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. EngineHones.com 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
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
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
.2 - .3 Micrometer
.3 - .6 Micrometer
.5 - .7 Micrometer
.6 - .8 Micrometer
.7 - 1.0 Micrometer
.9 -1.4 Micrometer
1.2 - 1.6 Micrometer
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 bore 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 dry hone. Insert the 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 rpms with a vigorous motion up and down in the bore for 60-80 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 60-80 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. http://www.scooterinvasion.net/forum/viewtopic.php?t=580&highlight=cylinder+porting . 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).
Flex-Hone® Color Code
Type of Abrasive
Silver (no color)
The sample Bore listing below. We will be adding to this chart in the near future. If your engine is not listed below and you do not know your bore size, email us with your year, make, motor size, and we will find the correct hone for you.