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A Couple Questions about Valve Specs

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This is my first time working on the valves on my 2007 CRF250R and I have a couple questions about the valve specs. One of the intake valve retainers cracked, probably because I mixed up the shims in a previous bottom end rebuild, and I replaced it and reshimmed the valves. I amn't sure what goes and what doesn't in the valve spec range. I'd really appreciate any help on this.

After installing the new shims, these are the clearances with the piston at tdc and the cam marks lined up with the head:

Left Intake: .003" clearance; 1.87mm shim.

Right Intake: .006" clearance; 2.85mm shim

Left Exhaust: .011" clearance; 2.4mm shim

Right Exhaust: .009" clearance; 2.2mm shim

My first question is, is it alright to run the intake at .003" and the exhaust a .009". I realize that the specs are .005" and .011" + or - 1, but I have seen a thread on crfsonly saying that a clearance on the tighter end of the range could actually increase performance http://www.crfsonly.com/forum/viewtopic.php?t=28415&sid=02bda1afc22aec22d2fc97b8890e7231. But are these specs too tight?

And my second question, if the clearance for the left intake is on the tight end of the range and the right intake on the loose end will that affect the performance? (sorry, it's my first time on valves). Will one valve opening before the other one cause any problems or do I not understand it?

Thanks in advance!

Edited by DeAndrae Loewen
To add information

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Judging by your shim sizes your left intake valve is bad and will lose clearance again quickly and needs replaced soon. If you reshim it it will just lose clearance again and need another smaller shim eventually it's better to get it replaced sooner rather than later. Do you know the history on the valves has the left one been reshimmed a bunch of times that's what it looks like. And while you're at it put a 2.15 shim in the right Exhaust. 

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Wow..I got confused on the measurements you posted.  You noted the clearance in inches, and then MM on the shims.  At first, I was thinking the clearance was in MM, and I was like, wow....those numbers are REALLY tight!  lol...

 

 

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4 hours ago, TPA-MX said:

Wow..I got confused on the measurements you posted.  You noted the clearance in inches, and then MM on the shims.  At first, I was thinking the clearance was in MM, and I was like, wow....those numbers are REALLY tight!  lol...

 

 

Haha, ya, it confused me a few times too when I was putting the measurements in the formulas

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8 hours ago, tom02cr250 said:

Judging by your shim sizes your left intake valve is bad and will lose clearance again quickly and needs replaced soon. If you reshim it it will just lose clearance again and need another smaller shim eventually it's better to get it replaced sooner rather than later. Do you know the history on the valves has the left one been reshimmed a bunch of times that's what it looks like. And while you're at it put a 2.15 shim in the right Exhaust.  

About the history of the valves... I actually know almost nothing about how they've been shimmed before I owned the bike. I forgot to mention this in my post, and I'll add it now, but the intake valve retainers were changed because one of them cracked. The reason the retainer cracked is because I had rebuilt the bottom end and misplaced the valves. It was the first time I had torn apart an engine, I had some help though, and didn't realize how important it is to keep the shims with their valves. But anyway it ran fine until I took it apart to look at a transmission problem and saw that the retainer was cracked. I lost one of the shims at some point and other than the 1.87'' shim currently in the left intake, none of the shims matched up with the valves even though the guy before me said he had shimmed it to spec.

So that's why I'm not sure if the valve is going bad. But using the other three shims I was able to measure the clearances and after a couple of tries these are the specs I got. As soon as I get to my bike again I'll see if the right intake would be a better fit for the 1.87" shim. I'll let you know what happens.

Edited by DeAndrae Loewen
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Okay, I should've tried this before, but stupidly assumed I had it right earlier.

I switched the shims on the intake valves. These are the new intake specs.

Left Intake: .005" clearance; 1.85mm shim

Right Intake: .003-4"* clearance; 1.87mm shim

*The .003" feeler slid in with very slight drag, while the .004" went in with some pushing.

The reason I'm not replacing the valves straight up is bc I had the shims mixed up earlier and the 1.87mm shim likely wasn't the same shim I had in the left intake when I bought it. It could possibly be though. I guess that's what I'm trying to figure out. 

Would you say the right intake is now in spec?

