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Yz400f Jeff

Stripped exhaust head threads

9 posts in this topic

Just put a crush washer in my yz400f and stripped half the threads in the head. Their was no crush washer when I bought the bike. Now that I do have one in there it takes up another 1/4 inch giver take. I think the bolt was to short to begin with but with no crush washer it was good. I do have a longer bolt in now and tight but my question is will it be strong enough with just half the threads catching. Would I be able to make it a permanent stud and nut just like the other side. If worst comes to worst I'll have to re tap it and try and do my first heli coil. I do take the header off often to check/ change my oil filter but was thinking of making my one oil filter cover bolt a stud and nut so I won't have to take the header off as much. Thanks Jeff

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If this is a 79 YZ400F, then the bolts on the cylinder that hold down the head are studs. Just take the stud off and replace it. If you can't take it off yourself, have a machine shop do it clean. As far as will your way of using the half thread of another bolt work, well time will tell I guess. I'm sure if it doesn't hold, you'll see exhaust escaping from that area between the head and cylinder. I'm sure it will leave soot there. If it doesn't, then I guess it's holding. I would opt to take the stud out and replace it fresh and there's no second guessing that. It's when you start to do stuff like this to your bike that you pay the price later when it doesn't hold. I got a 84IT490 from a friend for free a couple years back. Didn't do anything with the bike. It sat in my garage for years. Recently, I decided to restore it, and finding mismatched screws on it was not a pretty site. That's the beauty about bikes, you can jerry rig them and they still work, but truth is, when it breaks down, and you're in the middle of the desert for example with nothing but miles to walk back to came with, you'd be surprised how much it makes sense to think back and say, geez, I should of spent those $10 and replaced the stud. Hope I got the right 79 YZ400 in mind, if not, post some pictures of what you're dealing with and a lot of old school guys here know fixes that would surprise you.

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It's a 98 yz400f as for it being a stud it is not. The one side is a stud and nut the other is a bolt into the head. And about half the threads pulled out so I tried the longer bolt and it snugged up tight. But I don't like half a**ing stuff like this I may be younger but iv been there and done that. As for being in the middle of a desert and breaking down that won't happen in my lifetime I live in the middle of the great lakes and ride woods and open fields steps out of the garage door. This is the 4th thing I have stripped on this bike I almost swear the fasteners are made of cheese. And I don't really want to put thread locker on it unless I just try and make it into a stud and use a nut cause I'd like to be able to get it back off.

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Yz490 I'm talking about the bolt that holds the exhaust head pipe into the head of the motor. I think you were referring to a totally different situation just to clear it up abit lol

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Are we talking about the 79 YZ400F? From what I remember (I use to own one by the way), the exhaust pipe fits into the exhaust port on the cylinder and is held with 2 or 3 springs. Drop us a picture if possible. I'd like to see what it is you're talking about.

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My bad, ok, now I know what you're talking about, a 98 YZ400FK. Nope, never owned one of those, but I know what you're talking about now. Tap it out with the next size and drill out the hole on the exhaust flange to match the diameter and you should be golden. Using a bolt into the cylinder block only using 1/2 it's thread might hold, but remember, this is an engine that vibrates, so the worse case scenario might be the bolt breaks and you'll have to extract it anyway. Might as well do it right the first time and just go the next size up. On a frame, I normally fill in the hole with an arc welder and re tap it, but we're talking about an aluminum cylinder, so it's critical you get it done right the first time. A local machine shop would only charge (at least around here where I live) around $20 to do this. Better play safe than sorry when bad luck hits and like I said, the bolt breaks under stress, or completely strips out the rest of it. Good luck.

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Ok thanks guys. I'll probably drill it out tap it and put a heli coil in I can get my hands on a set from a co worker.

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