Frozen head Bolts

BRIELLY · #1 04-09-2012, 02:05 PM

I'm attempting to replace the head gaskets on a 96 yamaha 250. I have 2 head bolts that don't want to come out. I assume if I break them off in the block I'm looking at pulling the powerhead and having it drilled out by a machine shop. Most likely I'll run into more broken bolts trying to do that. So whats the best meathod for removal? I was thinkning of heating the bolts with a propane torch and trying again. Would an air impact wrench be good or would that break the bolts? I'm pretty sure penetrating oil will not make it into the block to help loosesn the bolt. I was also thinking about breaking the heads off the bolts off so I could at least get the cylinder head off and have a chance at getting the penetrating oil into the area where its seized. I could use channel locks or even weld a nut to the remaining stud at that point and have at it again. Any thoughts or suggestions would be greatly appreciated.

tsubaki · #2 04-09-2012, 02:58 PM

If you do attempt the heat, clean the head of the bolt free of paint, etc. This will localize the heat to the bolt for a short period of time. Hopefully making the corrosion a little more pliable.
It's really hard to judge just how much heat is needed. I've seen it take a little to enough to blister the surrounding paint.
Attempting to tighten the bolt sometimes helps.
An impact usually dictates having the need for a feel to judge when it's too much.
Problematically, wringing the head off might not help if the corrosion has it seized on the shaft of the bolt. Consider this as a last resort.

Destroyer · #3 04-09-2012, 05:13 PM

Well, there are two schools of thought here.

One says heat the bolts, hopefully to make the corrosion a little softer.

The other says that heat makes things expand, so if you heat the bolts that will just make them expand inside the cavity and make them even harder to loosen. That school of thought says heat the head and try to loosen the bolts as the heat is expanding the head.

Personally, before I tried anything else I'd go to Sears and buy a 1/2 drive hand impact tool. These are units that you fit a socket onto, put it on the nut or bold to be loosened and strike it hard with a hammer. (A drilling hammer works best). When you hit the tool the force of the blow does several things.. first, it helps loosen the bolt by delivering a shock wave from the hammer through the block. Second, each blow causes the socket to turn slightly, much like an impact hammer. Third, since you're driving the socket onto the bolt with a hammer shot, the socket is liss likely to round off the corners of the bolt.
Oh, and make sure you use a 6 point socket, not a 12 point.

These tools are indispensible for anyone that works on motorcycles since lots of the screws that hold a bike together are phillips head and will round out with the use of just about any other tool. They will break fasteners free when nothing else will, and they are not that expensive. In fact, they are on sale now for less than $20.

http://www.sears.com/shc/s/p_10153_1...1&blockType=G1

spareparts · #4 04-09-2012, 05:18 PM

hate to tell yo this, but I've never had any luck with getting bolts out of older Japanese motors. OMC went with a simular aluminum in the late 90's and I've had the same luck with them. I'd personally try an inpact gun, just let it hammer for a while, it'll shake some corrosion loose. Try a little heat on the head and block. Heat then let cool, try the impact, heat, cool, impact, repeat as needed. If you break them off, you can drill them out

THEFERMANATOR · #5 04-09-2012, 05:26 PM

If they're stuck in really bad, I like to cut the bolt head off and try and pull the head off that way. Then you can heat and cool the remaining bolt a few times to expand and contract the materials some a few times. Then use a pair of parrot nose pliers on the bolt sticking out and heat the block up and then work it back and forth a few times. Remember the aluminum block will expand faster than the steel bolt, and the aluminum will normally expand more than the steel to. By heating the bolt and letting it cool off a few times will stretch the aluminum out some and in many cases allow you to be able to work the bolt out. I have had nothing but broken bolts with impacts though, so I use hand tools for any stuck in bolt now.

lathehand · #6 04-09-2012, 06:06 PM

I've used this method more times than I remember of as a tool and die maker.First start by drilling the head of the bolt dead center .The trick is to use a left hand drill bit .Yes they do make them.manny time befor the head has fallin off the bolt has turned between the heat and the left hand friction.If not you continue with the proper drill size for your thread left hand.That way if it hasn't unscrewed by itself you just have to clean up the thread with a tap.Hope this helps it's never failed me