[YellowJacket RV9]

As I start to put parts on my engine, I wanted to clarify the Lycoming torque chart in their overhaul manual. It looks like most people assume that the note to "lubricate threads unless otherwise specified" applies to ALL fittings. On closer inspection, it kind of looks to me like this only applies to fittings in Table III, with the crush gaskets.



Can anybody confirm one way or the other what Lycoming means? Lubricating all the other fittings could result it very high torques...

Thanks!

Chris

 

[BillL]

In the engine world

aviation and otherwise, fasteners that need full tension will use lubricated threads for the torque. If the tension is not adequate to keep the fastener from coming loose, then locking washers are used. On no other application than aero engines have I seen locking washers. It was proven that with high strength fasteners, that lock washers provide less, not more, security of the bolted joint. circa 1980

To get maximum (and consistent) tension in a bolt lubrication is necessary to get consistent thread friction and lower torsional stresses in the shank.

Some large engines stress the bolt/stud so much that they use hydraulic cylinders to stretch the head bolts all together and then thread a sleeve down by hand with a 1/4" dia rod.

Actually, I was surprised to find that most aircraft fasteners are torqued dry. I learned that they are sized for taking loads in shear. Nearly all engine fasteners rely on tension and contact force to prevent shear movement.

 

[YellowJacket RV9]

Exactly why I love this site. Thanks Bill!

Chris

aviation and otherwise, fasteners that need full tension will use lubricated threads for the torque. If the tension is not adequate to keep the fastener from coming loose, then locking washers are used. On no other application than aero engines have I seen locking washers. It was proven that with high strength fasteners, that lock washers provide less, not more, security of the bolted joint. circa 1980

To get maximum (and consistent) tension in a bolt lubrication is necessary to get consistent thread friction and lower torsional stresses in the shank.

Some large engines stress the bolt/stud so much that they use hydraulic cylinders to stretch the head bolts all together and then thread a sleeve down by hand with a 1/4" dia rod.

Actually, I was surprised to find that most aircraft fasteners are torqued dry. I learned that they are sized for taking loads in shear. Nearly all engine fasteners rely on tension and contact force to prevent shear movement.