Zinc Oil Additive

Description

Zinc ZDDP Oil Additive for Vintage Honda Motorcycles | Rislone Hy-Per Lube

Modern engine oils don’t carry the zinc content your air-cooled Honda was designed to run on. Cam lobes and rocker arms — a common fail point on vintage Hondas — are where that shows up first. This ZDDP supplement adds the zinc back. Two ounces per quart of oil at every oil change. One 11 oz bottle covers about two oil changes on a typical twin.

Why You Need This

Modern motor oils lack the metals and minerals old engines need to protect their insides from wear and excessive heat. One of the most important is zinc — a soft metal that acts as a cushion between hard metal parts. Without it, camshaft lobes and rocker arms wear fast, especially on vintage Honda twins and fours where those parts are a known weak point.

Zinc ZDDP (zinc dialkyldithiophosphate) stabilizes modern oil and protects against viscosity breakdown caused by thermal cycles. It reduces friction, especially at startup, which means less wear and a cooler-running engine. It also makes the oil stickier, so it clings to metal parts and cylinder bores instead of draining back to the sump — an important feature for engines that sit through winter storage and cold-start in spring.

We’ve been recommending Rislone’s Hy-Per Lube Zinc ZDDP Supplement for every oil change on every vintage Honda we service — CT90 through CB750 — for years. Two ounces per quart is the dose we use in our own shop and in every one of our model-specific oil change videos.

Specifications

Use with mineral-based 15W-40 diesel truck oil. Honda’s factory SAE spec is 10W-40 for most of these engines, and a real 10W-40 motorcycle mineral oil works fine. But we get better results from 15W-40 mineral-based diesel truck oil — the detergent and metal additive package is closer to what these engines were designed to run on. Pair that with 2 oz of ZDDP per quart.

Avoid semi-synthetic and synthetic blend oils. Your Honda has a wet clutch — the clutch plates run in the same oil that lubricates the engine. Friction modifiers in most semi-synthetic oils can cause the clutch friction discs to slip. Shell Rotella T4, Chevron Delo 400, and Mobil Delvac 1300 — all long-time picks for vintage bikes — reformulated to semi-synthetic blends in late 2023. Check the current label before you buy. Look for “100% mineral” or “conventional”; avoid anything marked “synthetic blend” or “semi-synthetic.”

Oil Capacity — Reference

Use this table to calculate your additive dose at an oil change. 2 fl oz of additive per US quart of oil.

Capacities above are for refill after a standard oil change with filter service. First-fill dry-engine capacities can differ — consult your owner’s manual for those. CT90 figures reflect the OHC engine.

Installation

Difficulty: Beginner.

1. Change your engine oil as normal — drain old oil, service the filter, replace the drain plug with a fresh crush washer.
2. Calculate your dose: your engine’s oil capacity in US quarts × 2 = ounces of additive. Example: a CB360 takes 1.6 quarts × 2 = ~3 oz of additive.
3. Pour the measured additive into the crankcase first, then top up with your fresh 15W-40 mineral diesel oil to the correct fill level.
4. Run the engine for 2–3 minutes to mix, let it sit overnight, and recheck the oil level in the morning.

Measuring the dose. The bottle has graduated markings on the side. Precision isn’t critical — within half an ounce is fine.