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How to Inspect and Adjust the Drive Chain on the Honda CT90 / Trail 90

Updated

Applicable Models

All Honda CT90 / Trail 90 models (K0–K9, 1966–1979)

Overview

The drive chain on the Honda CT90 requires regular inspection, lubrication, and adjustment to maintain safe and efficient power transmission. A properly adjusted chain prevents premature sprocket wear, reduces drivetrain noise, and ensures smooth power delivery to the rear wheel. Honda recommends inspecting and lubricating the drive chain every 500 miles (800 km).

When to Inspect

  • Every 500 miles (800 km) — or more frequently in wet or dusty conditions
  • After installing a new chain or sprocket
  • If the chain appears loose, makes unusual noise, or the bike jerks at low speed
  • Before any long ride

Honda Factory Specifications

Specification Value
Chain Pitch 428
Stock Chain Length 104 links
Drive Chain Free Play (Slack) 15–25 mm (5/8–1 in)
Front Sprocket (stock) 15 teeth
Rear Sprocket (stock) 45 teeth
Rear Axle Nut Torque 3.5–5.0 kg·m (26–36 ft·lbs)

Source: Honda CT90 Factory Service Manual (1977–1979)

Inspection Procedure

  1. Place the motorcycle on its center stand and shift the transmission into neutral.
  2. Measure the drive chain free play midway between the front and rear sprockets on the lower chain run.
  3. Push the chain up and down by hand. The total vertical movement should be 15–25 mm (5/8–1 in).
  4. Rotate the rear wheel slowly and check the chain at several points — a worn chain will have tight and loose spots.

Replace the chain if:

  • Free play cannot be adjusted within spec (chain is stretched beyond adjustment range)
  • The chain has stiff links that won't flex freely
  • Visible rust, kinking, or damaged rollers are present

Honda Service Manual Reference — Drive Chain Inspection & Adjustment

Honda CT90 Drive Chain Inspection and Adjustment — Factory Service Manual Diagram showing slack measurement, adjuster nuts, and rear axle alignment

Honda CT90 Inspection & Adjustment Guide — Drive chain slack measurement, adjuster nuts, and rear axle alignment marks

Adjustment Procedure

If the chain free play is outside the 15–25 mm specification, adjust as follows:

  1. Remove the cotter pin from the rear axle nut and loosen the nut.
  2. Turn the chain adjuster nuts on both sides of the swingarm equally until the correct free play is achieved.
  3. Make sure the index mark aligns with the same graduation on the scale on both sides of the swingarm. This ensures the rear wheel is straight.
  4. Tighten the rear axle nut to 3.5–5.0 kg·m (26–36 ft·lbs).
  5. Install a new cotter pin through the axle nut. Never reuse an old cotter pin.
  6. Recheck the chain free play after tightening — the axle nut can shift the wheel slightly.

Important: Always turn both adjuster nuts the same amount. If the adjusters are set unevenly, the rear wheel will be misaligned, causing uneven chain and tire wear.

Honda Service Manual Reference — Drive Chain Installation & Master Link

Honda CT90 Drive Chain Installation — Retaining clip direction and rotating direction diagram from Factory Service Manual

Honda CT90 Service Manual (1977–1979) — Drive chain installation showing master link retaining clip placement and chain rotation direction

Lubrication

Honda specifies that the drive chain should be cleaned and lubricated every 500 miles. A properly lubricated chain can last significantly longer — Honda notes that power transmission efficiency can increase by 100% or more with a clean, lubricated chain compared to a dry, neglected one.

  1. Clean the chain with a stiff brush and kerosene or a dedicated chain cleaner. Do not use gasoline — it damages the rollers.
  2. Wipe the chain dry with a clean rag.
  3. Apply chain lubricant evenly along the full length of the chain, focusing on the rollers and side plates.
  4. Wipe off excess lubricant to prevent it from slinging onto the rear wheel or swingarm.

Tip: Lubricate the chain while slowly rotating the rear wheel by hand. This ensures complete and even coverage.

When to Replace the Chain

Even with proper maintenance, drive chains wear over time. Replace the chain if:

  • The rear wheel adjusters are near the end of their travel and the chain is still loose
  • Stiff links remain after cleaning and lubrication
  • Rollers are visibly worn, cracked, or missing
  • The chain shows signs of rust or corrosion that lubrication cannot resolve

When replacing the chain, inspect the front and rear sprockets at the same time. Worn sprockets will rapidly destroy a new chain. Look for hooked, pointed, or unevenly worn teeth.

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Parts You Might Need

Roller Drive Chain (428 Pitch) | Honda CT90 / Trail 90 — 104-link heavy-duty replacement chain with clip-style master link

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