TTY Bolt Alternative

[Turbo_Bimmer]

The reason I was thinking that a regular bolt would not make that big a difference, is because all the TTY bolts (BMW head bolts) and studs (ARP head studs for BMW engine), are 'undercut'.
For those that don't know what it means, it's that the middle part of the bolt or stud has a smaller diameter to permit the stretch. Like a 3/8" bolt will be 3/8 where the threads are, then go smaller, like 5/16 for the middle section, the go back to 3/8 one inch before the head.

The OE bolts on the stiffening plate are not undercut, so I don't think they will strech as much or as easily as an undercut bolt, or may be it's the grade of steel that is lower to permit the stretch?

[TiAgX5]

Originally Posted by jgold47

I did some more research last night. There seems to be a lot of misinformation and conflicting information about TTY bolts in general.


They seem to be clustered around.

1. is there such a thing as a tty bolt. As in, are they a unique bolt or
2. are they just normal bolts installed a certain way?

if #2 is correct, then there must be a very specific torque the OEM is trying to achieve and its possible they know the exact shear point of those bolts

#1 - if you try and buy a 'TTY' bolt, you simply wont find one for sale.

3. regular bolts can be installed with TTY LB's and procedures as the same effect would occur 'assuming the shear torque of the bolt is the same or higher'

4. you can use regular bolts if you take steps to ensure that a) they are as strong (which M10/10,9 bolts should be) and b) you ensure that the torque value doesn't change over time (use threadlocker)

The strange thing is that the 41lb + 90deg is a mathematical equation that should yield another torque value, less accurately (depending on the length of your wrench, and how accurately you measure 90deg).

I don't know, its all very confusing. People say toss'em, people say use'em, people say sub them with normal 10,9's.....


I'll give it a shot and report back...

The bolt itself itself is not defined as a TTY fastener, the size/grade/torquing/degreeing is what causes a standard grade bolt to BECOME a TTY fastener. The torquing/degreeing of the fastener causes the bolt/nut to deform, thus the YIELD in the TTY fastener definition.

A stronger bolt changes the deformation/shear threshold and thus changes the crumple properties of the chassis/suspension ass'y.

Using a good torque wrench and TTY gauge allow for precise tightening of TTY fasteners, regardless of wrench length.......