Cylinder honing

I have not seen much info online about cylinder honing doesnt look like most guys do their own stuff. But think it will be fun/neat skill to master.

I was wondering if anyone has experience or advice on stone selection using a rigid hone line a Sunnen Jn 95.

I plan to pick a few junk cylinders to practice and learn the in an outs. Just looking for some advice on stone selection. Dry versus wet honing.

Not sure if any engine builders willing to share info. Thanks


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Along the same line, does the KA100 require a re-honing when doing the top end?

I consider myself pretty mechanically inclined, there’s not much work I shy away from…that said, machining work I still outsource to trusted builders. I think you will find that if you talk to a few builders that the machine work is pretty reasonable if you are willing to do all of the rest of the labor.

Even with a proper $300-400 hone you are still at the mercy of hoping you have everything square when you try to hone the cylinder. You also need torque plates to torque the cylinder for honing to simulate it being installed because that slightly distorts the bore. Finally you are generally going to want .003 - ish cylinder wall clearance which means a really expensive set of calipers and bore gauge to be able to read to that level of precision. It all adds up in the end.

For a reference one of the biggest builders in the country will piston fitting (boring and cutting intake skirt) on my KT100 for $65 in machining fees. It would take me years and years to justify the $1000+ in investment it would take me to do it right myself when that’s all it costs to have one of the best in the business do it for me.

I have all the tech tools to do all the assembly and disasssmbly myself and that’s where I really save money. I send out for crank services and cylinder boring and do the rest myself.

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Kt100 is piston port engine and little more involved than doing reed valve engines.

I am a hobbyist and no intention on building a national level engine. I enjoy the mechanical side as much as driving.

I think it would be interesting skill to master. Sure you can blow thing up but no different when I split full size engine into a million pieces on a restoration project you always take the chance during learning curve when you do these things a hobby instead of profession.

I intend to pick up a couple of junk/used cylinders to practice technique.

I already made investment in nice set of dial bore gauges, caliper, micrometer, and deglazing tools.

It is of course cheaper to outsource most thing are in life but it nice to say I did it myself.

Split crank is still something I outsource for time being as quality tooling is expensive. I did a 100% overhaul on one engine and just sent out crank cylinder just needed to be deglazed and no honing needed as it was only .01mm out of round and so far so good just looking to expand my skill set.

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IIRC cylinder hone selection and crosshatch depends on ring type.
Good luck with it.

Moved to two stroke since that’s mostly where this is done frequently.

Require… probably not. However It’s always prudent so that you deglaze the bore and have a nice fresh crosshatch on there to seat the next ring. Oh and a square bore too.

I always say that if one is so inclined, it’s worth rebuilding a motor at least once to get a real sense of what goes into it in terms of time and expertise.

Also, paging @Mynameismcgyver he has a hone machine headed his way over winter I think.

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First of all, good for you to take on building your own stuff. It is both fun and empowering. With some builders charging $600 (not a typo) for a top end, plus the wait time and shipping costs, it’s even more incentive. That said, to do the entire job yourself, and do it right, requires a substantial investment in tooling. Cranks require a 20-ton press and expensive jigs and proper honing requires…a proper honing machine, mandrels, stones and accurate metrology equipment. A drill-driven hone, a can of WD-40, and a Harbor Freight bore gauge is not going to to the job right. The honing itself isn’t super difficult if you have the proper tools. A good honing job (proper grit stones, correct cross-hatch, round bore to within .0002") and piston/ring sizing is where a spec-engine builder makes his bones. It’s the only machining allowed. Other than base gasket choice and crank play, there isn’t much else a builder can do on a spec engine. If you have a Sunnen machine, you will need a CR-2100 mandrel and CR-14 280 grit stones (assuming you are honing a 125cc iron cylinder). Use Sunnen MB-30 honing oil. I’m not sure what Sunnen’s diamond stones are called, but you will need diamond stones if you are honing a Rotax or KZ cylinder with a nikasil bore. If you want to go nuts, the best mandrels/stones for kart cylinders are made by an Italian company called Their mandrels and stones are kart specific and longer than the cylinder bore. This makes getting/keeping the bore straight super easy. Sunnen stones are much shorter and require a deft hand to keep the bore straight.

