Do I need to hone a motorbike cylinder bore for new piston & rings?
The correct and only way to prepare cylinder bore for piston & rings if you want to achieve a good outcome - This applies to a 2 and 4 stoke engine
Information below applies to all 2 and 4 Stoke Cylinders - All brands of piston kits and ring sets - Vertex, JE, Meteor, Wiseco, Wossner, Athena, Prox and all Genuine KTM, Honda, Suzuki, Yamaha, Kawasaki, TM ect...Piston Kits.
2-Stroke
You can normally get away without honing a bore on a 2-stoke, (as long as the bore isin good condition and the clearance is correct) as 2-strokes do not have oil rings, so if the rings do not break-in correctly the engine will not use a lot of oil, unlike a 4-stroke would if not honed. But when fitting rings to any un-honed bore, the ring life will be reduced, and the engine will never achieve full power output as the ring-bore seal will never be as good if the cylinder-bore was honed. You may say this is not true, it has been proven hundreds of times, every ring manufacture states cylinder- bore must be hone correctly for rings to wok correctly, and of course why is every new motorbike cylinder-bore honed from new - I wonder?
4-Stroke
All 4-stroke bore must be honed when installing a new set of rings. If this is not done the engine will burn oil, the ring to cylinder wall will get compression blow-by (compression leaking past the rings), blow-by can courses all sorts of problems, high oil burning, blow oil out of the crankcase breather, burning oil from the piston-bore casing a seizure, leaking engine oil seals, low engine power. What is the point of fitting a new part when you want to achieve a good result, by missing out the most important part and for only a few dollars more it can be done right?
Why so important
The first few miles of a new piston-rings life have a major impact on how strongly that engine will perform, how much oil it will consume and how long it will last. The main purpose of correct cylinder-bore preparation is to have an outcome that the rings will have a good seal to the cylinder-bore walls. We are talking about the physical mating of the engine's piston rings to its corresponding cylinder wall. That is, we want to physically mate new piston rings to the cylinder wall until a good tight compatible seal between the two is achieved.
Proper engine break in will produce an engine that achieves maximum power output with the least amount of oil consumption since the piston rings have seated properly to the cylinder wall. When the piston rings are broken in or seated, they do not allow combustion gases to escape the combustion chamber past the piston rings into the crankcase section of the engine. This lack of "blow-by" keeps your engine running cleaner and cooler by preventing hot combustion gases and by-products from entering the crankcase section of the engine. Excessive "blow-by" will cause the crankcase section of the engine to become pressurized and contaminated with combustion gases, which in turn will force normal oil vapours out of the engine's breather, causing the engine to consume excessive amounts of oil.
In addition to sealing combustion gases in the combustion chamber, piston rings must also manage the amount of oil present on the cylinder walls for lubrication. If the rings do not seat properly, they cannot perform this function and will allow excessive amounts of oil to accumulate on the cylinder wall surfaces. This oil is burned each time the cylinder fires. The burning of this oil, coupled with "blow-by" induced engine breathing, are reasons that an engine that hasn't been broken in will consume more than its share of oil.
Proper engine break in will produce an engine that achieves maximum power output with the least amount of oil consumption since the piston rings have seated properly to the cylinder wall. When the piston rings are broken in or seated, they do not allow combustion gases to escape the combustion chamber past the piston rings into the crankcase section of the engine. This lack of "blow-by" keeps your engine running cleaner and cooler by preventing hot combustion gases and by-products from entering the crankcase section of the engine. Excessive "blow-by" will cause the crankcase section of the engine to become pressurized and contaminated with combustion gases, which in turn will force normal oil vapours out of the engine's breather, causing the engine to consume excessive amounts of oil.
In addition to sealing combustion gases in the combustion chamber, piston rings must also manage the amount of oil present on the cylinder walls for lubrication. If the rings do not seat properly, they cannot perform this function and will allow excessive amounts of oil to accumulate on the cylinder wall surfaces. This oil is burned each time the cylinder fires. The burning of this oil, coupled with "blow-by" induced engine breathing, are reasons that an engine that hasn't been broken in will consume more than its share of oil.
