How To: Basic Valvetrain Replacement
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    124
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    How To: Basic Valvetrain Replacement

    by 124 » Tue Apr 10, 2007 11:45 am

    Since my original was lost, I recreated this one. Please feel free to make it a sticky!

    This is the basic steps for valvetrain replacement. There may be specific items for the different displacements and/or models. The write-up and pics in this post are from a 2005 CRF450R.

    Some parts of the process described below assume that your replacing the valvetrain, not checking the clearances or shimming. The steps taken for either of the aforementioned may vary from below. The process below also assumes you know that clockwise tightens things, you can read specifications, and that hot things hurt when you touch them. :roll:

    1) Clean the bike thoroughly. Especially the airbox, engine, carb, and under the tank. Ruin your valvetrain because of a dirty intake; shame on you. Ruin your valvetrain again because of a dirty intake after rebuilding it; shoot yourself.
    Image

    2) Disassemble the bike and get it ready for engine teardown. Drain the coolant. Set the engine at TDC of the compression stroke.
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    3) Remove the valve cover.
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    4) Remove or release tension from the timing chain tensioner. Remove the cam gear, secure the chain, and remove the camholder asm. Cover the cam chain cavity. BECAREFUL - the shims will be stuck to the underside of the buckets. They may fall out when lifting the cam holder. Fishing them out after they've fallen down the cam chain cavity isn't fun.
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    5) Loosen the fasteners holding the head on in a criss-cross pattern a little at a time until all are loose. Remove fasteners. Carefully pull the head off.
    Bottom of the head:
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    Top of the piston:
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    6) You should have received your new valves and spring kit by now. And the piston kit if you plan on replacing it. Recognize that these thumpers are much more durable regarding cylinder/piston maintenance. You can typically get away with just doing the rings at this point if there isn't a ton of hours on the bike. With that said, I always do a piston kit when replacing the valvetrain. If you are also replacing the piston, remove the cylinder.
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    7) Remove the old piston and install the new one. Pay attention to the direction of the piston. In "the old days", 2-stroke pistons had an arrow that faced forward. 4-strokes, typically the arrow or indicator faces rearward, or toward the intake. But, always read the instructions included with the piston kit you have to clarify. Also, a quick way on our bikes is to notice that the intake valves are larger than the exhausts, and the "pocket" in the piston accomodate for it.


    8 ) Inspect the cylinder. The CRF "R"s and "X"s have a nikasil plated cylinder. It is approximately a 2-5 thousands of an inch thick alloy (nickel-silicon) plating that assists the cylinder in improved durability and cooling characteristics. You should not hone these cylinders. With that said, if you do, be very careful not to take too much material. It is possible to hone through the nikasil. My cylinder had good cross-hatching and only showed one area where it was slightly scuffed. After careful review and measurement, no action is needed.
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    A quick way to determine if a scratch is indeed a scratch; is the fingernail method. If you can catch it with your fingernail, it needs to be fixed. Millenium technologies does very good cylinder plating work.

    9) Clean the gasket surfaces thoroughly. Coat the cylinder and new piston with clean oil. Install cylinder.
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    A note about the valves: The reason behind the valve issue is related to the coating on the titanium. The coating on the valve where it meets the guide wears just enough that the valve starts to wobble in the seat. Once this starts, it is a deteriorating process and gets worse over time. The reason why stainless and other materials are more durable, is because of the different coating processes and/or the lack of a coating. Why use titanium then? I think it is to save weight. The valve parts:
    Image


    10) The headwork was done professionally. They removed my old valves, replaced the seals, repaired the valve seats, and installed the new Kibblewhite stainless steel valves and springs. My intakes definitely needed repair while the exhausts were cleaned up to remove some pitting. The new valves installed.
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    11) Install the new gasket and the head. Torque to spec in a criss-cross pattern.
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    12) Now, because the valve seats have been grinded, the shims that came in the bike from the factory will not work. There will be a small amount of adjustment lost because the valve sits deeper in the head. There will be some guesswork involved on what shim size to start with, unless you recorded the shim sizes the first time you shimmed the bike. In which case put in the original sized shims. Then check the clearance, make the calculations, and install the necessary shims to get you back to spec. Re-install the cam holder, and torque to spec in a criss-cross pattern.

