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82 xr500 overheating?

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i have a 82 xr500 with a new piston 2 sizes bigger, kn style air filter and the inside taken out of the exuhast.  it is like 85-90 degrees outside and when i ride up hill for like 15 min the engine seises and the tire locks up.  if i pull the clutch in for a few seconds i can pop it out and the bike restarts.  i am worried it is over heating mabey too lean, could that cause this?   i only have approx 150 mi new piston.

 

 

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Even most cars will heat up when pulling a load uphill for 15 minutes. Air cooled motors need time to get some air passing over the fins to stay alive.

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i have a 82 xr500 with a new piston 2 sizes bigger, kn style air filter and the inside taken out of the exuhast.  it is like 85-90 degrees outside and when i ride up hill for like 15 min the engine seises and the tire locks up.  if i pull the clutch in for a few seconds i can pop it out and the bike restarts.  i am worried it is over heating mabey too lean, could that cause this?   i only have approx 150 mi new piston.

  Did you rejet it when you made those changes?  That bike will suck a lot more gas now than before, and they ran lean to begin with.  And they run very hot to begin with too!

 Dangerous combination of heat/lean condition leading to more heat.  Then ride up hill...............................................................

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yes the bore is two sizes over i believe stock is 89 mm and it was 89.5 untill i put a 90mm piston in.    also i have not rejetted it yet, i moved the clip on the needle 2 spaces richer, and did not want to adjust the main jet untill it was fully broke in and i could hold wide open throttle to look at the plug.  I will probabally put a larger main jet in now, but i am worried that damage is happening.  it dosent feel like it, and it runs great otherwise.  has any body else ever had this happen, or can explain why the motor would temperally seize.  my plan is new plug, sythetic oil change, bigger main jet, and ride it, but i am kind of scared to damage the motor, and cannot afford another rebuild.

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yes the bore is two sizes over i believe stock is 89 mm and it was 89.5 untill i put a 90mm piston in.    also i have not rejetted it yet, i moved the clip on the needle 2 spaces richer, and did not want to adjust the main jet untill it was fully broke in and i could hold wide open throttle to look at the plug.  I will probabally put a larger main jet in now, but i am worried that damage is happening.  it dosent feel like it, and it runs great otherwise.  has any body else ever had this happen, or can explain why the motor would temperally seize.  my plan is new plug, sythetic oil change, bigger main jet, and ride it, but i am kind of scared to damage the motor, and cannot afford another rebuild.

I've rebuilt these motors and similar FT500 motors used for mini sprint racing and have seen this happen many times.  The racing club has found that if you are using a forged piston (e.g. Weisco), that the piston skirt swells more than the stock unit therefore the bore needs to be slightly larger than factory spec otherwise the motor will temporarily seize then cool down and release.  To rebuild I find the widest point on the piston skirt and bore the cylinder to 0.004-0.005 over that widest measurement.  This gives the piston skirt a little more room to expand.  This has been proven many times over and we run these engines at almost twice the rated RPM.

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Wiseco spec for the borer is o.oo4 and if such pison is used,the machinest should be advised of such...I also believe,you mite have not followed the break in procedures required,prior to putting the motor to stress and  ultimately seizure.

Theres a good chance youve scoured the piston and could result in ring seizure.

Stock jetting i believe is a pilot 55 and main 148-155.., I have performance zaust,modded filter and box and a Wiseco Hc,running a 160 main....

Its best to pull your plug after a good ride,if its very lite,well you need to richen up...let it rather be on the dark side and brownish at the porcelain....more fuel ..ideally motor runs cooler.

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