To Shim or Not to Shim - That is the Question

[CRF250R699]

I know there are 400 gajillion posts on valve shimming, head relplacement, etc. I know that having a motocross bike equals maintenance. I love the 05 CRF and would not trade it for the world...maybe for an 06.

I religiously check the valve clearance every five - six hours. The last time I checked the valves both the intakes were .004 and the exhausts were 0.11. They have not moved from the day I brought the bike home. I went to an SMDR ride at Budds Creek this past weekend. I was performing the routine maintenance after riding (i.e., oil, air filter, chain, etc.) and decided it was time to check the valves. Sometime within the last six hours the right intake valve went from .004 to 0. My smallest feeler gauge is .015. I could not get it to slide through. I have approximately 50 hours on the bike (I record the hours used each time i ride). I know the question is going to be asked....do you ride the bike on the rev limntier. The answer is no. I need some opinions as to:

1. Should I reshim the valves to see if the problem is corrected (period of time???);

2. Are the valves going bad. Replace them now to ensure the problem is corrected. If so, do the stainless steel valves really resolve the issue or do they just last a little longer?

3. What about the head. Could the head need to be replaced?

4. If the valves are replaced, how do you get them shimmed correctly? Do you start with a shim, check the clearance, and use the formula to calculate the correct size?

Thanks for your opinions.....

[stretzhs459]

you're a little tight, I would re-shim after the next ride just to be on the safe side.

[Gino_Tortellini]

I know there are 400 gajillion posts on valve shimming, head relplacement, etc. I know that having a motocross bike equals maintenance. I love the 05 CRF and would not trade it for the world...maybe for an 06.

I religiously check the valve clearance every five - six hours. The last time I checked the valves both the intakes were .004 and the exhausts were 0.11. They have not moved from the day I brought the bike home. I went to an SMDR ride at Budds Creek this past weekend. I was performing the routine maintenance after riding (i.e., oil, air filter, chain, etc.) and decided it was time to check the valves. Sometime within the last six hours the right intake valve went from .004 to 0. My smallest feeler gauge is .015. I could not get it to slide through. I have approximately 50 hours on the bike (I record the hours used each time i ride). I know the question is going to be asked....do you ride the bike on the rev limntier. The answer is no. I need some opinions as to:

1. Should I reshim the valves to see if the problem is corrected (period of time???);

2. Are the valves going bad. Replace them now to ensure the problem is corrected. If so, do the stainless steel valves really resolve the issue or do they just last a little longer?

3. What about the head. Could the head need to be replaced?

4. If the valves are replaced, how do you get them shimmed correctly? Do you start with a shim, check the clearance, and use the formula to calculate the correct size?

Thanks for your opinions.....

1. Yes - Reshim & Check more frequently and start buying parts and planning for a valve job & top end while your in their.

2. Yes - Jury is still out on SS.

3. Cut the seats MINIMUM. Or buy a NEW '06 Head with the new seat material. Or send your head out to a shop capable of replacing the seats with improved material (Trojan, AMPCO45, Berrylium Copper).

4. Least of your worries, Trial and Error & Use the formula.

Tough decisions, just DO NOT REINSTALL NEW In VALVES WITHOUT CUTTING THE SEATS, I did and got 13 hrs before a re-shim. Waste of a set of new In OEM Valves.

[Throttlejockey]

Don't bother shimming, if you lost that much clearance the damage is done.

I have 104 actual hrs on my 04 with the original valves and one set of springs and the seats recut. Last rebuild was around 40 hrs ago.

[CRF250R699]

FYI -- I just purchased new valves, springs, seals, and gaskets from my dealer. He indicated that part numbers changed for the valves. The new 05 intake valve part number is the same as the 06.

I am going to shim the right intake valve tomorrow (waiting on shims). I will be monitoring the valve. If it starts to tighten, I will remove the head and replace both intake valves.

Question, Will the old valve seals just push out and the new one push in? Do you need a special tool?

