Always replace those 10mm crankshaft pulley bolts after 60,000 miles or timing belt. - Miata Turbo Forum - Boost cars, acquire cats.

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Old 11-26-2010, 10:56 PM   #1
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Default Always replace those 10mm crankshaft pulley bolts after 60,000 miles or timing belt.

This is second time this has happened. Those 10mm bolts are simply too weak to be reused. I thought I had learned my lesson the first time with my 260 rear wheel horsepower 97 Miata. I torque the 10mm crankshaft pulleys to spec, 10,000 miles later...In the boost around maximum torque range, PLING. All four bolts shear...

Well last week, my 2004 Mazdaspeed Miata. Little Enchilada, 59,000 miles, crank shaft pulley removed to elongate timing plate and advance timing 2 degrees, reinstalled, torqued to spec... 10,000 miles later...10PSI right in the torque band climbing up a hill and PLING. All four bolts shear off and i'm on the side of the rode...

I'm lucky that in both circumstances, my crankshaft pulley was okay and I didn't **** anything up. My point is this, those 10mm bolts have never sheared on me in a naturally aspirated miata, but they simply won't hold up and the flanged heads have been known to shear with reuse torque to factory specs. I suppose that the bolts simply stretch and become weakened...

I'll either replace them with 10.9 grade equipment, or I may drill and retap for M8x1.25 hardware....

I honestly wish mazda used a little beefier bolt, not the smallest damn size to serve such a critical function...

That's like me using four 10mm bolts to affix a trailor hitch to my suv...
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Old 11-27-2010, 12:11 AM   #2
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I think you're doing it wrong, end of story.
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Old 11-27-2010, 12:15 AM   #3
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You overtorqued them.
you'redoinitwrong.jpg
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Old 11-27-2010, 12:22 AM   #4
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Those bolts are really shitty. When you over torque them... jk lulz
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Old 11-27-2010, 12:27 AM   #5
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Re-used mine several times. Re-used them on several other people's cars. No issues.

Sorry dude, install error.
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Old 11-27-2010, 01:02 AM   #6
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overtorque is the only way they fail its why i replaced mine with some 10.9 allen bolts they are harder to over torque
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Old 11-27-2010, 01:57 AM   #7
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torqued to 150 inch-lbs, torque wrench out of calibration? I think they get weaker and weaker everytime they are torqued and stretched. I mean were talking a M6x1.25 bolt. I may consider using a hex head, or lock-tite and a lower torque value.
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Old 11-27-2010, 01:59 AM   #8
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I am considering drilling and tapping to use M8x1.25 10.9 hardware.
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Old 11-27-2010, 02:59 AM   #9
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I torque mine "goodntight" by hand and have had the same one in there for a long time. I've snapped one or two during installation from over torquing them. Doesn't take much.
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Old 11-27-2010, 01:51 PM   #10
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In most supercharged set-ups those four bolts hold the supercharger drive pulley. Mine have been on for three years and been through a timing belt change (two years ago) with no trouble.
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Old 11-27-2010, 05:45 PM   #11
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I may try simply using a 1/4 inch ratchet since its pretty dang difficult to over torque... Possibly a 10mm nutdriver.
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Old 11-27-2010, 05:49 PM   #12
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I use the smallest possible ratchet possible when tightening bolts like that. Anything large could snap them at the smallest pressure
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Old 11-30-2010, 06:12 AM   #13
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Blue loc-tite if all else fails..
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Old 11-30-2010, 09:51 AM   #14
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Same has happened to me.

They are **** quality and won't take much abuse considering the job they have to do. For what it costs simply replace with higher spec job done.
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Old 12-04-2010, 04:31 PM   #15
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I reused mine on my 1.6 with no issues but i did a timming belt on the 1.8 i had imported and it threw the pully next day when i was driving spiritedly.
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Old 12-04-2010, 05:15 PM   #16
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I've snapped one of the OEM bolts during a charger swap and then did the job properly and got some socket headed 12.9 tensile rated bolts (I think OEM are a mere 8.8). These won't ever snap and are a breeze to remove.

The reason I uprated was because I run a 6-rib MP62 and knew it could be a possible weak point.
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Old 12-04-2010, 05:57 PM   #17
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The 6mm bolts that came with my Vishnu crank overlay kit snapped. I had the whole assembly drilled and tapped for 8mm bolts, and haven't had any problems with bolts loosening or breaking since (knock on wood).
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Old 05-14-2017, 01:12 AM   #18
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Quote:
Originally Posted by curly View Post
I torque mine "goodntight" by hand and have had the same one in there for a long time. I've snapped one or two during installation from over torquing them. Doesn't take much.

what did you do after you snapped them? I snapped one today while doing a timing belt replacement. It was my first time tackling this type of job.
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Old 05-14-2017, 01:40 AM   #19
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ask him again in 7 years

or extract it and try again
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Old 05-14-2017, 01:41 PM   #20
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I felt them stretched and was able to take them out and saw the necking I believe. Tossed the bolt and replaced. Somewhere between my post in 2010 and now I bought a HF in/lb torque wrench and always torque to 120 iirc. At work I use my 3/8 snap on torque wrench (the new one) goes down to 5 ft/lbs or 60 in/lbs.
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