Articles in this section

The Complete Disassembly of The Honda CB350 / CL350 / SL350 Twin Cylinder Engine

Caleb Foster
  • Updated
Follow

CB350 Engine Schematic.jpg

Welcome to the first half of our vintage Honda CB350 twin cylinder engine rebuild series! In these videos, we will tackle the disassembly of the Honda CB350 twin cylinder engines (this applies to the CL350 & SL350* as well). The Disassembly or "tear down" is the crucial first step of the rebuild process in order to bring one of these engines back to life. This video series is filmed in "real time" and is to act as a supplemental demonstration in use with the Honda factory service manual. Link below:

 

Honda CB350 | CL350 | SL350 Factory Service Manuals

 

For many the idea of tearing down an engine is daunting and intimidating. The fear of "breaking something" or "doing something wrong" is often the road block that stops the process. The Honda CB350, CL350, and SL350* engines are straightforward and forgiving engines to work with. especially for a first rebuild learning experience. It is our objective to provide this information so that you can rebuild a Honda CB350 / CL350 / SL350* engine at home. 

 

Honda Motorcycle Models That Use this Engine Architecture

CB350 K0 / K1 / K2 / K3 / K4 / K5 / G

CL350 K0 / K1 / K2 / K3 / K4 / K5

SL350 K0 / K1* / K2*

 

*SL350 K1 - K2 uses a slightly different architecture on the lower half of the engine. Cases were redesigned to eliminate the electric starter and have similar looking, but uniquely different physical castings and gaskets; these are not interchangeable with the CB & CL engines. While the casting and a few parts changed, notably the kick starter mechanism, the internal design and upper engine assembly is almost identical to the CB & CL.   

 

Part 1: The Stator and Starter Clutch

When starting an engine disassembly, we find it easiest to begin with the lower left-side engine cover and all components behind it. If you're unfamiliar with these parts, they include the magnetic rotor, stator coils, electric starter clutch, and electric starter chain. Before you dig in too deep, make sure to drain the oil!

 

Magnetic Rotor

One key component in this section is the magnetic rotor, which is fitted onto the tapered end of the crankshaft. To remove it, you'll need our #9000 rotor puller tool. This tool threads into the internal threads of the rotor and presses against the crankshaft, allowing you to safely remove the rotor. The electric starter sprocket retainer should also be removed at this time.

 

Pro Tip: When removing the rotor, hold the large electric starter sprocket firmly against the back side of the rotor to keep the starter clutch components together.

 

Electric Starter & Drive Chain Sprocket

Next, remove the starter chain and the small sprocket attached to the electric starter. Once these are off, you can remove the two screws on the end of the electric starter and slide it out through the casting opening. To complete the left lower section, remove the drive chain sprocket retainer plate bolts, then take off both the retainer and drive chain sprocket.

 

Ignition Advance & Points Plate

Now, turn your attention to the components behind the points cover. An impact driver is a great tool for loosening the M5 bolts on the cover and the JIS bolts securing the points plate. Once the points plate is removed, un-thread the 10mm bolt and washer from the end of the camshaft to slide off the ignition advance.

 

⚠️ Stuck Ignition Advance? Don’t Force It!

Sometimes, the ignition advance can be frozen in place. While it may be tempting to pry or hammer it off, excessive force can damage the fragile camshaft end, which is very brittle. Instead, try these steps:

  1. Apply penetrating oil to the stuck part.
  2. Use heat to expand the metal.
  3. With enough heat, the ignition advance should pop right off.

We've seen too many broken camshafts due to rushed removals—take your time!

 

 

Preparing for Camshaft Removal

With the advance unit out, the final step in this portion of the disassembly is to remove the screws for the camshaft bearing end cover and loosen the rocker arm shaft jam nuts. Before proceeding further, rotate the tick mark on the rocker shafts to the 12 o’clock position—this puts the rocker arms to their loosest setting, making camshaft removal much easier. We will finish the cam and rocker removal in Part 3.

 

Part 2: The Clutch and Oil Pump

 

In this stage of the tear down, we’ll be focusing on the lower right side of the engine to prepare for the top-end removal. The parts we will be focusing on are the right-side engine cover, including the oil pump, centrifugal oil filter, clutch basket, shift shaft and selector, oil pickup screen, and crankshaft-to-clutch basket drive gears.

 

 

Right Side Engine Cover

Start by removing the kickstarter arm. These can sometimes be stubborn, so using a screwdriver to pry it  off or wedge it into the clamp opening can help loosen it. Penetrating oil is your friend. Once the kickstarter is off, remove all the screws and right-side cover to expose the internal components.

