Hone a cylinder to break the glaze

A used bore has a smooth glaze. New rings do not seat well on it, so the engine burns oil and loses compression. Honing roughens the wall with fine criss-cross scratches that hold oil and let the rings bed in. Light honing is a home job when the bore is within limits. Honing to a larger size needs a quality hone, many measurements and a lot of time, and a machine shop does it better.

Safety

• Wear eye protection. Wear gloves and avoid breathing oil mist.
• Never hone dry. Use plenty of honing oil, or the hone and bore overheat.
• Clean up thoroughly afterwards. Grit left in the bore wears new rings fast.

You need

• A cylinder hone that fits the bore. A cheap hone is enough to break the glaze. A better rigid hone is needed for anything more.
• Honing oil. Plain oil is a weak substitute.
• Solvent, warm soapy water and clean rags.
• Micrometers or a bore gauge, and the clearance limits from your manual.

Decide first: hone or bore

1. Check the piston clearance and bore wear before any honing (Measure piston-to-cylinder clearance and bore wear).
2. Wear is greatest at the top of the bore and across the front and back. The bottom wears least and may still show old hone marks.
3. If the piston rocks front to back in the bore at top dead centre, the bore is badly worn. It needs boring to the next oversize and a new piston.
4. A ridge felt with a fingernail near the top of the bore is another sign of wear.
5. If clearance is within the manual limit, hone lightly and fit new rings.
6. A rigid hone can correct a slightly oval or tapered bore, but only with careful measuring between passes. A cheap hone cannot hold the shape and may make it worse.

Steps

1. Remove the piston and clean the bore with solvent.
2. Cover the crankcase opening with a clean rag.
3. Fit the hone. Coat the bore and hone stones with plenty of honing oil.
4. Work the hone up and down the bore at a steady pace while it turns, so the scratches cross at about 45 degrees. About a minute is usually enough to break the glaze.
5. Plated bores can be honed only a little. Use the stones the maker recommends.
6. On a two-stroke, break the edges of the ports lightly with a ball hone or a fine file, so rings do not catch.
7. Wash the bore with clean solvent, then with warm soapy water. Dry and oil it at once to stop rust.
8. Wipe the bore with a clean rag with a little fresh oil. If the rag shows dirt, wash the bore again. Repeat until the rag stays clean.

Check your work

• An even cross-hatch pattern with no bright polished patches.
• A clean oil rag after the final wipe.
• Piston and ring clearances still within the manual limits.

When to go to a workshop

• Bore wear or taper is over the limit, or the bore has rust pits, scoring or a burnt, blue-tinted surface.
• You need to bore to an oversize. A boring machine gives a much more accurate result.

If it did not fix the problem

• Fit the rings correctly: Fit piston rings and deglaze the bore.
• If smoke continues after the rebuild, see Engine still smokes after a rebuild with new rings.