Thanks for your help.....

[Throttlejockey]

Question, Will the old valve seals just push out and the new one push in? Do you need a special tool?

Thanks for your help.....

Yes, you just pull them off and push on the new ones. No special tool needed.

Be sure to check the seats when you have it apart.

[CMCHonda]

How do you check the seats? I haven't gotten a chance to ride mine since the re-shime but I'm already planning the valve job. Does everyone recommend the SS valves or the OEM? Do the seats always have to be redone when you replace the valves? Should I replace all 4 valves and springs at the same time?

Thanks

[Crazyced]

You have to re-cut or change the whole head block at every valve change? Let create some changeable seats!!!

It should be possible...

[Throttlejockey]

Do you have a manual? It's pretty clear explaining how to check them.

If you look at the valve face the seating surface should be centered and be 1/3 the width of the face of the valve, even on both sides.

Also check to see if the seats are pitted.

Interesting reading here- http://www.aa1car.com/library/2004/eb100434.htm

http://www.eng-tips.com/viewthread.cfm?qid=87314&page=1

[mx13w]

shimming the valves for the most part is a waste of time. i would maybe do them once after that just replace them or expect to start shimming every ride. you do not need to cut the valve seat if when you take it apart and look at the valve the valve head is cupped out. The steel seats are much harder than the Ti

[Throttlejockey]

you do not need to cut the valve seat if when you take it apart and look at the valve the valve head is cupped out. The steel seats are much harder than the Ti

You have no clue what you're talking about. You won't know if the seats need to be recut unless you check them.

[CRF250R699]

Thanks to all for your input....I am going to shim them once and then replace them if, I mean when, they move. Question....my clearance is currently zero on the right intake (maybe negative (i.e., the cam lobe may actually be depressing the valve)). The stock shim is a 185. My logic was if the clearance is 0 and I have to be at .12 mm (.005") that I could simply subtract the .12 from 1.85mm which results in a new shim size of 1.73 (173). Does this sound correct or am I off my rocker?

[Throttlejockey]

That logic will work if the valve is closed and you're at zero clearance. If it's partially open then the math won't work.

More like a 1.675, 1.65, 1.625 if the valve is partially open..

[CMCHonda]

Thanks to all for your input....I am going to shim them once and then replace them if, I mean when, they move. Question....my clearance is currently zero on the right intake (maybe negative (i.e., the cam lobe may actually be depressing the valve)). The stock shim is a 185. My logic was if the clearance is 0 and I have to be at .12 mm (.005") that I could simply subtract the .12 from 1.85mm which results in a new shim size of 1.73 (173). Does this sound correct or am I off my rocker?

My right intake was almost the exact same last weekend. I started @ 0 clearence on the right intake with a 188 shim. After many PM's with ThrottleJockey, He suggested starting with a 170 to get some kind of clearance measurement. I couldn't find a 170 but located a 160 locally and it turned out to be right on. The bike started on the first kick and felt like it had alot more compression on the kick. I haven't had a chance to take the bike out yet but I'm doing the research to get the valves redone this winter. Good luck.

[CRF250R699]

Here's the verdict....As I mentioned the stock shim was a 185. I started off with a 170. That shim resulted in a clearence of .008". I then proceeded to a 175. That shim resulted in a clearence of 0.004". I am all set now...see how long it will last. By the way, I found an easy way to replace the right intake shim without having to remove the timing chain (putting this on the first time took forever....). After you remove the cam caps, remove the exhaust rocker. At that point you can lift the cam enough to reach the right intake cap with a telescopic magnent. You have just enough room to reach in and place the new shim on the top of the valve. Replace the bucket, install the cam and then the exhaust rocker. One thing I did notice is that it took some time to get the cam caps lined up and back on. Is this ususally the time consuming part? The right cam cap went right on. The left one took me about 10 minutes.

ThrottleJockey - Thanks for all your help.....