Rebuilding Your Classic Motorcycle Starter

Vintage motorcycles, with their timeless charm and classic engineering, often possess a unique character. However, time and wear can inevitably take their toll on even the most robust components. One such component that can show its age is the starter motor. A failing starter can manifest as a sluggish crank, an inability to turn the engine over, or even complete silence when the starter button is pressed. While sourcing brand-new replacement starters for older models can be challenging and expensive, a more cost-effective and often more rewarding solution lies in rebuilding the existing unit. This guide will walk you through the process of installing a starter clutch rebuild kit, using a 1970 Honda CB450K4 as a prime example, to bring your classic machine back to life.

Understanding Starter Motor Wear

As reliable as vintage Japanese electrical hardware may be, everything has a service life, and that includes the starter motor on our subject 1970 Honda CB450K4. This particular bike had been displaying a tendency to drag and otherwise turn slowly, making the CB450 somewhat hard to start. This is a common symptom of wear within the starter motor's internal components, including brushes, bushings, and the planetary gear reduction system. Rebuilding the starter is a viable option when new parts are scarce or prohibitively expensive. Rebuilding your starter is a good option, and fortunately, kits like the one we got from Honda specialists Common Motor Collective are readily available. The $65 kit we purchased is very comprehensive, with all new wear and service parts including a new drive-end bearing and seal, a new brush plate assembly with brushes, starter housing O-rings and gaskets, planetary gear bushings, the armature support plate bushing, the rear cover bushing, and new fiber gaskets and replacement nuts for the starter battery cable post.

Assessing the Starter's Condition

Before diving into the rebuild, it's crucial to assess the condition of the core starter motor components. Once the starter has been removed, make sure the armature and field coils are good before going any further. You can research how to confirm all of this for yourself using a simple multimeter. However, we took both pieces to our local automotive electrical shop, where a quick test confirmed that:

• The armature was running true and the windings weren’t broken or damaged.
• The commutator end was in good condition with even resistance, needing only a light sanding to clean up the contact face.
• The starter field coils were good.

If it hadn’t passed these tests, we would have had to look for a used starter and start over. New starters for the CB450 haven’t been available for some time, and while used starters are typically for around $50-$90, it’s possible you’ll end up buying the same problems you already own.

Tools and Preparation

This project doesn’t require any special tools, although we strongly suggest having the proper JIS “Phillips” drivers and an impact driver for removing the necessary fasteners, especially the neutral switch, which also secures the alternator wiring. A small bench-top tool press comes in very handy, but you can get away without it; you just won’t have as much control when it comes time to press in new bushings and such. As ever, we recommend having a good shop manual on hand for parts identification and proper torque specs.

Getting all parts clean before reassembly is paramount. Brake and electric parts cleaner works best here; just remember it’s nasty stuff, so wear gloves and work in a well-ventilated area. Although not technically complicated, this can be a challenging project as it involves a fair amount of detail. We suggest giving yourself a full morning or afternoon so you don’t rush the job; give yourself time to work slowly and carefully. If you can do that, you shouldn’t have any problems, and you might even find it a fun challenge.

Step-by-Step Rebuild Process

1. Starter Removal

First, disconnect the negative lead to the battery. Disconnect the positive battery lead at the starter (the post is just visible on the end of the starter, under the left exhaust header). Remove the two bolts securing the starter. Remove the starter. Save for the hassle of having to remove the left side cover, which also houses the alternator, removing the starter on the CB450 is relatively easy. The side cover must be removed, as it’s otherwise not possible to re-engage the starter drive chain once the starter has been removed.

2. Accessing the Starter Internals

Remove the gear shift lever, then the final drive cover. Remove the two screws securing the neutral switch above the sprocket, which secures the alternator wiring. An impact-type driver is recommended as the JIS “Phillips” screws can be tight. The neutral switch is keyed. Note its orientation for reinstallment.

3. Disassembling the Starter Body

With the starter on the workbench, remove the two long bolts holding it together. If the bolts are tight, use penetrant and an impact driver. Remove the bolts, then the rear cover.

4. Removing Wear Components

Place the starter upright on the drive end. Remove the screw securing the lead from the starter motor field coils to the brush assembly. With the brushes still in place, lift the brush assembly and plate straight up and remove it from the starter. Remove the thrust washers from the end of the commutator. Clean and set them aside for reassembly.

5. Planetary Gear Assembly

Remove the drive end of the starter. The drive end is a planetary gear set for starter drive reduction. The starter motor spins the two smaller gears, which spin the starter output shaft. Remove the two small gears and set aside. Remove the armature support plate and any thrust washers under it. Remove the armature and clean it using electric parts cleaner.

