Hints and Tips - Broken Bolts

From: Mike Rambour
Sent: 18 January 2003
To: British-Cars-Pre-War; shop-talk
Subject: Best way to remove broken bolts

Excuse me for posting on the shop talk list about pre-war cars but it is related to shop work.

I need a good way to remove 6 broken bolts/studs in a 34 Singer motor. I removed the oil pan on my car and found that it was only held in by 2 wood screws and 4 bolts as the other 6 bolts were broken in the block. I assume they were studs. 4 of them are broken almost flush with the block, one is going to easier since it is broken slightly inside the hole and the other is sticking out about 1/4" but I am not able to move it with vice-grips.

I bought the car 2 years ago and finally am trying to get it on the road but I am unwilling to reassemble the oil pan with only 4 bolts. The motor is still in place and I can't flip it upside down on a drill press, I don't want to remove the motor and need to be careful of shavings although gravity should take of that for me. I need to drill these out but I never seem to be able to get the drills centered when drilling by hand and end up doing damage to the surrounding area, that will force me to put in helicoils but I am not sure I have the space since this is on the oil pan lip of the motor and only about 1/2 wide, it also looks like a pretty weak area. So drilling out is the only answer I can think of, I have purchased some left-hand drills since I have had good luck with those in the past at working out broken studs as they grab/drill into them but there are small 3/16" bolts, how do I center them ?

The 2 holes where the wood screws were are another issue but I will tackle that one later as bolts still grab some threads and while I can't tighten them will hold a little.

I am open to any ideas, short of removing the motor and doing it on a press, if I go that far I will take the motor apart and rebuild it, that will means months maybe a year before I get the car on the road.


From: J.E.A.Rich
Sent: 19 January 2003
To: Mike Rambour; British-Cars-Pre-War; shop-talk
Subject: Re: Best way to remove broken bolts


The first thing you're going to need is a Dremmel type grinder so that you can grind the broken studs down so that they are below the face of the sump flange. Then you will need a "transfer punch" of the correct size to fit the holes in the flange. Transfer punches are usually sold in sets but as you only need one perhaps you can borrow it? English sizes go up in 64th's of an inch so you will need to measure the exact size of the hole. When you have the correct size transfer punch you can use it to mark the exact centre of the broken stud. Once you've done that, drilling out the broken piece is easy but please wear eye protection when you're lying underneath the car. Although it takes a little longer, I like to start with a small diameter drill and increase its size no more than an eighth of an inch until the job is done. I like your idea of left handed drills, they are sure to help when you are getting close.

Cheers and good luck, "Bob".

From: Dave & Diana Dwyer
Sent: 19 January 2003
To: Mike Rambour; British-Cars-Pre-War
Subject: Re: Best way to remove broken bolts


If you have access to a MIG or TIG welder, try welding the corner of a bit of scrap steel (say 1X1/8) to the protruding bit of the stud.

This does 2 things: the heat helps to loosen the stud in the hole, and the steel gives you a lever to turn.

With luck the remains will screw out and you won't need to worry about swarf near your engine.


Dave Dwyer

From: Mike Rambour
Sent: 21 January 2003
To: British-Cars-Pre-War; shop-talk
Subject: Followup to: Best way to remove broken bolts

Wow, did I get some great responses on this question. THANKS TO ALL who responded and there were a lot of you.

On the one stud that was sticking out about 1/4" I followed the suggestion of welding a nut onto it and sure enough it came loose.

For the one broken below the surface I turned a small bushing on the lathe that fit into the hole and drilled a small hole in that busing while still on the lathe to be sure it was dead center and used it as a guide and drilled the broken stud, I then used the next size up drill bit (LEFT HANDED BIT) and the stud came out as I was drilling the larger hole...

For the other ones that were more or less flush with the block, I welded some locating pins on a piece of 1/8" thick flat steel, I then drilled 2 holes in another piece of steel to match the locating pins and put that piece on top and drilled a small hole through both pieces of steel. I then drilled the same size as the stud hole on the bottom piece of steel and clamped it up against the block. With the hole the same size as the stud I could center it pretty darn good, put the second piece up (that is why the locating pins) and drilled through it using the small hole that I knew was dead center to the bigger hole, I was able to see the stud as I positioned the metal with the large hole well enough that I was close enough to center to not damage the threads on 3 of the 4 studs. On the last stud I think the hole in my guide was getting worn and/or I didn't get centered close enough so I did damage the threads a little.

Overall, I think I will be ok, I will use something like JB Weld in the 2 holes that had wood screws in them and this last hole, all 3 damaged holes have some thread left and I think the JB Weld will fill in the damaged part quite well and I won't torque those down too tight.

THANK YOU for the responses, I would have never thought of making the bushing or welding a nut on, I was surprised at how easy the thing came out after i welded the nut on...awesome idea.

Todays project is get the pan on and put the carbs back on, fuel tank comes back from being cleaned up and repaired on Wednesday, that gives me time to make new fuel lines from the tank to the carbs and then its on to the brakes but i might try running it first just to hear it :) If all goes well another pre-war Singer will be on the road this weekend for a few months. I have been told not to trust 70year old white metal too much, especially since the motor has not run since 1968 so I will pull the motor and go through it properly soon. Oh yeah, have to rewire it too, rats enjoyed the wiring over the years.


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