Compression test on a 2008 WR450 reads 50 PSI

6 replies to this topic
  • Ariel101

Posted July 29, 2011 - 11:38 AM


The bike has 6600 miles. I ride mostly technical trails (average speed of 20 miles/hour) and don't rev it up to its higher limit. Occasionally moderate motocross riding. Oil changes every 320 miles. No apparent oil consumption between changes. Valves are checked regularly and haven't needed alignment, ever. the mechanic got 50 psi compression test, but didn't make a compression leak test. I rode the bike since and don't notice drastic change in performance, unless this degradation build up over time and i got used to it.

1. whould the bike perform well on such low compression?
2. is this test relevant at all? wouldn't the auto decompression make it meaningless?
3. are there other signs for low compression I should look for? before returning back and having a compression leak test


  • dgcars

Posted July 29, 2011 - 01:11 PM


Your auto-decomp negates any findings of a compression test.

  • Krannie McKranface

Posted July 29, 2011 - 02:15 PM


Normal reading

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  • SXP

Posted July 29, 2011 - 02:47 PM


Normal reading

More along the lines of a meaningless reading. As DG stated, the AD mechanism bleeds off compression. A leak-down test will tell you what you want to know about your top-end.

  • JDLowrance

Posted July 29, 2011 - 06:54 PM


The only way to get proper numbers performing a compression check is to remove the exhaust cam and cam chain. Not worth it. You can do a a leak down test that will tell you whether or not your valves or piston rings are in need of some attention. If you hear leaking from CC breather, your rings and possibly piston need to be replaced. If you hear air escaping from either intake or exhasut manifolds your valves are the culprit.

From what you've described, your rding style etc. you've got nothing to be concerned about. It's a WR after all!


  • Ariel101

Posted July 30, 2011 - 01:52 AM


thank you very much

  • MotoChris521

Posted July 30, 2011 - 01:59 AM


The only way to get proper numbers performing a compression check is to remove the exhaust cam and cam chain.



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