And I would always recommend a fresh hone when doing a top end on an iron bore cylinder. Not only does a new ring require a fresh crosshatch to properly bed, if you are diligent about top ends and honing, your cylinder will never really get out-of-round. If your bore stays round, you will only be removing a teeny amount of material when you put in a new crosshatch. It’s when your barrel gets ovalized that you will need to remove more material. In other words, I find with frequent, light honing your cylinder will last longer. Nikasil bore hardly ever need to be honed, and can be de-glazed with a scotchbrite pad when doing a top end.

With all that said, there are builders who will hone your cylinder and fit a piston for you for around $200. For cranks, there are tons of motorcycle shops that can rebuild a crank and hopefully true it to less than .001” on the bearing journals, probably for less than $150.

What is your opinion on sunnen jn95 portable hone?

I also contact effecieme about this portable unit.

Do you think it possible to complete a quality job with practice with portable hone?

Both Sunnen and Effeciemme units are around 500$ price point with selection of stones.

I made the investment in some quality measuring tools already as I been tracking wear on my engines. And it looks like the amount of wear on bore is surprisingly minimal and bores are really impressively straight round even after up to 30 gallons of use.

I been running one engine long and one engine short to get a feel for realistic wear patterns on engine.

I am club racer and not building national level engines. Just like to keep the engine as good as it was when left factory nothing special.

I think if you have round bores to start with they can work. I know one guy that is pretty good with a portable hone, but he has been using it for a long time and has a really good feel for it. Portable units are really designed for use at the track if a piston gets stuck, not for bench work. They will work, but it will be harder to get it as perfect as you can with a machine. That Effeciemme kit looks nice (all of their stuff is really nice), and the Sunnen unit is a proven piece for sure. The Effeciemme will likely come with a 330 grit stone, which is perfect for an iron bore. I have experimented with plateau finishing with a finer stone after the 330, but I did not like the results. The 280 grit Sunnen is fine, too.

One thing to remember, regardless of the tool used to hone, is washing the bore after you hone. I can’t emphasize this enough. You need to scrub the bore with a stiff, plastic brush and Dawn detergent under running water. Wash and scrub it far longer than it may seem necessary. Then scrub it again. Then dry it out and spray it with WD-40 (to prevent flash rust) until you are ready to reinstall it. When you are ready to install it, you can clean off the WD with carb cleaner. Wipe it down with some 2 stroke oil and install away. If the bore has any residual swarf when installed, it will combine with the fuel/oil to make a nasty grinding paste and turn your cylinder into a gray mess.

And you are correct about wear; cylinders can last a long time, especially if you make sure to have a clean airbox and keep the top end fresh.

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Some very good info here already, but I can fill in some more detail. I spent a lot of time working part time in a kart shop in the 90s, when I was racing seriously. Essentially I put time in, in the shop, in order to get parts at cost, and have access to the full machine shop to build my own motors. I fit pistons to motors that won GNs. I never won a GN behind the wheel, but I did qualify on the front row at a sprint GN (KT-LT…not a joke class in the 90s) in the US with a motor I built myself, which was kind of cool. I was not as good at setting up a kart and driving as I was at the mechanical side of things…

You can do first rate work with a JN portable hone. I personally used a JN-89 (predecessor to the 95…same size), which would go from 50-66 mm. I personally could do a better job with a JN than with a traditional Sunnen horizontal machine. It all came down to feel, just as someone said before. I really liked the feel of holding the drill motor in my hands and “feeling the cut” more directly.

Hone, measure…hone…measure…watch temperatures… You will get a feel really quick.

