CR500 rod and Piston in KX500

[hillclimber147]

Has anyone tried the CR500 rod and piston in their KX500? If so what year rod would be better, the 139mm 86 rod, or 87 and newer 144mm rod? I'm looking to build a big bore KX, starting with a 90mm piston. That should give me 547cc's.

[doordie]

You can stroke it to 88mm and bore it out to 88mm and use the 2mm oversized Wisecopiston.
You have to make a spacer underneath barrell too.You can adjust porttiming with it at the same time!

Many have done this mods and it working very well.

[hillclimber147]

With a CR500 rod I can bore it all the way to 91mm. Then if that's still not enough I'll look into stroking it. Both have the same big end pin diameter, and once I get the port timing difference between the two figured out it should be fairly simple, maybe. Thought I'd see if anyone else has done this.

[kx666]

if you could find a way to stroke itm, i would love to hear it. i thoguhgh the kx and cr had the same bore and stroke.
 

[hillclimber147]

KX 500 - Bore 86mm, Stroke 86mm

CR 500 - Bore 89mm, Stroke 79mm

[doordie]

Use 144mm H...da rod,and you don?t need to "shave off" barell so much,only 1mm difference between KX500 (145)and CR500(144).

I think you have to resleeve if you go bigger than 90mm in bore
The cylinder walls will be thin and maybe crack if you only replate

I think we have a few bigbores guys out there,help him out please!

[hillclimber147]

When extra base gaskets are added to raise port heights, how much are you guys raising the cylinder by? This mod shifts the power band up in the rpm range correct?

[stroke.n.smoke]

Can you not just raise the transfers instead of lifting the whole cylinder up.  The exhaust port hieght goes up as well, I think that is why the powerband increases to the upper rpm limit.  What about widening the transfers and exhaust port and leaving the cylinder where it is at.  I think widening the exhaust port gives a (wide) increase in the powerband.  Increasing the torque as well.  I would send the cylinder out to someone who knows the 500's ports and let them massage it to where it makes the most power all through the rpm.  Speaking of that, is there someone on here that knows where to send the 500's cylinder out for the best porting???

[hillclimber147]

I just got done crunching some numbers with the information Wiseco gave me about pin to timing edge height for a CR and KX piston. With a 139mm CR rod, the rod and piston combo is 3.2648mm shorter from crank center to piston timing edge. With the 144mm CR rod the combo is 1.7352mm longer.
                                My question is if I go with the shorter combo how much can be shaved off of the cylinder base, and how much can the cylinder be "raised" before port timing is out of wack.

If I go with the longer CR rod I would have to have a cylinder spacer of at least 1.7352mm thick to compensate. Which way would you guys go?

[kx666]

hmmm... doesnt kawi make a +1 head gasket....then just find a +.7352 base gasket or makew a spacer???>
i am going to keep an eye out for a 144mm rod for s&g's

[Johnniespeed]

 Hillclimber147,  Could a  90mm piston ( CR)  be special ordered with the piston pin hole machined in the KX location ? Or could you purcahse the unmachined piston forging and you machine the pin hole to KX diameter and location. That would allow your 90mm bore,rod would be unchanged and port timing would not be changed. Using a shorter rod increases the thrust angle and places more thrust on the cylinder wall, not good.. And moving the barrel upwards, increases the crankcase volume which is not good in theory. I see no gain in using the CR rod except that it would fit onto the CR piston.
   Since we are only talking here, I thought that moving the pin hole was easier than changing the rod and fussing with barrel height. John

[hillclimber147]

I haven't been able to find anyone who does custom pistons. And from the last I heard you had to order a large number of them.

[Paul]

Any piston manufacturer will machine you any piston you want. I have a set of 4.040" SBF Ford pistons that use a Chrysler rod, Chevy rings, a 4.15" stroke and have a "39cc" dish in the top to achieve 8.8:1 CR for my FI engine. While expensive, it isn't impossible to get what you want / need. As far as I was told (by JE) these are the only pistons of these deminsions they have ever made.

[Paul]

I haven't been able to find anyone who does custom pistons. And from the last I heard you had to order a large number of them.

This may very well be the case for a single piston.

[hillclimber147]

I just talked to Wiseco and they can make any size KX 500 piston I want. A run of four, 92mm pistons(with rings, circlips, and wrist pin) would cost $252 a piece, a run of 8 would cost $208 per piston. The price per piston is what I would expect for a custom piston it's the number I would have to buy thats painful. Anyone interested in a 571cc KX? LA Sleeve's big bore KX 540 sleeve has a 95mm OD, which is plenty big to house a 92mm piston.