The ARP web site, which URL I've lost, has a good explanation of how to
torque bolts, very much in line with Larry below. A detail is that the
torque (in Lbs/Ft, not PSI) to reach a desired stretch can vary widely
depending on the type of lube - engine oil (which i use on threads) needs
higher torque than moly paste, which is what ARP recommends. Getting the
pre-load (stretch) is the important thing, though.
One thing I've always questioned - the amount of stretch to give a certain
amount of preload will vary depending on the length of the bolt being
stretched, which I assume is the distance from the bolt to the first
engaged thread. This can vary depending on the depth of the rod cap
(assuming a threaded hole in the rod, not a nut), and I have rods that vary
from a half inch to almost an inch in this dimension. If the application
is for a nut and bolt (like Cooper S 1275 A-series), then the distance is
about 1.75". Yet I torque all of these fasteners (all 3/8" fine thread) to
the same rough value of 35 - 40 Lbs-Ft. A 3/8" head stud, with 3" or so
fastener length, is torqued to 55 Lbs-Ft. I wonder how to calculate the
amount of stretch for different fastener lengths?
Brian
At 08:58 AM 1/5/01 -0500, lwdent wrote:
>No lock tite. No locking tabs. Just clean well, lube and torque to
>spec.
>
>For rod bolts stretch is best.
>
>Get a stretch gauge from Speedway in Neb. and stretch to spec. Gauge is
>only $65.00.
>
>Or use a mike to determine stretch.
>
>On new bolts mike each before installing and record. When they are over
>torque's they will not come back to original reading and have reached
>yield and should be tossed. Mfg of bolts will give spec on how much
>stretch, usually around .0063 to .0067 at 40 PSI torque.
>
>You can use them over till you over torque and they yield. THEN TOSS.
>
>Larry Dent
Brian Evans
Director, Strategic Accounts
UUNET, A WorldCom Company
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