Snapped ARP Conrod Bolt
Turbo Mini Forums

It's an elongation guage, it measures the length of the bolt before and after so you can mathematically "calculate" the strain.

Did they not send you a set of tables as the load/elongation (stress/strain) will be different with different diameter bolts ???

Without getting too technical, it's a pretty crude way of doing this - it relies on the two ends of the bolt being precision machined to accept the gauge ends.

Schrödinger's cat - so which one am I ???

Their ARP bolts so already have the dimples at both ends of the bolts.

The dial measures the change in length/stretch though not the length before and after.

ARP 1275 rod bolts need stretching between .0065" and .0070", but you have to pre-load the gauge betwee, .2" and .4". I'm sure it's easy enough.

http://turbominis.co.uk/forums/index.php?p=vt&tid=170151

OK, so they did supply some figures specifically for the 1275 bolts (ie, figures based on their diameter and length)

The change in length before/after is the stretch (strain being the technical word, whatever they say) which mathematically computes to final stress in the bolt.

So long as they have given you a figure to "stretch" it to, and you can manipulate the guage to read the measurements accurately, you'll be OK.

My only reservation about doing it this way is the "rather crude" guage reading being accurate before/during/after.

I'm not trying to diss it, but it is a very unreliable way of measuring induced stress accurately.

Schrödinger's cat - so which one am I ???

I think at nearly £200 a set the gauge should be pretty damn accurate!

It's a lot better than torquing and the prefered method by ARP so I'm doing it their way so if anything brakes I have something to go back to them with.

http://turbominis.co.uk/forums/index.php?p=vt&tid=170151

ARP suggst the best method to preload the bolts is by measuring the stretch. They supply with all their bolts the required stretch values to achieve the design preload. Its available on their website and I also linked to the ARP instruction sheet for the Big Journal A series rod bolts somewhere else on this forum.

setting the preload using the stretch method is the most accurate way to tighten the bolts to the design values, it does not then matter about thread friction

Agreed that measuring "stretch" (elongation) is by far the best way of setting pre-load - it's what we do with all the high integrity bolting in my industry - but that device just seems rather a crude way of doing it compared to what I'm used to.

But I suppose there is a limit as to how to measure it accurately on such small bolts :)

Schrödinger's cat - so which one am I ???

what kind of gauge is used to do head studs in this way? i assume its like a dial indicate that mounts on the head next to the stud?