88v8 Ivor Duarte Gloucestershire UK (1041 posts) Registered: 02/11/2010 04:29AM Main British Car: 1974 Land Rover Lightweight V8 |
Broken bolts in alloy
You know how it is. A simple job, ten minutes.
Going to change the thermostat. Four bolts into the alloy housing. Gently with the spanner. Ping! Head gone. Try another one. Ping! Arrrgh. So now, out with the blowlamp, MAP blowlamp, and a point & shoot thermometer so I can see when things are hotting up. Next one comes out, hooray. UNF thread. You'd think Rolls-Royce with all their alloy experience would have known better than to put fine thread into alloy. Last one.... ping! I heated to 170F, maybe not high enough or long enough. So now I have three 5/16" seized stubs to get out. Reason I'm posting is that this must be a pretty general problem, and I'm hoping you have some cunning plans I haven't thought of. What I intend.: Plusgas, leave a day. File the top flat, not flush but flat. Pop and drill about 7/64". Now cut a small step in the edge, and use that as a point of purchase so I can rotate it out by tapping tangentially with a blunt chisel. Heating meanwhile. If that fails, Plusgas, leave a day. Then use the hole as a point to inject plumber's freeze spray, so I'm heating the alloy housing, and cooling the stub, then tap it some more. This sounds easy, but judging the boundary between heat and cold is hit and miss, and if I overcool the stub it could shatter. If all else fails, drill it out some more and use Easy-outs, surely the most misnamed tool of all time. I have doubts about this, as in my experience it's hard to get an accurate centring when working freehand, and anyway, the Easyouts have a tendency to snap in the hole. Other than not having started the job in the first place, any magic ideas? Don't have a welder. I could also use magic for my Rover V8, where some of the water pump bolts are going to snap off if I ever try to disturb them. Alloy engines, don't you love them. Ivor |
ex-tyke Graham Creswick Chatham, Ontario, Canada (1165 posts) Registered: 10/25/2007 11:17AM Main British Car: 1976 MGB Ford 302 |
Re: Broken bolts in alloy
Bolts should have had high heat before removal attempt.
If all else fails, I'd drill out the remaining studs and retap with NC threads (even if you have to use helicoils to repair a damaged area) Bottom line is that the housing can be salvaged. |
BlownMGB-V8 Jim Blackwood 9406 Gunpowder Rd., Florence, KY 41042 (6470 posts) Registered: 10/23/2007 12:59PM Main British Car: 1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS |
Re: Broken bolts in alloy
It's not easy but can be did. Aluminum melts at around 1200° F so you can heat it up to around 900 without worrying too much. If you can deposit some carbon on it (yellow flame of any type) you can heat until that burns off and that's about right. At that temp your bolts should turn out easily.
Jim |
DiDueColpi Fred Key West coast - Canada (1365 posts) Registered: 05/14/2010 03:06AM Main British Car: I really thought that I'd be an action figure by now! |
Re: Broken bolts in alloy
Here's what usually works for me Ivor.
Before you even try to remove a suspected stuck bolt, give it a couple of good raps with a hammer. (only if the piece can handle it of course) This is to shock the bond between the two parts and hopefully free them up. Next is to soak the area in rust penetrant and let it sit. A couple more shots from the hammer to help the penetrant wick into the joint is also helpfull. If you can, use an impact driver with a suitable socket to loosen the bolt. The idea here is to use a socket that rests on the mating area or flange and briefly compresses the joint while you attempt to loosen it. Once the bolt starts to move, work it back and forth to slowly remove it a bit at a time. Patience is the key here. If the bolt has broken off. Resist the urge to weld a nut to it. While this does work very well in some cases, if it doesn't you are left with a broken / hardened bolt that is extremely difficult to drill out. File the bolt flat. Center punch it and drill an 1/8th inch hole all the way through it. Now you can try heat. Heat the bolt only, as hot as you dare. Use drops of engine oil on the surrounding metal to check temp. If they smoke and burn off rapidly then you are as hot as needed with aluminium. What you are trying to do is expand the bolt. Once it cools and contracts it will hopefully have broken the bond enough to come free. Next fill the hole with penetrating oil and start drilling the hole larger in small increments until you are as close to the thread size as you can get. Drilling in small steps lets you correct for off center as you go. Now you can use the largest bolt extractor that will fit. Be careful because a broken off extractor is a whole new kind of misery. If the extractor doesn't provide any joy, grab your Dremmel or die grinder and carefully grind away until you expose the root of the threads. With a pointed punch carefully chip away at the remaining threads. Once done chase it with the appropriate thread chaser and your good to go. It's a bit tedious but you are left with an original part and the original threads. If it all goes to hell in a hand basket, a helicoil is a perfectly good option in most cases. Just make sure it goes in straight and isn't close enough to an edge or sealing surface to cause problems. Cheers Fred |
Dan B Dan Blackwood South Charleston, WV (1007 posts) Registered: 11/06/2007 01:55PM Main British Car: 1966 TR4A, 1980 TR7 Multiport EFI MegaSquirt on the TR4A. Lexus V8 pl |
Re: Broken bolts in alloy
Fred, I have seen my brother Jim do exactly what you describe. You are right about it being tedious!
