Seized engine mounting bolt - How do i get it out!?


Poor English kid getting into bikes and loves it!
Hey all, I have a CG125 engine that I want to slot into my XL125RC because the 200 Chinese engine in it shat itself (after 2 bottom end rebuild I cant be fucked to split the cases again... dont get me started on them...). The CG engine is from my old CG that I retired and I personaly put about 12,000 miles on the engine before removing it and it was running fine. The only problem is, when I went to undo the nut on one of the mounting bolts, it sheered off and the bolt head did too when I was trying to release it. I have oiled it and heated it and beat both ends until I
am blue in the face but can't get it to move.

Any suggestions?




Keep in mind that it is easier than you might think to destroy your case hitting it with a hammer, so be careful. Grind the bolt flat and flush with the case on both sides. That will enable you to make an accurate center punch in the center of the bolt. Use a smaller drill to bore a hole through the center. It is not that long, so if you are careful, you should be able to drill a hole from both sides that intersect in the middle. If you have to do this with a hand drill, get a friend to help your aim by looking at it 90 degrees away from your viewpoint and helping guide the drill. With care and patience you should be able to keep from drilling through the side of the bolt and into the case. Once you connect the two holes, drill deeper alternating from both sides and you will start to get the two bores to get more centered where they meet. Drill the hole bigger until the wall thickness of the bolt is as thin as you can get it without cutting into the case, but but don't drill all the way through from each side - leave a step in the center. Get a drift or even a bolt the size of the larger hole and grind the end flat. Heat the case very hot with a heat gun or propane torch and drive what's left of the old bolt out. The aluminum will expand considerably more than the steel bolt, but corrosion expanding between the case and the bolt can create a mighty grip. With a little luck, the bored out bolt will be weakened enough to release some of the grip the corrosion has on it. It is important that the step is substantial enough and the drift you use is close fitting and flat ended enough to not expand the bolt internally. Keep heating the case and tapping from both sides and hopefully you will drive out the bolt. Patience is your friend here. If you are not successful, bore the holes larger from both sides until you contact the case, but leave the step and try again to drive out what is left. At this point you can plug one end and fill with penetrating oil and leave overnight and try again. This is worth doing now because the penetrant has access to most of the length of the bolt. With access only at the ends, you could submerge in penetrant for a year and not get very far. If that still doesn't work, you will be left with just boring the whole thing out. If you were careful from the beginning, you should have a pretty good shot at doing minimal damage to the case.
Another option is to weld a bar onto the bolt and try to break it loose. Make sure to heat it exactly the same as jpmobius described when attempting to break it free.
You can also try slotting it with a dremel and using a flat head bit on your impact driver.
Thanks for the great suggestions. I will have another go tomorrow in the light and hopefully get my bike back on the road, as I am already missing it!

Do you have a tap set man? what you need to do is clean up that mess you have, drill into one or hell even both ens to keep from having to do it twice, drill .5 - .75 the size of the bolt so you have good meat left, tap the hole and get a bolt in it... while you have the drill handy drill several small 1/8" holes in the case along the length of the bolt stopping when you start to drill the bolt its self... PB blaster in those holes and ends, if you have a little torch heat the bolt(s) so they heat the old nasty bolt, then see if you can rock it loose... THEN tap it out with a drift.

RD :eek:
I have another idea for you. Take a hack saw and cut the engine casing across the full length of the bolt. This will releave the grip the case has on the bolt and it will allow you to get a lubricant to the entire seized area. When the bolt is removed get the cut welded.
Just remember not to weld the area where the cases join.

Hope this helps.

Good Luck


  • Sia7Dql.jpg
    124.4 KB · Views: 219
This is a bolt that runs right through, with a head on one end and a nut on the other?

Maybe I'm missing something, but nobody has suggested grinding off one end so it can be tapped out? Is the bolt turning at all?

If it was a mounting bolt (i.e. holds it into the frame) it would be longer and I'd be surprised if it served double duty as an engine case bolt holding the halves together, but I've been surprised before. Never seen a bolt like this do double duty.

Regardless, I'd be grinding off one end completely and tapping it out until I could grab hold on the other end and pull.

Also, it's a steel bolt through aluminum. Heating the aluminum carefully with a torch will expand it more than the steel bolt expands, providing some additional relief.
try using a dremel, for a horizontal cut, and then unscrewing it out with a screw driver first. if not try everyone elses idea.
Git reelz bikez maan! Y u no git reel bike? Just kidding, looks like you studded the ends there, its not threaded i guess? Heat is your friend, as aluminium alloys expand more from heat than steel. I would not cut the case, this is probably piss poor dirty useless chinese luminijum that is pointless to try and weld. But if you cut it, dont use an angle grinder, use a hacksaw, the minerals from the cutting disc will contaminate the alloy, making it even MORE horrible to weld.
If anyone is interested I couldn't shift it, so I tried drilling out and a.nice chunk of the crankcase came off :( so I just rebuilt the engine with some crankcases off of ebay, turns out the small end on the conrod had seized at some point so I put a bronze bush in there and used a piston from a later CG that had a 13mm pin! Just put the engine in frame yesterday and should have it on the road today!
Top Bottom