    Verify the piston is at TDC. Line up the cam gear with the mark on the case. Make sure the cam lobes are facing rearward and install the cam chain. Maintain the exact line-up of the piston TDC, the cam gear lined up with the mark on the case, and install the bolts. Tighten the fasteners to spec. Install and set the cam chain tensioner to the proper tension and re-check that the timing is correct. Set the decompression clearance and turn the engine over a couple times. Re-check the timing and valve clearance again. Re-adjust if necessary.
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    13) Put the valve cover back on, fill the bike up with fluids, and complete the re-assembly. Done!!

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    70' Honda CT70 (Trail 70; Gold)
    16' KX450
    16' KX85
    12' YZ125
  • DeskRacer
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    by DeskRacer » Wed Mar 03, 2010 9:02 pm

    124 - Thanks for the post. I'm tearing into my '05 450X for a top end (or more) rebuild. Can you tell me if there is a trick to getting the cam chain tensioner released without the $80+ special tool from Honda?

    Thanks

    jrw
    southwest232@cox.net
  • User avatar
    124
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    Joined: Wed Feb 16, 2005 1:37 pm

    by 124 » Thu Mar 04, 2010 6:06 am

    DeskRacer wrote:124 - Thanks for the post. I'm tearing into my '05 450X for a top end (or more) rebuild. Can you tell me if there is a trick to getting the cam chain tensioner released without the $80+ special tool from Honda?

    Thanks

    jrw
    southwest232@cox.net


    Remove the center 8mm bolt. Insert a small screwdriver and release the tension. While holding it, use a small pair of vise grips on the screwdriver.

    Also, you can just remove the entire cam chain tensioner. This is what I do. Loosen the center bolt. Then remove the other 2 screws in equal turns until the tension is off. Then just pull the whole thing out.

    When reinstalling, leave the center bolt out. Install the tensioner making sure to tighten the bolts in steps. You don't want to wedge it in there. Then insert the small screwdriver, release all the tension, then pull the screwdriver straight out. It'll snap back in and apply the correct amount of tension on the chain. Put the center bolt back in, done.
    70' Honda CT70 (Trail 70; Gold)
    16' KX450
    16' KX85
    12' YZ125
  • DeskRacer
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    Joined: Wed Mar 03, 2010 10:26 am

    by DeskRacer » Thu Mar 04, 2010 7:05 am

    Thanks again, 124. Not looking forward to the rest of the tear-down. I'm pretty sure that running around at Glammis with only 75cc's of oil in the crankcase (as my son did) did more than just stick an intake valve and roast the cam....

    Lesson learned.
  • bamm

    yup

    by bamm » Thu Mar 04, 2010 7:19 am

    :shock: :shock: :shock:
  • DeskRacer
    Posts: 3
    Joined: Wed Mar 03, 2010 10:26 am

    by DeskRacer » Thu Mar 04, 2010 7:56 am

    Yeah. Not happy.
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    riverworm
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    by riverworm » Thu Apr 14, 2011 7:27 pm

    Great write up! What is the best break in procedure for top end rebuild? Including a new cam? Thanks
  • User avatar
    124
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    Joined: Wed Feb 16, 2005 1:37 pm

    by 124 » Fri Apr 15, 2011 5:50 am

    Use regular dino based oil, no synthetic.
    Warm engine up.
    Use a long straight away and go through the gears hard, but not full throttle.
    Allow the use of engine braking to slow going back down through the gears, avoiding any rev limiter spikes.
    Let cool down.
    Check oil level.

    Repeat 3 times, change oil, and then ride it like you stole it!
    70' Honda CT70 (Trail 70; Gold)
    16' KX450
    16' KX85
    12' YZ125
  • User avatar
    riverworm
    Posts: 33
    Joined: Thu Jan 11, 2007 6:53 pm

    by riverworm » Sat Apr 16, 2011 5:52 am

    Thanks 124! That sounds simple enough!
  • motorboy1128
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    by motorboy1128 » Sun Aug 14, 2011 12:13 am

    how are those kibbles holding up? How many hours? How many adjustments? Looking to do this for a 250r. worth it or stick with the ti?

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