most of the torque specs for the mini are in Nt-M, easily enough converted to ft-lbs. You twist the bolt using a maximum recommended Torque, hoping thread and head friction is minimized so the appropriate tension is loaded into the bolt by virtue of the tensile strength of the bolt and the amount of stretch your torque produced.

My question is why are a few bolts singled out and given a lesser torque value than other equally sized fasteners and then brought up to full tensile load by turning another 90 degrees? Mini head bolts and the front subframe-to-body bolts are specified this way. I might point out that in both of these cases, a nice hardened washer is used beneath the head. Presuming this gives a more accurate tension load, the head bolts make sense, but why the subframe bolt, especially since the remaining 8 bolts are all torqued the usual way to 74 ft-lbs.?

any gyros out there care to comment?

I know Helix won't because he is too wimpy to drop the subframe. heh, heh!

 

so....so much for "mechanics intuition"?

 

Bolts that are spec'd as "torque to X (ft-lb or n-m) plus y degrees" are usually a "torque-to-yield" type of fastener. These bolts are designed to stretch when torqued. However, the metal is not elastic- it does not "unstretch" when the torque is released as they are removed. Since the stretch is permanent, the same clamping force cannot be guaranteed if the fastener is re-used. Worse yet, the fastener might fail if re-used. The failure might not occur during the initial tightening on re-use, but it is still a very real danger, and sucks even more if the bolt fails while the conjoined parts are in operation.

If the manual says use new hardware, please, do so. It's well worth the money to replace those fasteners and know they're sound.

 

You've noticed that too?
So do you want to do my front sway bar?

 

Most subframes have "stretch bolts" or "torque plus angle" or "Torque To Yield" bolts. You can't/shouldn't reuse them. TTY bolts are good for an extra 25% clamping power. As to why only 4 of them are TTY, I can only guess :smile: I'd say that the 4 TTY bolts locate the subframe and probably prevent it from being tweaked during installation and the rest are just there for additional clamping possibly less critical portions?

--
Cheese

 

the main alignment of the subframe-to-frame is done by a conventionally torqued (100N-M) 12mm bolt (up high in the front, both sides...the subframe locks onto a hollow dowel pin through which goes the bolt). then there are six more, locking the rear of the subframe to the chassis, also 12mm.

only after all these are fully tightened do you install the two remaining 11 mm (59 N-M + 90 degrees)TTY bolts which attach the control arm bracket end of the subframe to the body. At this same point, an odd detail is the tab on the subframe has to be twisted (at the factory) to match the angle of the body at the connection point. Additionally they cut the tab partially through at the twist. Do you suppose this is some sort of collison fail-first point?

I've re-used those 11 mm bolts, so I'm now going to replace them.