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Broken head bolt

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1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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greg850r
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Broken head bolt

Post by greg850r » Tue Jun 12, 2018 11:42 am

Anybody have any luck getting the last 1 1/4 inch of threads out when a head bolt breaks off in the block?


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Re: Broken head bolt

Post by RickHaleParker » Tue Jun 12, 2018 3:33 pm

I got one out of a 2.9L that broke off flush with the bottom of the well.

1. Flooded the bottom of the well with Liquid Wrench and let it soak for days.
2. In the mean time, I made a drill guide that fits the well and a little taller then the well is deep so it could be pulled out of the well.
3. With the drill guide in the well, I used a left hand drill bit to back out the broken part.

The drill guide keep the bit on center and after the long soak, the bolt turned as soon as the drill bit started to bite.

If you do the math right and the bolt does not back out. The guide will keep the cutting true and the bit will just kiss the tip of the hole threads. After the cut, chase the threads with a tap to remove the remaining material.


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Re: Broken head bolt

Post by SuperHerman » Tue Jun 12, 2018 3:54 pm

RickHaleParker's recommendations are solid and a very prudent approach.

Usually once the head is off the pressure on the bolt is relieved and they come out rather easy. But, sometimes they are stuck pretty good with grunge. What do the other head bolts look like, specifically the ones closest to the one which broke? Did all the others come out with minimal force once the first turn or two was accomplished?

I would be hesitant to do anything other than what was suggested as you need to maintain the ability to drill straight and true. Maybe trying a needle nose vice-grip if you have the clearance would be worth a go as you will just mess up the sides, but do not mar the block surface.

Do you have enough exposed threads and clearance to try using two nuts and then backing it off without even drilling?

Post a picture and it will help with suggestions.



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Re: Broken head bolt

Post by greg850r » Tue Jun 12, 2018 4:40 pm

The bare block has a larger hole halfway down and the second half of the hole is threaded and smaller diameter. It is broken off exactly where the threads end and only the tip of the bolt is still in there. Laid side by side with a whole one and the last 1 1/4" of threads are missing. I like the idea of a guide and was already thinking that. The LH bit I did not think of, so I'm off to buy one. A pic won't show much, I'm afraid, as it is an inch and a half down before the bolt is broken off flush with the top of the threads. Every one of them sounded like it was breaking, we used a floor jack handle to extend the 1/2" breaker bar. Once broken loose, however, they all backed out with a Milwaukee electric nut driver I wouldn't trust to tighten a lug nut, so not much force required. Hopefully with the stress removed and break free soaking it will come right out. My EZ-outs are too short for this if it won't, although I'm sure they make longer ones.


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Re: Broken head bolt

Post by RickHaleParker » Tue Jun 12, 2018 5:47 pm

It is broken off exactly where the threads end and only the tip of the bolt is still in there.

Exact same conditions as the 2.9 I did. I my case we did not break the head bolt. By the color of the break we could tell it was broken long before I got the car. If a break is fresh, the break will be shiny. If the break is dark, it has been that way for some time. I suspect a previous owner of the 2.9 had reused the head bolts, by doing so stretched them twice, which is a no no.


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Re: Broken head bolt

Post by WhatAmIDoing » Tue Jun 12, 2018 9:10 pm

I personally would pay a machine shop or engine rebuilder to remove the broken bolt. The price might suck, but the job will be done quickly and you won't be liable for damage to the head resulting from removing the broken bolt. However, if you are skilled and confident in your abilities, then go for it.


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Re: Broken head bolt

Post by abscate » Wed Jun 13, 2018 5:06 am

That’s an expensive tow for a simple operation.


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Re: Broken head bolt

Post by greg850r » Wed Jun 13, 2018 5:19 am

The head is off, so the only thing I can damage would be the threads in the block, which do not come all the way to the top. Only the bottom half of the hole is threaded. The entire threaded surface of the block at the bottom is still filled with the piece of bolt that's left in there, so it broke on us. Had it already been broken, the rest of the bolt would have been free sitting there and pulled straight out without turning.

The top 1 1/2" of the hole is .55" in diameter and does not contact the bolt at all, hence the ability to use a guide to keep the bit in the middle easily. If I don't find something suitable I'll have a friend who machines his own rifle barrels make me one. 5.5" OD x 3/8" ID x 2" long should be an easy thing to make and then can be a loaner tool or I'll have it for the next time. Given the way these sound when you break them loose it will happen again someday.

I dropped the frame and am going to use it, the short block, transmission and steering in another car I had previously put a fresh head on only to find it leaking antifreeze out the block behind the water pump. Doing it myself will save me tearing it down any further, and it should be easy because I'm building this thing on the floor and then installing it from the bottom as a finished motor.


99 C70 Convertible
96 850 R wagon
96 850T wagon
95 850 5spd N/A sedan
95 850 5spd N/A wagon -sold
66 GTO 421 4spd
67 GTO 455 T400
02 Powerstroke 4x4
85 Yota 4x4
24' 454 Challenger
07 Softail Custom
02 Sportster Custom
Parts cars that come and go

RickHaleParker
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Re: Broken head bolt

Post by RickHaleParker » Wed Jun 13, 2018 7:00 am

I'll have a friend who machines his own rifle barrels make me one.

That is good, he has the tools to work with real hard metals. He could make a guide the drill bit will not wear out quickly.


1997 S90, B6304S, AW30-42
1998 C70, B5234T3, AW50-42

RickHaleParker
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Re: Broken head bolt

Post by RickHaleParker » Wed Jun 13, 2018 7:18 am

That’s an expensive tow for a simple operation.

I assume you meant tool. For a one off, you can sleeve the left hand drill bit with a rubber hose then turn the diameter of the hose down with sandpaper. However if the bolt does not start backing out, I recommend one call it quits and not use this rubber guide to cut the bolt.


1997 S90, B6304S, AW30-42
1998 C70, B5234T3, AW50-42

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