We hear this lot - I can still see hone marks in the bore so I thought I could just get away without honing it. This is the worst mistake that seem to be made, and just because you can see the old hone marks means nothing.
Even if you can still see the worn hone makes after 5-10 hours work you still must hone the bore every time new rings are installed. Once the raised hone points are rubbed off, a new hone job is needed.
Honing a bore creates very light raisers on the bores surface, these high points in the hone is what makes the ring mate to the bore to create a good seal. Honing attaches like a very light file to make both surfaces smooth and even and to mate, it also protects the rings for contacting the bore during run in.
Honing a bore must be done by an experienced person with good knowledge of what they are doing.
Honing the bore correctly should be done by a person with years of experience and good knowledge of this job. By using the correct grade diamond hone, correct hone machine with the correct speed and revolutions, to achieve the correct finish to what type of bore material is being honed. Even using the correct type of lubrication during the hone is important.
Below is showing the surface finish, with different crosshatches. A professional will normally use surface finish gauge to check the bore finish is correct.
When a cylinder is new or overhauled the surface of its walls are honed with a diamond hone to produce the correct surface finish that will help wear the piston rings in. This roughing up of the surface is known as "cross-hatching". A cylinder wall that has been properly "cross hatched" has a series of minute peaks and valleys cut into its surface. The face or portion of the piston ring that interfaces with the cross hatched cylinder wall is tapered to allow only a small portion of the ring to contact the honed cylinder wall. When the engine is operated, the tapered portion of the face of the piston ring rubs against the coarse surface of the cylinder wall causing wear on both objects.
Each tiny groove acts as the oil reservoir holding oil up to the top level of the groove where it then spreads over the peak surface. The piston ring must travel up and down over this grooved surface and must "hydroplane" on the oil film retained by the grooves. Otherwise, the ring would make metal-to-metal contact with the cylinder wall and the cylinder would quickly wear out.
However, the ring will only ride on this film of oil if there is sufficient surface area to support the ring on the oil. When the cylinders are freshly honed the peaks are sharp with little surface area. Our goal when seating the rings on new steel cylinders is to flatten out these peaks to give more surface area to support the rings, while leaving the bottom of the groove intact to hold enough oil to keep the surface of the cylinder wet with oil. At the point where the top of the peaks produced by the honing operation become smooth and the tapered portion of the piston ring wears flat break in has occurred.
Very important after honing the bore must be cleaned thoroughly in hot soapy water, and then apply a very very thin lay of oil so the surface does not start to rust. Do not use CRC as this can damage the rings if left on when fitting the piston into the bore.
Can a plated cylinder be honed?
Yes, you can hone a plated bore.
And no the plating is not that thin that the cylinder cannot be honed or honing a cylinder will remove all the plating. Cylinder plating is normally .10mm or 004" when a cylinder is honed with the correct hone a diamond hone it will only remove .01mm or .00025" this is barely removing any materiel from a good condition cylinder.
Below is the type of machine that is used to hone a plated bore with a diamond hone correctly. So, take the cylinder to some that does. If you do not get the correct people to hone the bore and the engine smokes or gets oil blowing out of the crankcase breather hose, it will not be the piston or rings that has cause this, It will be because the bore was not honed correctly.
Never use a ball/bead hone
Ball/bead hones should never be used in bores with ports, as the balls on the hone can clip the plating. What happens is the balls a forced in/out of the 2-strokes ports at speed this can clip the edges of the plating causing big problems down the track. Ball/bead hones are very cheap workers tool and not really that great on any bore. A ball/bead hone is normally used because they cannot use or afford a diamond hone machine which can cost $80,000, and the person doing the job with a ball hone does not understand why a bore is honed.
Ball/bead hones should never be used in bores with ports, as the balls on the hone can clip the plating. What happens is the balls a forced in/out of the 2-strokes ports at speed this can clip the edges of the plating causing big problems down the track. Ball/bead hones are very cheap workers tool and not really that great on any bore. A ball/bead hone is normally used because they cannot use or afford a diamond hone machine which can cost $80,000, and the person doing the job with a ball hone does not understand why a bore is honed.
Do not hone plated bores with hones below as the outcome will be a poor hone job and the engine may use oil or smoke
