Hone This

[Martin Secrest]

I'm wondering about people's opinions on how the KT100 cylinder should be honed.

Let's presume it is being done correctly, on a Sunnen machine.

I know the old saying about what opinions are like -- but I'd like to hear 'em all anyway.

[Walt Gifford]

It's not rocket science and, you don't need a big sunnen machine.

I use aluminum torque plates top and bottom and put on an old header. The bottom torque plate has a tang for holding the cylinder in the vise and I use a squirt bottle with kerosene to keep the stones from loading up.

My hone is an Ammco 3950 small engine hone and, I don't use the 2 felts but, instead use 4 stones. I believe it is stone set #3952-1 and they are the finest stones made for that hone. You have to keep the set together so the stones wear evenly. Don't mix with other sets. If one stone gets damaged you have to replace the set. A hand held drill provides rotation.

You should hone from both ends and controll the stroke so the stones don't pop out of the bore too much and bell mouth the end. Your hone may cut slightly more on one end than the other but, if you know which end and, measure often, you can use this to advantage. Vary the length of stroke, speed of the stroke, speed of the drill and flip the cylinder often and this will give you a nice even bore with a random crosshatch.

With OEM Yamaha pistons I use a piston clearance of .0025" for engines I intend to give a good break-in, .003" for engines that get a break-in during morning practice and .0035" for customers who run them hard right off the bench. I have used down to .002" clearance but, there seems too be too much piston scuffing even after a proper break-in.


Giffy
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FAA certified jet engine and aircraft technician
Nicholson Speedway class champion 2001
Yamaha KT100 Service Center
40 years karting experience

[Pete Muller]

I have a Sunnen MBB-1660 floor model honing machine.

For a KT-100 (and most other 100cc cylinder), I use a Y56-2000PE keyway mandrel (single stone with 2 brass shoes opposite).

I spend at least 75% of the total job time setting up the mandrel. I use a truing sleeve that is as close as possible to the bore size (preferably exactly the bore size) to set up the mandrel.

I typically use around a 280 grit stone on a KT-100, though I have used a number of stones on either side of that.

Lots of time is spent getting the cylinder ready for honing... top torque plate, exhaust header flange, intake manifold... all installed and torqued in exactly the same sequence and with the exact same torque increments as when assembling the engine.

Once the mandrel has been set up and lapped-in to the bore size (using the truing sleeve), and the cylinder is ready to go... honing is a very simple process.

Using the above procedure, I have run KT-100 engines with a piston to bore clearance as tight as .0005 (half a thousandths) clearance when running direct drive. (more clearance is required depending on type of exhaust pipe, piston taper, and a number of other things).

'bout it
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Muller Machine
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[George Petry]

What’s your opinion on ball hones? If you read there sales literature you would think That Sunnen hones are a thing of the past. Do any of you folks have any experiences or opinions on ball hones? I We used ours a little to often in our pits at Road America last weekend.

[Martin Secrest]

What's a ball hone? Is this a "manual" device?

And to Pete -- have you ever used a two-stage hone process? That is, a first coarse cut, followed by a fine cut?

[John Kuntze]

I knew a guy that used a ball hone on his Yamaha because it was cheaper to get honed. It screwed up the cylinder so bad it took a cone shape and he had to trash it he never did that again.
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John Kuntze
ekart99@aol.com

[Pete Muller]

[Pete Muller]

[Jack Burroughs]

The only place I ever use a ball hone is in briggs cyls, and other straight holes with NO ports, and basicly for de-glazing, 'cause all they are is a expensive, glorified glaze breaker. NEVER use in any 2-stroke cyl., the balls will get into every port hole and bell-mouth to where it will render it useless. A 2-stroke should be de-glazed, (if thats what you want to do), with a hone, and the truing fixture is an essential part of doin' the job right.

[Martin Secrest]

I've never honed a KT100 cylinder, and I don't know the first thing about it ... but ... how does the crosshatch interact with the fuel charge, i.e., the oil? Does the crosshatch trap the charge, thus enabling the compression?

[John Burgess]

[Martin Secrest]

Right -- but why does an uneven surface (i.e., the crosshatch), enable the compression? I presume it does so by providing cylinder wall "valleys" in which the fuel charge can accumulate, leading to compression (?)

If this is true, then don't bigger valleys (that is, a coarser crosshatch) presume higher compression?

[Chuck Bunnell]

Remember that it's an uneven surface on a very small scale. And there's some magic about riding peak to peak versus surface to surface where you have less drag going peak to peak. I know there's more to it than that, but it escapes me right now and I think that's the gist of it. The droplet size of the oil on the walls should be small from the atomization and needs to be kept small to keep drag down too. Something like that.

[Pete Muller]

[Martin Secrest]

I see. But then, Pete, what's the best procedure or process to maximize a Yammie's compression? Other than using castor, that is?