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Join Date: Mar 2013
Location: NorthLA
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Rod Bolt Stretch Gauge - tightening sequence

ARP bolts and ARP stretch gauge, using proper lubrication
Question: when tightening, go from 0 to full stretch in one step ? Torqueing is typically a three step progressive process. side to side.
Stretch gauge instructions from ARP and the web make no mention of the technique of "stepping" or just tightening the one side to full stretch.
Using the gauge, I can't see how the adjustment can be done accurately without performing in one motion.
Old 03-02-2018, 08:08 AM
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What I do, is take the other bolt that does not have the stretch gauge on it to about 50% of desired, final torque. Then stretch the bolt with the gauge.

Switch the gauge to the half-torqued bolt and release torque. Then stretch it to spec.
Old 03-02-2018, 09:41 AM
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I did my stretches in one sweep....well....I did each bolt "snug" first to hold the cap in place, then did each bolt in turn to achieve the stretch in one sweep.

ETA: I did stretch my fasteners out-of-situ first, to the lower stretch dimension....a) it burnishes any thread roughness, and b) I can measure each one to ensure it didn't go elastic

ETA (again): In that out-of-situ pre-stretch routine, I used my torque wrench set at the lower limit....torqued it, measured the stretch, then adjusted the torque wrench setting until the stretch was within spec. I then knew that by using my torque wrench to fasten the bolt "proper" that the stretch would be correct. Of course, after each operation, I used the stretch gauge to verify (and indeed, they were all fine)

I'm far from a metallurgist or a fastener specialist but I think the reason to torque in stages is to ensure that you have the correct pre-load tension on the threads, but my concerns have always been about overcoming the stiction on each fastener to start it moving for the second/third stages - I'd always heard that any torque wrench operation should be done in a single, smooth sweep, not stop-and-start, for this reason.

Conversely, by measuring the stretched length of the fastener, you've achieved (directly) what you're trying to accomplish (indirectly) with a torque wrench....so when using a stretch gauge I see no difference in either doing that in one sweep or multiple sweeps, in order to get into that window of thread stretch as specified by ARP or whoever the vendor is.

Just my 2p....
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Last edited by Spenny_b; 03-02-2018 at 09:48 AM..
Old 03-02-2018, 09:43 AM
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Quote:
Originally Posted by Drbraunsr View Post
ARP bolts and ARP stretch gauge, using proper lubrication
Question: when tightening, go from 0 to full stretch in one step ? Torqueing is typically a three step progressive process. side to side.
Stretch gauge instructions from ARP and the web make no mention of the technique of "stepping" or just tightening the one side to full stretch.
Using the gauge, I can't see how the adjustment can be done accurately without performing in one motion.
One turn always, even when torqueing. You are removing the starting friction each time you turn the bolt or nut.

Best way is to seat each bolt of nut to a lower number like 15fl/lbs or 20 Nm whatever units you are using. then loosen one at a time, stretch and record.

This after you have checked the parting lines are clean and no burrs and the underside of the bolt or nut has lube.

Make sure you are using the same grease each time as different grease will give different results. The ARP ultra should be used with their recommended stretch numbers.

Make sure you measure the free length of the bolt first and record this. You want to make sure the bolt returns to this length after checking. If not, do not use.

As long as the bolt returns to its original free length, do not be afraid to stretch the bolt multiple times. They should be stretched in the DIY use, 3 or 4 times.

Time # 1. The shop that rebuilt the rods should have stretched them in resizing the BE.

Time # 2. The DIY checking the machine shop work. This step can be skipped if the rods are returned, assembled and together.

Time # 3. The DIY checking the rod bearing ID size to calculate the bearing clearances.

Time # 4. The DIY doing the final engine assembly.
Old 03-02-2018, 10:51 AM
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Thanks guys for the guidance.
The rods were balanced, BE sized (at ARP torque values) and returned assembled. The crank was mic'd, magnafluxed, and polished. I checked clearances with plastigage.

Did assemble today, using ARP ultra:
Step 1: hand tighten, then tighten with box wrench evenly to mate cap/rod to 0 ft lbs.
Step 2: put box wrench on nut, install ARP stretch gauge with proper pre-load. Zero out, then stretch to final spec.
I'm guessing the total sweep from zero to 0.010" was ~ 120'ish degrees. With the gauge in the way preventing one sweep to get the entire travel, the box wrench needed to be reset about twice - never removing the stretch gauge.

Again, thank you for the help and input
Old 03-02-2018, 05:27 PM
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