The Honda CB600F (known as the Hornet in Europe and Brazil and 599 in the U.S.) is a standard motorcycle manufactured by Honda. It is powered by a 599 cc (36.6 cu in) liquid-cooled inline-four engine, originally a detuned version of that in the Honda CBR600 sport bike, which currently produces around 102 bhp (76 kW). The 'Hornet' name was not taken to North America as AMC, and its successor, Chrysler, had trademarked the name with the AMC Hornet.

The Honda CB600F Hornet was introduced for Europe in 1998. It was based on the CB250F that was restricted to 250 cc (15 cu in) at its home-market (Japan) because of local laws (this bike was released only in Japan from 1996 or 1997 until 2015, when it was succeeded by the CB300F). The bike has a six-speed transmission. Its suspension consists of a single shock in the rear and a conventional telescopic fork in the front until it was succeeded by an upside-down fork in 2005. Its brakes are dual-disc, Nissin twin piston in the front and single-disc, Nissin single piston in the rear. It was given the 16 in (410 mm) diameter front wheel and 17 in (430 mm), 180 section rear wheel setup from the Fireblade.

As a sport-oriented motorcycle that provides an upright riding position, it is considered a standard or "naked bike".

In 2000, Honda updated the Hornet, changing the 16 in (410 mm) front wheel for a 17 in (430 mm) to help corner stability and increasing the strength of the brake pass-over system on the front, making the brakes stronger. However, Honda did not increase the size of the fuel tank. A faired version, the CB600FS, was also introduced in 2000.

In 2003, Honda gave the CB600F version a make-over, with a larger fuel tank (17 L or 3.7 imp gal or 4.5 US gal as opposed to the former 16 L or 3.5 imp gal or 4.2 US gal), and 'sharper' styling. The CB600S faired version was discontinued.

In 2005, the instrument cluster was modernised, and more importantly, it was fitted with inverted front forks, to improve road-holding and cornering stability.

Honda took the Hornet to the United States and Canadian market for the 2004 and 2006 model years. It was called the 599.

The highly revised CB600F model came out in April 2007. The engine of the new motorcycle is a detuned version of the engine available in the 2007 CBR600RR giving a maximum output power of approximately 102 bhp (76 kW).

In 2011, the model got a facelift. The headlight assembly was changed and the instrument cluster uses LCD display. This bike shared many of the same components – swingarm, fork, frame, engine – as the Honda CBR600F that was reintroduced in 2011.

In 2014, the model received a major update and got a displacement increase of 49 cc, the new model is called CB650F.

What follows is a focused, practical, workshop-style guide to repairing gearbox housing damage on a Honda CB600F (Hornet). It covers why the repair is needed, how the gearbox works, each relevant component, how to disassemble, inspect and repair the housing, reassembly, and testing. Read every safety note and consult the official Honda service manual for exact torque/specs and shift drum/shim values — those numbers vary by year and should be followed exactly on your bike.

Safety and preparation (non-negotiable)
- Work in a clean, well-lit, ventilated shop. Stable bench and engine stand or secure wooden blocks.
- PPE: welding respirator/hood if welding, eye protection, gloves, hearing protection, cut-resistant gloves, chemical-resistant gloves for solvents.
- Have a fire extinguisher rated for oil/metal fires nearby.
- Disconnect battery. Drain engine oil and gearbox oil fully into a container for proper disposal.
- Label and bag fasteners and small parts. Photograph each step for reassembly.
- If you are not experienced with TIG welding aluminum or precision machining, have the welding and machining done by a qualified aluminum welder/machinist. Improper repair will ruin the gearbox.

Why this repair is needed — theory and symptoms
- The gearbox housing (the cast aluminum crankcase halves / gearbox cover) serves three primary functions:
1) Structural shell: holds and perfectly aligns the gearbox shafts, bearings and transmission components.
2) Oil containment: keeps gear oil sealed inside for lubrication and cooling.
3) Mounting base: attachment points for engine mounts, clutch cover, stator, and external items.

- Damage types: cracks (impact, fatigue), stripped threads, broken studs, gouged mating surfaces, and missing material where bolts/dowels seat. Any of these can cause oil leaks, misalignment of shafts/bearings, shifting problems, noisy gears, accelerated bearing/gear wear, or catastrophic failure.

