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Question on Vave Clearance

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I just checked the valve clearance on my '02 YZ250f and could not get my thinnest feeler gage (0.038 mm) between the cam and pad. It was the same on all three intake valves, but my exhaust were fine. My question is, since my bike started fine, hot or cold, and ran fine, does this make sense? I know using your bikes ability to start is just a seat of the pants indicator of needing to check/adjust your valves, but I expected it to be a better indicator than almost no clearance. Any ideas or input before I tear into would be appreciated.

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I know this maybe a redundant question, but did you trim down your feeler gage to make sure it fits the intake cam lobes/valve cover space? The exhaust side is large enough to get a standard gage to fit, but the intake side requires you to trim the feeler to get it to fit right. If this is not the case and you truly couldn't get the smallest feeler (0.038mm) in there, then you have a problem! Don't ride your baby until you get that intake side in spec. However, I can't believe the intake side is that tight, unless the valves have been re-shimmed multiple times and now you require a total valve replacement. Are you the original owner? Do you know how many times the valves have been adjusted? These are important questions if in fact the clearance is less than 0.038mm. Starting may not be a problem for you right now, but your next symptom may be a blown motor and need for a $2500 top end if you continue to ride it like it is.

Cheers :)

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I am not the original owner, so I don't know if the valves have ever been shimmed. I trimmed by feeler gages so they fit. I can't believe that they are that tight either. As soon as I try to push the gage in, it starts to buckle and bend. I notice that there is some variation (a degree or two) when trying to find TDC. It appears as though the the tick marks on the intak and exhaust cams don't both line up extact with the case line on the head.

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Go to griotsgarage.com they have a metric feeler guage with tapered blades that works great on the intakes Rick

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I just checked the valve clearance on my '02 YZ250f and could not get my thinnest feeler gage (0.038 mm) between the cam and pad. It was the same on all three intake valves, but my exhaust were fine. My question is, since my bike started fine, hot or cold, and ran fine, does this make sense? I know using your bikes ability to start is just a seat of the pants indicator of needing to check/adjust your valves, but I expected it to be a better indicator than almost no clearance. Any ideas or input before I tear into would be appreciated.

Do yourself the favor of taking 30 mins out and putting a smaller shim in there so that you can get a clearance reading. I'd go down 0.25mm from whatever is already in there and then reassemble and try to take a measurement. You're going to have dissassemble/reassemble twice, but you'll save yourself from blowing the motor. Before you do all of this I'd check again that you had the motor at Top Dead Center.

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I checked the motor again. This time I used a straight edge ruler to make sure the tick marks on both cams are aligned. I still can not get the feeler gage completely under the lobe of the cam. I get the gag about to the middle of the contact point between the lobe and the pad, then the feeler gage starts to bend. I'm just going to pull the existing shims out this week and determine what size the new ones should be. My bike is in pieces right now.

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You are definitely going to need to change the shims based on what you are saying. You will need to find out what size shims you have in there. Your tolerance on the intake side should be 0.10-0.15mm, so assuming you are not able to get a 0.038mm feeler in there, I would go down 2-3 shim sizes (they are sold in 0.05mm increments). Reassemble and check the tolerances. This may take a couple of trials to find the right size shim given how tight it currently is. Of note, since you are not the original owner and have no idea how many times the valves may have been adjusted you probably will not have a good baseline to tell when it is time to no longer adjust via shimming and when it is time to replace the valves. This by no means is exact, but most of our bikes come from the factory with 175-185 numbered shims (intake and exhaust). So, if you find you have a 160 in there, you may be looking at a valve job and not just an adjustment. Hard to say not knowing the exact history of the bike.

Good luck :)

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Just to give a little update; I pulled my intake cam and shims. They are 185, 182, and 186. The 8's were almost illegible. Based on the table in the manual, I should be ok. I don't know about others, but I had to use a magnet to get the shims out.

One question, Will I need to pull the exhaust cam to get the timing chain back on? Even though I pulled the chain tensioner, it didn't seem like there was much slack.

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from what I have just been told about a similar situation, if you have wear on the intakes, you need to change your air filter more often. The valves do not like the dirt/dust particles over time. which makes sense. My exhaust valves were perfect.

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if it is infact the dirt/dust particles that cause the intake valves to wear fast than.... dean how often did u change your airfilter...

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The numbers you have on your shims (numbers ending in other than 5 or 0)indicate that it has either never been shimmed before and these are the original shims from the factory, or it was done at a shop where the mechanic had a selection of OEM shims left over to choose from. I would reshim them and then check them frequently from this point as it appears it has worn through the coating on the valve faces. If that is the case, it will loose clearance rather quickly and the valves will need replacement soon. This is exactly what happened to mine.

This is a normal pattern for these engines and it does not necessarily indicate that you have had dust in the intake.

Each .20mm reduction in shim size indicates about .11mm of actual wear at the valve face. That's about .004", and I don't expect the nitride coating on the valves is much deeper than that, so once you arrive at that point, it's time for new valves.

On the cam chain question, I assume you removed the tensioner. If you did, and did not rotate the engine, you probably just have to tilt the cam and rock it into place. If you find you that still have trouble getting the cam back in, you may want to take the time to peek behind the flywheel to see if there is a link hanging off the bottom. You'll need to pull the flywheel in order to do this, but if you think it's possible (and keep in mind, it's built so that this will not easily happen), it will be worth your while to fix it. running ity that way would certainly cause the cams to skip time as the link was picked up.

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Thanks for the tip on reinstalling the cam. I did remove the chain tensioner, so I will try exactly what you suggested. I'll check them after a couple of rides to see if you predictions hold true.

I picked up the shims last night and plan to put the motor back together tomorrow. I had to call 3 shops to find one that would sell me these shims. I think the service department keeps what they have for themselves. Apparently these shims are also used in some of Yamaha's sport bike motors. The parts person also showed me some feeler gages from motion pro that are made for this application. Unfortunately they were out of the size that I needed.

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I installed the new shims (175-L, 170-C, 175-R) and the left and right are still tight; left is between 0.076 and 0.102 mm, right is between .051 and .076 mm, and the center is between .102 and 0.127 mm. I'm planning on getting 170 for right and left and a 165 for the center. My question is based on your statement pertaining to the coating on the valve faces wearing:

I would reshim them and then check them frequently from this point as it appears it has worn through the coating on the valve faces. If that is the case, it will loose clearance rather quickly and the valves will need replacement soon. This is exactly what happened to mine.

How long (hrs of operation) did you end up replacing your valves?

Did you replace intake and exhaust?

Is it recommended that I replace the other misc. components springs, etc?

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I can't speak for grayracer, but here are my opinions on your questions:

How long (hrs of operation) did you end up replacing your valves?

This really depends, but if you go by the book, at 20 hours seems to be the minimum. However, this is based on a "race" enviroment. Many here have gone way past that time mark.

Did you replace intake and exhaust?

Yes, you should do both if you are there.

Is it recommended that I replace the other misc. components springs, etc?

Definitely replace the springs, cam chain, but the guides should be fine.

Sounds like your bike is going thru its first adjustment. Hopefully the shimming will be all that is needed for the time being. I would be very dilligent about checking your clearances from this point on. Maybe checking every 20 hours or so should be fine. Trying to figure out if your valves are out of spec by feel, hard starting,etc. is not the right way, get in there and check them for yourself.

Good Luck :)

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