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Flywheel bolt torque A friend was installing his flywheel and he torqued the bolts to 65 lb/ft per Les Andrews "Red" Book. He pulled the threads on two of the holes.
Upon further looking, the "Red" Book says 65 lb/ft in one place and 55 lb/ft in another. Bratton's catalog says 55 lb/ft. I have never seen this happen before. Does anyone have a suggestion on a fix and correct torque spec? |
Re: Flywheel bolt torque Insert a Helicoil. Use an old flywheel to align the drill and tap or machine something up. In his instructions, Terry Burtz says to use 55 foot-pounds. The Helicoil will hold more than the original threads because there is more thread area. Drag racers will install Helicoils in the blocks used for racing to hold the heads on. They are just as good or better than the other kinds of inserts.
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Re: Flywheel bolt torque i have found there to be a few lines of incorrect or conflicting info in the Les Andrews books.
best to use it as a guide but not as a bible. |
Re: Flywheel bolt torque Hmmm
I have to ask a couple questions Did the crank flange actually pull the threads out I find that highly unlikely if the proper length and quantity bolts used In addition I typically test the threads after welding flange for Chevy seal at 75 # torque and never pulled one out Better take a look at the bolts John |
Re: Flywheel bolt torque Something had been running loose at one time in the past.
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Re: Flywheel bolt torque Quote:
Two of the bolts held, two pulled out. He got some Time-Serts he will be installing in those two. |
Re: Flywheel bolt torque Quote:
:d:d:d:d |
Re: Flywheel bolt torque be careful, if you drill and or tap the holes not to wipe out the rear seal in the block. there is not much room between the flange and the seal.
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Re: Flywheel bolt torque The stock flywheel attachment bolt is a 7/16 diameter with a fine thread and a drilled head for safety wire. The application of the 4 bolts is predominantly shear due to the large inertia of the flywheel, and some tension due to the actuation of the clutch and the drive-line angle.
The length of the bolts is critical, because if their length exceeds 0.75", the bolts may crack the oil slinger of the rear main bearing. The crankshaft is forged steel. Since tension is not the ruling bolt load, bolt torque need not be so high as to develop the classic 75% of the bolt's yield strength. In this case, torque gives uniformity of the clamp-up of the flywheel to the crankshaft. I am currently installing a flywheel, and I will be torquing the bolts to 40 lbs-ft. By the way, a fine thread is stronger in tension and shear than a coarse thread of the same diameter. Fine threads have less tendency to loosen because their thread angle is less. |
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Re: Flywheel bolt torque Hmm, I've not had an issue with installing a flywheel. But, STUFF happens.
I doubt the bolts need to be that tight. Tight is good as long they are equal and laced. I agree with installing Heli-coils, they should be fine. |
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Re: Flywheel bolt torque Katy,
you are right, the thread form is 60 deg, what the theory is that a 20 pitch is less inclined angle in rotation. Sorry, not buying that either. FWIW, helicoils are not stronger than the base metal, IMHO, only used for thread repair if necessary. Timeserts are much stronger due to the solid form unlike a wire, which can roll. Part of the mystery about bolt torque is when you get close to the yield strength of the fastener. I have had grade 8 7/16-20 bolts yield at 45 ft# torque. the quality is just not there sometimes. Now, get into higher grade fasteners such as rod bolts, same 7/16-20 and designed for clamping you do not torque, you measure the amount of stretch overall. BTW, it is approx 70 ft# torque. John |
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