The REAL reason...CRF Valve problems

[Woody_393]

Amen. Moving to the KB. Good stuff.

Thanks again FFR. You ARE the Man.

[cowboyona426]

Does this benefit all thumpers, or just the high performance ones? What I'm wondering is if we should start setting the TT-R 125 at TDC when it gets parked.

[Woody_393]

I wouldn't think it would hurt anything, that is for sure. I don't think it is a bad idea for any thumper. Keeping the springs as fresh as possible would be good for anything IMOP.

[MotoMan]

Yeah, I will back Woody up on that one.

It can't hurt.

[Woody_393]

The thought just occoured to me that we should be doing this whenever we stop the bikes, not only when we are done riding. I'm guessing you all already knew this, but Bates and I only back the engine off when we are done riding. I don't think that is cutting it. Gotta do it when ever you stop the motor.

[TexTwister 393]

Yes you got it, the piston is at the top of the compression stroke which means the valves are closed releaseing pressure from the springs....

[Franky]

I'm on this forum for about 10 hours and already so much smarter!
I'm confident i'll find the exact questions to my answers for my 450 crf.
Here's a pic of my bike for the moment

I'm gonna do it all by myself because some guy wanted to do it for me and it costed me 210 euro's for a used piston!!,what consulted in a big smoker!!!
(sorry for my bad writing,i'm a Belgian trying to write english) :

[psycho393]

Welcome Franky nice to have you here Sure hope you enjoy the site as much as the rest of us.

[MotoMan]

Welcome to ATM Franky!!!

Hope you visit us and post often bro!

[Franky]

Originally Posted by MotoMan

Welcome to ATM Franky!!!

Hope you visit us and post often bro!

you can count on it

[Franky]

Here's a picture of my baby

[Kirtwell]

[QUOTE=FFRacing]RE: CRF450 Valve(?) problems
Posted: 06.05.2003 17:28

the problem has been around for along time the first time i had to deal with it was with the little honda engines atc 90s parents would get theses 3 wheelers for there kids and they would run them in low gear with the throttle pegged to the bar. these little engines were capable of over 11000 rpm what would happen is when they were shut off and let to cool they would not restart because of lack of compresion the intake valve would loose its clearance and then be held open when the motor cools. all most all engines gain clearance when hot.



I don't mean to be a skeptic here but what you are saying in your first paragraph makes absolutely no sense to me

I learned in science class that heat=expansion or growth....therefore the valves would "loose" clearance when hot...but when the engine cooled...shouldn't the valves return back to their original specs or very close?

Clearances on small bikes are minimal I'm sure ....however...it would be "IMPOSSIBLE" to get a typical steel valve to grow .005" to .007" in length causing the valve to remain open...I'm not buying that!

Can you explain how the clearance of a small honda engine is decreased and in your words:?
"loose its clearance and then be held open when the motor cools."

My CRF450 lost the intake valve clearance due to fatigue in valve itself...
I could clearly see that the valve had totally destroyed itself.... banging against the seat....and sure it could be the agressive cam action..I buy that completely.
I was informed that the valve has a coating to increase strenght and in the event the coating wears off, which is what happened with my CRF, the valve will fail very quickly and unfortunately you will need to replace them.
There's nothing wrong with going back to stock valves...I put some Farrea SS valves with larger valve springs in mine ..Just to make sure

I believe Honda had the original valve integrity on the CRF correct, However, I also believe that their vendors who manufacture and coat the valves could have had some quality control issues..and that may explain why so many people do not have the valve problem and others do.

[MotoMan]

Originally Posted by Franky

you can count on it

Excellent man!

[ENRIQUE SCHMIDT]

Originally Posted by Franky

I'm on this forum for about 10 hours and already so much smarter!
I'm confident i'll find the exact questions to my answers for my 450 crf.
Here's a pic of my bike for the moment

I'm gonna do it all by myself because some guy wanted to do it for me and it costed me 210 euro's for a used piston!!,what consulted in a big smoker!!!
(sorry for my bad writing,i'm a Belgian trying to write english) :

welcame FRANKY DO IT BY YOURSEF IS THE BEST MY ENGLISH IS LIKE YUORS IAM FROM CHILE SOUTH AMERICA IN THIS PAGE I HAVE LEARN A LOT I HOPE YOU TOO

[tonymtona]

Originally Posted by FFRacing

Woody, as long as the bike has a kickstarter, using it to get to TDC is just fine. The reason we :back" it off with the DTers is 1) the don't all have a kickstarter and 2) it stops the motor just "after TDC" so it is easier to bump start. Either way you are accomplishing the same goal...taking the pressure off the springs. TW

this sounds really interesting and i am pretty new with 4 strokes i have a 2001 yamaha yz426f..can you kindly explain to me why its good to do this procedure thanks

[Woody_393]

Because it releases the pressure on the valve springs so they don't sit between rides with tension on them, which should in turn make them last longer and not sack out as quickly.

[DRGSin393]

Great find. Is everyone doing this w/ their 4 strokes?

[tonymtona]

Originally Posted by Woody_393

Because it releases the pressure on the valve springs so they don't sit between rides with tension on them, which should in turn make them last longer and not sack out as quickly.

so they dont sit with tension while you just got done riding the bike right? oh yeah and how would you know when they are sacked out already thanks guys some good tips im so glad i am a memember

[Woody_393]

Unless the motor stops at top dead center there is tension on the valves springs (actually there is always tension, but at TDC, there is the least amount possible while still installed in the bike). Often times they do actually stop at or near top dead center. I don't worry about it unless I'm putting the bike away for the day though, as they aren't THAT weak that having some tension on them is going to ruin them. It's just a preventative measure that adds some peace of mind to those of us that worry about these types of things.

It's pretty tough to know if they are sacking out unless you take them off and measure the spring tension. One symptom could be your valves start losing clearance really quickly due to the valves floating because the spring can't keep tension on the valve as it descends from the top of the cam lobe, hence they slam shut causing the lip of the valve to cup. Valve float is a bad enough problem on some of these racing machines that having a weaker than spec valve spring just exacerbates the problem.

Anyway, hope that answers your question -- at least that's how I understand all of this to be.

[MotoMan]

Originally Posted by DRGSin393

Great find. Is everyone doing this w/ their 4 strokes?

No.......