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Valve help

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My kx250f has a scratch in the intake valve from previous owner not replacing shims.

Any idea of a way to avoid getting new valves besides reshimming more often? Also one of the shims gets worn down alot faster because of this.

Edited by Monster Kawi250

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Thanks for the replies. Im still kind of a newbie with the motors, but im not sure if it would be better just to sell the bike. My neighbor has been racing for a long time and is a mechanic and he told me if i get new valves i would possibly have to get a new head to fit correctly

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Man ive put new valves in stock seats un recut. Leak downed and been fine. Ive lapped 40 year old valves numerous times. Your head could be warped. But test for that on glass. But if theres no cracks get new valves. If you can afford it. Cut seats and valves. 3 angle job. Go stainless steel. All this is is metal legos man.

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Even a new head can have seats that are not perfect.  I would send it in to a shop that specializes in head work and have them tell you what you can get away with.  They do its everyday and give you an honest and practical answer.  You would not have to replace your head if you got new valves, but, your seats should be checked and a machine shop can do that.

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I checked all my valves to make sure they were in spec and my one intake valve was way out of spec. I couldnt get the .04mm feeler in there when it suppose to be .10mm-.15mm. So my issue is i know i have to replace the shim in the one but im not sure what size shim i should order

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I checked all my valves to make sure they were in spec and my one intake valve was way out of spec. I couldnt get the .04mm feeler in there when it suppose to be .10mm-.15mm. So my issue is i know i have to replace the shim in the one but im not sure what size shim i should order

 

 

Depends on the bike? there is usually a formula used to get the proper shim size. In my experience it is this. You will need to figure out which feeler gauge you can get in there. So go to the next one smaller until you get one that gets in the gap with just a little resistance. This is you current valve clearance.

 

(current valve clearance - manufacturer spec clearance) + Current Shim Thickness = New Shim Size

 

In most cases your "new shim size" will not be exactly what is available so you go with what is the closest shim size available. In your case if you valve was zeroed out it may look like this on paper.

 

(0 - .15) + current shim size = New Shim Size

 

If you are zeroed out you may have to do this more than once. So put the new shim in and then check the clearance again to see if it brings it into spec. If so good to go. If not repeat and your next try should get you into spec.

 

There are lots of youtube vids to help you through this process step by step.

 

You will need a decent micrometer to measure your current shim size because usually you cannot read the size after they have been run. I bought a basic digital from Harbor Freight for like $10 worked fine. You can order a whole shim kit, or if you have a parts store close by they usually carry shims of all sizes and if you bring your old one in they will match it up with the new shim size. If you have do it twice, you have to make the trip to the parts store twice. Which is why getting the shim kit makes sense for some people. However, the kits are like $70 - $80 and a single shim is like $5. If the valves are moving on you that much you may need a to think about getting some new ones and a good grind on the head from a reputable shop.

 

Hope this helped

Edited by MountainManiac

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I checked all my valves to make sure they were in spec and my one intake valve was way out of spec. I couldnt get the .04mm feeler in there when it suppose to be .10mm-.15mm. So my issue is i know i have to replace the shim in the one but im not sure what size shim i should order

 

 

It is important to keep things in the same place when dismantling your bike. I usually make a diagram of how everything is positioned in the head. I stick with this diagram throughout the process and write all of the measurements in relation to where they are located. Makes assembly easier and avoids costly engine damage.

 

Again, I used YouTube to get me through this process and it was VERY helpful.

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A = (B – C) + D

[A] Replacement shim thickness (the shim needed to obtain the correct valve clearances)

[ B] Measured Valve Clearance (current clearance not within spec)

[C] Specified valve clearance (target or proper clearance we are trying to obtain)

[D] Present shim thickness (incorrect shim removed from motor)

And buy a shim kit with numerous shims in case you guess too tight or too loose

Use torque specs on cam caps and watch a video on how to do the chain so theres tension on the front side so the tensioner takes up the slack on the back side. Need this for correct timing.

And do yourself a favor and buy the manual... Its a machine

Edited by notoriousE-R-I-C

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I checked all my valves to make sure they were in spec and my one intake valve was way out of spec. I couldnt get the .04mm feeler in there when it suppose to be .10mm-.15mm. So my issue is i know i have to replace the shim in the one but im not sure what size shim i should order

Only way to know what shim to order is you have to know what shim is currently in there. Do not rely on the numbers on the shims either, i always recommend measuring each shim with a micrometer.
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Back again i put the correct shim in i believe and it had good conpression now. It just started up but died quickly after. Then once i started kicking it i noticed the compression went down alot. We took the spark plug out just to see if it wasnt on or something but once the spark plug was out it had good compression again. So im just confused now.

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Just put new shims in and put it all back together, had good compression and it started up for a second then died and afterwards seemed to lose alot of compression. We were curious if it was something with the sparkplug so we took it out and with the spark plug out it now had compression so now im just confused.

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Back again i put the correct shim in i believe and it had good conpression now. It just started up but died quickly after. Then once i started kicking it i noticed the compression went down alot. We took the spark plug out just to see if it wasnt on or something but once the spark plug was out it had good compression again. So im just confused now.

Are you sure your timing is set correctly. There should be no resistance with the spark plug out. If with the spark plug out you are getting resistance (Compression?) you may have a mechanical bind. Never kick the bike over right after pulling a cam or the timing chain. Always double check your timing marks and turn the engine over by hand once the marks are lined up and the tensioner is tensioned. I typically turn it over by hand slowly to full cycles (4 revolutions) and verify the marks line up before kicking the bike over for the first time. Not doing so is a sure fire way to bend valves if the timing is off.

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I know with my bike that there is a decompression adjustment lever on the cam that needed to be adjusted as well. Not sure about Kawasaki?

 

You can't do a compression test on a 4 stroke dirt bike. They have auto decompression valves that don't disengage at kicking speeds.

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