting the insulating collar on one locating post.

 

15. Our early alternator required adding a Y post for the new 4-wire stator. We drilled a 5mm hole in the position shown, then used a mylar insulating collar and mylar washers to isolate a fixed mounting post made from a 4mm bolt with one nut fixing it to the cover and another to fix the fourth wire and the spade terminal connection.

 

16. Next, install the new stator in the alternator cover, making sure it’s clocked so the stator wires freely pass through the cover as shown. This photo shows the new stator’s fourth wire secured to the Y post we installed.

 

17. Install the junction block for the stator wires and solder the wires in place. It doesn’t matter which goes where. If necessary, ream out the holes for the wires using a small drill bit. Clip the excess off the wires when done.

 

18. We next swapped out the original diode board, a simple matter of removing the four Allen screws securing it to the engine. Some engines had rubber mounts for the diode board. Ours did not. 

 

19. Before installing the new diode board we wired in a new power lead to the main terminal on the starter. This is to ensure a solid voltage path.

 

20. The original power lead from the wiring harness was redundant. To keep it available but isolated, we insulated the connecting spade terminal with shrink wrap tubing.

 

21. Connect the wiring to the D+ terminal on the back of the new board (the new wire from the starter is also shown connected). Note: Our early bike required shortening the original diode board mounting screws 0.25 inch each to mount the new diode board.

 

22. Next, we installed the new rotor, using the supplied new bolt and lock washer and torquing it to 14ft/lb.

 

23. Install the alternator cover and stator. To keep the brushes clear of the rotor slip rings, carefully pull the brush springs back, cocking them on the brush holder mounting posts. Snug the bolts down to roughly 6ft/lb. Do not overtighten. Reseat the brush springs.

 

24. With the alternator installed, connect all the wiring as shown. The blue wires are additional grounds.

 

25. Our final step (we could have done this at any time) was to replace the original voltage regulator and install the optional charging light energizing circuit. The fuel tank must first be removed to gain access to the voltage regulator.

 

26. Replacing the regulator is a simple matter of disconnecting the regulator harness before removing two bolts, transferring the harness to the new regulator and bolting it to the frame. The optional charging light circuit attaches to one of the regulator D+ wires using a Posi-Lock tap connector.

 

27. The other end of the circuit connects to the right ignition coil on the spare blade for the switched battery circuit to the coil, which is a green/blue wire. Finally, we reinstalled the front cover before reconnecting the battery. MC

Adjusting 1977 Suzuki GS750 Valves

How-To 

Suzuki’s 1977-1983 2-valve 4-cylinder GS series engine was one of the best. Whether in 550cc, 650cc, 750cc, 850cc or 1,000cc guise, these air-cooled twin-cam fours were praised when new, and over the years they’ve proven themselves to be remarkably robust, able to withstand gross negligence and abuse. That’s good news, because it means that with proper care, you can expect a GS to run, well, almost forever.

BikeMasterAn often neglected maintenance item on these engines is valve adjustment, although experience shows that gently ridden machines tend to hold to spec for tens of thousands of miles. Our subject 1977 Suzuki GS750 is a perfect example of this. An original condition survivor, it shows a low 12,500 miles on the odometer and looks like a bike that was only ridden when it was nice outside, and put in the garage when it wasn’t. Checking the valves confirmed this: All the valves were within specification and no adjustment was needed.

The valve clearance (or lash) on the 2-valve GS750 is very tight; 0.03mm-0.08mm, or 0.001in-0.003in. Loose is better than tight, and in our case the valves were all on the high end at 0.0025in-0.003in. The valves are shim over bucket, with adjustment shims carried in a recess in the actuating bucket. Removing shims requires the correct valve shim tool, readily available from Motion Pro for $16.50. Shims are available from various sources individually or in kits, with individual shims costing $12-$15 and kits around $75-$100. Local shops typically stock the shims, and once you know what you need you can usually purchase them from the local Suzuki dealer or independent shop.

You’ll need a good set of feeler gauges, making sure the set includes the thin sizes needed for the Suzuki. Besides that, all you’ll need are standard hand tools. The actual checking doesn’t take too long, but be prepared to either let the bike sit as you locate the necessary shims — or do the job twice if shims aren’t available locally and you need to keep your bike on the road while waiting for them. As always, have a good manual at hand to confirm proper specifications.

 How-To

1. The first step is to remove the gas tank. There are two lines to the petcock, a fuel line and a vacuum line that opens the petcock when the engine is started. They’re different sizes and only go on one way. Remove and plug the lines. Remove the single bolt at the rear of the gas tank.

 How-To

2. Remove the gas tank, then remove the horn from its mount. Remove all four spark plugs. This makes it much easier to rotate the engine as you index each camshaft lobe as you won’t be working against compression.

 How-To

3. Next, remove the four camshaft cover end caps. Use the proper JIS Phillips head driver. One end cap screw on our GS was damaged to the point we had to drill it out, using successively larger bits until the head of the screw broke off. From there it was easy to remove the remaining screw shaft.

 How-To

4. Working in a cross pattern, remove the valve cover retaining bolts and the valve cover breather cover; the valve cover won’t clear the frame for removal with the breather cover in place.

 How-To

5. Remove the right side ignition cover. Using a 19mm wrench, rotate the engine clockwise until a camshaft lobe is straight up. Here it’s the #4 exhaust.

 How-To

6. Check the lash, then rotate the engine as necessary to get each camshaft lobe in the position shown, checking each one. As it turned out, our engine needed no adjustment, each valve coming in at 0.0025in-0.003in clearance.

 How-To

7. If necessary, adjustment is done by changing the adjusting shim. To do this, insert the shim tool as shown, hooking it under the camshaft and positioned so its raised center ridge contacts the edge of the valve actuating bucket. Rotate the tool down and toward you and depress the bucket.

 How-To

8. With the bucket depressed, remove the shim using a magnet or tweezers. Any oil under the shim will tend to hold it in place. If necessary, use a dentist’s pick to lift it from its seat. It will then pull free.

 How-To

9. The 2-valve GS750 engine uses 27.5mm-diameter shims. The shims come in 0.05mm increments from 2.15mm-3.10mm. Choose the proper shim by subtracting the readings and shimming up or down as necessary. If the valve is loose, you’ll need a thicker shim. If tight, you’ll need a thinner shim.

 How-To

10. Once the valve lash is correct, clean the valve cover gasket surfaces. Install the half moon end plugs, two on each side. If the new valve cover gasket has strengthening ribs as shown, cut them off before installing the gasket and valve cover. Install the gasket and plugs dry.

 How-To

11. Install the valve cover followed by the valve cover breather cover. The valve cover bolts on our engine were mildly corroded. We wire brushed them clean, then coated the threads with engine oil before installing them.

 How-To

12. Tighten the cover bolts evenly, working in a cross pattern. Install the spark plugs, side covers and ignition cover. Install the horn. Install the gas tank and reconnect the fuel and vacuum lines. MC