And is the right exhaust okay to run at .009-10"?

 

Edited by DeAndrae Loewen
Corrected a couple things
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I am learning very fast that you don't want to play Russian roulette with your valves. If they go unattended or not maintained correctly, the damage it can cause is significant compared to the amount of time it takes to check them.

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12 hours ago, TPA-MX said:

I am learning very fast that you don't want to play Russian roulette with your valves. If they go unattended or not maintained correctly, the damage it can cause is significant compared to the amount of time it takes to check them.

Okay, I know what you mean man, but I think I'll run it for 1-2 hours on these specs and then check for valve movement. I know what the measurements are, it's just I don't know for sure that the valves are going out bc I don't know their history. And I'm not ignoring your advice, I just want to see if the valves still have plenty of life or not.

Really appreciate the input though.

Edited by DeAndrae Loewen

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13 hours ago, tvalliere220 said:

if it runs sure. Make them right...

I don't quite get what your saying here... Is it alright to run the intake at .003", tvalliere or anyone else who's tried it?

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Soon after I got my brand new CRF250R when I checked the valve clearances the left intake was .003 inches and I just left it Go and rode it for a long time and the clearance never changed but after a while then i eventually did reshim it from .003" to .004". Then after 175 hours the valve clearance all of a sudden went away and I replaced the valves both intakes and had the valve seats cut smooth.

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6 minutes ago, tvalliere220 said:

I mean if the bikes running and starting fine go for it. I would correct it if it was my bike. Takes an extra 20 minutes max. 

Okay, thanks man, I might just order the shim and ride it this way until then.

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If it was mine and I was in the same situation I would probably do just as you are planning.    I own the same rig,  have a head with different seats on it,  and from my experience I would be planning on some serious head work soon.  In the meantime,  you can see what if anything changes in two hours of running.   

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6 minutes ago, tom02cr250 said:

Soon after I got my brand new CRF250R when I checked the valve clearances the left intake was .003 inches and I just left it Go and rode it for a long time and the clearance never changed but after a while then i eventually did reshim it from .003" to .004". Then after 175 hours the valve clearance all of a sudden went away and I replaced the valves both intakes and had the valve seats cut smooth.

So it sounds like it wasn't a problem. Thanks for letting me know. I really wanted to know if someone else had tried it.

Out of curiosity, was there any performance difference between the .003" and .004"?

 

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1 minute ago, ossagp said:

If it was mine and I was in the same situation I would probably do just as you are planning.    I own the same rig,  have a head with different seats on it,  and from my experience I would be planning on some serious head work soon.  In the meantime,  you can see what if anything changes in two hours of running.   

Okay, thanks for confirming it!

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It wasn't a problem for me but for you you might have a valve wearing down so it will continue to slowly lose clearance. I highly recommend getting it replaced ASAP if it loses more clearance again and you should invest in a shim kit it's always good to have in case you need them or for after getting the valve job done you'll want a shim kit for figuring out what size shim it will need.  I did not notice a difference. 

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2 minutes ago, tom02cr250 said:

It wasn't a problem for me but for you you might have a valve wearing down so it will continue to slowly lose clearance. I highly recommend getting it replaced ASAP if it loses more clearance again and you should invest in a shim kit it's always good to have in case you need them or for after getting the valve job done you'll want a shim kit for figuring out what size shim it will need.  I did not notice a difference. 

Okay, right now I'm planning on running it for an hour or two and then check the clearances. If the clearance changes I'll probably take your advice and replace the valve(s).

Yeah and about the shim kit, I wish I new that before I started. Sometimes you gotta learn the hard way...

Thanks for helping me out on this! I'll let yall know what happens.

 

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yep. I would ride it a couple times then check, and check again after about 10 or 15 hours. 

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Hey, 

I ran the bike for a ~40 min. in 2-3 short rides (I've been pretty busy and there's a sand storm outside rn), and am wondering if that would be enough time for the valves to shift if they are going to. My understanding is that once the valve face wears off, the valve needs to be reshimmed much more often. Would 40 minutes be enough time for this to happen if the valves are worn off?

And the bike has been really hard to start if that says anything.

Edited by DeAndrae Loewen

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