- Symptoms that point to housing damage: persistent oil leaks from a seam or crack, visible cracklines, gear engagement problems (grinding or false neutrals) after impact, wobble in shafts, or bolts that no longer hold torque.

How the gearbox works — plain-language overview
- Think of the gearbox as two parallel bicycle gear trains (mainshaft and countershaft), stacked so pairs of matching gears transmit power. Gears mesh and rotate; some gears are fixed to shafts (always engaged) while others slide (dog engagement) to change gear ratios.
- The shift drum/selector moves shift forks that slide the gears via selector dogs. Bearings in the housing locate and support shafts so gears mesh with correct centers and backlash.
- The housing is like the boxed frame of a precision clock — if the frame twists or a bearing moves, the gears won’t mesh properly any more.

Relevant components — what each does and what to inspect
- Crankcase halves / gearbox housing: cast aluminum; mating faces sealed with gasket or sealant; contains bosses for bearings, dowel pins, bolt holes and studs.
- Bearing bores: machined holes where gearbox and crankshaft bearings sit. Inspect for ovalization, wear, or cracks nearby.
- Dowel pins: precise locator pins that ensure halves align; damaged or missing dowels cause misalignment.
- Studs/bolt bosses: threaded inserts or cast bosses that accept bolts/studs. Check for stripped threads or broken studs.
- Gasket/seal surfaces: mating flange faces (flatness critical). Check for nicks, corrosion, or warpage.
- Shift drum and selector: rotates to move shift forks; damage here causes shifting faults — inspect for cracking at drum ends or grooves.
- Shift forks: engage sliding collars/dog gears; inspect for bend or wear at contact pads.
- Shafts (mainshaft, countershaft, layshaft depending on design): check straightness and wear on splines or journals.
- Bearings (roller, ball, needle): check noise, play, pitting.
- Oil seals: check for leakage. Replace if housing repaired.
- Clutch basket/pressure plate area (if accessible): any damage to housing around clutch cover or primary chain is important.
- Threaded inserts/helicoils/Timeserts: repair hardware used to restore stripped threads — check condition or plan to install.

Inspection and diagnosis steps
1. Remove external items: seat, tank, exhaust, footpegs, covers that obstruct.
2. Drain oil, remove oil filter, and remove clutch and stator covers as needed to access gearbox cover.
3. Thoroughly clean the housing with degreaser. Remove paint/local coatings where repairs planned.
4. Use a dye-penetrant (fluorescent or visible) crack inspection kit on cleaned dry surfaces to reveal hairline cracks. Tap-test suspected areas with a plastic mallet — a ding will change sound over a crack.
5. Pressure test for leaks (plug openings and pressurize with low-pressure air under water to see bubbles) or use solvent to see seep paths.
6. Inspect bearing bores with a bore gauge or feeler: check for out-of-round; measure diameters against spec.
7. Check flatness of mating surfaces with a long straightedge and feeler gauges — any gap indicates warp; note exact locations.
8. Photodocument and mark cracks/defects.

Decision: repair vs replace
- Small hairline cracks in non-critical bosses or bolt areas — repairable.
- Cracks through bearing bores, major alignment surfaces, or heavy distortion — replace the case. If the cost of machining and welding approaches replacement part cost, replace.
- Stripped threads and broken studs are usually repairable with inserts or re-tapping.

Repair options — pros and cons (choose by damage type)
1. TIG (heliarc) aluminum welding (professional method)
- Best for structural crack repair in cast aluminum cases when done by a skilled welder.
- Requires proper filler (commonly ER4043 for Al-Si castings; sometimes 5356) and preheat.
- Preheat to 120–200°C (250–400°F) depending on casting alloy to avoid thermal shock (do not overheat).
- Use back-purging or jigging to align, grind out crack into a V-groove, weld in short runs to avoid warpage, allow controlled cooling (don’t quench).
- After welding, stress-relieve (gradual cooling) then machine the mating surface if needed.
- Pros: strong, permanent if done correctly; cons: requires skill and can distort housing if misdone.

2. Metal stitching / cold metal repair (e.g., Lock-N-Stitch, metal stitching)
- Mechanical method that “stitches” cracks with pins and creates a metal bridge without high heat.
- Good when welding would risk distortion or for threaded boss repair.
- Pros: no heat distortion, strong; cons: requires specialized tooling or a professional service.

