How-to Hone an Engine Cylinder

[Moses Ludel]

When you find that your engine repair includes cylinder honing, apply this process properly.  The optimal honing finish will have the right cross-hatch pattern with correct angles.  If you're unsure of the right "look" or angles, look closely at the photo below, the magazine's cylinder barrel after machine honing at L.A. Sleeve Company: 

 

 

Hand honing will involve the correct diameter stone hone or flex hone ("glaze buster").  Your cross-hatch pattern will depend upon the right pressure and speed of the hone as you run it up and down in the cylinder.  At our tools forum, you will find my comments on the two most common cylinder hones and their applications. 

 

Once you choose the correct hone and decide what you want the cylinder wall to look like when finished, clean the cylinder carefully and take measurements.  If you're honing in an automotive engine bay with the head off and the rods and pistons removed, make sure to protect the crankshaft journals from honing debris.  This debris is abrasive and will instantly damage new rod and main bearings!  Wrapping the journals with clean shop rags is one method of protecting the crankshaft.

 

I like to use a suitable honing oil.  Some will use an actual machine shop honing oil.  I like "Lube Guard Assembly Lubricant" for its lubricating and cleaning ability.  As you hone, the cylinder must slough off abrasive from its pores.  There is both the cylinder material and the hone material to consider here, each highly abrasive!

 

When honing, I like to use a rhythmic pattern up and down in the cylinder, moving the hone uniformly and with the same speed and force over the full cylinder.  In the day, my mentors recommended moving the hone "in slowly, out quickly", and that pattern is good, too.  If you're unfamiliar with the speed of a hone, try a one-second-down, one-second-up kind of count that's easy to follow.  I use a 1/2-inch hand drill motor with cross handles if possible to maintain center while honing.

 

     Note: For some motorcycle barrels, it might be practical to use a drill press and suitable holding fixture for the barrel.  Simulate the honing equipment found in an automotive machine shop.  You have good speed (usually adjustable on most presses) and alignment control.  Set speed to your needs.  Use plenty of lubricant while honing this way!

 

With a stone hone, you can adjust the stone pressure against the wall and also choose a suitable stone grit.  If you have no idea what grit, there are usually manufacturers' recommendations for each stone set type.  These are general recommendations and reflect speed and pressure as well. 

 

Cylinder wall material can vary widely.  Iron is often alloyed with nickel or even chromium and moly like L.A. Sleeve Company's "Moly 2000" liners.  If in doubt, use a moderate grit, it may take longer but will not chew up a cylinder wall and require re-boring.

 

     Warning: Both automotive and motorcycle engines that have Nikasil bore plating require special honing with a diamond hone.  Do not attempt to hone this material with a conventional stone hone or glaze-buster silicone flex hone.  Sublet honing to a shop with appropriate equipment.

 

A good approach when determining a cross-hatch pattern is to match the original cross-hatch that is evident at the top of the bore above the taper.  This ledge or "ridge" is not affected by the piston ring travel and therefore should show a pattern that the engine manufacturer (or a machine shop rebuilder) has used. 

 

 Note: This works fine for most honing jobs, although there are some very exotic OEM hone patterns like the late '80s to 1990 4.2L inline six AMC/Jeep engines.  Jeep had a problem with ring seating (likely due to consumers having no idea how to "break-in" an engine by that era).  AMC went to a radical "swept" hone pattern:  course, irregular and circular—not the conventional "X" look of typical power honing.

 

The simplest ways to have a new hone job go sour would be failure to thoroughly clean the cylinder of debris after honing and failure to sufficiently break-in or "seat" the new rings.  I tested many Jeep and other 4x4 trucks for OFF-ROAD Magazine in the '80s to mid-'90s (Argus Publishers days) and also tested vehicles on behalf of the Portland Oregonian newspaper in the early '90s.  I recall several tests involving vehicles with very low miles on the clock that were using/burning oil.  The cause was previous testers running these engines too hard without consideration for break-in.  I never reported the oil consumption in these vehicle evaluations; this was driver error, not a manufacturing defect. 

 

In particular, I recall a 1989 Jeep YJ Wrangler with a 4.2L carbureted inline six that used a quart of oil every 50 miles and also a TBI Chevrolet Silverado V-8 pickup that used a quart of motor oil every 300 miles.  Each of these engines had rings that had not seated.  I was able to reduce the oil burning dramatically during my test intervals by simply treating these near-new vehicles with consideration and allowing the rings to seat properly.  If given enough time, I'm certain the oil consumption could have been overcome.

 

Some practical considerations include selecting piston rings designed for a reasonable break-in period.  Unless building an all-out racing engine with forged pistons, I avoid "chrome" rings.  Moly rings work very well and respond quickly to a properly finished cylinder wall. 

 

Make sure your cylinder(s) is spotlessly clean before applying either a light engine oil or Lube Guard to the cylinder walls for both piston and ring insertion and the initial engine startup.  A new oil pump and pickup screen is always wise for automotive engines during a rebuild.  You have the oil pan down anyway, replace the pump.  For domestic engines, I've always run a Melling "High Volume" replacement pump and screen.  Cheap insurance policy for a long engine life.