#1 - You need the right portable hone. That has already been covered.
#2 - You need a low speed high torque drill motor with a good handle. I use an ancient SKIL reversible slow speed drill. You can probably fine one on ebay for $50.
#3 - You need torque plates. I made my own on a lathe & mill, with a special arm fixture that I could bolt into a bench vise. You can buy a set from LAD for $120, and then add a fixture arm.
#4 - Use proper honing oil, and lots of it. Or you can use WD-40. I did that at the track more than once…and the motor ran just as well! Honing oil is thicker and does not give as good of feel, but I am sure it is better, or it would not exist.
#5 - You need one decent .mic of the appropriate size. It does not even need to be calibrated, because you are going to use a dial bore gauge, and zero the dial bore gauge to the piston measurement on the mic. You can find one for under $100 if you are patient.
#6 - You need a decent dial bore gauge, reading in tenths. Mitutoyo is good. Sunnen is better. Figure $150-$600 depending on how good of a gauge you want to get.
#7 - Get the right stones. I liked to use JN200 to size to +.0000" / -.0001". Then I would plateau finish with 400 or so. Plateau finishing is literally a few strokes with moderate pressure and you are done. Any more and you are losing oil holding capability. A plateau like this is essentially speeding up and cleaning up break in.
#8 - Learn the speed to get proper cross hatching at 45 degrees. The faster you turn, the faster you stroke. You have to continually readjust the cutting force dial know to maintain MODERATE cutting pressure. As cutting pressure relieves, you will feel torque drop and speed will rise. That is your cue to increase stone force.
#9 - One of the most important things is to have ST Truing sleeves to keep the stones dialed in. This is how you get straight bores. I usually kept the truing sleeves about .010"-.015" smaller than the bores I was working. That way a newly trued set of stones would not chatter.
#10 - There is an ART to zeroing in a dial bore gauge to a mic dimension you transfer off the piston. This is the MOST critical step.

I personally use Sunnen Dial Bore Gauges and use a Sunnen setting fixture to zero to dimensions measured off the piston (I then also double check the setting against the actual locked in mic setting), but that is because I like the absolute numbers to be correct, but this is NOT required. You can fit pistons perfectly without calibrated tools, if you get good at zeroing the dial bore gauge to the mic within .0001".

One thing I strongly believe is that people do not fit new pistons often enough. Whatever the conventional wisdom is about how long you should go before fitting a new piston…I cut that in HALF if you want a strong motor. This is not practical for most people, but I had all the tools…so that is what I always did.

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Thanks for information!

Can you give some more insight on how you dressed new stones with the truing sleeve?

You start out by boring the sleeve on a lathe to a diameter just under the small end of the cylinder range you will be working with. Then you just hone out the sleeve a bit now and again. Because the sleeve is only used for truing, it stays very straight.

dont hone yur self with a drill & hone take to shop for professional or someone that can do its not guess work u need a bore gage to proper piston fit

Nonsense. If you have the right tools, you will probably do a better job than a shop as it is your own stuff. The key is getting the right tools. They are not that much money if you buy used, and will pay for themselves after 2 or 3 rebuilds. This is not difficult stuff or magic.


I think Larry was advising against a drill and I tend to agree. Unless you are totally stuck (pun intended) at the track or something and there’s no alternative… It’s best to have it done with the correct tooling…

Lets talk about what the right tools are then…
Hone machine, bore gauge, stress plate, micrometer… what else


check out Millenium, they do it right and aren’t crazy expensive

Millennium I’d usually go with for nikasil plating, but there’s dozens of kart engine builders that can hone a cast iron cylinder.

For the most part it’s shifters that’s run nikasil. But 100cc are almost universally iron liners.

This was discussed earlier. A JN, and few sets of stones, torque plates, a truing sleeve, a vise, a 2-3 mic and a bore gauge are all you need. I have honed hundreds of jugs with a Sunnen JN-85 (predecessor to the current JN-95) driven by a low speed drill motor and can do just as good a job as anyone could do on a MB. In fact, when I was working in a shop and was doing my own, I used the JN with a drill motor over the MB. I can split tenths and hold bore top to bottom. In fact, I think I can do a better job with a JN than most can do on an MBB. Better feel… Where an MBB really shines, is throughput. If you hand a grunt 200 rods and ask him to size the lower ends to within 2 tenths, you better have a fixed machine.

Millenium? They do first rate work. I use them to re-hone my dirt bike cylinders, and also to re-build cylinder heads. But I would never send them an iron lined jug. I don’t think they want to work on one either.

I should clarify I mean a hand drill when I say (don’t use a) drill. Drill press would be acceptable, at least for me :slight_smile:

I could be wrong, but I get the feeling you are a machinist in some capacity. Bear in mind that many do not posses that skill… at least not yet.

Rotax Max and all shifter engines are Nikasil, I assume that’s where it was coming from. Although we are talking about iron here.

That said, it made me curious enough to look it up and Millenium have a page of services specific to iron bores.

My DIY portable honing tank with torque plate. I machined out the combustion chamber of an old head to use as the base of the torque plate. Fuel lift pump for honing fluid delivery. Baseplate weight and it being fitted to a square pale keeps it from moving with a foot on each side.

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