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Broken Bolt - correct torque ? |
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8122pbrainard 
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Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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 Topic: Broken Bolt - correct torque ?Posted: December-10-2020 at 7:25am |
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Graeme'
Yes, the bolts should be shouldered. Keep in mind that the bolts in this application are in shear more than tension that holds the damper plate onto the flywheel. I feel that's why the high tensile strength.
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11118 |
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Posted: December-10-2020 at 7:13am |
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You'd think that such a simple question should have a simple answer, but it doesn't always work that way.
Your bolts if original look like the ARP bolts in the link below. You'll notice the unthreaded section at the top that's about1/4 inch long. You should be replacing what you have with the same style whether they're ARP or some other brand. The unthreaded part gets this referred to as a "shoulder bolt" by a lot of people. Whether that's technically right or not hardly matters.........The smooth shank does a better job of fitting closely in the hole than if the bolt was fully threaded. The ARP are harder than a Grade 8 bolt (180,000 psi tensile strength compared to 150,000 for a Grade 8 bolt and their torque value for their ARP bolt is 24 ft lbs when lightly lubricated during installation It's not too easy to go to the local hardware store and find a bolt with the dimensions of the one in the link, (5/16-18 by 3/4 inch with about 1/2 inch of threads and 1/4 inch of smooth shank) but that's what you need to fit correctly and avoid slop and movement of the plate in the future. I might have seen "somewhere else" that you're wondering if you should replace the damper too while things are apart. it sure can't hurt since you really can't tell the condition of yours right now and if it dies a week into your season, you'll have some work to do. You can buy the expensive damper or the cheap damper (Alto ALTDA-106A) and I'd buy the ARP bolt kit too to go along with whatever damper you use or just the bolt kit if you decide the old damper is going back in The cheap one is what mostly gets used and recommended here on CCF. It only uses 3 mounting bolts instead of 6 so if you get the ARP bolt kit, you'll have 3 spares.  |
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gmars70970
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Joined: November-06-2013 Location: Scotland Status: Offline Points: 235 |
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Posted: December-10-2020 at 3:57am |
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Thanks JQ
I'll get new bolts and go with the 30 ft-lbs 👍 |
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Jonny Quest
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Joined: August-20-2013 Location: Utah--via Texas Status: Offline Points: 2979 |
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Posted: December-09-2020 at 6:36pm |
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It’s called a “damper plate”. I use a thread locker and go with 30 ft-pounds of torque. Several options to choose from in the USA...some have to be trimmed to fit and some not. Some are more-or-less triangular in shape and some are circular. USA costs range between $80 to $175.
JQ
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gmars70970
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Joined: November-06-2013 Location: Scotland Status: Offline Points: 235 |
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Posted: December-09-2020 at 4:59pm |
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Another daft question..... I sheared two bolts fitting what I think is called the "Drive Plate" today on my 351w :( Fortunately got both broken bolts out, Is this part called Drive plate? Pressure plate? and what is the correct torque for these bolts? I've read 25 ft-lbs and 35 ft-lbs online. Hoping to get the transmission refitted this week all going well. 
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