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#1
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Just scored on a lot of grade 12.9 crank pulley bolts
I'm in the middle of tearing apart my engine to replace the timing chain guides, and I've read on the forum that sometimes the crank pulley hex socket screws can shear.
so I decided to go ahead and replace the six of them with new screws. this began a journey into learning about hex socket screws. I went down to my local ace hardware, and comparing my original screw it turns out these are M8 (8mm thread) x 30mm (length) and 1.25mm pitch. ![]() ![]() They were listed as "grade 8.8". huh? turns out metrics strength grades are different. standard fasteners range from grade 2 to grade 8, whereas metric grades range from 8.8 to 12.9. from Frequently Asked Questions on Bolting Matters ![]() then I realized they had stainless screws as well. why not baby my baby for a few dollars more? ![]() however, after reading about it, it turns out stainless fasteners aren't as strong as the strongest steel fasteners (mostly because they are low carbon so they can't be heat treated as effectively?). so then I started searching online for hex screws, and I stumbled upon this: ![]() score! the size I need in 12.9 strength, at $0.30 a piece! I only need 6 of them, so if anyone else is planning on having their crank pulley off in the near future, PM me and I'll ship some to you.
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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz |
#2
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more on the metric strength grades from Metric Bolt Properties, Grades, and Strength
Quote:
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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz |
#3
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this is sweet!
I may put them in a sticky in the parts forum. help ya get em all sold. please PM me when they are gone to remove the sticky!
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! ![]() 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#4
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thanks vstech!
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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz |
#5
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came across these torque specs from US & Metric Bolt Torque by Grade
I wonder how these compare to the service manual's values? ![]()
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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz |
#6
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12.9 might be really brittle and shear-off easier than a 10.9 or 8.8.......
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-diesel is not just a fuel, its a way of life- ![]() '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k) |
#7
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what Hardness do OE bolts use?
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! ![]() 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#8
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They are usually 8.8.....the new bolts I put on one of our diesels from the dealer were 8.8
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-diesel is not just a fuel, its a way of life- ![]() '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k) |
#9
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ahh. then, I'd not recommend using them in a high stress area... if OE used 8.8, that's what I'd stick with!!!
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! ![]() 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#10
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d'oh, hadn't thought about that.
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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz |
#11
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FYI
In the mid 1970's MB delivered the 616 and early 617 with grade 10.9 pulley bolts.
Failure was embarrassingly quick, the bolts where superseded to grade 8.8, and mandated NEW fasteners for every remove/install = the issue vanished. .
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ASE Master Mechanic https://whunter.carrd.co/ Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 2003 Volvo V70 https://www.boldegoist.com/ |
#12
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thanks for the confirmation whunter.
vstech, you can remove my sticky ![]()
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OM617 in a 67 chevy pickup http://tinyurl.com/projectgmbenz |
#13
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FYI: The bolts now provided by Mercedes-Benz are grade 10.9, not 8.8 like the originals. Let's hope they hold up.
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Stop paying for animal enslavement, cruelty, and slaughter. Save your health and the planet. Go vegan! I did 18 years ago. https://challenge22.com/ DON'T MESS WITH MY MERCEDES! ![]() 1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C 1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles |
#14
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I'm confused... higher grade should equal higher tensile strength, right? Maybe the 10.9 that failed so bad were poorly manufactured?
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'85 300TD "Puff The Magic Wagon" - Rolling Resto '19 Mazda CX-9 Signature - Wife's sled '21 Morgan 3-Wheeler P101 Edition '95 E300d - SOLD '84 300TD "Brown Betty" - Miss this one '81 240D "China Baby" - Farm grocery getter |
#15
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Ok, I'm thinking now that lower grade actually flexes more and would not shear the heads off.
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'85 300TD "Puff The Magic Wagon" - Rolling Resto '19 Mazda CX-9 Signature - Wife's sled '21 Morgan 3-Wheeler P101 Edition '95 E300d - SOLD '84 300TD "Brown Betty" - Miss this one '81 240D "China Baby" - Farm grocery getter |
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