PorKen

Same as oiled? Reduce torque by 15%?

I'm trying to calculate the torque for both a 8.8, and a 10.9, 8mm x 1.25 bolt, but this should apply to all the bolts on the car.

You're supposed to reduce by some %, compared to a dry bolt, as the Loctite lubricates the threads, correct? Does this sound right?

8.8: 17 - 15% = 15 ft/lb
10.9: 24 - 15% = 21 ft/lb

SteveG

Oh, crap. I went the other way (not the Pcar, who cares). AT transmission pan bolts: I cleaned the bolts with WD40 and wire brush. There was some residue left on the female side and they were not easy to turn in, so I thought there is some resistance here and I guessed at 12 Ft lbs where it called for 8.

PorKen

Maybe this contributes to the problem of the tensioner arm shoulder bolt? Makes it too easy to stretch that bolt when using Loctite, even if you are using the WSM bolt torque spec?

Big Dave

Thanks for the tip. How does anti-seize impact the torque?

PorKen

AFAIK, anti-seize also acts as a lubricant, and so requires less torque.

Oil differs from Loctite in that oil makes it easier to unscrew too!

So far, doing web searches, I haven't found any concensus on torque values. Generally, the advice is to use a strain gauge on the individual application.

Charley B

Not to sound dumb, but what is a strain gauge?

jon928se

Lubricant can in theory reduce the torque required by as much as 50%!

If you're talking about torquing a bolt into an alu anything then the grade of steel bolt has no real relevance to the equation unless its head bolts or main bearing bolts which have a long threaded section (compared to a nut).

Other than that I'ld say 15% or 20%, IF and only IF the original spec called for a dry (no lube) fit, and assuming it wasn't a highly torqued bolt. (The more tension the torque induces in the bolt the more friction there is) - Just about anything will lube the bolt to a degree, be it WD40, grease, Optimoly TA, Loctite, Duralac, even water. (Ever tried to press two very small pieces of wet glass together and get all the water out from between them ?)

Rod Underwood

Strain is "change in length per unit length" under load. When you apply load - tighten in this case - anything, it will change length to absorb the stress. Since all materials have specific relationships (Modulus of Elasticity) between stress (load per unit area) and strain, it is possible to determine the exact stress in any material be knowing how much it has changed length or dimension under a specific load.

So, a strain gauge attaches to the material and measures how much a typical portion changes length as you apply load.

That's the technical explanation, not a dumb question at all.

Rod

marton

I believe the 928 torque figures are based on "lightly oiled" bolts?

Marton

SharkSkin

For most non-critical applications(Anything on a 928 other than heads, rod & main caps, certain trans/gearbox assemblies) I think you can consider the loctite to be roughly equivalent to the spec "lightly oiled threads". YMMV.