CV bolt Torque

[surflvr911sc]

Just want to confirm the CV bolt torque on my SC. Bentleys says M8 bolt 30 ft-lbs, M10 bolt 60 ft-lbs. 101 Projects says 61 ft-lbs for ’69-’89 911s, 34 ft-lbs ’65-’68.

This seems like a no-brainer but as I torque to 60 ft-lbs, is seems like a lot. Just want to be sure before I strip something. Thanks.

[stevef]

Yeh, I was wondering the same thing. I recently replaced some gaskets and retorqued the bolts to 30 ft lbs on my 69. Thought my bolts were M8 cos they have 8mm allen heads. And 60 ft lbs seemed high. However I received some feedback from a previous post that I need to make sure they are M10 measured by bolt shank diameter and that they are torqued to the higher number. I think because there are only 4 bolts at 10M and they are fairly long the higher torque seemed reasonable to me.

[jmohn]

Dr. Ryan:

I don't any ref. material here with me, but I think your SC has 8mm bolts and should be torqued to 34-36 ft. lbs. - 60 ft. lbs. would be way too much IMHP.

Jerry M
'78 SC

[Jbabic]

as I have suffered these bolts to back out while driving...the tigher the better....since then I have had no problems with the upper torque specs.

[surflvr911sc]

Here’s an idea, why don’t I measure my bolts, duh. They’re 8mm, I guess that settles it, 30ft-lbs. I actually pre-torqued them to 35 ft-lbs so I’ll leave them there. I’ll check the torque in a couple hundred miles to be sure they’re still tight.

Thanks for the replies.

[Jbabic]

Check after 75 to be sure...If they work loose, it doesn't take much time..I actually suffered after about 25 miles....

[GeorgeK]

The factory quotes 32 NM for the 8mm bolts on my 951Cup. Seems very little, but no problem in 2 years. NEW bolts every time!
GeorgeK

[Rick Lee]

Well, I'm doing this job tomorrow, assuming we get my new 3.2 all buttoned up and new spring plates installed. I have new CV bolts, but don't know their specs or have any ref. materials with me here. What's the torque spec. for my '87 Carrera? Thanks.

[surflvr911sc]

Just measure the bolt. Big difference between 8mm & 10mm, you'll know.

[Rick Lee]

Originally posted by surflvr911sc
Just measure the bolt. Big difference between 8mm & 10mm, you'll know.

I'm pretty sure mine are 10mm. So does that mean 60 ft/lbs?

A 25% increase in diameter means 100% increase in torque?

[Jim Sims]

Sigh! 101 projects needs an erratum issued for this CV joint screw torque spec. For some years it is just plain wrong; my '76 has 8 mm screws and if they were torqued to 60 ft-lbs some would likely shear off! Screw/bolt strength is determined by cross-section area; area increases by the square of the diameter times the constant PI/4. Thread friction increases approximately linearly with diameter. And yes, the product of these two increases combine to just about double the required torque. 10 mm (across the shank or diameter of the bolt, not the wrenching feature size) screws of the 12.9 class used in CV joints require 60 ft-lbs (threads not oily or greasy) to properly tighten. Also gents, the length of a screw or bolt has essentially no bearing on required torque. The torque with very few exceptions will be the same for a 50 mm or 100 mm long screw or bolt of the same diameter and thread type. The longer screw or bolt may turn or "wind up"more but the torque setting on the torque wrench will be the same. Cheers, Jim

[Rick Lee]

Whew - looks like my parents' money was well spent on my NE prep school. I had forgotten that one.

[MBAtarga]

Jim, there is a corrections list of errors on the 101 Projects Web Page

I think what you're talking about is listed:

Project 41: Incorrect Torque Specs: Using a torque wrench, tighten up the bolts to 83 N-m (61 ft-lb) for cars with four M10 bolts on the flanges, and 47 N-m (34 ft-lb) for cars with six M8 bolts on the flanges. For 1965-68 911s, tighten them up to 47 N-m if you have the Nadella axles (M10 bolts), or 43 N-m if you have the early Loebro CV joints (M8 bolts).

[Jim Sims]

The website correction is valid as far as it goes. I would add not to try and reference the torque by year of manufacture but to instead measure the screws. Is the the correction website in the book? My son hauled our copy off to college. Jim