WR450F 2008 Shims and Valves

8 replies to this topic
  • Hoody UK

Posted October 10, 2013 - 01:44 PM




I have a Yamaha WR450F 2008, I have just stripped the shims out as the bike was a nightmare to start. All the inlet gaps are less than 0.05mm, two shims are 1.2mm and the third is 1.35mm. So I have worked out I need two 1.05mm shim's and a 1.2mm. The Hotcams Shim Kit I have ranges from 1.2mm to 3.5mm. Does this mean I have run out of shim range, if so can you advise what is needed to resolve this matter. I presume I need new valves, but is there anything else I need to change, springs, valve seals, and which products standard Yamaha or any preference to aftermarket products? I only started to race endurance this year and this is my first dirt bike so I would really appreciate any good advice.


Thanks in advance


Hoody :-)

  • Krannie McKranface

Posted October 10, 2013 - 02:34 PM


Yes, your intake valves are sinking into the head, and you can't find a shim small enough to fit.

You can try the smallest shim and see if it wills start, BUT, you run the risk of breaking off a valve at the stem if you do not replace the valve train and re-cut the seats very, very soon.

  • Hoody UK

Posted October 11, 2013 - 09:35 AM


Hi Krannie


I have placed an order for new intake valves and springs, they are stainless steel 'Pro X', also new valve stem oil seals and a head gasket - original Yamaha. The only thing that worries me is; are the valves stretched or have the valves worn the seats? Is it a case of taking the valves out and measuring them to answer that question or is there another way of diagnosing if it the seats have worn, besides rebuilding it to find the same gap as before? Also, should the new stainless steel valves be lapped in, I believe you should not do this with titanium valves. Lets hope when I take the head off tonight (uk time) there is no more nasties, else I will have to spend more of my pocket money on it lol. I would appreciate any opinions and help, first time for me working of a engine like this, only worked on car engines previously.


Thanks............. Hoody

  • Krannie McKranface

Posted October 11, 2013 - 10:58 AM


Valves don't stretch, they cup at the mating surface to the valve seat.

You should get oem valves and parts, and have the seats PROFESSIONALLY RE-CUT to match the new valves.

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  • Hoody UK

Posted October 12, 2013 - 06:53 AM


In that do you mean replace with Titanium valves rather than swop to stainless steel one, if so why? I was told I may loose a little power, but there again I am not  factory rider ;-)



  • Krannie McKranface

Posted October 12, 2013 - 06:08 PM


In that do you mean replace with Titanium valves rather than swop to stainless steel one, if so why? I was told I may loose a little power, but there again I am not  factory rider ;-)




Titanium valves are uses so the entire valve train of reciprocating weight is reduced, increasing rpm rise (not hp per say) so the bike accelerates more quickly.

Yamaha Ti valves are not like Honda or KTM valves; they do not break down after hundreds of heat cycles and begin to mushroom, UNLESS you run the bike too lean all time (like the stock jetting).

There is no reason to go SS in the Yamaha engine.

OEM parts are fine, and work great.

  • Hoody UK

Posted October 13, 2013 - 02:54 AM




thanks for the information, I will do some more head scratching, get it! lol



  • Hoody UK

Posted October 18, 2013 - 01:17 PM




Well I decided to try the Pro X steel valves, I am just in the middle of rebuilding, this may take a while remembering where everything goes, good job I have a manual. Time will tell if it was worth it or not, I will provide updates good or bad. I do have a contingency plan, but that mean spending quite a lot of cash.


.......... Hoody

  • Hoody UK

Posted October 26, 2013 - 07:31 AM


Hi all


Finally finished putting the WR450F back together today, it started second press of the starter button upon initial start up and starts first time on the button since, which is a  relief as this is the first time I have rebuilt one of these engines. First impressions are good, but the true test is when I ride it.


............ Hoody


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