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Author Topic:   snapped bolt
specktrout posted 08-16-2001 11:55 PM ET (US)   Profile for specktrout   Send Email to specktrout  
I have an '89 90hp Johnson on my montauk which I am about to paint. The previous owner had had a large planing plate added to the lower unit (turbo lift). The crossbar holding this in place ran through the space for the zinc anodes and bolted to the hole which used to hold the anodes. In removing this bolt today, it snapped off flush with the surface. Needless to say I was concerned. I don't think this bolt is structually necessary, but the whole point of the project was to clean up the engine as no anodes and increased water turbulence from the fin had really removed a lot of paint. Does anyone have any ideas about what to do now? I figure my options are : 1-take it to a dealer (if I can find one to fix this problem) and spend lots of $$$. 2- try drilling out the bolt with progressively larger drill bits, then re-tap (Can't figure out how to mount the entire 300+ pound engine plus 17ft boat on the drill press) 3- drill a new hole somewhere nearby and attach the anode that way. If both my anodes are still on the transom mount, do I really need to do anything? Thanks for any help.
Tom W Clark posted 08-17-2001 12:38 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

From your description I'm not sure where this bolt is and how large it is but I'm not sure it matters. The broken off bolt can be removed and it can be removed by you if you are patient.

I have recently had quite a bit of experience with sheared off stainless steel fasteners in aluminum castings. I've been working on an old ('65) OMC sterndrive on one of my boats and after 13 years in a barn many of the fasteners were seized up do to corrosion.

The four keys to success here are: penetrating oil, a screw extractor, time, and heat.

If you have snapped the screw or bolt off flush as you say then you will have to use a screw extractor like an EZ out. These can be had at your local hardware store for a few bucks.

Use the appropriate sized drill for the extractor you've bought and drill into the shank of the broken fastener. This is not as hard as it sounds. The trick is to try and keep it centered. It helps if you use a new, or at least sharp drill bit. It needn't be an exotic bit, just a regular high speed twist drill bit will do, though it may not be too sharp after you're done drilling into stainless steel.

I just use my cordless drill and some oil (WD-40) to drill the hole. It will be very helpful if you can get some WD-40 or some other penetrating oil like "Liquid Wrench" onto the end of the broken fastener and let it soak into the threads. I'm talking overnight or even several days with, perhaps, addition applications of the penetrating oil each day.

With the screw extractor inserted into your hole and turned counter clockwise enough for it to dig in a bit, you are ready to apply heat. I use a propane torch. The idea is to heat the metals up and cause them to expand. You must, of course, be cautious about the heat from the torch but you really need to get it pretty darn hot. Use wet towels as a heat sink if there is something nearby that might burn or melt, but the fastener must get really hot. You are about to paint your motor so don't be upset if the paint darkens or is scorched.

When you are all ready, give the extractor a turn and see if the bolt budges at all. If it does move, even just a bit, you are home free. Maintain a positive frame of mind and you will succeed.

Whalerdan posted 08-17-2001 07:26 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
One more thing I've found. Before you start drilling use a center punch on the broken bolt so your drill doesn't jump around, and you get the hole down the center.
Soho posted 08-17-2001 08:54 AM ET (US)     Profile for Soho  Send Email to Soho     
Great advice and technique. I have "heard" that if you gently "tap" the area where you are applying the pentrating oil that the vibration will help the oil work into the areas you want it to. Obviously this is almost impossible to really and conclusively test, however whenever I tackle this sort of problem I apply the oil and then tap, tap, tap a bit.....

Good luck



Bigshot posted 08-17-2001 09:32 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Honestly I would try but not kill myself over it. You have 4 main bolts on the side and a Big bolt that holds the front. The smaller bolt next to it goes through the anode into the upper. If you broke the main big bolt behind it, that would be critical. The one you broke, basically holds the zinc in. Just my .02 cents.
Tom W Clark posted 08-17-2001 09:59 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
whalerdan makes a good point. You won't be able to keep it centered if you do not use a center punch. If the bolt is broken off a little bit below the surface, you may be able to use a Vix Bit to start the hole on center, but do not use the Vix Bit to drill out the bolt or it will dull the bit quite a lot.

Soho is on the mark too. It's not so much light tapping that allows the penetrating oil to work into the threads but rather a strong blow that helps break that initial bond caused by the corrosion which seizes the bolt. Use a drift punch, or whatever, and strike the end of the broken bolt as hard as you dare.

JimU posted 08-17-2001 09:59 AM ET (US)     Profile for JimU  Send Email to JimU     
Tom Clark's technique is right on target. I've use it many times. It's a piece of cake.
SuburbanBoy posted 08-17-2001 11:40 AM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
Just one more comment...
Some hardware stores will sell "backwards" drill bits. The process of drilling the hole will help to loosen the frozen stub. Additionally, I would suggest a smaller pilot hole, followed by the larger hole.


JDH posted 08-17-2001 01:49 PM ET (US)     Profile for JDH  Send Email to JDH     
'burb Boy is right on:

Use a left handed bit.

Myself I no longer do any of it. My main hobby is old Toyota Land Cruisers (the Boston Whaler is the TLC of boats ;p) and I tought myself MIG welding. ANything breaks off, I just take a nut with an ID a little smaller than the OD of the stub and zap it on. The heat usually loosens it enought that I can back the stub out with my fingers (after it has cooled). I don't have tri-gas in my tank right now, so if I wanted it out badly enough, I would take it to a marine shop and have them do it for me for a 6 pack....

BTW- the absolute best penetrating oils are Mouse Milk (sold by aircraft supply places and Kroil. WD-40 is for getting label residue off of things and cleaning - it plain old sucks for anything else.
Just my $0.02


GAwhale posted 08-18-2001 12:58 PM ET (US)     Profile for GAwhale  Send Email to GAwhale     
I deal with stuck screws (usually Phillips head) on airplanes almost every day. Tom W. Clark's adivice is right on the money. Patience and a New Drillbit are key. I have never heard of Mouse Milk.

We use a great tool called a Screw Knocker. It is a hardened steel handle that fits in a Rivet Gun. As you apply the rivet gun gently turn the handle counter clock wise. Wear earplugs; it is very loud. If that doesn't work get a sharp EZ Out and sharp drillbit. The correct drillbit size is stamped on the EZ Out.

Penetrating Oil applied a few times and given time to work; and heat can be very helpful.

JDH posted 08-20-2001 01:51 PM ET (US)     Profile for JDH  Send Email to JDH

Also for aircraft guys you can go to:

Do a search for Mouse Milk.

Surprised you have't heard of it.


lhg posted 08-20-2001 02:18 PM ET (US)     Profile for lhg    
Sears has some kind of a new "screw extractor" tool they are advertizing lately for $20, that fits into a power drill.
whalerron posted 08-20-2001 11:32 PM ET (US)     Profile for whalerron  Send Email to whalerron     
If you decide to drill it out yourself, try using cobalt drill bits. They work very well in stainless steel and they are still sharp when the job is done. Use a center punch to center the drill bits and start with the smallest bit you can get. Keep increasing the size of the bit until you are almost to the bolt threads. Then, with a little patience and an ice pick, you can pick whats left of the bolt out of the threads. When you are done, you don't even need to retap the hole. I have done this many times and although it does take awhile, it always works.

- ron

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