Thread: High Tensile Bolts

According to Google

Roughly 50-60 Ft/pounds

US & Metric Bolt Torque by Grade

disregard my original post was for 10mm bolts (wrong look up chart I used the 10mm being mislead by the bolt head size)

generically an 8mm is flat out at about 60ft/lb for a fine pitch thread and 50ft/lb for a coarse pitch. (numbers reworked from the Nm scale and made easy)

more importantly why do you want to know this number....

you might as well do the joke answer I give when someone asks me how tight to do up a bolt

"crank it up till it snaps then back it off half a turn for thread relief."

Originally Posted by Blknight.aus

disregard my original post was for 10mm bolts (wrong look up chart I used the 10mm being mislead by the bolt head size)

generically an 8mm is flat out at about 60ft/lb for a fine pitch thread and 50ft/lb for a coarse pitch. (numbers reworked from the Nm scale and made easy)

more importantly why do you want to know this number....

you might as well do the joke answer I give when someone asks me how tight to do up a bolt

"crank it up till it snaps then back it off half a turn for thread relief."

I ask because I just had to change my injector seals and when I went to take off the rocker arm I snapped 5 of the 6 bolts. The manual says they should only be tightened to 24 ftlbs or 32 Nm. I was wondering what tension the person who put them in must have tightened them to in order for me to shear them off on removal. The one that didn't shear off completely was sheared half way through and it is apparent that the shearing happened on the way in rather than out.

I wanted to get a figure of how much it taked to shear one off so when I go and tear the "Land Rover Expert" who last "fixed it" a new a***hole I wanted to have some figures to share with him.

before you do that....

take some photos (the highest res you can and preferabley on a macro capable camera with good lighting) of the shear point it may not be an over torque failure.

Ive got some great torqued past yield bolts to show up in comparison

High tensile bolts are more prone to fatigue failure than low tensile bolts.
rocker bolts are subject to cycling stresses.

Thats what I was thinking.

BUT if hes talking about the retaining stud on a TDI injector thats a different story and its not a rocker but a "claw"

The bolts I'm referring to are the bolts that hold the rocker shaft in place in a Td5. The rockers attached then actuate the injectors. The head was only recently done (approx 18k km ago). The bolt that is still intact shows the shearing in a twisting fashion in the direction of tightening the bolt. All of the others also show the 'tang' (remaining thread) left behind pealing off in the direction of tightening the bolt. I also noted that all the bolts had sheared in line with the top of the receiving thread implying that the received thread has pulled away from the rest of the bolt.

If they failed due to cycling I would assume they would still be able to be removed at a similar torque to when they went in. These bolts took for more than 24 ft.lbs to move before they let go.

Originally Posted by Blknight.aus

"crank it up till it snaps then back it off half a turn for thread relief."

I think the guy who did these up last was possibly using this school of thought.

Originally Posted by Blknight.aus

take some photos (the highest res you can and preferabley on a macro capable camera with good lighting) of the shear point it may not be an over torque failure.

Ive got some great torqued past yield bolts to show up in comparison

I'll try and get some today