Always replace those 10mm crankshaft pulley bolts after 60,000 miles or timing belt.
11-26-2010, 09:56 PM
#1
Senior Member
Thread Starter
iTrader: (11)
Join Date: Sep 2007
Location: Killen, AL, 35645
Posts: 794
Total Cats: 10
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...
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...
Reply
0
0
11-27-2010, 12:57 AM
#7
Senior Member
Thread Starter
iTrader: (11)
Join Date: Sep 2007
Location: Killen, AL, 35645
Posts: 794
Total Cats: 10
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.
Reply
0
0
11-27-2010, 01:59 AM
#9
Cpt. Slow
iTrader: (25)
Join Date: Oct 2005
Location: Oregon City, OR
Posts: 14,178
Total Cats: 1,129
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.
Reply
0
0
12-04-2010, 04:15 PM
#16
Junior Member
Join Date: Oct 2008
Location: Manchester, UK
Posts: 272
Total Cats: 0
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.
The reason I uprated was because I run a 6-rib MP62 and knew it could be a possible weak point.
Reply
0
0
12-04-2010, 04:57 PM
#17
Supporting Vendor
iTrader: (33)
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,659
Total Cats: 134
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).
Reply
0
0
05-14-2017, 12:41 PM
#20
Cpt. Slow
iTrader: (25)
Join Date: Oct 2005
Location: Oregon City, OR
Posts: 14,178
Total Cats: 1,129
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.
Reply
0
0
