JE Piston & Ring install tips?

8 replies to this topic
  • box986

Posted August 13, 2008 - 12:09 PM


Hello all,

I am ready to install a new JE 77mm piston and rings with my freshly-bored cylinder. Any tips from those who have done this job? Gap position of the rings? Places to use/not to use assembly lube? Gaskets go on dry?

As far as gap position goes, I have been told two different ways: Upper ring gap at 7 o'clock & lower at 1 o'clock (180 degrees) or upper at 7 & lower at 4 (33 degrees)?? Both parties did stress that upper gap stay on the intake side.

I am also installing a new head w/new valves/springs along with a new cam chain and tensioner.

Any other tips on doing this install?

Any input is appreciated, this site has helped out tremendously!

  • box986

Posted August 25, 2008 - 05:21 PM


bump :thumbsup:

  • Baja trail Rider

Posted August 25, 2008 - 08:05 PM


Check your bore to piston.we run ours at two thousand.Alot of guys bore your clyinder to 4or 5 thousand then your bike is worn out in 6 months using oil

  • box986

Posted August 26, 2008 - 04:42 AM


Check your bore to piston.we run ours at two thousand.Alot of guys bore your clyinder to 4or 5 thousand then your bike is worn out in 6 months using oil

XRO did the bore already, no way to change that at this point.

However, as far as ring gaps go, I have been told to gap the upper ring to .014 by JE techs but have read here (and XRs Only also) to use the calculation of .004 gap per inch of bore which would equal .012 (3.031 x .004=.012).

Should I gap the rings at .013 to be right in between these two numbers? JE also told me to gap the 2nd ring at .016?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • ado

Posted August 27, 2008 - 01:24 AM


you should still check your piston to bore clearance... machinists have been known to make mistakes before.
0.004-0.005 is acceptable, but wouldnt want any bigger.
0.002 as recomended by baja trail rider sounds tight to me for an air cooled(but i am not saying it wont work)

ring instalation
usually is a data sheet supplied in the box with the rings, if not check the manufactures website.

ring end gap.. go with manufactures spec(they know the expansion rate of the rings they supply). 0.004 per inch of bore is a good rule of thumb if you have no specs. (0.002 increase in end gap will never be noticed in performance, and if the gap is too small it will mean another rebuild!!)

ring gap position.. set the gaps so they are not in a line with each other, other than that it will make no difference where they are.( i personally try not to align any ring gaps above the gudgeon pin, or in the middle of the thrust side of the piston)

most important before doing any assembly work!!!!

everything should be clean!!
the area you are working in!!
the parts you are installing!!
the engine you are putting them into!!
and you!!! clean hands!!!

about 50% of premature engine failure i see are due to poor assembly(mainly dirt)... the rest are poor running in proceedures and general abuse.

if youre not confident in what you are doing, get someone who knows(not thinks they know) to help you. or it could easily end in tears.

let us know how its progressing and what we can help with.
take your time, better to stop and ask question than screw it all up!.


  • box986

Posted August 28, 2008 - 02:15 PM



  • box986

Posted August 28, 2008 - 06:38 PM


What is the proper way to measure the bore-piston clearance? A .005 feeler gauge easily slides down into the gap, .006 will slide in w/a little force. Not sure I have the piston at the proper place, I am measuring it at the tightest spot which seems to be below the 2nd ring slot on the piston at the top of the bore? There is more gap at the very top of the piston. JE specs call for a .002 clearance.

  • ado

Posted August 29, 2008 - 04:19 AM


bore to piston clearance cannot be measured with a feeler gauge. you will require internal and external micrometers as a minimum, and a proper bore gauge would be prefered.

if the piston was supplied to, or by the machine shop that did your rebore, you will have to trust they have done it right, but you can ask them what they set the clearance at.

the piston to bore clearance is measured on the skirt of the piston. the ring lands(area above, below and between the ring grooves) at the top of the piston will be a smaller diameter than the skirt(which is actually, slightly oval shaped).

tell the guys who did the rebore you want to learn more about this sort of stuff, and usually they are more than happy to explain it to you. but try not to take up too much of thier time. time is money!.



  • box986

Posted August 29, 2008 - 09:23 AM


XRO claims they bore the cylinder-piston gap to .002, and they did have the piston while doing the bore.

Oil rings: Do I gap these? JE said they should be gapped at .015-.055 but XRO said do not touch the gap at all (currently these rings have no gap)

Main rings: JE said go with the .004/inch of bore which equals .012 and they said gap the 2nd ring .002 greater than the top which would be .014. Is this the best setup?


Related Content


XR400 Rebuild (Partial) by BluntMachete

Dirt Bike   Make / Model Specific   Honda   XR250/400
  • * * * * *
  • 5 replies

86' + Piston kit in a 84' 250R? by MythicJoker

Dirt Bike   Make / Model Specific   Honda   XR250/400
  • 6 replies

XR400 - Will I have problems with 440 Big Bore Kit and Hot Cam Stage 1? by jallangreen

Dirt Bike   Make / Model Specific   Honda   XR250/400
  • 17 replies

xr400 yoshimura trs exhaust by jakebing

Dirt Bike   Make / Model Specific   Honda   XR250/400
  • 9 replies

XR400 Scrambler by jmour

Dirt Bike   Make / Model Specific   Honda   XR250/400
  • 12 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.