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Discussion Starter · #1 ·
Hello, all!

I was going to replace my thermostat and housing and the bottom bolt sheared off. While I was using a left hand extractor, the bolt came out, but the bottom of the bolt hole cracked off. Do I need to get a whole new head?
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20210406_202648.jpg 20210406_202648.jpg
 

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D'oh, You Kids!
1984 633CSi, 1985 635CSi, 1985 325e, 1987 325is, 1993 325is, 1995 318is, 1995 M3, 2003 F150
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Welcome to Bimmerfest!

Short answer is yes, unfortunately.

Long answer is you can probably have that welded up and save the head, but it will be expensive, regardless.
 

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Ouch!! :O

Yeah, that can be repaired with a competent tig welder. Check out the fabrication series on you tube, justin is fantastic, and this doesn't look anywhere near as complicated as some of the repairs he has done. At least you can gather an idea as to what needs to be done to repair this.

It probably won't be as much as a used head, and will require finishing at a machine shop if the welder isn't set up to provide a finished surface to mate the t-stat housing, but if you sent it in as a core you would not get your full refund, if any, because of the damage.

Lmk, though, as I do have a head if you need one. It would need reconditioning.



df
 

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Discussion Starter · #5 ·
Ouch!! :O

Yeah, that can be repaired with a competent tig welder. Check out the fabrication series on you tube, justin is fantastic, and this doesn't look anywhere near as complicated as some of the repairs he has done. At least you can gather an idea as to what needs to be done to repair this.

It probably won't be as much as a used head, and will require finishing at a machine shop if the welder isn't set up to provide a finished surface to mate the t-stat housing, but if you sent it in as a core you would not get your full refund, if any, because of the damage.

Lmk, though, as I do have a head if you need one. It would need reconditioning.



df
I'm really hoping I don't need the full replacement, because that'll just lead to me putting in the baddest cams, valves, and everything else I can find into it (and it also might lead to my wife killing me when she sees the bill)
 

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Discussion Starter · #6 ·
So, here's the update: had a welder fix the head, bought new bolts, anti-seize and went to install the housing. I cleaned everything and made sure(using a digital microscope) that there were no burrs and no damage to the threads. Another bolt head snapped off on top of the housing this time. I was using a digital torque wrench, and I did everything I was supposed to do. Why does this keep happening? I spent the extra on the OEM bolts! I am not happy.
 

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Discussion Starter · #7 ·
Nuclear option is a new head and all new parts. I'm eventually going to supercharge this engine anyway, so should I just go with a stock head, or are there better, higher performance options out there?
 

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in order to snap the bolts, one of 3 conditions needs to be met.

1, crossthreaded. this usually occurs when a bolt is installed and tightened down to spec before the other bolts have been installed.

2, bottomed out on a blind hole. this occurs if the bolt is too long or there is debris in the hole. also if too much material, such as antisieze, rtv, or thread lock are applied and essentially hydro lock the hole, creating the same conditions as a bottomed out fastener.

3, over torqued fastener. this can occur on ant threaded hole when too much force is applied to the bolt.


so where did the bolt break, threads, shank, or the head??

were all of the fasteners installed and hand tightened to ensure no crossed threads??

were all of the hoels cleaned?? how much antisieze was applied?? these are tiny holes, and as such usually take a stronger fastener. normal is 8.8, but grades 10, 12, and 14 (.something) are often used on the skinny bolts. even still, physics is physics and just a thin coating is sufficient to do the job.

lastly, was it the same bolt that broke before??

pics are always helpful, and j know it's frustrating, but the good news is that the fastener usually always comes out easily except when cross threaded.



df
 

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Discussion Starter · #10 ·
in order to snap the bolts, one of 3 conditions needs to be met.

1, crossthreaded. this usually occurs when a bolt is installed and tightened down to spec before the other bolts have been installed.

2, bottomed out on a blind hole. this occurs if the bolt is too long or there is debris in the hole. also if too much material, such as antisieze, rtv, or thread lock are applied and essentially hydro lock the hole, creating the same conditions as a bottomed out fastener.

3, over torqued fastener. this can occur on ant threaded hole when too much force is applied to the bolt.


so where did the bolt break, threads, shank, or the head??

were all of the fasteners installed and hand tightened to ensure no crossed threads??

were all of the hoels cleaned?? how much antisieze was applied?? these are tiny holes, and as such usually take a stronger fastener. normal is 8.8, but grades 10, 12, and 14 (.something) are often used on the skinny bolts. even still, physics is physics and just a thin coating is sufficient to do the job.

lastly, was it the same bolt that broke before??

pics are always helpful, and j know it's frustrating, but the good news is that the fastener usually always comes out easily except when cross threaded.



df
I cleaned and inspected each hole, including g the use of a digital microscope, looking for damage. The anti-seize was applied at a minimum, after following multiple recommendations from numerous sources. They were brand new OEM bolts. All bolts were hand tightened and torque wrench tightened in a crossing pattern. A brand new (and calibrated) torque wrench was used. This is a different bolt than the last one. I will say, this bolt broke in the exact same place as the last one, like the bolt is too long is how it feels. Still, the bolt shouldn't be snapping off with that little force applied to it.
 

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Discussion Starter · #12 ·
Are you using a plastic or aluminum thermostat housing?
Aluminum
Are you using a plastic or aluminum thermostat housing?
what torque value were you applying?? 89 inch pounds isn't a lot, it's like 7, 8 ft pounds??


df
Both manuals I have call for 10ftlbs of torque. Could it be bottoming out? Is the plastic housing thicker than an aluminum one? I still can't believe that 10ftlbs would snap a bolt like that.
 

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ok, yeah, 10lb ft wouldn't snap the bolt, at least not unless maybe it is bottoming out.

did you get the broken bolt out??

i would thread the bolts in and tighten them down until they bottom out without the housing. measure the distance sticking out for each bolt and compare that with the thickness of the aluminum housing. shorter bolts or washers may take up the space, if any, to fasten the head.


df
 

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Discussion Starter · #14 ·
Here's the update: All broken bolts extracted, looked up the torque specs in Newton Meters and they are slightly different than the Haynes Manual. Everything is installed. Thank you, everyone for the help. I have one more question, something that's really bothering me. The old thermostat did not have an arrow stamped on it, the new one does, and I can't remember if I aligned it when I installed it. Is this a big deal? Should I take it out to make sure?
 
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