 

The Oil Filter Nut

One of the trickiest parts of this section is removing the oil filter basket retained by a special notched nut, which secures it to the crankshaft. You’ll need the #9005 Oil Filter Nut Tool for this step, it is a must have tool. 

  1. Remove the oil filter cover by taking off the snap ring and pulling the cover off by hand.
    • If the cover is stuck, you can insert a long M6 x 1.0 screw into its internal threads and tighten it until it touches the end of the crankshaft. Continued threading will push against the crankshaft and pop the cover loose.
  2. With the cap removed, you’ll see the oil filter nut and its locking tab washer. If there’s dirt and debris packed around it, take a moment to clean it out.
  3. Use a flat head screwdriver and or punch to bend the lock washer tab away from the nut so that the nut tool sits cleanly on the special notched nut
  4. To prevent the crankshaft from spinning, wedge a penny between the top of the clutch basket and crankshaft gears.
  5. Using a 3/8" breaker bar or an impact driver with an extension, break the oil filter nut free and remove the oil filter nut, special tabbed lock washer, curved lock washer, and oil filter rotor.

With the oil filter rotor removed, you’ve completed one of the toughest parts of the disassembly!

 

Oil Pump & Clutch Basket

Next, remove the oil pump and clutch basket—these must come out together since the oil pump piston is attached to the back of the clutch basket.

  1. Pry back the lock tabs on the oil pump retaining bolts and remove the 3 of them.
  2. Take out the four bolts and springs securing the front of the clutch basket.
  3. Remove the front of the clutch basket, then take out the 8 clutch friction discs and 7 steel plates.
    • ⚠️ Note: The 8th steel plate is held behind a large snap ring and does not need to be removed.
  4. Remove the snap ring inside the clutch basket, then slide out the entire clutch basket & oil pump assembly as one unit.
    • ⚠️ Note: We do not recommend removing the filter screen from the oil pump. The rubber that holds the screen is typically brittle and may crack upon removal. There are no new replacements for this part so it's best to keep it on the pump body. 

Shift Shaft

The last component to remove in this step is the shift shaft. Over time, dirt and debris can accumulate around the end of the shaft where the drive chain runs. Before removal:

  • Use a wire brush to clean off as much grime as possible for an easier extraction.
  • Pull down the shift hook on the right side.
  • Slide the entire shift shaft out of the engine in one piece.

With the shift shaft removed, everything left in this section will be taken out during the bottom-end disassembly.

 

Part 3: Camshaft and Cam Chain Disassembly

Part 3 is where things start to feel a bit more intense for many. At this point, we’re fully opening the engine, going beyond the level of disassembly required for regular servicing. In this step, we’ll be removing the camshaft and rocker arms, key components in the engine’s valve operation.

 

Preparing for Camshaft & Rocker Arm Removal

Back in Stage 1, we loosened the left-side rocker arms—now, we’ll do the same for the right side. Start by removing the tachometer drive cover and cable to access the rocker arm shafts. Next, break loose the jam nuts and remove them altogether with the washers.

Once the nuts are off, rotate the tick marks on the rocker arm shafts so they point straight up at 12 o’clock. This puts them in their loosest position, reducing tension when pulling them out. Now, remove the four JIS screws securing the right-side cover / cam bearing to the rocker box.

 

Opening the Engine & Accessing the Camshaft

With the right-side cover removed, it’s time to open up the top of the engine.

  1. Remove all eight acorn nuts and washers from the engine studs. These nuts are specialized hardware—don’t lose them, as they aren’t easy to replace.
  2. Pull off the top breather cover and baffle plate, exposing the camshaft and rocker arms.
  3. Rotate the engine until one of the camshaft sprocket bolts is visible. While a 10mm wrench works, we recommend a long-handle offset box wrench for better leverage. Break loose and remove the first bolt, then turn the engine to access and remove the second bolt.

A critical note: these cam sprocket bolts are unique and different from each other. One has a small shank that fits into the matching recessed pocket on the camshaft—be sure to keep track of where each bolt belongs.

Once both bolts are out, gently wiggle the cam sprocket off the camshaft to relieve pressure on the cam chain.

 

Cam Chain Tensioner & Camshaft

Before pulling the camshaft and rocker arms, we need to remove the cam chain tensioner at the back of the engine.

  • Unscrew the four bolts securing the tensioner mechanism and remove it.
  • This component keeps tension on the cam chain, ensuring smooth operation. Early CB350 and CL350 K0 engines used a hydraulic tensioner, while most later models use a more reliable spring-loaded plunger style. If you have an early hydraulic version, it’s worth swapping in the plunger-style tensioner for better long-term reliability.

