Engine Through Bolt - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 11 Old 04-25-2018, 07:31 PM Thread Starter
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Engine Through Bolt

I recently tried to install a set of crash bars to my 2013 Vstrom 650. The bars are fixed in place using the engine through bolt shown in the pic. The crash bar manufacturer supplied a Ssteel through bolt and recommended that I torque this bolt to 75 Nm. I lookedup the manual for the Vstrom and 93 NM is specified for the torque for this bolt. Anyway the bolt supplied snapped and the crash bar manufacturer is graciously sending me a new bolt.

My question is - If I ever replace the engine through bolt with the OEM bolt what torque should I use Ie. 93 Nm or something less?
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post #2 of 11 Old 04-25-2018, 10:01 PM
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Lemme see, the makere says to torque to one value and you ignore the information. RTFM and try to do what makes it work best.
Oh, be sure your torque wrench is operating properly.
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post #3 of 11 Old 04-25-2018, 10:14 PM Thread Starter
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Originally Posted by notacop View Post
Lemme see, the makere says to torque to one value and you ignore the information. RTFM and try to do what makes it work best.
Oh, be sure your torque wrench is operating properly.
Thanks for your input. Just to make things clear I did RTFM and that is why I got myself in this mess.

I asked if I reinstall the original through bolt back into the motor - do I tighten to 93 NM or something less. I ask this because it is well documented that the workshop manual has incorrect torque figures for the smaller bolts in this bracket. If anyone can help me I would appreciate it. Unhelpful comments are a waste of airspace.
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post #4 of 11 Old 04-25-2018, 10:57 PM
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The oem bolt was 93nm, and if using that I would use the 93 spec. If the bolt supplied by the crash bar manufacturer said 75 nm with their bolt, I'd use that--but I suspect its not the same hardness as the oem bolt. Probably longer to compensate for the crash bar mount thickness as well.
Here is what you can do and have it all: Go to a Fastenal store or Fastenal.com. Get your new bolt from the crash bar maker and measure it for length in a grade 8.8 or 9.8 harder metric bolt in the same length and thread pitch as what the new bolt is.
This thru-bolt, as in the SV650 in my garage, is a 12mm X 1.25 thread pitch bolt. So you need a harder 12mm X 1.25 thread pitch bolt in the same length as supplied by the crash bar company.
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post #5 of 11 Old 04-26-2018, 02:39 AM
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You should use the recommendation of the manufacturer, in this case the crash bar maker.

All bolts are not equal - the higher the number the greater the tensile strength of the bolt. A 6 for bolt on things but up to 8 or 9 for critical parts. The strength number is usually on the head of the bolt.

Beware though that all torque wrenches are also not equal. There is a very informative discussion here https://www.stromtrooper.com/dl650-dl...-breaking.html of often faulty torque wrenches, and also how to use them.
Wrench settings are quoted in manuals meaning clean, dry and unlubricated bolts and the spec should be reduced by up to 20% where any lubricant is present.

When you replace the original bolt use Suzuki's recommended torque setting.

2010 Weestrom; 2017 Kawasaki Versys-X300; 1988 Suzuki GSXR1100
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post #6 of 11 Old 04-26-2018, 03:56 AM Thread Starter
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Thanks all for your comments. They are confirmation of my thoughts. One of the reasons for me to initially doubt the torque settings of the crash bar manufacturer is that I thought Suzuki required 93Nm of torque to hold the engine in place and that the 75 Nm quoted by the crash bar manufacturer didn't meet Suzuki's specs. Hence a problem arose.
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post #7 of 11 Old 04-26-2018, 04:27 AM
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Torque to 75nm, mark it, check it in 500 miles.
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post #8 of 11 Old 04-26-2018, 04:54 AM
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The bolt popping like it did, might be an indication of a danger in having a crash bar that uses that bolt. Imagine if you will, dropping your bike, and the leverage the crash bars will place on that bolt. Take it easy on the torque if you want a bike you can ride home after a drop.
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post #9 of 11 Old 04-26-2018, 05:27 AM
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You'd have to ask the crash bar manufacturer to be sure, but it may even be the case that the bolts were deliberately made of a weaker type of steel than the OEM bolts. This would then introduce a known weak link into the crash bar system, so that if you have a crash that exceeds certain parameters, the bolts break before they do damage to the engine or frame.
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post #10 of 11 Old 04-26-2018, 07:55 AM
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Absolutely use the recommended torque supplied WITH the aftermarket bolt. If ever in doubt about torque, look up torque specs for that diameter fastener. Compare those with what you have written. Big disparity means you should figure out which is right before torquing.

Factory thru-frame bolts are meant to hold tension more than shear. They are likely a higher grade of steel with different heat treatment. The aftermarket bolt is probably good steel, simply longer ( dramatically effects torque effect ), and not heat treated quite as hard. That may be on purpose as the crash bars introduce a "shear" load. The softer bolt would probably be better there.

Then there is the "to lube or not to lube" factor in torque application. 93nm on a fastener with oil on the threads is a LOT more torque than it was designed for if the factory spec is dry, clean threads.

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