2019 CRF250R piston question
  • ejk
    Posts: 5
    Joined: Tue Jul 30, 2019 4:40 pm

    2019 CRF250R piston question

    by ejk » Thu Aug 08, 2019 5:17 pm

    I am periodically testing the compression with a differential compression tester on this bike. So far the piston ring & valves are completely tight as I can not measure any pressure loss. My question is if a piston is about to fail by fracture will it necessarily have compression loss first? Or, how common is it for a tight piston to fracture? Bike has about 35 hours on it. Whole reason the the testing is to avoid having an engine failure on a large jump causing an endo crash as recently happened to Hunter Lawrence. Not sure if there is much of a correlation between low/high compression and piston failure.
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    JimDirt
    Posts: 3288
    Joined: Sat Nov 25, 2006 6:31 pm

    Re: 2019 CRF250R piston question

    by JimDirt » Fri Aug 09, 2019 8:03 am

    If your compression is good/within spec and you are not riding the bike into the ground and you change oil regularly , 35 hours is not much unless you are racing Pro class , to me it is just starting to break in good , you should be able to get 100 hours on a piston (average joe weekend warrior) , I have probably 150 on my 02 since last piston change , which is only the 2nd piston since I have owned it since 08 (don't have a hour meter , but one of the guys I regularly ride with does and I use his time to estimate mine) , my last piston was fall of 2016 and I track ride almost every weekend (well actually I ride almost every weekend since 2018 due to some health issues I had that prevented me from riding 2017) :cry:

    If you use good oil , especially Synthetic , you should be able to run 50 hours minimum even if amature racing , my friend with a KTM , has over 300 on his 13 450SX on the same piston , and tore it down , and ended up just replacing the head gasket and is still running the same piston ..... good oil and changing it before it gets real dirty is the key to piston life , and stay off the limiter....... Remember , the "recommendation" in the manual is just that , a recommendation , and for serious racing , not what the average rider does , and is only a reference guide , not mandatory , if you are not abusing the bike like a Pro would , just pay attention to the compression , if you notice a drop and its not valve related (you can do a Leak Down Test and it will tell you if air is getting by valves or the rings) , then its probably time for a piston .... If you tear it down and the skirt does not look like the pic below , then you are probably good

    Top piston is worn , Bottom is used but not worn:
    Image
    02 CRF450R
    06 CRF450X
    Image
    Weiser , Idaho
  • Back2-2
    Posts: 747
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: 2019 CRF250R piston question

    by Back2-2 » Fri Aug 09, 2019 10:19 am

    To answer your question. No, you will not be able to detect a piston pre-failure by compression testing. It will require Zyglo inspection to see any cracks or fractures in the piston. The cost of doing that procedure is not cost effective unless you have connections to get it done free.
    That is why there are service intervals recommended by the engineers that designed the engine.
    To confer with Jim, I changed my piston at 200 hrs and it measured near new limit's. But I changed the piston and rings together since it was apart and they are very reasonably priced.

    Hope that answers your question.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring

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