Fastener quality for 7.5 Helix clutch

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Abarthnorway - Remi L
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Fastener quality for 7.5 Helix clutch

Post by Abarthnorway - Remi L »

Hi Guy!

Maybe an obvious answer to this one but here we go:

I am about to fit a Helix clutch to a NA 2 liter 8V tc with 131 flywheel - I need some guidence regarding what quality of bolts to use.

Best regards

Remi

The setup
The setup
Clutch net.jpg (86.03 KiB) Viewed 6427 times
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Guy Croft
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Re: Fastener quality for 7.5 Helix clutch

Post by Guy Croft »

8.8 grade will easily take the shear load on that.

G
engineerted
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Re: Fastener quality for 7.5 Helix clutch

Post by engineerted »

Remi,
Yes, I agree with GC, as I recently did this with a 7.25 Tilton unit. Are you going to use thru bolts or drill and tap the FW. I did the latter as there were 2x dia. bolt thickness in the FW. Side note: what are you going to use for a clutch release bearing as it is difficult to find an after market one that will accept the 1.020" dia, guide sleeve on the transmission and have a large enough dia. at the contact face?

Ted
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tmvolumex
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Re: Fastener quality for 7.5 Helix clutch

Post by tmvolumex »

You should make sure that the transition from bolt thread to unthreaded section does not line up with the flywheel surface/ pressure plate interface. Ideally you want and an unthreaded portion of the bolt at that interface, to be below the flywheel surface.
Tom
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Guy Croft
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Re: Fastener quality for 7.5 Helix clutch

Post by Guy Croft »

Although what you say is true Tom and it is an ideal from an engineering standpoint - whether it's vital is another matter, it depends largely on the applied torque. I have only once ever in a 7.25" clutch app bothered with it.

I have not included any stress concentration factor in the calc below - if my math is right - you can see the torque from an atmo 2 liter 8v is unlikely to lead to any problems even if (as I cite) the shear load at the joint of clutch cover to FW is taken entirely on the threads.

G

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tmvolumex
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Re: Fastener quality for 7.5 Helix clutch

Post by tmvolumex »

Guy,
Great spread sheet, thank you for doing that. I may be a bit overboard on this one, but I hate pulling a trans or an engine because of a broken clutch. So I am ultra-conservative on this subject.
I have had my fair share of broken clutch disks, that were rated for far more torque than my VX engine puts out, so I am ultraconservative in this area. Besides, what is the actual driveline torque / shock / stress on the bolts when you let your friend drive your car and he dumps the clutch? I don’t know the answer to that one, my friend always says he didn’t do it!
Scarey thing is, sometimes that friend is me.
Tom
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Guy Croft
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Re: Fastener quality for 7.5 Helix clutch

Post by Guy Croft »

Understood Tom

Standard induced preload from 14-16lbf ft (assuming adequate bolt thread & underhead lubrication) should be sufficient to withstand the kind of shock & cyclic load you refer to. That joint stiffness calculation is a lot more involved and I have never had to do it with this application and hope not to have to start now!

G
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Re: Fastener quality for 7.5 Helix clutch

Post by Guy Croft »

REVISED CLUTCH BOLT SHEAR LOAD SPREADSHEET

GC
Attachments
clutch bolt shear stress_Rev01.GIF
clutch bolt shear stress_Rev01.GIF (23.63 KiB) Viewed 6252 times
Clutch bolt stress_rev01.xls
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