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YZ125 stuck bolt in cylinder

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I was trying to take a bolt out of my cylinder to take out the power valve assembly but it won't budge. I've tried the hardest I can without stripping the bolt. Any ideas? Also, if I took it to a shop, do you think they would be able to take it out? Thanks Picture of bolt: ImageUploadedByThumper Talk1382582845.214313.jpg

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I was trying to take a bolt out of my cylinder to take out the power valve assembly but it won't budge. I've tried the hardest I can without stripping the bolt. Any ideas? Also, if I took it to a shop, do you think they would be able to take it out? Thanks

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Heres a picture of the bolt, its in a weird spot, so I can't get pliers or anything into that space ImageUploadedByThumper Talk1382583428.848810.jpg

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You can tap the butt of the screwdriver while trying to unscrew it (like an impact would do) and that may do the trick. I wouldn't recommend heating it.

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I agree tapping the end of a #2 philips screwdriver with a hammer to loosen and then pressing as hard as you can while turning might work. If not, you could try Grabbing with vice grips. You will need to use a new screw of course. A bolt might be better.

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I agree tapping the end of a #2 philips screwdriver with a hammer to loosen and then pressing as hard as you can while turning might work. If not, you could try Grabbing with vice grips. You will need to use a new screw of course. A bolt might be better.

I was gonna say vice grips too. Depending on how much room you have to work with that will more than likely get it out

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I agree tapping the end of a #2 philips screwdriver with a hammer to loosen and then pressing as hard as you can while turning might work. If not, you could try Grabbing with vice grips. You will need to use a new screw of course. A bolt might be better.

I've tried vice grips but theres no room to get into that space. I usually use those to get stuck screws off but i can't with this.

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Just for future knowledge the phillips head screws on dirt bikes are constructed to JIS (Japanese Industrial Standard) and not SAE (Society of Automotive Engineers) or ISO (International Standards Organization).  A conventional phillips head screwdriver (SAE) does not fit the JIS screw properly and that is why they are so easy to strip.  But, impact drivers WORK.  And if it is possible to do it quickly to avoid damaging surrounding areas usually using an acetylene torch with a number one tip for this case. Heat the bolt head until it has a light red glow.  This relieves the tension on the bolt and shrinks it slightly then it will come out with almost no effort.  I'm working on a motor operated fire monitor right now and have had to use unusual means to extract all but maybe 5 of the 30 screws on the thing.   The fastest method was to silver braze a nut to the top of the old screw.  Between the heating and added leverage they all came out on the first try except one that took three and there was only paint damage to surrounding areas.  These screws are all about the same size as what you are dealing with.  There are a few others that I simply drilled the head off which also releaves the tension on the bolt and then Vise Grips were enough to break the remains free.

 

In this case, the Yamaha 250's have the same one so I am familiar with it, the bolt is not seized you just used the wrong screwdriver.  An impact driver will most likely free the bolt without any need to heat.  If not it will certainly free up with heat.  I would try to avoid heat as you may need to replace the small steel spacer below as it will heat as well affecting the heat treatment causing it to wear faster.  Then you will have to buy both the bolt and the clip.  If you buy the replacement bolt at your local hardware store it will be of the SAE type so your regular screwdriver will be able to remove it easily for any future rebuilds.

 

That said, the first thing I do on all of my dirtbikes is remove the JIS phillips head screws in all of the Nissin master cylinders and replace them with stainless flat head screws (usually available at Ace for $0.60 a piece) because the originals ALWAYS strip out.

Edited by 1987CR250R

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You need an impact screw driver..and heating the area around the screw with a small propane will be okay. You will most likely ruin the seal but that is replaceable. 

 

The only thing I have to add to this is to peen the Phillips Head with a small Ball peen hammer to get more bite with the screw driver. heat the screw also to loosen the locktite.

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I would avoid heat. I have taken that same bolt out before when mangled like that. ViceGrips makes a tool that is needle nose like and will definitely fit in there, but even small sized normal ones will be able to grip it from the top. Another option is to cut a slot across the screw head (using a dremel wheel perhaps) and then use a slot screwdriver to remove. Impact driver should also work but don't hit too hard.

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