Technical Hone Information

What diameter size should I order?
A hone tool's diameter is determined by the nominal bore size in which the tool is to be operate. A cylinder hone is always produced and used in an oversize condition. The degree of oversize creates pressure and a soft cutting action on cylinder walls. For example a 1" Flex-Hone® tool is ordered if a 1" bore (I.D.) is to be finished, the built in oversize provides the proper cut. Remember that all tools are provided in over-sized, so do not add inches or mm's to the ID that you are machining.  If the bore size is between standard Flex-Hone® sizes, the next larger standard Flex-Hone should be selected.

What GRIT should I order?

Hone grit is one of those topics that will vary vastly from OEM manufacturer, ring designer to professional engine builder and will depend on how bad the cylinder wear is and whether a deglaze will do the job . If you have a poor condition bore with rust or deep grooves you will need to use a 120 grit hone to remove the rust and remove the deep grooves. Then follow up with the appropriate grit depending on ring application. For a basic deglaze to refresh the engine just use the grit depending on ring type. has built several engine mules (our guys race too!) to investigate the grit question with on-track results. The table below which was derived from our engines, ring manufactures and technical literature. Our best seller to commercial engine rebuilders and power-sports shops is the 240 grit hone. Our guidelines are as follows:

Iron Cylinder Ring Type:
OEM Iron rings: 180 or 240 grit
Chrome rings: 240 or 320 grit
Moly Rings: 320 or 400 grit
Plasma Rings: 320 or 400 grit
not sure ring type: 240 grit


Manufacturers Recommendation:

 Hastings 240 grit
Akerly & Childs (Ductile Iron)

240-280 grit

Akerly & Childs (Moly)

400 grit

Perfect Circle (Ductile Iron) 240-280 grit
Perfect Circle (Moly) 400 grit
Sealed Power (Moly) 400 grit
Speed Pro Hellfire (Ductile Iron) 240-280 grit
Total Seal (Ductile Iron) 240-280 grit
Total Seal (Moly) 320-400 grit
Harley Davidson(stock) 320 grit
Wiseco (chrome top) 320 grit
Mahle (Moly/Chome top) 280 grit

If the Ra (surface finish) of the part being machined needs to change more than 20 to 30 points, you may need to use steps to achieve the proper final Ra.  As an example, if you were trying to change a 80 Ra to a 20 Ra, you may need to start with a 120 or 180 grit hone and then finish with a 240 or 320 grit. 

To assist in selection of proper hone, this information is a good starting point.  Actual measurements must be made after honing, as numbers will vary depending on the material being honed and the media used. 

Grit Finish Range

600 grit Ra 8-12  .2 - .3 Micrometer
400 grit Ra 10-20 .3 - .6 Micrometer
320 grit  Ra 18-26 .5 - .7 Micrometer
240 grit Ra 24-32 .6 - .8 Micrometer
180 grit  Ra 30-40 .7 - 1.0 Micrometer
120 grit Ra 35-50 .9 -1.4 Micrometer
80 grit Ra 45-64 1.2 - 1.6 Micrometer
60 grit Ra 60-80 1.5 - 2 Micrometer

How do I refinish my bore
There are several steps in refinishing your cylinders in preparation for new rings. The first of course is to remove all bearings leaving a bare block. The metal from the honing or deglazing process with go everywhere. Note that the worst thing about honing is the block cleanup. You can never spend to much time cleaning your block. With the engine bare and cylinder ridged reamed (if necessary) place the Flex-Hone® (registered trademark of Brush Research Manufacturing) in a hand drill or drill press. Lubricate the cylinder with 10-30wt oil or Flex-Hone® hone oil (recommended). Spread the lubricant in the bore with a brush or your fingers. Make sure the cylinder is completely covered. For the first use of a new hone lubricate the Flex-hone and bore walls completely several times as the hone itself will absorb some of the oil. Future cylinder honing will not require as much oil as the first was with a new hone. Insert the lubricated hone with the drill rotating slowly while inserting in to the bore. With the hone in the lubricated bore, run the drill at 600-800 rpm with a vigorous motion up and down in the bore for 40-60 strokes. How vigorous a motion? basically as fast as you can move your arms. You are seeking a 45 degree crosshatch in the bore. If you are not achieving a good crosshatch (see tech section below) then you will need to slow the drill speed down to achieve a MUST HAVE 45 degree crosshatch. Run the drill for 40-60 rotations and wipe the bore with a clean cloth. Inspect the bore. If a dull grey is visible (it will stand out from the freshly honed surface) continue until the bore is completely resurfaced. While honing continue to squirt oil in to bore as a medium to wash away the cylinder material. Once the bore dull grey color is not visible STOP honing. The most important step is the cylinder wall cleanup. Use a nylon cylinder wash brush or a clean cloth soaked in warm soapy water and run up and down the bore. Continue this process while flushing the bore with warm soapy water. The goal is to remove every microscopic particle that is embedded in the cylinder wall grooves. After extensive scrubbing take a clean white lint free cloth with warm water and wipe up and down the cylinder bore with force. Inspect the cloth, if you see grey on the cloth, and most likely you will, you need to go back and clean the bore again. Repeat until you see no grey on the white cloth. Once each and every bore is perfectly clean then coat each cylinder with oil to preserve until piston placement. Once again the bores must be clean or you just left lapping compound in your high dollar engine.

