[300EX Piston, Cam, Rockers, Valves & Springs] - ATV Riders Forums - Honda, Yamaha, Suzuki, Kawasaki, Polaris, CanAm, Arctic Cat, Kymco ATVs

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300EX Piston, Cam, Rockers, Valves & Springs
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Posted by: Lonestar_R

What is everyones opinion on what to buy. I am building a mildly modded engine for my stepsons 300EX. I need everything. the cam doesn't have any lobes left, so whats that tell ya. So if I'm buying I might as well do it all and then I won't have any problems. I hear things like TC racing uses stock rockers with his builds. And then on the other hand people say you must use harden rockers. Does anyone have TC's phone number. I don't think Tom has a website anymore. I'm not looking to resleeve this motor and I don't want to go straight to an .080 over piston, this is so I have some room left if I need to rebuild again in the future. And what are the best valves to use? SO if anyone can give me some inut on any or all of this stuff. Thanks in advance

Posted by: Sjorge300EX

yo, just get a .020 11:1 Wiseco with a mild cam and HD valve springs. I would keep the stock honda valves and just get a valve job with them and everything. That will really wake the motor up and he will be able to handle it

lol

Posted by: Lonestar_R

whose cam and do I need the harden rockers. I was thinkin maybe a .040 over piston. A good round number and it doesn't cost any more for the bore or the piston

Posted by: Sjorge300EX

quote:
Originally posted by Lonestar_R
whose cam and do I need the harden rockers. I was thinkin maybe a .040 over piston. A good round number and it doesn't cost any more for the bore or the piston

yeag that could work for the piston. You really dont need the hardened rockers they juste reccomnecd them. Most people dont even like the thought of hard welding the rockers.

Posted by: bwamos

I'm still using unhardened rockers w/ my FST cam. But, your rockers need to show like no wear marks.

If you have to buy new ones anyway you may as well get them hardened for a WEB Cam.

0.040" over 11:1 would be good. Stock valves should be fine but kibblewhite makes good valves if you need to replace them. Snag some mild porting, and have the valve seats and dome cleaned up. Grab an all-around cam. HD springs will be good too. The stockers are pretty light.

If the clutch starts to slip after the rebuild.. you can get some heavy clutch springs for like $35. But, if it doesn't slip, no need to add more clutch lever pull resistance.

If you don't have one already and jsut have a slip-on silencer, an aftermarket header really wakes up the 300ex.

Posted by: Lonestar_R

Thanks bwamos. I have a full White Brothers E Series Exhaust that was on my old 250X ready to go on this 300. I'm not sure what cam to go with, Sparks, Web, Hetrick Racing has a cam also. My cam is completely junk. So I'm gonna eat the core charge no matter what I go with.

Posted by: dork

if you buy a billet cam then you can run stock rockers. any welded cam though and you should run hardfaced rockers to be safe. also upgrade your springs like bwamos said.

Posted by: quadfamily

White Brothers makes an all around cam for use with stock rockers. They recommend getting new rockers though.