6. Drive End Housing and Bearings

Flip the drive end over. Remove the keeper ring for the end bearing, then the snap ring on the output shaft. Push the output shaft free of the drive end housing. Remove the thrust washer from the shaft. Clean it and the shaft and set aside for later reassembly. Place the housing on wooden blocks or a vise and drive out the end bearing using a flat punch. It should come out fairly easily. With the bearing removed, use a seal extractor or suitable tool to remove the drive housing seal. Thoroughly clean the housing.

7. Installing New Bearings and Seals

The original bearing features a metal shield on the engine side, while the replacement bearing has rubber shields on both sides. It could be argued that this change makes the starter seal unnecessary. Regardless, we did install the new seal, which should be pushed into place with the open side up. With the seal seated in the housing, install the bearing using a bearing driver, making sure it’s inserted deep enough for the securing clip to be installed. Install the clip. Push the output shaft with thrust washer installed back into place and reinstall the snap ring.

8. Bushing Replacement in Planetary Gears

To remove the bushings in the planetary gears, we supported the gears on a suitably sized socket (open end up), then used a small press and a 1/4-inch drive, 5/16-inch deep-well socket to push the old bushings out. The new bushings are chamfered at one end to ease installation. Start the bushing by hand, making sure that it’s square with the gear, then press it fully home using the press.

9. Armature Support Plate Bushing

Clean the armature support plate, removing any old gasket material. Press out the shouldered bushing in the plate, then press the new bushing in with the shoulder in the same orientation. Install the new support plate gaskets with the narrow gasket facing out and the wide gasket to the inside of the starter.

10. Reassembling the Starter

Slip the cleaned armature back into the starter body. Install any thrust washers removed earlier, followed by the armature support plate. Loosely install the drive end housing.

11. Rear Cover Bushing and Wick

To remove the rear bushing, we first tapped 8mm threads into the bushing. We then threaded a bolt into the bushing, through a flat plate placed over the cover opening. Tightening the bolt pulled the bushing out easily. With the bushing out, remove and save the felt oil wick as the kit does not include one. Clean the cover. Reinstall the wick and press the new bushing in flush. Oil the bushing.

12. Final Assembly and Brush Plate Installation

Stand the starter on the drive end. Install the new O-ring seal on the starter body. Pull the brush springs back and slip the brush plate over the commutator. Ensure the coil wire aligns with the insulated brush set and the tang in the plate aligns with the notch in the starter body. Attach the field coil wire. Replace the thrust washers removed earlier. Smear a thin film of oil on the end of the armature shaft. Install the rear cover, making sure the brush plate is properly aligned.

13. Securing the Starter Body

With the rear cover in place, install the two long Phillips bolts through to the front housing and screw them home tight. Turn the starter by hand to ensure it does not bind.

14. Drive End Housing and Cable Connections

Install the new O-ring on the drive end housing and grease lightly. Remove the old starter cable nuts and insulators and replace them with the new ones in the overhaul kit.

15. Reinstalling the Starter

Hold the starter drive chain and sprocket in position and install the starter, making sure the sprocket and starter drive ends spline together. Secure the starter with the two bolts. Ensure the sealing surfaces for the engine and side cover are clean. Install a new gasket. The dowels will hold it in place. We did not use any sealant.

16. Reassembly of Covers and Controls

Finally, reinstall the side cover with the alternator, the alternator wiring securing plate, the final drive cover, and the shift lever. Secure the positive battery lead to the starter. Connect the negative lead to the battery.

Testing the Rebuilt Starter

If everything went right, your starter should spin right over. A successful rebuild will result in a strong, consistent crank, bringing your classic motorcycle back to its former glory.

Common Issues and Troubleshooting

Q: My starter still drags after the rebuild. What could be wrong?
A: Check the battery voltage and condition. Ensure all connections are clean and tight. Verify that the armature spins freely without binding. There might still be an issue with the starter motor itself or the wiring.

Q: I can't get the flywheel off. What's the best way to hold it?
A: Using a dedicated flywheel holding tool is the most effective method. If you don't have one, you might need to improvise with a strap wrench or a custom-made tool, but be cautious not to damage the flywheel.

Q: Where can I find specific parts for my vintage motorcycle starter?
A: Specialist suppliers for vintage motorcycle parts, like Common Motor Collective for Honda models, are your best bet. Online marketplaces and forums dedicated to your specific motorcycle model can also be valuable resources.

Q: My starter clutch wasn't the issue; I was missing the chain and sprocket. Where can I find these?
A: This is a common problem with older bikes where parts may have been removed or lost over time. Used parts from reputable suppliers or online auctions are often the only way to source these. Forums dedicated to your bike model can be excellent places to ask for leads.