With the cam chain pressure relieved, remove the each camshaft bearing end covers and begin pulling out the rocker arm shafts and rocker arms. Remove the rocker arms one at a time, keep them with their respective shaft and label which position they were removed from. IE: Left Intake, Right Exhaust, etc. They will be reassembled in these position they were removed from.

Now, with the rocker arms removed and the cam sprocket loose, carefully slide the camshaft out of the engine from the right side. You may need to rotate and maneuver it to align with the cutouts in the casting and cam sprocket for a smooth removal.

At this point, the cam chain and camshaft sprocket will be sitting loose in the engine. Let them drop down—they’ll be fully removed later when we take off the cam box.

 

Part 4: Removing the Cylinder Head, Cylinders, and Pistons

 

With the camshaft (Part 3) and oil filter (Part 2) removed, we’ve tackled the toughest parts of the disassembly. From here on, as long as nothing is seized, the process should be relatively smooth.

Removing the Cam Box & Cylinder Head

With the camshaft out of the way, remove the four screws securing the cam box and lift it off the engine studs. Once the cam box is removed, you can take out the camshaft sprocket.

Next, remove the cylinder head. It’s attached to the cylinder with just two bolts—remove them, and the head should slide straight up off the engine studs. If it’s stuck, use a rubber or plastic mallet to gently tap a thicker part of the casting. Never hammer on the engine fins, as they can easily break.

Note: This guide doesn’t cover valve train disassembly, but if you need help removing the valves, check out our valve removal tutorial using our valve removal tool.

 

 

Removing the Cylinders

With the cylinder head off, it’s time to remove the cylinders. If they are stuck to the upper crankcase, tap gently on the middle front and back of the cylinder casting using a plastic mallet or a block of wood with a hammer. Avoid striking the cooling fins—they’re fragile and can easily crack.

Dealing with Seized Pistons 
If your pistons are seized in the cylinders, this guide doesn’t provide specific instructions for removing them since there are varying levels to which a piston could be seized.

However, here are some general tips:

  • Start with minimal force and gradually increase when needed. 
  • Apply penetrating oil and heat—a torch can help loosen things up.
  • Take your time, it may take a few hours or days along with multiple penetrating oil + heat applications to start seeing some movement between the pistons and the cylinder wall. 
  • Your goal is to get things apart with minimal damage. Pistons can been seen as sacrificial versus the cylinders and connecting rods. In extreme cases, cutting or destroying the pistons might be the only option.
  • If you’re dealing with a severely seized piston, email us about our cylinder boring core service.

 

Removing the Cam Chain Guide & Tensioner Wheels

Once the cylinder is removed, remove the cam chain guide by pulling out the lower pin and sliding the guide up through the cylinder. The large and small tensioner wheels can also be pulled out from the bottom-end casting on the cylinder base surface.

⚠️ Careful: Don’t drop the small cushions for the large roller pin into the engine.

 

Removing the Pistons

To remove the pistons from the connecting rods, follow these steps:

  1. Remove the outer wrist pin clip on one side of the piston.
  2. Push the wrist pin out from the same side. If everything is in good shape, the pin should slide out easily, allowing you to remove the piston.
  3. If the wrist pin is stuck, try the following methods:
    • Apply heat and penetrating oil.
    • Remove the clip on the opposite side and use a socket to push on the edge of the wrist pin. 
    • Be careful not to hammer on the connecting rod—this can cause serious damage.
  4. Repeat the process for the other piston.
  5. Label each piston as "Left" and "Right" based on the sitting position on the motorcycle.

 

Neutral Ball Detent Removal

Before moving to the bottom-end disassembly, remove the neutral ball detent:

  • Use a screwdriver to bend down the lock washer.
  • Loosen and remove the large hex cap.
  • Take out the spring and ball bearing inside the cap.

 

Part 5: The Complete Bottom End Assembly

 

We’ve arrived at the step that many fear—opening up the bottom end of the engine. While it may seem intimidating, Honda’s bottom ends are incredibly durable and rarely present major issues. However, inspecting, cleaning, and servicing this section is always worth it. Opening it up is the only way to ensure everything is in good shape, remove decades of built-up grime, and prevent future problems.

 

Splitting the Crankcase

Start by flipping the engine upside down, resting it at an angle on the engine studs and the rear top edge of the case. In the previous step, we already removed the crankcase bolts from the top. Now, it’s time to remove all the bolts securing the crankcase halves together.

📌 Pro Tip: Use a cardboard template to keep track of the bolts! Draw the shape of the crankcase on a piece of cardboard and push each bolt into the corresponding position on the drawing.

