Setting the X - Dimension Correctly on a 200


43 replies to this topic
  • Supertrunk

Posted January 11, 2009 - 02:21 PM

#1

It always amazes me how much "bad" information there is about setting the X - Dimension out there.

First: There is no "stock" gasket thickness. It is determined at the time of assembly to take into account manufacturing tolerances.

Second: You probably won't hurt your bike with the incorrect X - Dimension as it is hard to get too little clearance between the piston and head, but it could happen in rare cases. Most likely you are just leaving performance on the table.

Here's the deal on setting the X - Dimension correctly:

Posted Image

Oh, and the Austrians mean "ping" not "pink", (I don't think they know Carey Hart's ex.......................).

  • highmarker

Posted January 11, 2009 - 02:46 PM

#2

why not just call it deck height? also while your at it measure the inset on the head surface to squish band, add the two and use that total (squish clearance) to adjust your base gaskets. It'd be crazy to just confirm the X and not know the resulting squish.

  • Supertrunk

Posted January 11, 2009 - 03:40 PM

#3

Why not?

Because KTM chose to call it the "X-Dimension", and supplies 5 different thicknesses of base gaskets to set it with. It affects port timeing as well as squish clearances.

Many, many folks also trim a little off the head, reducing squish, and then reshape the width of the squish band to gain considerable punch down low on the 200's.

  • Redrodent

Posted January 11, 2009 - 03:54 PM

#4

I found it very hard to measure accurately with calipers due to the step in the cylinder. It was easier for me to lay a feeler gauge across the top of the piston. When the proper thickness gauge is level with the step, that's your X dimension. You should be able to feel +/- .002 accuracy with just your finger.

  • highmarker

Posted January 11, 2009 - 06:52 PM

#5

Thats' the problem, if one only payed attention to the X dimension and got a hold of ahead that was cut he could easily be too tight using just the X. Why I mentioned it was important to know what the finished squish clearance was, the X is only part of the dimension. Not trying to be a stick in the mud, it's good that ktm has you checking and using available gaskets during assembly. For most that aren't too anal about this stuff it might be easier to note what gasket came off and replace it with the same. Even better is to check your squish before disassembly then you can do the math and order the right gasket.



Why not?

Because KTM chose to call it the "X-Dimension", and supplies 5 different thicknesses of base gaskets to set it with. It affects port timeing as well as squish clearances.

Many, many folks also trim a little off the head, reducing squish, and then reshape the width of the squish band to gain considerable punch down low on the 200's.



  • kenr74

Posted January 13, 2009 - 09:05 PM

#6

So the "X" is measured from the top of the piston to the top of the jug or to the step just inside the jug? The picture looks like it is measured to the step so if you piston is right on the step your "X" would be 0?

  • llamaface

Posted January 14, 2009 - 08:29 AM

#7

I found it very hard to measure accurately with calipers due to the step in the cylinder. It was easier for me to lay a feeler gauge across the top of the piston. When the proper thickness gauge is level with the step, that's your X dimension. You should be able to feel +/- .002 accuracy with just your finger.


I measured mine by putting the end of a good metal straightedge across the edge of the piston, resting on the top of the cylinder, and putting feeler gauges underneath it. I used thinner gaskets until the piston itself hit the straightedge, then went very slightly thicker, ending up with very close to zero x-dimension.

As far as squish, I just measured it and sent the cylinder and head to jbone motorworks. doesn't make sense to me to try to adjust that with base gaskets. The bike is considerably stronger with the squish done right.

  • llamaface

Posted January 14, 2009 - 08:30 AM

#8

So the "X" is measured from the top of the piston to the top of the jug or to the step just inside the jug? The picture looks like it is measured to the step so if you piston is right on the step your "X" would be 0?



yes, measured to the step, and yes, your target is 0.

  • Veccster

Posted January 14, 2009 - 10:47 AM

#9

OK, so what the hell is the "squish band"?

I understand the x-dimension.