3. Thread repair (Timesert/Heli-Coil)
- For stripped threads, use a Timesert (solid insert) or Heli-Coil (coil) to restore threads to original size.
- Timesert is stronger and preferred in high-load areas (engine mount bolts).
- Procedure: drill, tap, and install insert; use recommended sizes and adhesives (if specified).

4. Cold metal epoxies / aluminum repair compounds (J-B Weld variants)
- Temporary or cosmetic seal only. Not recommended for structural repairs or bearing seats.
- Pros: simple, cheap; cons: not structurally reliable under torque, heat, or vibration.

5. Plugging and patch plates
- For localized spall or missing flange material, machine a plated steel patch and bolt/weld in place, set with epoxy and machining to final surface.
- Requires precise machining and sealing.

Detailed step-by-step repair workflow (typical for a cracked case/boss)
Note: adapt to your specific damage. Use the shop manual as a map for disassembly sequence and torque specs.

A. Full disassembly (necessary to access and ensure correct reassembly/alignment)
1. Remove engine from frame if required (many gearbox repairs need case split).
2. Remove clutch assembly, alternator/stator, outer covers, foot controls, chain, sprockets, and any parts bolted to the case.
3. Unbolt dowels/stud areas carefully and separate case halves using case splitters or carefully tapped soft wedges. Keep track of all shims, washers, and bearing locations — label them.
4. Remove shafts, gears, shift drum, forks and all internal gearbox parts onto a clean bench on a parts map.

B. Inspect components removed
1. Bearings: replace all bearings that show wear. If housing was damaged near a bearing, replace the bearing regardless.
2. Shafts/gears: inspect for pitting, nicks, worn splines or teeth; replace if necessary.
3. Shift forks/drum: check groove wear, alignment, cracks.

C. Prepare the housing for repair
1. Clean paint and oil from repair area. Grind a V-groove along the crack to remove oxidation and allow good weld penetration.
2. Drill small “stop holes” at the ends of the crack to prevent propagation.
3. If using TIG welding: preheat casting to recommended temperature (120–200°C typical). Use a torch and temp sticks or pyrometer. Clamp and align halves if welding through seam.
4. If using metal stitching: drill holes for stitch pins per vendor instructions and install pins and plates.

D. Welding procedure (if chosen)
1. Use AC TIG for aluminum or qualified TIG alloy welder. Use the appropriate filler rod (ER4043 often for Al-Si castings).
2. Weld in short passes, peening between passes if recommended for the alloy, and maintain consistent heat control to reduce warpage.
3. After welding, allow slow cooling (insulate with blankets if needed) to room temperature — avoid quenching with water.
4. Pressure test the welded area before machining: block openings, fill with solvent or pressurize slightly and check for bubbles/oil leaks.

E. Post-repair machining and restoration of surfaces
1. Machine or surface-grind the mating faces flat. Service manual specifies maximum allowable warpage; aim for better than that.
2. Re-bore or ream any bearing seats that were welded or distorted — replace bearings as matched-fit. This must be done on a precision machine.
3. Replace threaded inserts or install Timeserts for stripped bosses.
4. Clean all machined surfaces, remove chips, and deburr.

F. Reassembly and setting clearances
1. Fit new bearings, seals and reassemble shafts/gears in the exact order and orientation documented.
2. Reinstall shift forks and drum; verify free movement and correct indexing (no binding).
3. Set mainshaft and countershaft endplay per manual using shims as required. This is critical: incorrect endplay leads to gear noise and premature wear.
4. Apply the specified gasket or RTV sealant to mating surfaces as instructed by manual. Use new gaskets and seals everywhere disturbed.
5. Torque fasteners to Honda specs in the correct sequence. Use thread locking where specified.
6. Reinstall external components (clutch cover, stator, etc.) and torque to spec.

G. Final checks and testing
1. Fill with fresh recommended engine/gear oil and new filter.
2. Static test: rotate engine by hand (with spark plugs removed) to feel for smooth gear changes, binding, or unusual resistance. Cycle through all gears while stationary where possible.
3. Start engine and run at idle; check for leaks and listen for abnormal gearbox noises.
4. Short test ride at low speed, cycling through gears carefully. Re-check for leaks and torque on bolts after initial heat cycles.
5. After some hours of operation, re-check mainshaft/countershaft endplay and bearing torque if applicable.

