Keeping your Honda 175 in prime shape often comes down to handling the small components that quietly protect the engine every time it runs. One such part is the oil separator bar. When it clogs or wears, the crankcase can build pressure, oil can migrate into the intake path, and power drops. This guide walks you through removing that bar safely, inspecting it, and putting everything back together so your motor keeps humming.
Understanding the Oil Separator Bar
What the Oil Separator Bar Does
Inside a four-stroke engine, oil mist and blow-by gases have to be routed back to the crankcase or intake without soaking the air filter or gumming up valves. The separator bar sits in the crankcase cover and forces that vapor through tight passages, letting liquid oil drain while only fumes move onward. Think of it as a mechanical sieve—simple, but essential for clean combustion.
Signs the Separator Needs Attention
- White-blue smoke from the exhaust after warm-up
- Oil residue in the air box or carburetor throat
- Erratic idle caused by oil-rich fumes upsetting the fuel mix
- Persistent oil leaks around the crankcase breather
If you spot two or more of these, plan on pulling the bar the next time you change oil.
Preparations Before You Start
Tools & Supplies
| Item | Notes |
|---|---|
| Metric socket set (8 mm–12 mm) | 6-point sockets grip best |
| Torque wrench (5 – 25 N·m range) | For reassembly |
| Flat-blade screwdriver | Prying the cover gently |
| Rubber mallet | Taps parts loose without marring |
| Oil drain pan | Holds at least 2 L |
| Shop towels & parts tray | Keep bolts organized |
| Non-chlorinated brake cleaner | Final rinse |
| Fresh gasket or liquid-gasket compound | Depends on model year |
| Engine oil (per owner’s manual) | Refill after work |
Safety Precautions
- Cool engine only. Hot oil scalds skin in seconds.
- Disconnect the spark plug cap to prevent accidental starts.
- Ventilate the area; vaporized brake cleaner and oil mist are harmful.
- Eye protection whenever spraying solvents.
Workspace Setup
Elevate the bike or generator (many Honda 175 variants power equipment) so you can slide a drain pan under the crankcase. Lay a clean cardboard sheet nearby—small parts show up against a neutral background and won’t roll away.
Step-by-Step Removal Procedure
1. Isolate the Fuel System
Turn the petcock to OFF and pinch the fuel hose with a clamp or line pinch pliers. This avoids a dribble when you tilt the unit.
2. Drain the Engine Oil
Remove the 17 mm drain bolt. Let the oil flow until it drips only once every few seconds. Reinstall the bolt finger-tight to stop residual seepage while you work.
3. Remove External Covers
On motorcycle trim, pull the right-side foot peg bracket first; on industrial versions, unbolt the plastic shroud. Take note of bolt lengths—Honda often mixes two lengths to prevent over-torquing thin sections.
4. Locate the Separator Bar
With the crankcase cover exposed, you’ll see a cast aluminum chamber. The bar sits horizontally within it, held by two small shoulder bolts.
5. Unbolt and Extract
- Using an 8 mm socket, back out both bolts evenly.
- Gently rock the bar side to side while pulling; dried oil varnish can make it stick.
- Place the bar on a clean towel immediately to prevent grit contamination.
Inspecting and Cleaning the Separator
Cleaning Techniques
- Soak: Submerge the bar in kerosene or diesel for 15 minutes.
- Brush: Use a soft nylon brush; wire brushes scar the surface.
- Flush: Blow compressed air through the internal channel, pushing loosened debris out the far end.
Wear and Damage Assessment
Look for scoring, deep grooves, or cracks. Surface staining is harmless, but pitting means the metal is weakened—replace it. Double-check the O-ring (newer designs) or gasket strip on either side of the bar; any flattening calls for a fresh part.
Reinstalling or Replacing the Separator Bar
Proper Torque Settings
Honda specs vary slightly by year, yet most 8 mm shoulder bolts tighten to 10 N·m. Apply a drop of medium-strength thread locker to keep vibration from working the bolts loose.
Sealing & Gasket Considerations
- Paper gasket: Wipe both mating faces with acetone, then position the new gasket dry.
- Liquid-gasket: Lay a 2 mm bead around the entire perimeter, skip the oil return hole, and wait 60 seconds before fitting the cover.
Seat the bar, hand-start both bolts to avoid cross-threading, then torque in two passes.
Testing the Engine After Reassembly
Checking for Leaks
Crank the starter with the kill switch OFF for 5 seconds—oil pressure builds without firing. Peek under the cover; any dampness means the gasket compressed unevenly.
Monitoring Oil Pressure and Smoke
Start the engine and let it idle for three minutes. Typical oil pressure on the 175 platform ranges 55–65 psi when cold. A slight haze at first is normal; if smoke persists, check the separator again in case a new O-ring slipped during installation.
Troubleshooting Common Issues
Persistent Oil Smoke
- Possibility: Worn piston rings rather than a separator fault.
- Check: Perform a compression test—below 120 psi signals ring work.
Oil Leaks Around the Cover
- Cause: Over-tightened bolts warping the cover.
- Remedy: Remove, flatten the cover on a glass plate using 320-grit wet-dry paper, reinstall with fresh gasket.
Unusual Engine Noises
A ticking note right after reassembly can be valve lash previously masked by oil drag. While you’re at this depth, set the tappets to factory spec:
- Intake: 0.10 mm
- Exhaust: 0.12 mm
Preventive Maintenance Tips
Oil Quality and Change Intervals
Use the viscosity that matches your climate—10W-30 for moderate temperatures, 20W-50 for sustained heat. Change every 2,500 km or 50 hours of runtime, whichever comes first.
Air Filter Care
A clogged filter spikes crankcase pressure and overwhelms the separator. Clean or replace the element alongside every oil change.
Riding/Operating Habits
Long idle sessions on rich mixture engines dilute the oil with fuel, forming sludge. Occasionally revving to mid-range RPM for a minute or two clears moisture and keeps the separator cleaner.
Frequently Asked Questions
Can I remove the bar without draining oil?
Technically yes, but oil pooled in the cover will spill once you break the seal. It’s far tidier to drain first.
How often should the separator be serviced?
Check it every second oil change. Replace only if clogged or damaged; it’s designed to last the engine’s life when oil is changed regularly.
What if bolts are seized?
Apply penetrating fluid and wait at least one hour. Use a hammer-style impact driver with a fresh bit—avoid vice grips that round the heads. Heat is a last resort; excessive heat can warp the cover.
Final Notes
Remove and clean the oil separator bar on your Honda 175, and you restore proper crankcase breathing, reduce exhaust smoke, and protect valve seats from carbon buildup. The task takes an afternoon, minimal tools, and rewards you with smoother running and longer engine life. Stick to the schedule, keep your parts organized, and your Honda will reward you with many more trouble-free rides—or hours of reliable service on the job site.