2003 yz450f pounds of compression?

2 replies to this topic
  • jturnbull329

Posted December 19, 2009 - 05:46 PM


I have a 03 yz450f and i was wondering what the stock pounds of compression is? and what is the lowest it should get before i do a topend?


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  • jaybird67k

Posted December 20, 2009 - 06:09 AM


I have never checked a bike but I've checked alot of car engines. Never seen the need to check a bike since it has one cylinder and car engines having multiple where your comparing cylinder pressure. Although you can tell alot about a engines health with a simple pressure test.
Most stock cars have about 140 to 150 new but they run fine at 120 PSI.

As you know dirt bike pistons, rings, and cylinders are replaced by amount of time in service but I say if it runs good run it, after all I put 400 hours on my 426 before rebuilding.
The 426 has 12.5 to 1 compression ratio I believe so I always thought the PSI would be 185-200 PSI..........but that's a guess.

Ok, rambling is over for now.

Later, Jason

  • grayracer513

Posted December 20, 2009 - 09:05 AM


Since the bike has auto decompression, a meaningful compression test can't be done. If it didn't have it, you couldn't kick it through, so...

Leak down tests are the only accurate gauge of cylinder sealing and condition.

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