'03 YZ450F head gasket replacement

13 replies to this topic
  • Wrennch

Posted May 22, 2013 - 07:29 AM


My buddy has an '03 yz450f it has been losing coolant and leaking it out the weep hole on the head. It smokes white and smells like coolant so im sure thats what it is. Neither of us have a service manual for it so I was wonder if anybody could tell me the torque specs for the cam caps, the head, valve cover, and cylinder ( i may just put a top end in it while its apart). Also the timing info i need to re-time it (cam to cam pin# and tdc).


  • DC_Excitement

Posted May 22, 2013 - 08:37 AM


find your specs here http://www.yamahaown...ook.com.au/?r=0

  • Wrennch

Posted May 22, 2013 - 08:41 AM


cool thanks i havent done much work on these 5 valve motors. anything different? can i use the same 9.48 shims to adjust the valve lash?

  • grayracer513

Posted May 22, 2013 - 09:14 AM


Yes, they use the same 9.48 shims as do other 450's.

If you find yourself confused by the description of the torque procedure in the manual, visit this post:


  • Wrennch

Posted May 22, 2013 - 09:27 AM


That manual doesnt say anything about the number of pins between exhaust and intake cams. Just says align punch marks with the surface of the head. I enlarged the picture and there is a 2nd punch mark on both sprockets. I counted the pins and got 15. Is that correct? Awful close. My kx450f is 29 pins.

  • grayracer513

Posted May 22, 2013 - 10:45 AM


That manual doesnt say anything about the number of pins between exhaust and intake cams.

That's because it's the wrong way to time cams on a YZF.

I counted the pins and got 15. Is that correct?

No. Reread my post above.

  • Wrennch

Posted May 31, 2013 - 06:14 AM


Ok, so I have the bike back together. It started on the 3rd kick and idled with the choke out for a few minutes then started idling rough and died. Since then the bike has been really hard to start. When it does start it pops and back fires. The exhaust pipe will start glowing red all the way back to the silencer. I'm pretty sure the carb is super lean. Does any body know the correct jetting for this bike stock? And the position of the throttle needle and turns out on the fuel screw?


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  • grayracer513

Posted May 31, 2013 - 06:29 AM


OEM 2003 YZ450F® Jetting:

Main Jet: 165
Pilot Jet: 42
Starter Jet: 72
Leak Jet (if any): N/A
Fuel screw/Setting: 2.0-2.5 turns out
Needle/Position: NCVQ-4


Your pilot jet may well be partially blocked:


The bike should not be idled with the choke on for any number of minutes larger than one, if that long. The choke should come off as quickly as the engine will tolerate it to avoid fouling the plug by being so rich. Neither should it be expected to idle longer than 60 seconds when warm without showing signs of excessive heat. Circulation is poor at idle, and there's no air flowing over the radiators.

  • Wrennch

Posted May 31, 2013 - 07:22 AM



  • Wrennch

Posted May 31, 2013 - 11:04 AM


The pilot screw is missing from the carb

  • grayracer513

Posted May 31, 2013 - 11:21 AM


That does happen. It's probably not all that's missing, though. There is a pilot screw, and on the screw there goes a spring, a brass washer, and a small O-ring. See this illustration for the layout of the parts: https://www.thumpert..._carburetor.gif

You can order them as a set from Yamaha as PN 5NL-14105-00-00, or separately from Honda (for a CRF450).

  • Wrennch

Posted May 31, 2013 - 10:42 PM


Ya all those parts are gone. I am just going to order an a/m one so I don't need a screw driver to adjust it

  • grayracer513

Posted June 01, 2013 - 05:52 AM


The aftermarket screw may or may not have the other three parts included. Just a heads up.

  • Wrennch

Posted June 01, 2013 - 07:19 AM



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