Stripped Set Screw on Decompression Plug

11 replies to this topic
  • yz450MIKE

Posted January 26, 2006 - 07:32 PM


I removed my stock decompression plug to install one of the TT replacements on my 2003 yz450f. When I removed the set screw, the threads came with it. I think somebody probably used red lock tite to install it. What would be the best way to fix it? Can I just drill and tap it to the next larger size bolt, or should I just jb weld the damn thing back in there and call it good? Thanks for any ideas.


  • jjjyz450f

Posted January 26, 2006 - 07:38 PM


I would try a heli coil if possible, a time cert is probably too big.

  • MNellis

Posted January 26, 2006 - 09:22 PM


The same thing happened to me last year. I went down to the local auto parts store and they had the apropriate heli-coil. The problem with drilling to a larger size and tapping is that the bolt that hold the plug and decompression shaft it has a grove in them that the stock bolt fits. I suppose you could modify a larger bolt to work but installing the heli-is pretty easy.

  • Dolce_Grappa

Posted January 26, 2006 - 09:26 PM


Heli-Coil, i've repaired two of my friends bikes. For some reason they didn't buy into the torque wrench theory.

  • yz450MIKE

Posted January 26, 2006 - 11:25 PM


Thanks for the quick replies. I completely forgot about heli coils. I'll be the guy at the auto parts store tomorrow getting the heli coil. Amen to the torque wrench. I'm always amazed by guys torquing the hell out of bolts into aluminum.

  • yz450MIKE

Posted January 26, 2006 - 11:32 PM


One more question. Do you think its okay to leave the engine sealed up and just use a shop vac to suck out any metal shavings, or is it necessary to open up the top to ensure no metal gets inside the engine.

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  • MNellis

Posted January 27, 2006 - 08:04 AM


I left my engine sealed up. I stuffed a paper towel into the decomp hole so the chips wouldn't be floating around in there. After the procedure I pulled the paper out and used a vacuum. It seemed to work fine.

  • grayracer513

Posted January 27, 2006 - 08:30 AM


If you also grease the drill bit and the tap, the grease will hold the majority of the chips created in the process. Follow with an oiled cotton swab both into the bolt hole and up into the shaft bore. Should be easy.

READ THE INSTRUCTIONS for the Heli-Coil, especially if you've never done one. Not difficult, but just a little tricky, and it needs to be done right.

It doesn't apply to how yours was damaged, but don't make the very common mistake of failing to align the locking groove with the bolt hole visually. The bolt is not a set screw. The ground nose of the bolt is supposed to drop into the groove in the shaft or plug. If the nose hits the shaft outside the groove instead, only 1.5-2 threads will be in contact at that point, and it will strip easily. You should be able to bottom the bolt head with very little resistance.

  • bruntz505

Posted January 27, 2006 - 09:00 AM


I also can speak from experience on this subject.I had mine strip out this summer,too.My bolt would seat and tighten if I removed the copper washer on it,so I talked to a Yamaha service tech and was told to just remove the washer and machine the thickness of the washer off the tapered end of the bolt.Since it is a flange bolt,the head will seal to the engine.I did this and my problem was solved.But if you don't machine off the difference,it won't seat completely.The tech told me that when you replace the plug or to replace the plug,that you can just have the bolt and the plug holes welded shut.The serve no purpose and he said some people have them filled,they are only there because when Yamaha went to auto decompression,they didn't want to make a new design a new head.My $.02

  • grayracer513

Posted January 27, 2006 - 10:36 AM


The tech told me that when you replace the plug or to replace the plug,that you can just have the bolt and the plug holes welded shut.The serve no purpose and he said some people have them filled,they are only there because when Yamaha went to auto decompression,they didn't want to make a new design a new head.My $.02

The really cheap way to block it off (no, not JB weld) is to pound a steel cup plug (freeze plug, you know?) into the seal pocket and replace the bolt.

The reason they left the bore there is in case any die hards wanted to convert back to manual. (Just not machining the bore would have been the cheapest thing to have done) They offer, or used to, at least, a complete kit for this purpose, 5TA-W1228-00-00. I wonder how many they sold....? Anyway, the whole thing isgone on the '06.

  • fowler175

Posted January 27, 2006 - 06:49 PM


Actually, when my decomp plug fell out, I just used a 1/4" NPT tap, and installed a stainless pipe plug. Cheap, easy, looks sweet, and works like a charm!! I just used a thread sealant on the set bolt, and put it back in place.

  • yz450MIKE

Posted January 28, 2006 - 10:03 PM


Thanks for all the info. I got a Heli-coil and installed the plug/retainer screw today. Used a rag in the decompression hole as well as grease on both the drill and tap. Followed up with a shop vac. Seemed to catch all the metal shavings. Worked like a champ and took only 20 minutes start to finish. Thanks again for the information. I just recently joined this website and it has been nothing but a reliable source of information, help, and advice. Thanks all.


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