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

Replace Honda CB450 Swingarm Bushings

Honda CB450 swingarm bushings have a reputation for wearing out prematurely. Early CB450s like our subject 1970 CB450K4 used metallic bushings, while later ones apparently switched to plastic, a material more than a few manufacturers embraced for ease of installation.

Whether early or late, CB450 swingarm bushings don’t appear to last more than 10,000 miles or so. Our subject bike doesn’t appear to have led a particularly difficult life, yet with a mere 13,000 miles showing on the clock the swingarm bushings were shot, exhibiting an easy 1/8 inch or more of slop on the swingarm pivot pin. Although a small amount of play won’t show adverse effects, too much results in a wandering rear end, the back wheel moving left and right, generating an uncontrollable steering input. Typically, once the wear becomes great enough to notice, it accelerates rapidly.

As originally fitted, the swingarm on the CB450 (and many other Hondas, including the CB500T, CB500 and CB550 Four and all pre-1979 CB750s) had a single bushing on either side of the swingarm followed by a felt sealing washer, a thrust bushing and an outer metal dust cap. Original replacement bushings are still available, but experience shows that if you’re actually riding your bike you’re wise to consider fitting aftermarket bronze bushings like the ones we sourced from Honda specialists Charlie’s Place.

The bronze bushings from Charlie’s Place do away with the felt sealing washers and the thrust bushings, and at $70 a set they are only marginally more expensive than stock (typically around $55-$65 for bushings, thrust bushings and felts), and thanks to their superior material it’s unlikely you’ll ever replace them again. BikeMaster

Better yet, the bronze bushings are very easy to install. The factory bushings have no shoulder, requiring the installer to ensure they’re properly inserted to the correct depth inside the swingarm. The bronze replacement bushings are shouldered, making insertion installation much easier: Just press them in until they seat.

While installation is easy, the old bushings can be difficult to remove, particularly the early metallic style, which can become seemingly welded to the swingarm. The solution is often to cut them out or press them out with a hydraulic press, if available. Thankfully, ours removed quite easily using nothing more than a hammer and a blunt punch.

As we show, installation is a snap, but you might have to give the bushings a quick pass with a small brake cylinder hone to get a proper fit for the swingarm pivot. The bushings are a light interference fit with the swingarm, so they tend to compress slightly. If you have to hone them, do so in short passes, checking the fit of the swingarm pivot pin frequently. You don’t want to remove any more material than necessary for the pin to slide into place.

This is a fairly straightforward job, easily within reach of the average weekend mechanic. The only special tools you might need are a small 3/4-inch to 2-inch brake cylinder hone and a torque wrench for final tightening. Budget a morning to get the job done, and as always, we recommend having a good shop manual on hand for parts identification and proper torque specs.

 

1. Put the bike on its centerstand. Disconnect the chain. Disconnect the brake stay at the brake hub. Disconnect the rear brake actuating rod. Remove the rear axle cotter pin, loosen the axle nut and then remove the rear axle and finally the rear wheel. Remove both lower shock absorber mounting bolts.

2. Remove the swingarm pivot bolt nut on the left side of the swingarm.

3. The end of the swingarm pivot bolt is dimpled. Using a suitably sized punch, gently knock the pivot bolt through the swingarm. Remove the bolt.

4. With the pivot bolt removed, pull the swingarm straight back and free of the frame. To give ourselves a little more working room, we removed the left shock. Although we didn’t, removing the chain guard simplifies chain installation.

5. Once the swingarm is free, remove the dust caps and thrust washers (thrust washer pictured). Set the thrust washers aside; you won’t use them with the new bronze bushings.

6. Next, using a suitable drift, remove the swingarm pivot pin. It should knock out easily, but accumulated grease, dirt and corrosion can make it a little stubborn to remove.

7. Here’s our pivot pin after knocking it out of the swingarm. Thankfully, it cleaned up well, as replacements are getting quite difficult to find.