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minorv8 Jukka Harkola (269 posts) Registered: 04/08/2009 06:50AM Main British Car: Morris Minor Rover V8 |
Re: Broken bolts in alloy
Quite often it is not the treaded section but the shank of the bolt that gets stuck. I have sometimes simply broken the housing to reveal the sheared bolts or studs. Of course this is not an option it there is no spare available :-)
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waterbucket Philip Waterman England (112 posts) Registered: 07/30/2011 01:08PM Main British Car: 1972 MGB GT |
Re: Broken bolts in alloy
I would go along with what Fred has said but with another variation, I would get a set of left hand drill bits, drill the 1/8 hole as per Fred .If this does not remove the broken stud/bolt, heat and let the penetrating oil soak overnight, then drill one size larger. As you are drilling there is an equal and opposite reaction and the stud will be trying to unscrew. I have used this method several times and it still leaves the option of using a using a stud extractor as a last resort or continuing drilling until the threads show. There is a possibility that if the next drill size is too small an increment then there will be insufficient reaction to undo the stud.
regards Philip |
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88v8 Ivor Duarte Gloucestershire UK (1041 posts) Registered: 02/11/2010 04:29AM Main British Car: 1974 Land Rover Lightweight V8 |
Re: Broken bolts in alloy
Mmm, never had left-hand drills. I ought to buy a set. I'll put them on my shopping list.
Got one bolt out today. Yesterday I levered the stat housing off, even that was corroded onto the bolt stubs and I had to heat it. Then left the bolts - actually, setscrews - soaking in Plusgas overnight. Today, out with a small blowlamp, heated the stub then left it an hour. Then, the MAP blowlamp and heated the alloy housing to about 450F this time, that seems to be as far as I can get with this blowlamp as the alloy inlet manifold leaches the heat away. Was tempted by the length of stub, so I put a good Mole wrench on it and still heating, very carefully started to turn it out. After a couple of minutes heating and twiddling, out it came. To get at the back pair of stubs I need to remove the stat - guess what, it's stuck fast grrr. I heated it and the housing until the fusible plugs melted, and levered at it, but it's still stuck. More Plusgas. Tomorrow is another day. Ivor |
Re: Broken bolts in alloy
I keep searching the 'net for a suggestion about using electrolysis to treat the corrosion of the threads. My thinking is that it might be possible to reverse the chemical reaction at least a bit. Nothing definitive yet. I'm just not sure which part should be the anode and cathode.
Edit: Try attaching the negative side of a D cell battery to the steel bolt and the positive side to the aluminum. Edited 1 time(s). Last edit at 02/19/2016 08:44PM by pcmenten. |
roverman Art Gertz Winchester, CA. (3188 posts) Registered: 04/24/2009 11:02AM Main British Car: 74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L |
Re: Broken bolts in alloy
So as you drill, ever larger with your LH. bits, it is also relieving "some" pressure. If you select the right interference fit, LH bit, you "might" tap it in the hole and use it as an extractor. For extractors, I like Proto Blackhawk/etc.,(4 flute with aggressive positive rake) on the flutes. These grab better than the spiral types. Consider replacing bolts/studs with stainless ? Cheers, roverman.
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88v8 Ivor Duarte Gloucestershire UK (1041 posts) Registered: 02/11/2010 04:29AM Main British Car: 1974 Land Rover Lightweight V8 |
Re: Broken bolts in alloy
Got them all out by the same method. Lots of heat.
The stat itself was so stuck that I not only had to heat the housing, but at the same time spray the stat with plumber's CO2 spray. The three larger bolts - 5/16" - the UNF threads in the alloy housing were OK, but the smaller bolt - 1/4" - the thread was part stripped so I drilled right through the housing and made a much longer thread. On replacement, I put Hylomar Blue on the bolt threads to try and seal them against damp. All well now. Many thanks for all the advice. Ivor |
Beau Dirt Beau Dirt Minneapolis, MN (35 posts) Registered: 05/02/2012 03:23AM Main British Car: 1973 Morris Mini, 1930 ford Model T, 1926 Model T 1 liter Suzuki and Four 215's |
Re: Broken bolts in alloy
I had this problem. I grabbed a hand full of nuts about the same size hole as the bolt. Hold the nut up to the busted bolt head and weld the nut on to the broken bolt. The heat from the weld helps heat up the bolt and you have something to put the wrench on.
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