What can go wrong — failure modes and how to avoid them
- Distortion from welding: if mating faces warp, gears will misalign. Avoid by preheating, welding in short passes, and precision machining after welding.
- Improper thread repair: wrong insert size or poor seating will lead to broken studs or loosening. Use Timesert for load-bearing bolts; torque to spec.
- Contamination: metal chips, aluminum filings or debris left in the gearbox will destroy bearings and gears. Clean thoroughly, blow out with compressed air, and use solvent baths.
- Wrong shim values or lost shims: causes endplay errors, gear noise, or transmission damage. Label and measure all shims; replace if uncertain.
- Inadequate sealing: use correct gasket/sealant type and surface flatness.
- Welding cracks reappearing: poor preparation, wrong filler alloy, or inadequate stress relief cause recurrence. Use correct filler and technique or choose metal stitching.
- Heat damage to nearby parts (bearings, seals) during welding. Remove bearings or shield them if welding nearby.

Quick analogies to make it intuitive
- Gearbox housing is the picture frame for a delicate painting: if the frame warps, the painting (gears) won’t hang straight.
- Thread repair is like repairing a stripped screw hole in wood: a cork alone is weak (epoxy), a properly glued dowel (Timesert) or a new threaded insert restores full strength.
- Welding without preheat is like trying to glue a brittle cookie back together — it cracks again.

Tools, materials and consumables checklist
- Tools: torque wrench set, socket set, Allen, Torx, screwdrivers, pry bars, case splitters, bearing pullers/press, dial indicator, straightedge, feeler gauges, bore gauge, micrometer, drill/ream/tap set for inserts, Timesert/Heli-Coil kit, cleaning brushes, solvent, compressed air.
- Welding: AC TIG machine for aluminum, appropriate filler rods (ER4043/ER5356), weld rod, temp sticks/pyrometer, grinding wheels, flap discs.
- Consumables: new bearings, seals, gaskets, oil, threadlocker where required, Timesert/Heli-Coil inserts, shop rags, gasket remover.
- Special services: professional welding/metal stitching and precision machining (surface grinding, boring) recommended if you lack equipment.

Final notes (short and practical)
- If the crack affects a bearing bore or the crankshaft/gear alignment, strongly consider replacing the case or having a professional repair and re-machine it.
- Keep meticulous records and photos during disassembly to ensure correct reassembly.
- If you do welding yourself, practice on scrap castings first. Incorrectly welded cases are often worse than stock.
- After repair and reassembly, re-check torque and clearances after the first few heat cycles and a short service interval.

This is a comprehensive workshop-level outline. Follow OEM service manual procedures for torque numbers, shim thicknesses, bearing preload and endplay specifications. If any repair step (welding or precision machining) is outside your skill set or equipment, have that portion done by a qualified shop.
rteeqp73

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Tools & materials
- 8, 10, 12 mm socket and ratchet (common fasteners on CB600F tank/seat)
- Phillips and flat screwdrivers (for clips, hoses)
- Long-nose pliers (clamp/hose removal)
- Side cutters or small diagonal cutters (clip removal)
- Small pick or stiff dental tool (remove O‑ring/hose if stuck)
- Torque wrench (recommended for tank/seat bolts; see manual)
- Clean rags, small container for fuel drip
- Replacement PCV/crankcase breather valve (OEM part for your CB600F year or a correct 1‑way check valve rated for engine vacuum)
- Replacement vacuum hose or small hose clamps (if original is brittle)
- Light engine oil or silicone spray (to ease hose installation)
- Safety gloves and eye protection

Safety precautions
- Work on a cool engine and in a well-ventilated area away from sparks/open flame. Gas vapors are flammable.
- Put bike on centerstand or paddock stand for stability.
- Disconnect the negative battery terminal before removing the fuel tank/electrical connectors.
- Turn fuel petcock to OFF and have a small container ready for a few drips when disconnecting fuel line.
- Keep rags under the work area to catch fuel; dispose properly.
- Avoid overtightening fasteners or clamps — follow torque spec in the service manual when available.

What the part is and how to test the old one
- The “PCV” on a motorcycle is a one‑way crankcase breather/check valve between the crankcase and intake/airbox. It should let flow from crankcase → intake only.
- To test: blow into the intake side of the valve. Air should pass one way only. Reverse direction should be blocked. If it passes both ways or is sticky, replace.

Replacement parts required
- OEM PCV / crankcase breather one‑way valve for CB600F (match year/model) or equivalent one‑way check valve sized to the hose.
- Replace any brittle vacuum hose or clamps you disturb. It’s inexpensive and prevents future leaks.

