Valve Job / Head Rebuild

4 replies to this topic
  • bonifacev

Posted October 25, 2008 - 08:49 AM


My son who is in the Navy wants to know how often he needs to check valve clearences, do a valve job and/or do a top end rebuild.

He would also like to know what the symptoms are of a bike needing a valve job.

The bike is a 2004 yz450f. Since he's not riding much right now he thought this would be a good time to make sure its in tip/top shape.

Any feeback would be very much appreciated.

  • KJ790

Posted October 25, 2008 - 11:38 AM


Check the valves every 10-15 hours of riding to be safe. Yamaha's are known for their great valve life, so they shouldn't need adjustment for at least 100 hours if you keep a clean airfilter in at all times (dirt going through the valves destryoes them quickly). Once they have needed to be adjusted 3 times I would change the valves to be safe. I change the piston and cam chain every 50 hours.

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  • grayracer513

Posted October 25, 2008 - 11:40 AM


If he has had to adjust the valves more than one shim size tighter, it probably needs a valve job. Two sizes, definitely. If not, it doesn't need it right now.

The first symptoms, other than loss of clearance, would be loss of compression and hard starting when cold.

  • Yodiracer

Posted October 25, 2008 - 01:15 PM


Like grayracer said hard cold starts, and I would add that a failure to idle properly is another indicator that a valve job is required. Check your compression. To do it properly make sure your gauge is in proper working order. Check your manual for specs/instructions. You must hold the throttle WFO during the test (don't pump it just whack it open and leave it there). If you have low readings insure compression gauge is properly seated/tightened and has a viable o-ring installed. If these all check out and your not riding a beater then check valve clearances, correct as necessary and do another compression test, if you are still out of specs it's probably a worn valve/seat. To determine accurately what specific part of the engine is causing a leak you must perform a leak down test with a leak down tester which also requires that you have a fairly good air compressor and a mechanics stethoscope available. - Good Luck! http://buy1.snapon.c...rch_Keyword.asp

  • grayracer513

Posted October 25, 2008 - 04:48 PM


Old school compression checks are not practical with YZF's. A healthy manual decompression engine simply can't be kicked through the compression stroke, especially at full throttle, and the a compression check on a engine with auto decomp would be pretty meaningless. The proper test is a leak down test.

No compression test specs are listed in the manual.

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