Once all bolts are removed:

  1. Lay the engine on its side.
  2. Use a punch and mallet to gently tap the crankcase at Honda’s designated hammer points:
    • Front of the engine: A small ledge around the electric starter casting.
    • Rear of the engine: A dedicated separation point in the middle of the case.
  3. Tap just enough until you see the cases begin to separate.
  4. Flip the engine back upside down and lift the bottom crankcase half off.

 

Transmission & Crankshaft

With the case split, the transmission shafts can now be removed. These should be kept together as a set.

  • The outer bearings of the transmission shafts are held in place by:
    • A small pin &
    • A half-ring clip (which looks like half of a piston ring).
  • Remove these carefully—replacements are NOT available.

Next, remove the crankshaft:

  1. Loosen the four bolts securing the crankshaft center bearing holder.
  2. Lift the crankshaft out of the upper crankcase.
  3. Remove any remaining pins from the crankcase.

 

Disassembling the Shift Drum & Shift Forks

The shift drum and shift forks are next. These are held together with small spring clips and metal pins, so be extremely careful—losing them means scavenging parts from another engine.

  1. Remove the shift fork clips and pins:
    • The spring clips slide out to the side.
    • Use a magnet to pull out the small metal pins.
    • Do this for all three shift forks.
  2. Remove the neutral light switch:
    • Loosen the screw holding it in place on the left crankcase exterior.
  3. Remove the shift actuator:
    • Loosen and remove the hex bolt securing it.
    • Do NOT remove the JIS bolt at the end of the shift drum.
    • With the bolt, washers, and spring removed, slide the shift actuator off.
  4. Remove the shift drum:
    • Slide it out toward the right side of the upper crankcase.
    • ⚠️ Critical Step! As you pull it out, remove the shift forks while keeping them in the same order and orientation for reassembly.
    • As soon as the shift drum is out, reinstall them back on the shift drum to keep everything together.

Kickstarter Shaft

The last component to remove is the kickstarter shaft.

  1. Remove the small snap ring on the end of the shaft.
  2. Be careful! The entire assembly is spring-loaded—pieces may fly off.
  3. Slowly pull off each component in order, placing them carefully so you know how to put them back.

💡 Heads-up: Some CB350, CL350 & SL350 engines have slightly different kickstarter shaft assemblies. If yours doesn’t match what’s shown in our video, take a photo before disassembly to remember the order.

 

 

Your CB350 / CL350 / SL350 Engine is Fully Disassembled!

 

 

Next Steps: Cleaning & Inspection

Before jumping into reassembly, it’s crucial to:
✅ Thoroughly clean all components, removing old oil, carbon buildup, gasket material and debris.
✅ Inspect wear components for damage, excessive wear, or anything that needs replacing.
✅ Use the Honda Service Manual to check specifications and tolerances for key engine parts. A service manual is your best friend during this process. It provides detailed inspection guidelines, measurements, and specifications for every wear component in your engine. Key measurements such as valve guide wear or cylinder wear must be done with precision measuring tools, IE micrometers, snap gauges or dial bore gauges. Calipers are NOT accurate enough to determine internal wear service limits. If this is beyond your scope of knowledge we can help, see below. 

 

Honda CB350 | CL350 | SL350 Factory Service Manuals

 

Need Cylinder Boring or Head Rebuild Work? We’ve Got You Covered!

If your engine has over 15,000 miles or shows signs of pitting, scarring, or excessive wear, your cylinders and cylinder head may need professional inspection, measurement & machining.

🔧 We offer complete cylinder and head inspection & rebuild services to get your engine back to factory-spec performance. Learn more about our machining services here: 

Cylinder Boring and Honing Service

Cylinder Head Rebuild Service

 

Rebuild Parts & Replacement Components

A smooth rebuild starts with having the right parts on hand. We carry replacements for all major wear components, including:
🛠️ Gasket kits
🔩 Cam chain tensioner system
🪛 Cam chain
🧰 Oil Seal Kit
⚙️ Engine hardware
🔧 Honda Bond 4 Gasket Sealer

 

Browse our store to get everything you need for your CB350, CL350 or SL350 engine rebuild

Reassembly

Once everything is cleaned, inspected, and prepped, you’re ready to begin reassembly. Stay tuned as we walk through each step, ensuring your Honda engine is rebuilt with precision and care! 

 

Be sure to check out our full assembly article when you are ready to rebuild the engine right here - Coming soon

 

image.jpeg

 

Related articles

Comments

5 comments

Date Votes

Please sign in to leave a comment.