  • toyota_mdt_tech

Posted January 14, 2009 - 10:56 AM

#10

OK, so what the hell is the "squish band"?

I understand the x-dimension.


Squish band is the outer ring of the head, around the bowl. Measure this by inserting a 1mm thick piece of solder. Then gently roll the piston past TDC, renmove solder and measure. Make sure the solder goer to the outer edge of the cylinder and dont get it into a port, it will shear it off and fall down inside. Measure this and adjust. If "X" is set, then you need to mill head. Too little will require race fuel, so be warned.

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  • llamaface

Posted January 14, 2009 - 02:36 PM

#11

Squish band is the outer ring of the head, around the bowl. Measure this by inserting a 1mm thick piece of solder.


In my limited experience, it requires thicker than 1mm. I used a 3-4mm thick piece, and i think the squish measured around 1.7mm or so before I had the head milled. Such solder (high in lead for malleability) was not found in the local hardware stores.

  • Redrodent

Posted January 14, 2009 - 04:11 PM

#12

Too little will require race fuel, so be warned.

Too little will require the piston to hit the head :p
The volume in the head can be machined (after your squish is corrected) to any fuel you chose to run :thumbsup:

  • Dave mac

Posted January 14, 2009 - 06:08 PM

#13

Too little will require the piston to hit the head :p


even with the step up :thumbsup:

  • Redrodent

Posted January 14, 2009 - 06:59 PM

#14

My 200's squish is at a safe .036in. My understanding is that the rod can stretch up to .025 at full revs. The bigger engine, the heavier the piston = more stretch = larger squish needed. Stack on a couple thou for the main, rod, and pin bearing clearances + crank flex. That .036 gets used up in a hurry.

  • Veccster

Posted January 15, 2009 - 06:37 AM

#15

I'm so naive at this but I'm trying to learn because I would like to do a top end soon.

Here's a video that also explains it pretty well:

He even shows how to measure the squish with solder.

Which gasket do you change to inc/dec the x-dimension?

Which gasket do you change to inc/dec the squish?

  • llamaface

Posted January 15, 2009 - 07:45 AM

#16

Which gasket do you change to inc/dec the x-dimension?
[COLOR="Blue"]base gasket, at bottom of cylinder[/COLOR]

Which gasket do you change to inc/dec the squish?

[COLOR="blue"]You don't change a gasket, you have the head milled properly. This is pretty cheap to have done if you're only having the head worked on. ($50 or so?). I would recommend that any 200 owner spend $200-ish tho, and get the full cylinder/pv/head treatment from jbonemotorworks.com . It's the best money I've spent on the bike.[/COLOR]

  • kenr74

Posted January 15, 2009 - 09:25 AM

#17

[COLOR="blue"]I would recommend that any 200 owner spend $200-ish tho, and get the full cylinder/pv/head treatment from jbonemotorworks.com . It's the best money I've spent on the bike.[/COLOR]


That's good to hear. My cylinder/head are on the way to him now. :thumbsup:

  • ulmanb

Posted January 15, 2009 - 09:30 AM

#18

llamaface
can you tell us more about the improvements you gained by having the cylinder and head worked on?

  • llamaface

Posted January 15, 2009 - 09:33 AM

#19

llamaface
can you tell us more about the improvements you gained by having the cylinder and head worked on?


more power pretty much everywhere.

More improvement to low-end than you get with a gnarly pipe, but not giving up anything at the upper end.

  • toyota_mdt_tech

Posted January 15, 2009 - 11:08 AM

#20

[COLOR="blue"]You don't change a gasket, you have the head milled properly. This is pretty cheap to have done if you're only having the head worked on. ($50 or so?). I would recommend that any 200 owner spend $200-ish tho, and get the full cylinder/pv/head treatment from jbonemotorworks.com . It's the best money I've spent on the bike.[/COLOR]


Llama, did you just send in the top end or did you have to send in the engine assembly?




 
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