Broken Bolt Plan of Attack - PeachParts Mercedes-Benz Forum

Bimmer-Bob · #1 06-11-2017, 01:20 PM

If you're following my VP thread, you already know this, but I wanted to get more eyes on this topic before I proceed.

I recently snapped one of the 10mm bolts that hold the vacuum pump to the timing case. I continued putting everything back together, hoping the other five bolts would create a good enough seal, but of course it leaked. Got everything taken apart again and this is what I'm faced with:

Broken Bolt Plan of Attack-broken-bolt.jpg

Not enough thread sticking out to grab on to with vice grips (or anything else). I don't relish the thought of trying to drill out such a small bolt, but I don't see what other option I have. My tentative plan is as follows - please let me know if you think it is sound, or if there is anything else I should be thinking about:

1) First, gonna take a Dremel and grind the bolt as flat as possible (I don't own a rotary tool yet - this is a great excuse to get one - but do I need to be looking for any specific accessory or attachment, or will the standard kit work?).

2) Next, gonna take an automatic center punch to mark the center as close as I can.

3) Next, right-angle drill with good-quality left-handed bits. Probably start out as small as possible, 1/16th - I don't think I'll be able to go up much from there, if at all, without hitting threads. Hopefully, the left-handed bit is enough to grab and spin out the bolt. It was recently removed, so at least I know it's not seized or rusted in. I want to drill slowly, right?

I know this isn't rocket science, but I just want to get some feedback before I do this. I'm going to work slow and deliberately, but I feel like I'm only going to have one shot at this before I screw it up, and end up having to drill out a bigger hole and use HeliCoils or something.

Thoughts?

ROLLGUY · #2 06-11-2017, 01:37 PM

I would not use a tiny drill bit, you risk breaking it. Then you will have to find a way to get the hardened bit out first. I suggest using a little heat (propane torch?). After you get a decent hole for an easy-out, apply the heat while using the easy-out.
If you are really ambitious, you can find a machine shop that can make a drilling fixture out of an old vac pump casting for you. Have them mill the hole to fit a drill bushing (3/16 is close to the size needed) snugly. I have done this with the water pump housing on a 617. I had the shop precision drill an old water pump to fit the bushings into. I can now drill out the seized screws in the casting using a 3/16 bit.
Water pump housing broken bolt repair fixture
EDIT: looking back at the photo, you could use the VP as a guide (take measurements from) to machine a fixture that bolts to either side of the offending bolt hole, with the drill bushing in the middle.

OM617YOTA · #3 06-11-2017, 01:45 PM

Know anyone who tig welds? A skilled operator with a little 120v(read: portable) machine could weld a nut onto that without much trouble. Paying a pro to come do it would probably be costly.

I've had almost zero luck with "easy outs". Part of the way they work is by applying outward pressure, which seems to generally get things stuck even worse. I've had much better luck cutting a slot and using a straight blade screwdriver. Even if you have to cut into the block a bit, you have enough space to do so without causing further damage.

Mxfrank · #4 06-11-2017, 03:38 PM

Tell you what I'd do. And I know I'll be yelled at. I'd put a light bead of formagasket on the mating surfaces, tighten the other nuts, and call it a day. There's no pressure there, it should be fine.

ROLLGUY · #5 06-11-2017, 04:31 PM

Quote:

Originally Posted by Mxfrank

Tell you what I'd do. And I know I'll be yelled at. I'd put a light bead of formagasket on the mating surfaces, tighten the other nuts, and call it a day. There's no pressure there, it should be fine.

I thought of that too, but did not want to be the first one to suggest it

ykobayashi · #6 06-11-2017, 05:27 PM

Quote:

Originally Posted by OM617YOTA

I've had much better luck cutting a slot and using a straight blade screwdriver. Even if you have to cut into the block a bit, you have enough space to do so without causing further damage.

