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2008 Mazda 6 Motor Mount Stud spinning

I changed my right motor mount yesterday and when I was torquing the bolts, one of the nuts on the stud would not torque. It just kept spinning. When trying to remove the nut, it came half way off and then the stud started to spin out as well. I then screwed the stud with an allen key then tried torquing the nut again. Unfortunately the same thing happen. The mount seems solid and does not move but I’m not sure if it’s safe to keep driving around now. Has this happened to anyone? If so, how did you fix it? Any advice would be appreciated.

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does stud have a small hex head? common to see that where the stud can be unscrewed from mount body. hold stud and turn nut.

Thank you for the reply. Yes, the stud has a hex head. That’s what I used to screw the stud back in when it came off. By holding the stud with an allen key, how will I be able to torque it? Or should I just wing the tightening?

You need to examine the threads on the nut, stud and where the stud screws into the block. One of them is damaged and should be replaced. If it’s the block, it becomes more difficult but not impossible.

BTW what torque value are you trying to achieve?

I looked at the threads when the stud came off and everything looked good. If it is the block, do you think I would have to tap it with a larger bot size?

The torque is 76 ft/lbs per the repair manual.

If the female threads in the block are damaged, you might have a few options . . .

use a thread chaser to clean up the threads . . . this might work, depending on if the threads are merely “rough” or it might not work, if they’re heavily damaged

install a heli-coil, time-sert, or something to that effect. Depending on access and your bravery level, this might be a good choice

Big question . . . is the block aluminum alloy?

If so, I’m kind of leaning towards the female threads being stripped out

I took out the stud and at the end of it it seemed clean but had left over aluminium all over it. So I assume that the surface it screws to is aluminum. Guessing the next step is to use something like Helicoil. Or is there something else someone can suggest?

The stud is way harder than any aluminum. Harder than cast iron as well but if you see silver flakes, you are screwing into aluminum. You will need a heli-coil kit for the stud diameter and thread pitch. This kit usually contains a drill, a heli-coil tap and a insert tool. Not difficult, just take your time.

Apply JB Weld to the threads of the stud,

screw the stud back in, let the JB-Weld set, and tighten the nut.

How many times do you think you’re going to have to remove that stud from the engine block in the future?

Tester

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heli-coil and time-sert are both reputable

The next step is to figure out what size the stud is . . . for example M10 x 1.5

And then buy the appropriate kit, as @Mustangman said

it goes without saying you’ll have to chase the stud before reusing it . . . even if it appears to be clean, there may be more aluminum shavings on it than you initially suspected

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If the stud is coming out just by twisting on the nut, the nut/stud interface seems like it would have to be damaged or corroded. What I’d do first is just replace both the stud and nut with a new parts, vacuuming out any debris from the hole first. I’d probably put some thread lock (the non-permanent type) on the stud’s thread. If that didn’t work you still have the options above at your disposal.

The stud is a m12 x 1.75. I tried looking online and it is at the earliest a 2 week wait for me which would not work. Guess getting a helicoil is the next step or should I try the jb method mentioned above?

on a 11 year old car, I’d do the JB Weld.

Get some Brake clean and clean the hole and stud, they need to be free of oil, grease.

The stud screws into mount. It bottoms out. Nut goes on same way. As you tighten nut it in turn tries to tighten stud. If nut keeps turning than the stud is stripped. You only use hex to hold stud when you try to loosen the nut. You can replace stud with any threaded rod. You can almost for sure remove mount that is bolted to block if it is damaged.

2 week wait for what . . . ?!

Yea guys looks like I’m screwed. I took out the motor mount bracket to check out where the stud screws into. It was cracked. Don’t understand how it could have cracked since I was following all the torque guidelines.
Now I really don’t know where to go from here. The car is over 11 years so last time I checked it was worth less than 2k. I’m assuming bringing it to a shop could cost more than half the price of the car. The part where the stud screws into is part of the engine block itself. It is just to screw in the stud but idk.
Is there anything I could do it myself?
The other stud for the motor mount bracket is holding strong per torque guidelines.

I’d take a metal plate of the right size with two holes so it sits flat on the engine block,

Clean the surfaces, apply JB Weld on the engine block surface and slide the plate over the studs onto the engine block. Let the JB Weld set, install the motor mount.

Tester.

What type of metal plate are you speaking about? By that I mean what thickness. And what purpose would the metal plate have? Only asking as I assume the stud would still need to screw into the broken mount surface for it to have a strength purpose. Or am I wrong?

A metal plate of 12 gauge. .125 thick.

That metal plate will reinforce the cracked mounting boss as it’s called.

JB Weld the stud into the hole. Just make sure the top of the metal plate is clean so the motor mount will lay flat.

That repair will last until the vehicle goes to the bone yard.

Sometimes you have to think outside of the box wrench.

Tester

I will definitely give it try. Homedepot is closed at the moment so it will be done tomorrow morning. I have jb weld at my place. Should I do the stud part right now?