 

     Note: On motorcycle engines, at least measure the oil pump rotor and pump gears, check the housing for pitting and damage.  Make sure parts are within specification from the manufacturer.  Replace parts as needed.

 

I'd like to follow up this article by creating an HD video how-to on cylinder honing.  I'll look for an iron motorcycle cylinder or an engine block in need of honing.  It would be productive to share the "art" of cylinder honing in video!

 

Moses

 

 

[forman]

Great article Moses!  Lets say that you have just been able to touch up the crosshatch pattern and in the process increased the size of the bore slightly over what it was when new.  Would you use new slightly oversized rings?  

 

If you need a cylinder for your video I have one.  

[Moses Ludel]

First, it's all about piston to wall clearance and ring end gap measurement.  These must stay within the manufacturers' guidelines for acceptable limits.

 

Years ago, in automotive circles, rings were commonly available for in-chassis engine overhauls or "ring and valve jobs".  Perfect Circle, I recall well, had piston rings to fit 0.000"-0.010", designed for the OE standard size pistons.  Filing ring end gaps to size was common practice if a bore was only slightly oversize and the new ring end gaps were too close.  This approach worked okay for "in the day" engines to 8:1 compression ratio that ran with 160-180 degree F thermostats.

 

When ring gaps are too narrow, there is no room for normal gap changes at different cylinder wall and piston temperatures. Gaps too narrow, and the rings can actually seize in the cylinder.  My tools include two hand-operated ring gap filing fixtures, and I've used modern power files on custom ring sets (packaged without sizing) for high performance engines.  Typically, new replacement ring sets for popular bore sizes or oversizes are accurately gapped from the factory.  Filing rings is a rare need today.  If you buy standard or oversized rings to match the piston size, the ring gaps should be correct if the bore diameter is accurately on measure.  When in doubt, measure the ring gaps with each ring or spacer level in the bore. 

 

The issue today is that manufacturers and consumers have shifted to "remanufacturing" of exchange engines or a rebuild at the local machine shop.  In the process, an engine block is always bored and finish honed, and the standard U.S. automotive oversizes are 0.010", 0.020" and 0.030", sometimes to 0.040".  (Similarly, metric oversizes typically run .25mm, .50mm, .75mm and 1.00mm.)  This has become so common that the "reman" shops like to bore every first-time go around U.S. block to 0.030" if possible.  Tooling can be readily adjusted and pistons for this bore size cost less at the wholesale level.  Today, the other oversizes are often special order.

 

Caution: 0.060" or larger bore sizing is considered a high performance approach for blocks that do not have core shift or thin walls.  I recommend ultrasonic testing of cylinders before considering 0.060" oversize on a Jeep 4.0L inline six block.  Ford "351M/400" V-8 blocks are notorious for core shift and should be ultrasonic tested for boring even to 0.040" oversize.

 

For motorcycle and automotive engines, slight honing should stay within end gap norms for the new piston rings.  The piston to wall clearance measurement should also indicate whether or not you've exceeded the ring gap limit.  If you have too much clearance, you'll need to bore the cylinder(s) for the next oversize piston and ring size.  Typically, the two measurements coincide, so if you use the OE piston as a measurement baseline and come up with acceptable piston-to-wall clearance after honing, the new rings for that bore size should also have acceptable ring gap measurements. 

 

Footnote: Forman...Hone and do the piston measurement before ordering new rings or a new replacement piston for your Kawasaki KLR thumper motorcycle engine.  What size rings are available for the KLR650 engine?

 

Honing should not remove much material.  If the cylinder has too much taper, it's wise to re-bore and machine hone for the next size piston and rings.  If there is noticeable taper, the traditional approach is to carefully cut the area above the taper with a ridge reamer and remove the ledge.  That cut ridge diameter, once honed with the rest of the bore, becomes an appropriate point for measuring the piston-to-wall clearance. 

 

Note: If the engine block or cylinder can be honed after cutting the ridge, a stone hone would be mandatory for truing and uniformly sizing the bore of the cylinder...If there is significant cylinder taper and a noticeable ridge, the added cost of machine shop boring and fitting of an oversized piston(s) and rings would be advisable.  I refer to "cylinder(s)" because our members and guests range from single cylinder motorcyclists to V-8 and V-10 automotive/truck owners.  If you need to resize any one cylinder in a multi-cylinder engine, you must resize all cylinders to the same oversize.  Matched new pistons and rings in that new size would be mandatory.

 

Minor honing with a drill motor is typically limited to engines with very light cylinder wear and the need for seating and sealing a new set of rings.  For motorcycle engines, especially two-strokes, it is not uncommon to have a bore size still within tolerance, both before and after honing, with the installation of a new piston, pin, circlips and rings.  This is especially true with Nikasil plating.  After cleaning, if a Nikasil bore looks unblemished and still shows a strong cross-hatch pattern, leave it alone.  If there is a need for honing a Nikasil cylinder, I strongly advise having L.A. Sleeve Company or a similarly qualified machine shop perform that work. 

 

Moses