Conflicting torques and defective parts

[AggieZ]

Temperature differences over time creates metal fatigue. If you are torqueing into a camshaft that doesnt have 35 years of heat and cold, then the original specs of the aftermarket manufacturer sprocket might be ok for the application. Food for thought.

[JimmyZ]

Diseazd probably has his sprocket happily on by now... and torqued right. Certainly hope so.

A cam sprocket bolt is not a heavily loaded fastener. There is no taper to be engaged and the assembly relies on indexing from the keyway. How can there be any substanitial tensile loads on this fastener? In my mind the only reason they made the thing so large was to allow someone to apply enough torque to turn the engine from the cam without breaking the fastener. (If for God knows what reason the need should arise)

The issue then is getting enough preload on the bolt to keep it from loosening. Overtightening a fastener severely limits the # of cycles it can face before failure. The only way there could be such a divergence in torque figures from one book to another (FSM vs Frank H) is if there was a different material or diameter of the fastener being used.

One might argue the extra torque could be used to sandwich the sprocket better and make life for the key a little easier. You could also argue that minute load reversals on the sprocket could loosen the fastener. (Not happening with red loctite) This still ignores the fact that you might be exceeding the elastic limit of the fastener. This makes it something worth a little less than a skipping stone.

The female threads in the cam whether it be G4000, 8620 etc are a non issue with the engaged length of the cam bolt. If they were a sloppy (class 1) fit then that might be another story.

Jim

Edited August 17, 2008 by JimmyZ