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Old 03-11-2015, 08:42 PM   #1
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Default Broken Crankshaft Bolt?

Is getting a new crankshaft the only way to fix this? The other half is in the crankshaft.

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Old 03-11-2015, 09:01 PM   #2
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If you can use and easy out, you might be able to pull the remainder out. It shouldn't be that tight.

Biggest problem is getting a drill in there without pulling the front of the car apart.
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Old 03-11-2015, 09:16 PM   #3
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I have no problem taking the radiator and sway bar out to get a drill in there if it means not removing the engine. The bolt was in there pretty damn tight though. You think a lot of PB blaster, heat, drilling and using an easy out would work?
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Old 03-11-2015, 09:20 PM   #4
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You gotta try. The alternative is new crank, and that involves pulling the engine. Not any other choice.

Take your time. Rushing may snap off a drill, or worse, the easy out. Then you're screwed.
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Old 03-11-2015, 10:10 PM   #5
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If the bolt broke taking it out then you are going to have a hell of a time. You might need to fully drill out the bolt.

If it broke tightening it then you're gonna have an easier time.
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Old 03-11-2015, 10:17 PM   #6
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Centerpunch, drill, apply heat, and use an extractor. Nothing to lose.

Just tore a core down with the crank bolt torqued to ~200ft.lbs and half a dozen things RTV'd when they shouldn't be. I hate bad mechanics.
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Old 03-11-2015, 11:31 PM   #7
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Buy left hand drill bits, center punch it exactly in the middle (take your time) and then start drilling it out. if you do it right, you can drill it out until it's basically a bolt with a hole in it so bit, there is hardly any bolt LEFT, mostly just the threads. With a left hand bit it will grab and back the bolt out when it gets loose enough vs a right hand bit that will grab and thread it in farther.

Or break an extractor off in it, I know they work sometimes, but I've never had great luck with them. If you go this route, but a badass/name brand extractor, and again drill it out as big as possible to get the largest size extractor possible in there (bolt is weaker, less likely to break a bigger extractor too).

Good luck! Left hand bits have always worked in my experience, FWIW.
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Old 03-12-2015, 03:35 AM   #8
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I'm going to vote machine shop. Yes, you can do all the above, but if you have to ask, it might not be the best idea. Stack the odds in your favor.
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Old 03-12-2015, 04:50 AM   #9
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Quote:
Originally Posted by PatCleary View Post
I'm going to vote machine shop. Yes, you can do all the above, but if you have to ask, it might not be the best idea. Stack the odds in your favor.
What, are they going to mount the whole car on the mill?

Generally I agree on the "take it to the machine shop" approach, but considering how much of a PITA it is to take the crankshaft out this is probably one place I'd try the home remedies first.

--Ian
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Old 03-12-2015, 01:27 PM   #10
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If he takes it to a machine shop, he's gotta pull the engine. Might as well try it himself, just be careful/don't ruin the crank in the process. If he fails, he's still either taking it to a machine shop, or getting a new crank/engine. So not much risk at this point considering the other "option" is time/money intense.
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Old 03-13-2015, 01:23 PM   #11
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Quote:
Originally Posted by patsmx5 View Post
Buy left hand drill bits, center punch it exactly in the middle (take your time) and then start drilling it out. if you do it right, you can drill it out until it's basically a bolt with a hole in it so bit, there is hardly any bolt LEFT, mostly just the threads. With a left hand bit it will grab and back the bolt out when it gets loose enough vs a right hand bit that will grab and thread it in farther.

Or break an extractor off in it, I know they work sometimes, but I've never had great luck with them. If you go this route, but a badass/name brand extractor, and again drill it out as big as possible to get the largest size extractor possible in there (bolt is weaker, less likely to break a bigger extractor too).

Good luck! Left hand bits have always worked in my experience, FWIW.
Extractors work almost 100% of the time if you broke the bolt off tightening it (unless it broke because it bottomed out), extractors work about 10% of the time if you broke it trying to loosen the bolt.

If you were loosening and broke it, drill it out from the center in increasing sized drill bits till there's not much bolt left and you might get it out with an extractor and heat, at least then if you do break the extractor off you can normally pry it out with a screw driver then your best option is to keep drilling until you get to the drill bit the same size as the minor diameter and then you should be able to pick the threads out and clean it up with a tap. If you drilled this off center like at all you're probably buying a new crank.

IMO if you broke this tightening and it wasnt from bottoming try it yourself, if you were loosening I'd probably bring it to a machine shop.
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Old 03-13-2015, 01:37 PM   #12
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Originally Posted by Cococarbine View Post
The bolt was in there pretty damn tight though.
Bolts are tight because we stretch the shank, pulling against the head of the bolt on one side, and the threads on the other. By breaking the head off like you did, you released all tension.

If the bolt threaded in easily by hand, theoretically (if you could grab it) it'll thread out just as easily. Again, use a left hand drill. However I'm guessing you distorted the threads (hopefully of the bolt, not the crank) by over torquing, or bottomed out on something, like oil, debris, old locktite, etc.
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Old 04-10-2015, 01:07 AM   #13
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The bolt extractor didn't work, so I ended up getting a used crankshaft and putting it in. I used the new bolt I got to turn the crank over while building it. I didn't know this, but it turns out if you don't use the pulley boss as a spacer, the crankshaft bolt will hit the bottom of the tapered bolt hole, mashing the threads at the end of the bolt, making it near impossible to get it back out. I had to get a 14x1.5 tap and die to rethread both the new crank and bolt. Lesson learned, and I think that was what happened the first time and why I couldn't get it out. All's running well now.

I did install a new Flyin' Miata clutch while it was out, so there is a silver lining. Just have to figure out to adjust it because it barely disengages with the pedal to the floor.
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Old 04-10-2015, 02:24 AM   #14
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Quote:
Originally Posted by Cococarbine View Post
The bolt extractor didn't work, so I ended up getting a used crankshaft and putting it in. I used the new bolt I got to turn the crank over while building it. I didn't know this, but it turns out if you don't use the pulley boss as a spacer, the crankshaft bolt will hit the bottom of the tapered bolt hole, mashing the threads at the end of the bolt, making it near impossible to get it back out. I had to get a 14x1.5 tap and die to rethread both the new crank and bolt. Lesson learned, and I think that was what happened the first time and why I couldn't get it out. All's running well now.

I did install a new Flyin' Miata clutch while it was out, so there is a silver lining. Just have to figure out to adjust it because it barely disengages with the pedal to the floor.
Glad it's fixed.

Before you did all that, did you try left hand drill bit?
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