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First of all i want to introduce myself.

My name is José, I´m from Chile and i´m an industrial engineer.
I ride motorcycles since i was 8 years old. Now i´m 25 years old. I race motocross and enduro in the chilean nationals, and also i´ve been racing/riding in the US numerous times, especially in Socal, Florida and Nort/South Carolina.

I ride a 2009 CRF 250r, engine completely stock, but some days ago i had to replace the intake valves so i did a valve job. I cutted the seats and put OEM valves on it.

My question is:

I know the intake valve clearance recomended by Honda is 0.005 +-0.001 but i´ve heard that is better to leave the valves in a tighter especificaton in order to extend it´s life.
In other forum a guy said that he recomends leaving the stock valves at 0.0035-0,004 because this will increase the valves life due to the valve closing speed against the seat will be reduced.

I know it sound logical, but someone have ever heared or tried this?

p.s. The guy who said this is a NASCAR engine mechanic,

P.S.2 Sorry for my english, it´s not my mother lenguage

Welcome to the site, Your English is perfect!

Yes, the tighter clearance spec will prolong valve life and add a small amount of duration to the cam.

Intakes at .004" (.10mm)

Exhausts at .009" (.22mm).

~, do you reccomend this slightly tighter spec when using kibblewhite intake valves? I've set one intake to .005 and one to .004 and exhausts are both at .010

All the valves are brand new and haven't been run yet.
This is a 2004 CRF250R.

Thanks.

Sure. .004" and .009" are fine to run them at.

When we bench shim heads with new valves, we set them at ,005" and .010". They will often seat slightly as they are new. We usually wind up with those exact figures after an hour or so.

surprised you never get tired of answering that question, awesome you still have the patience! maybe an idea for a sticky.....?

Thanks Smith, I think I'll try to get that one intake valve up to .005 so it can wear into the .004 position rather then hav it wear into a .003.

I have a intake which can’t fit anything and an exhaust which measures 0.06 can I keep my exhaust valves how they are ?