8. With the pivot pin knocked free, remove the felt sealing washers at either end of the swingarm and discard them. The new bronze bushings don’t use these.

9. Next, remove the old bushings. Ours pushed out fairly easily using nothing more than a blunt-ended punch and a hammer, but they are known to be difficult to remove, sometimes requiring a hydraulic press to push them out or a hacksaw blade to cut them out.

10. Here’s one of our old bushings removed from the swingarm. Before moving on to installing the new bushings, clean any debris or grease from the inside of the swingarm tube.

11. Next, install the new bushings. We pressed them in using a simple homemade tool made up of a piece of all-thread rod, with washers and nuts at each end, steadily tightening the nuts until the shoulders of the bushings seated against the swingarm.

12. Here’s one of the bushings fully seated in the swingarm. With the new bushings installed, we found the swingarm pivot pin to be a tight fit.

13. To make the swingarm pin a sliding fit in the bushings, we lightly honed them with a small brake cylinder hone, removing only enough material to allow a tight sliding fit. After honing, thoroughly clean the bushings with brake parts cleaner.

14. With the bushings honed, our swingarm pivot pin (visible inside the bushing) slipped into place. With the pivot pin installed, lightly grease the dust caps and install them on either side.

15. Using a grease gun, push the old grease out of the swingarm pivot bolt until only fresh grease comes out of the lubricating holes in the bolt.

16. Push the swingarm back into place in the frame, then insert the swingarm pivot bolt through the swingarm from the right side.

17. With the swingarm pivot bolt in place, thread the pivot bolt nut onto the bolt and then torque it to 51-65ft/lb. We went for the middle of the range, 58ft/lb.

18. Next, using a grease gun, grease the swingarm pivot until fresh grease just starts to show around the dust caps. Reinstall the rear wheel, the drive chain, the brake stay and the brake linkage. Adjust the chain as necessary and tighten the axle nut, making sure to reinstall the cotter pin.

Replace Norton Commando 850 Clutch Plates

If you’re actually riding your old Norton Commando 850 — and we hope you are, because they’re one of the great bikes of the ’70s — chances are good that at some point you’ll have to replace the clutch plates. The original setup used five alternating bronze friction plates keyed to the center clutch hub, with four plain steel plates keyed to the outer clutch drum followed by a pressure plate and a single diaphragm-spring plate compressing the plates. It’s a fine setup, but eventually the plates wear. Slippage and overheating take a toll, as well: Once the steel plates start to blue, they’re toast, and both the steel and the bronze plates can warp from overheating.

The good news is, replacement clutch plates are readily available and the design of the Norton clutch makes servicing quite simple. Only one special tool, a diaphragm spring compressor, is required. You can buy the tool for $26 from donelsoncycles.com, or you can make your own if you want (go here to see how).

There are a few points to appreciate, one of them being the stacked height of the clutch plates. According to various sources, Commando 850 clutch plates should have a stacked height — the total thickness of all the plates stacked together — of approximately 1.17 inches. However, replacement clutch plates (even stock Norton items) rarely stack out to that exact specification. The height matters because of the nature of the diaphragm spring clamping the plates together. A shorter stack allows the spring plate to push farther into the clutch hub, resulting in a stronger pull at the clutch lever, while a taller stack means the spring plate is flatter, resulting in a lighter pull. That makes a taller stack desirable, but only to a point. If the stack is too tall the clamping pressure is reduced, increasing the risk of clutch slip. Back in the day, variations in stack height were routinely balanced by inserting a fifth steel “shim” plate to compensate, but shim plates are now hard to find.

BikeMaster

So what to do? Well, as we discovered with our Barnett plates, which had a stack height 0.145 inches shorter than recommended, there’s lots of room for variation, as our installed clutch requires only moderately strong pull and shows every indication it will work just fine. Bottom line: As long as the installed assembly is below the diaphragm spring retaining clip, you’re probably fine.

