Correct con rod nut torque?

[Silverbullit]

67s w/ new bolts/nuts: Manual says 36 lb. ft. Dempsey book says 20 lb. ft., then turn 90 degrees, which far exceeds 36 lbs.
What would be the correct number in ft. lbs>?
Thanks

[edmayo]

Who do you think you should believe? The factory manual or Dempsey. Are you using stock bolts? If so where did you get them? What kind of usage will the car see? Above 5,000 ever?

[Silverbullit]

Thaks Ed, Well, it's a Haynes manual, so.......
Stock bolts from Pelican, stock 67S motor, car will be a cruiser, but driven 'spiritedly'. Went with 40.5 ft.lbs. from a reliable source! Thanks, Brian

[edmayo]

I'm not confident of stock bolts, haven't been for many years, there are counterfeit ones out there that's why I asked where you got them. We will only use ARP or some such similar bolt.

[sithot]

Going along with Ed's view; what Dempsey is quoting is "Angle Torque". Used by "big diesel" engine mechanics for years and now finally bleeding over into the auto community.

[StephenAcworth]

"Angle Torque".

can you explain the difference: and maybe the conversion ratio? it is mighty confusing for a newbie like me... thanks!

[Flieger]

The torque of a bolt doesn't really matter. What you are trying to achieve is clamping force so that the friction between the two surfaces being clamped (rod and end cap) carries all the shear loading. The bolt then carries tensile loads and needs to have enough clamping pressure so that if the joint is compressed then the clamping force does not reduce too much and allow the two parts to slide against each other (fretting).

Clamping force has a very well-defined correlation to bolt stretch because it is just the modulus of the bolt and the tensile area, and tests in a lab can be used to find these values. This is why ARP and other aftermarket rod bolts use micrometers to measure the actual elongation of the bolt.

Sometimes it is impractical to measure bolt stretch. In this case, torque is used. The problem with this is that the amount of torque required depends on friction in the threads and this will vary based on what kind (if any) lubricant is used, whether the threads have been burnished, etc. Manufacturers therefore call for a specific lubricant to be used, and that the threads be burnished so that the torque to clamping force relationship will have less scatter and be more in line with what they determined in the lab.

One way around the friction torque problem is to make the bolt/nut "snug" (so that there are no air gaps between parts), then use a certain angle of twist after that. The reason this works is that the thread pitch times the angle will give a length, and this is the amount of stretch since there wasn't any air gap to take up. The final torque isn't really that important as long as the fastener doesn't get stressed too much in torsion to the point it might fatigue fail or break the head off. If you use lubricant this should not be an issue.

[Silverbullit]

Going along with Ed's view; what Dempsey is quoting is "Angle Torque". Used by "big diesel" engine mechanics for years and now finally bleeding over into the auto community.

Yes, I've encountered this application in Saturn and Subaru head bolts.

[gled49]

When I use to update the service manuals, there were pages added and pages replaced. When they wanted a torque spec page replaced with a torque angle page, I usually didn't. I put both pages in and hi-lite them so people could make their choice. Starting in 84 with the 9mm rod bolts there was only a torque angle spec. Step one was a threshold torque of 20nm (15 ft lbs) + 90* angle torque +- 2*. The only comparison that I came up with was head torque with old style gray hardware of 32nm (24 ft lbs) and the new plated hardware of 15nm (11 ft lbs) threshold torque + 90* +- 2* angle torque.
I also only use ARP rod bolts and stretch them with dial indicator bolt stretch gauge. Gordon

[Silverbullit]

Thanks all for the info. For my application and with my hardware, I came upon Bruce Anderson's reccemended 40.5 ft lbs, and was able to confirm this with Jerry Woods. I have confidence in them. Brian