Step-by-step procedure (workshop detail)
1. Preparation
- Park bike on centerstand/paddock stand. Let engine cool.
- Disconnect negative battery terminal to avoid accidental starts or sparks.
- Turn fuel petcock OFF.

2. Remove seat(s)
- Use appropriate socket or key to remove seat mounting bolts. Lift off seat and set aside.

3. Remove/raise fuel tank
- Remove tank mount bolts (usually 8–10 mm). Use socket/ratchet.
- Before lifting, disconnect fuel feed line(s) from the tank/petcock. Put a rag under and a small container for any drips.
- Disconnect vent hoses and any electrical connectors attached to the tank (fuel level sensor if present).
- Carefully lift tank straight up and back; there are rubber mounts—wiggle gently. Support the tank with a block or have an assistant hold it. Do not let it hang by fuel lines.

How the tool is used: use the socket and ratchet to remove the tank bolts; use flat screwdriver or pliers to pull off hose clamps; use side cutters for plastic clips if required.

4. Locate the PCV valve
- With the tank lifted, locate the crankcase breather hose on top of the engine/crankcase. The one‑way valve is usually inline between the crankcase and the airbox/throttle bodies. It’s typically a small plastic check valve in a rubber hose.

5. Remove old valve
- Note orientation of valve (arrow or which side goes to crankcase vs intake). Mark or photograph to ensure correct reinstallation.
- Use long‑nose pliers or flat screwdriver to loosen clamps (spring or screw clamps) and slide them back.
- Twist the valve gently while pulling it off the hose. If the hose is seized, use the pick to get under the hose lip, or apply a little penetrating oil around the connection and work it free.
- Catch any oil residue with rags. Inspect hose for cracks/soft spots—replace if brittle.

How the tool is used: pliers remove spring clips; screwdriver loosen screw clamps; pick for prying O‑rings or stuck hose.

6. Fit the new valve
- Confirm orientation: arrow must point from crankcase to intake (direction of flow to intake).
- If using a new hose, cut to length and slide onto fittings. Lightly lubricate inside of hose with a dab of engine oil to ease installation.
- Push valve fully onto hose until seated, then re‑position clamps and tighten snugly. If using screw clamps, tighten until secure but don’t crush the hose. For spring clamps, compress and locate in groove.
- Replace any O‑rings if present.

7. Reinstall fuel tank and seat
- Lower tank back onto rubber mounts, reconnect vent hoses, fuel line, and any electrical connectors. Ensure hoses are routed without kinks.
- Reinstall tank bolts and tighten to spec (use torque wrench if available; otherwise snug to manual spec). Reconnect battery negative terminal.
- Reinstall seat(s).

8. Start and check
- Turn fuel petcock ON, start engine. Let idle and observe.
- Check for any fuel drips and ensure crankcase hose connections are sealed.
- Listen for abnormal sucking or backfiring that could indicate incorrect valve orientation or leaks.
- If idle is rough initially, it may be normal for a short time while the engine re‑learns mixture; recheck all connections.

Common pitfalls & how to avoid them
- Wrong orientation: the valve only works one way. Mark orientation and install arrow toward intake.
- Reusing brittle hose: old hoses often crack. Replace hose if >5–7 years old or if you see cracking.
- Damaging plastic valve while prying: use gentle twisting motion and a pick around the hose jaw; don’t lever directly on the valve body.
- Tightening clamps too much: over-tightening can collapse hose or crack plastic valve — tighten just until secure.
- Forgetting to close petcock or disconnect battery: results in fuel spills or sparks. Always turn petcock OFF and disconnect negative battery.
- Not testing the old valve: if you reinstall the old valve thinking it’s fine, you may not resolve PCV-related issues. Test for one‑way operation.
- Kinking fuel or vacuum hoses when reinstalling tank: route hoses free and secure them so they are not pinched.
- Incorrect replacement part: get the correct OEM valve or a rated aftermarket valve—size and vacuum flow characteristics matter.

Quick testing after install
- With engine off, blow into intake side of the valve to ensure it blocks flow in the reverse direction.
- Start bike and check idle stability and vacuum hoses for leaks.

That’s all. Replace valve with correct one‑way breather, observe orientation, replace any suspect hose/clamps, torque fasteners to spec, and test.
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