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  #1  
Old 07-01-2011, 05:49 PM
RVG8tor's Avatar
RVG8tor RVG8tor is offline
 
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Default AFP Bracket torque

The AFP FI comes with an anodized bracket that is held in place with 4 socket head bolts, they go into the same holes as the carburetor studs and are 5/16-18 (coarse thread) The AC43 Torque value for this is 80-90 in lbs but the Lycoming overhaul manual has 204 in lbs for this size bolt. The US torque specification for a grade 8 bolt this size is 216 in lbs. The instructions say to use Loctite so I have some High Temp stuff (Red) but wondered which torque you others would use here. I am leaning toward the Lycoming # but wonder whey there is such a big difference between the two specifications. It also seem the US Torque table is a little higher for socket heads even though the threads are the same size, interesting.

Thanks
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  #2  
Old 07-01-2011, 07:12 PM
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flion flion is offline
 
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Default

Go with the Lycoming numbers. This is not the same kind of application that AC 43 covers, nor are those the same kind of bolts.
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  #3  
Old 07-01-2011, 08:28 PM
terrye terrye is offline
 
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Default Bolt torque

Recommended bolt torques are usually based on the yield strength of the bolt material which is why SAE Grade 8 bolts have a higher recommended torque than SAE Grade 5 bolts. SAE does not have a classification higher than Grade 8, but most socket head cap screws have a higher material yield strength than SAE Grade 8, so they can be installed with a higher torque, and the socket head cap screw manufacturers will list this torque in their literature.

If installed as a cap screw, then the installation torque may depend on the material it is screwed into as the limiting factor may be the shear stress of the female thread rather than the shear stress of the bolt body.

If I understand correctly these cap screws go into a female threaded aluminum housing. Therefore I would go with the Lycoming specified torque value for the fastener.
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  #4  
Old 07-01-2011, 10:26 PM
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RVG8tor RVG8tor is offline
 
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Default thanks

Great help here at VAF as usual

Cheers
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  #5  
Old 07-02-2011, 08:18 AM
Don at Airflow Don at Airflow is offline
 
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Default 5/16-18 SHCS torque

RVG8tor,

Per my pm to you 95 - 125 in-lbs will work on these cap screws.

Don
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  #6  
Old 07-02-2011, 09:02 AM
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RVG8tor RVG8tor is offline
 
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Default Update to thread

Quote:
Originally Posted by Don at Airflow View Post
RVG8tor,

Per my pm to you 95 - 125 in-lbs will work on these cap screws.

Don
Don,

Thanks after reading your email this morning I was just logged onto update this thread and you beat me to it. Thanks glad I did not already try to torque them otherwise I would have used 204 in lbs.

This is really why I asked the question in the first place there always seem to be some torque values that don't make sense just following the Overhaul Manual. The bolts holding the alternator bracket will be my next research project.

Cheers
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