Decompression Cam Swap

4 replies to this topic

Posted October 04, 2006 - 04:45 AM


I was thinking about changing the cam in my 98' YZ400F so that I could get rid of the decompression lever setup. Which cam do I need to purchase? Is the procedure much more than changing cam, plugging decompression hole, and setting the valves? Any different timing issues? Now the head on this motor is off of a 2000 WR. Does that change anything? I'm going to assume not because it works good on a 98' motor. Any help would :devil: be wonderful. Thanks. :excuseme: :thumbsdn: :thumbsdn:

  • grayracer513

Posted October 04, 2006 - 08:28 AM


Buy the Hot Cams AD cam for a 426 and install it as if it were a stock cam, or,

Buy the OEM Yamaha YZ 450 cam (WR450 if you want a milder engine), and follow these instructions:


Apart from an undetermined number and size of valve shims, the cam is the only part required either way.

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  • YZ426F Rider

Posted October 04, 2006 - 09:24 AM


Apart from an undetermined number and size of valve shims, the cam is the only part required either way.

Hey now...let's not forget about the plug for the decompressor shaft hole! The rubber oem plugs suck and it is not uncommon that they blowout. You can use a freeze plug of proper size (Gray knows...cuz he knows everything there is to know :thumbsdn: ) but the TT plug is sano... http://shop.thumpert...p/qmr-03dpb.htm :devil:

  • grayracer513

Posted October 04, 2006 - 02:31 PM


True, you do need something suitable...if you remove the manual decomp shaft. You can also use an 18mm freeze plug. Sort of a challenge to install, but they work.

Or, you can just leave the shaft there as long as the return spring stays with it. But that's not very clean looking, and it's in the way if ever the right exhaust valve needs adjustment. :devil:

  • John Wayne

Posted October 08, 2006 - 04:08 PM


[COLOR=Blue]This was the best mod I have done, had it done last week. Today was the 2nd day of starting it and started 1st kick with choke on. I put the WR cam in insted of the YZ for more tractable power through the band. i ride woods so this suits me. The durattion is different between the 2. No more 5 min routine for starting and it kicks over easier than my CR250[/COLOR]

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