As noted, we sourced all our plates from Barnett, known for quality clutch parts. The Barnett friction plates are fiber, not bronze, which brings up the age-old issue of whether to run the clutches in engine oil or, as some prefer, automatic transmission fluid. Barnett notes that their clutches are made to run in engine oil, but are also designed to work in ATF, as well.

As to cost, Barnett sells the friction plates as a set for $65.53, while the steel plates are sold individually at $8.10 each. Primary case gaskets are readily available from a variety of sources for $4-$5. As always, we recommend having a good shop manual on hand for parts identification and proper torque specs.

 

1. Remove the three nuts and washers securing the brake/foot peg assembly to the aluminum sideplate. Remove the brake/foot peg assembly. Place a drain pan under the primary cover. Using a 13/16in socket, remove the center primary cover securing nut. Remove the primary cover and let the oil drain.'

2. With the 13/16in socket, loosen the clutch adjuster lock nut. If it’s stuck, give the socket wrench a quick rap with a hammer. It should shock loose easily. Unscrew the clutch adjustment screw.

3. Next, install the clutch diaphragm removal tool. Screw the center bolt into the clutch to engage at least five threads. Lock the bolt with its lock nut. Next, tighten the outer nut while holding the bolt until the clutch diaphragm spins freely in the clutch hub.

4. Next, remove the wound circlip securing the diaphragm. The circlip has a slotted opening in its free end. Insert a screwdriver into the slot and pull the circlip toward the center of the clutch hub, then pull the circlip free.

5. The clutch diaphragm should now simply fall out, exposing the outer clutch pressure plate. Note the clutch adjustment rod protruding from the center of the clutch hub.

6. Next, remove the outer clutch pressure plate, examining it for any signs of scoring. If it’s badly blued from being overheated, consider replacing it as it could be warped.

7. Next, remove the clutch plates. There are five bronze friction plates and four steel plates. The plates alternate, starting with bronze and ending with bronze. On bikes with any kind of mileage, these will generally show signs of scoring and/or overheating.

8. The Commando 850 clutch works best with a stacked height of approximately 1.17in. A thicker stack equals a lighter pull, but also introduces the risk of more slip, which causes overheating and wear. Our original plates had a stacked height of 1.053in.

9. Our replacement Barnett plates had a stacked height of 1.025in. Although shorter than the stock recommendation, they worked fine and with good pull at the clutch handle. It was once standard to insert a fifth steel plate of the needed thickness to make up the difference. However, custom steel “shim” plates are no longer available.

10. Before installing the new fiber plates, soak them for a few minutes in quality engine oil or automatic transmission fluid, depending on what you plan to use in the primary case.

11. Drain the plates after soaking. Wipe off excess oil with a lint-free cloth. Install the new plates, starting with a fiber friction plate and alternating with steel plates, ending with a fiber friction plate.

12. With the new clutch plates installed, install the outer pressure plate. If reusing the original, lightly scuff the surface with a Scotch-Brite pad and then clean it with brake parts cleaner or similar before installing.

13. Next, with the removal tool still attached, place the diaphragm spring in place, then secure it with the large wound circlip. Make sure the circlip is seated in its groove, then loosen the outer nut on the tool to release the diaphragm. Remove the tool.

14. Before installing the clutch adjuster, remove the inspection cover on the right outer transmission cover. Make sure the clutch release arm is properly located and that the cable is secure as shown.

15. Screw the adjuster into the center of the diaphragm and loosely fit the locking nut. Screw the adjuster in until it just touches the release rod, then screw it back out 1/8-1/4 turn. Lock the nut in place.

16. Remove the larger primary cover rubber “O-ring” seal. Clean the groove it sits in, then install a new seal. When installing the new seal, place the bonded end joint at the highest point as shown to diminish the chance of an oil leakage from the primary cover.

17. To further discourage oil leakage from the primary, place a suitably sized O-ring over the outer primary cover stud. The O-ring will crush when the outer cover is installed.

18. Finally, fill the primary cover with 300cc of quality engine oil or, if preferred, automatic transmission fluid. Reinstall the brake lever/foot peg assembly.

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.