What I was going to say. I use a dremel with a cut off wheel to do it. Penetrant and heat to make sure it comes out without much force. Edit - oh yeah, and do not get cutting disk dust into your engine.

I broke off an easy out once. I forgot what I did after that. I try to block out traumatic stuff like that. I don't think it ended well and hence I blocked out the memory. If you think drilling out a broken bit is tough try drilling out an easy out.

vonsmog · #7 06-11-2017, 05:33 PM

If its at least a 8mm bolt I would try welding a nut on it first, most times the heat from welding will allow it to turn right out, if that does not work, them grind flat and drill with the left handed bit. I like to start small and work up to a size where there is nothing but the threads left, most times it will spin right out when the hole gets that big. Then run a tap thru to clean the threads and you will be good to go! The key is to take your time when drilling, so as not to break off the drill bit.

Bimmer-Bob · #8 06-11-2017, 05:51 PM

Quote:

Originally Posted by vonsmog

If its at least a 8mm bolt I would try welding a nut on it first, most times the heat from welding will allow it to turn right out, if that does not work, them grind flat and drill with the left handed bit. I like to start small and work up to a size where there is nothing but the threads left, most times it will spin right out when the hole gets that big. Then run a tap thru to clean the threads and you will be good to go! The key is to take your time when drilling, so as not to break off the drill bit.

The bolt head was 10mm. The threads are about 5mm at max diameter.

Bimmer-Bob · #9 06-11-2017, 05:58 PM

Quote:

Originally Posted by Mxfrank

Tell you what I'd do. And I know I'll be yelled at. I'd put a light bead of formagasket on the mating surfaces, tighten the other nuts, and call it a day. There's no pressure there, it should be fine.

Not a bad idea, if all else fails. I've never used this stuff - d0 you know the differences between the varieties (No. 1-3)? Also, will they make future removal of the VP more difficult? Gonna be in here again for IP work.

Dubyagee · #10 06-11-2017, 06:28 PM

Anaerobic Flange Sealant. Cures to almost a plastic. No globs of RTV floating in the engine.

Mxfrank · #11 06-11-2017, 08:29 PM

There ya go.

BodhiBenz1987 · #12 06-11-2017, 08:52 PM

I would try JB Welding a small nut to it. I don't find JB Weld is ever as strong as it's supposed to be, but without the head on it, I'd think the remainder of the bolt should come out without a lot of force as long as you can get a purchase on it. Would be easier than finding someone good enough at TIG to come over and do that, though that would be much stronger.

OM617YOTA · #13 06-11-2017, 09:06 PM

Tricky on a bolt that size, but on my own engine, I'd rig up a test fixture and practice welding to bolts that size a few times with mig(which I have). Depending on how that went, I may give it a shot on the real deal.

Bimmer-Bob · #14 06-11-2017, 10:01 PM

Quote:

Originally Posted by BodhiBenz1987

I would try JB Welding a small nut to it. I don't find JB Weld is ever as strong as it's supposed to be, but without the head on it, I'd think the remainder of the bolt should come out without a lot of force as long as you can get a purchase on it. Would be easier than finding someone good enough at TIG to come over and do that, though that would be much stronger.

Not a bad thought, and easy enough to try before more risky methods. Worst case I have a little bit of JB Weld to grind off and I'm back at square one.

Quote:

Originally Posted by OM617YOTA

Tricky on a bolt that size, but on my own engine, I'd rig up a test fixture and practice welding to bolts that size a few times with mig(which I have). Depending on how that went, I may give it a shot on the real deal.

I don't weld, but if it does come to drilling, I'm definitely going to practice with the same size bolts in a vise before I tackle the real thing.

Blazemaster · #15 06-11-2017, 10:13 PM

I have a machine shop and get out broken bolts quite a lot. You are going the right route with the left handed drill bits but as someone else mentioned, I wouldn't start with a tiny bit.

You can also try just using a center punch to grab and turn the bolt out.

I am also not too far from you and am a tig welder if you get stuck.

I hate easy outs.