What if my cylinder is Nikasil Coated?
Nikasil coated cylinders are more delicate than the iron bores typically used with Flex-Hones®. Nikasil is an electroplated oleophilic nickel matrix silicon carbide coating that allows the use of aluminum cylinder walls without a steel sleeve. This coating reduces friction and wear. Great advantages come with the use of Nikasil on coated aluminum blocks or jugs, one of them is the increased heat removal from the piston, pin and ring assemblies. The other advantage is the tighter tolerances can be achieved. Most Nikasil coatings are 0.0003" to 0.0008". To deglaze and freshen up the bore walls you must use an aluminum oxide material based hone. This softer material works well with the hard walls. Use the hone like described above with the exception of much less rotations. Run the hone for 10-12 rotations in the bore and inspect. If the overall cylinder looks touched then you are done and remove the tool.

Achieving A Cylinder Crosshatch Pattern
Another misunderstood and highly discussed topic is the subject of cross hatch angle. The resulting cross hath angle produced by the Flex-Hone or a three spring hone (or a rigid hone for that matter) is strictly a function of stroke rate versus RPM. Most OEMs and ring manufacturers state the angle of the scratches in the crosshatch pattern should be about 27 - 45 degrees with 45 degrees the optimum. This angle is referenced from the top of the deck. The crosshatch angle should be consistent throughout the cylinder walls. If the crosshatch angle is too steep the cylinder walls will not retain sufficient oil to aid in the rings seating process. The problem is that the rings will pump oil and rings will rotate too quickly leading to accelerated ring and ring groove wear. To shallow of a angle can cause a chattering affect as the ring passes over the valley preventing the ring from receiving proper lubrication again leading to excessive ring wear, excessive ring break in time and the possibility of engine smoking with no ring seating. To achieve the desired 45 degree crosshatch run the drill at 600-800 rpm and vigorously run the drill up and down in the bore. This vigorous movement of your arm is exhausting but you only need to run the tool in the bore for 10-15 seconds. Then inspect the cylinder surface. If you see a dull grey surface that indicates the hone was ineffective in that area thus continue to run the hone until the complete bore looks exhibits a fresh cut with a cross hatch pattern.

Will it remove too much material?
No. The Flex-Hone® tool is a surface finishing tool, not a material removal tool. We are reducing the rough peaks of a surfaces micro-structure and typically we only remove a small amount of material. Typical 30-40 strokes to achieve the cross hatch will remove just under 0.0001" of material.

Honing Tools For Two Stroke Engines
A common question we always get is, "Can the Flex-Hone be used in 2-stroke engines?" We recently discovered a nice Scooter forum that discussed the different options available for cylinder hones. . The discussion talks about Flex-Hones vs. the brake caliper hones (the ones with the 3 spring fingers) and the benefits to both. The conclusion, the easy-to-use "ball hone is friendly on the port edges of [their] two stroke engines."

It is important to understand why each tool is used and the benefits and drawbacks to using either of them. The 3 finger brake caliper type hone is meant for material removal. If your bore is out of round or has other geometry issues like taper, poor cylindricity or excessive ovality, material must be removed to bring the cylinder back into specification. Great care must be taken when using the 3 spring tool because it will alter the dimensions of your cylinder. Using this type of tool is as much art form as science and a cylinder can easily be ruined if it is not used properly. Ports in two cycle engines present an additional challenge as the rigid edges of the honing stones tend to catch on the port edges causing damage to both the ports and the honing tool. The three finger hone can be used for deglazing but requires a skilled touch as not to damage the cylinder. The Flex-Hone tool, by contrast is not a material removal tool. Because it is self centering it follows the existing bore geometry. This is great if you are trying to freshen a cylinder prior to re-ringing but it will not correct out of roundness or remove taper from a cylinder. The tool is only slightly oversized for any given cylinder diameter and will not damage ports or cause excessive radius at the port edges nor does floating on and off the port edges damage the tool.

Bought a Hone and Forgot what Grit or Type it is?
The Flex-Hone®Tool is manufactured in an extensive range of abrasive types and grit sizes. The Flex-Hone® Tool is color coded for convenient identification. The color code consists of a colored end marking at bottom of tool (below ball stones) and a band of color around the stem (above the ball stones). 

 Stem Marking Type of Abrasive Symbol
No Color Silicon Carbide SC
Black Aluminum Oxide AO
Gold Boron Carbide BC
Tan Tungsten Carbide WC
Green Levigated Alumina LA
Red Zirconia Alumina Z-Grain #1525
White Zirconia Alumina Z-Grain #1549


 End Marking Grit Size
Brown 20
Purple 40
Gray 60
Orange 80
Silver (no color) 120
Cardinal Red 180
Navy Blue 240
White 320
Yellow 400
Pink 600
Light Blue 800