Removing broken head bolt?

[creia]

Well, it was bound to happen eventually....
We broke off our first head bolt tonight on our 1974 Briggs 5 HP All of the engines we work on are 30-45 years old, and we always take all of the usual precautions, and exercise patience, whenever taking these apart. By the looks of most of them, most appear to not have had bolts removed in MANY years, likely decades. I guess that we have been very fortunate thus far, having only broken off a few smaller bolts, of relatively less importance, and was able to remove and re-thread them. Tonight it was a cylinder head bolt, broken off nearly flush with the block. As can be seen from the photos it was one of the longer (rear) bolts. This one was right next to the exhaust manifold, which I suspect was a contributing factor due to the proximity of heat. This particular bolt is actually a "through" bolt - the ONLY head bolt to be one I believe. The other (lower) end, while visible, is for the most part inaccessible for all practical(extraction) purposes. The engine is actually in reasonably good shape, and certainly is a candidate for one of my son's restorations, with some minor rebuilding. We would really like to work with it.
Yes, I already know about "easy outs"(personally I think they are over-rated in my experiences), and the process of drilling successive holes of larger sizes,both of which I have used with limited success on bolts other than head bolts. What I am looking for is real-life tips and pointers that you professional have used specifically for removing broken head bolts over the years.This will be my first attempt at head bolt extraction, and I would sincerely appreciate any help you could provide.
Thank you and regards,
Michael

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[smitty6398]

Michael; most siezed steel bolts in aluminum are a result of airborne moisture causing chemical reactions to the two different metals, add the heat expansion rate difference of the cylinder block and cylinder head bolt and they really get tough. I've had some limited success using two different methods for extracting bolts such as this.
It appears that there is a couple of threads protruding. Placing an unplated nut over this protruding portion and arc-welding the end of the bolt to the nut , allowing heat from the weld to flow into the block, and then quenching the nut and bolt with cold water can sometimes break the bond.
I've also drilled the bolt almost thru, used an acetylene torch to heat the bolt cherry and then used an oilcan to squirt water into the drilled cavity to cause the bolt to cool faster than the aluminum; preheating the aluminum will help but you can melt it before you realize it .
I think if it was mine, I'd take it to a machine shop and have them run a mill thru it and put oversize threads in it; but then expense becomes an issue.

If you weld it, you probably won't be able to drill it later; if you drill it , it will probably be too fragile to weld later.

Good luck, SMITTY

[bobodu]

Use the head as a guide ( put in a couple of bolts) the use the hole over the busted one as a guide to drop a canter punch through. This'll get you centered.
Then drill Baby drill.
IO only use EZouts on brass jets and seats....nothing worse than a bushed extractor.

[Lawnranger]

A few years ago I had a similar situation and drilled the offending bolt using successive drill bits until I broke through on one side of the threads. Unfortunately I could not drill exactly in the center but it really didn't matter in my case. I then was able to use a pick and turn the remaining piece out. Drilling off center and through one side of the threads damaged the block but I successfully used a Helicoil and I'm using my push mower to this day.

In your case, due to the restoration project, you may not want to damage the block and I fully understand that but if all else fails......

[David]

Would Kroil or some custom blend of acetone and automatic trans fluid be of any possible help in a situation like this?

I am an amateur here but I guess this is where a left handed drill bit and a drill that runs in reverse would be good?

[38racing]

when I did one will the successive drill sizes I finished it with the thread tap size for the hole and it cuts the remainder of the bolt out. Currently drilling out deck spindle bolts and will trying centreing jig as Bo suggested.

[bgsengine]

I agree with bobodu - Put head on, use it for a guide, - or if you have a 5/16" nut you can "just" start it threaded on, and get the broken bolt center punched, use *SHARP* drill bits (We keep a set of cobalt bits JUST for the purpose) and drill out as close to center as you can. (Careful not to break off the bit in the bolt, or your block is trashed! - Practice drilling technique on some scrap first if you don't have a feel for it - bits like to break just about as you're about to break through - a light touch is needed, and lots of patience. ) and progress from about a 1/8" dia to just a hair under 5/16" then dig out the rest of the threads, drill out and install a heli-coil kit - unless you have the luck to get the drills perfectly centered, you'll have too much thread damage once the bolts come out, to re-use the original threads - we always will put in a heli-coil - if the drills are even slightly off center, you'll have lopsided threads that will only just seize again (and/or allow carbon build up that jams threads in place again) , hence the heli-coil to finish the job. (and use the head as a drill guide to drill out for the helicoil *AFTER* removing the steel bits of the bolt - any remaining steel in the bolt hole will lead your drill off-center, as it will drill the aluminum much faster. )

[Arkie]

Just some off hand thoughts! (I smell wood burning)never mind, it's just my head overheating!
I've also only drilled out part of a bolt just enough to get some threads and install a stud and then nut on top. Threaded Stud stays in place if future diaassembly required! Sometimes you can find a reduced shank stud for example a 3/8 thread and a 5/16 stud shank or if you have to tap larger or use a helicoil and then use a stud and the block threads will remain good for the rest of its life if disassembly required the stud stays in place.

Doubtful in your case, but if you have room on the bottom, drill it out and insert a bolt with a nut on the bottom when re-installing the head. Nut may have to be partically relieved for room on the backside. (just a thought as it's not clear in the pic how much room for such.

I would really keep a heads up and keep the drill bit centered, because you may not have much clearance when going by the intake and exhaust ports internal in the block if try to deep drill.

As a last resort if it's for yourself, might get longer bolts for the other two head bolts, make a 1/4 piece of bar stock steel, some spacer collars for the two bolts and and the one missing bolt and when the two head bolts are torqued on each end the center has force applied in place of the stripped bolt. The cross bar is on top of the cooling fins!

I would not go any further for a customer, too much time and possible future failure, etc!

In one of your pic's it appears the old head gasket was starting to leak at the cyclinder area. I would lap the head flat using piece of glass and sandpaper before test re-installing.

I also on my own eq I usually install studs for the exhaust muffler threaded block holes. (this allow two shots when removing, just the nut or the complete stud when removal later. Helps prevent bolt twist off at this area and a stud will hold better than a bolt in this heat/cool area. (use double jam nut on the stud for initial tightening of the stud into the block)

[creia]

Thanks guys for all of the detailed replies- I am TRULY humbled by the support of all of you rallying around my situation and trying to help out. All replies are duly noted and are being taken into consideration- Please keep them coming?! It appears that I have a more serious (and grave) situation than I originally thought that I had.....
Regards,
Michael
Sidebar: Yes, this is our OWN engine (not repairing for a specific customer), however, it would be a candidate for resale after it was fully rebuilt and restored. If I perform a successive "drill-out", I've got a little more than 1" of depth of bolt to drill out. Without a (large) depth drill press, is it even possible to drill this out straight and plumb using only an electric variable speed hand drill?
Thanks again guys!

[creia]

Ah, the sweet feeling of SUCCESS!!
I thought that you all would be interested and appreciate if I posted an "epilogue" to my head bolt story.
After careful consideration of everyone's replies (thank you all again), I was just not comfortable trying to drill a 1" straight hole through the center of a 5/16" head bolt w/o bunging up the sides(threads). At best, I'd probably have to redrill, rethread and heli-coil. I decided to go the welding route that some of you had suggested. I have a local small welding shop guy that's helped us out before, and I thought his idea was pretty ingenious. (He claimed he had done it many times before) I'll let the photos tell the rest of the story.... ENJOY
Regards,
Michael

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