stretch gauge beginner question

[Trakrat]

So... I have an ARP stretch gauge to make sure I am properly measuring my ARP 2000 rod bolts.

Please forgive my ignorance on using this stretch gauge.

1.) When I read on here to 'zero out the stretch gauge'... does this mean to turn the dial to ZERO while the gauge has a bolt in it that isn't yet torqued down? If so... the smaller dial on the face won't go to zero (I'm not even sure what that very small dial represents)

2.) The dial numbers are confusing to me... what does the very small dial represent? Why are there red numbers next to some of the other numbers in the larger dial? What does each number represent? (meaning.. if the indicator is on 10.. what does this mean?)

3.) When I turn the screw at the top of the gauge, it turns the dial, but when the gauge is on the bolt, it doesn't do much... why would I want to do this? If I turn it too much, it comes right off.

4.) What would I use the black markers for... is this like a memory of where the measurement was? (If so... just touching the gauge tends to throw the reading off)

5.) And finally.. it would be helpful if I had a step-by-step on what to measure, how to read the gauge, etc...

I THINK I know what to do, but need someone to verify it.
Step 1.) Please a bolt in the gauge and turn the dial to zero. move the marker to this position
Step 2.) Tighten the bolt onto the rod using the ARP documentation's recommended torque settings.
Step 3.) Use the stretch gauge to measure the bolt attached to the rod and mark it's location.
Step 4.) verify that the difference is within the recommended measurement of ARP's documentation.
----but what exactly do the numbers on dial represent in terms of measurement?

[jons911]

1) To zero the gauge, rotate the bezel which should turn the outer face so the 0 aligns with the needle. You do this for the loose rod bolt to set a reference. Then, once the rod bolt has been tightened down, you check again without having changed your reference on the gauge. Now the needle will be offset from 0 indicating the amount of stretch. The inner dial is to tell you where in the overall range the needle is at. It looks like it says 0-10 on the face, so I'm guessing you have a 0-10mm dial indicator. In which case, in the picture above, the needle is maybe 1-2 mm (hard to read) through it's range of travel. The range of motion for the needle is fixed, so you can't change the small inner dial.

2) The outer numbers should represent length in 0.01mm increments. So 5 is 0.05, and 10 is 0.10. The numbers in red are just the reciprocal to make it easier depending on which direction you are measuring. For the smaller dial, see #1.

3) Honestly, I can't remember.

4) The black marker is just that, a marker. Use it to mark a specific measurement to compare another measurement to, or whatever else you see fit. Specifically for measuring rod bolts, I would say you don't need it.

How to install your rod bolts with a dial indicator:
1) Put the gauge on the loose rod bolt and zero it out. If you would like to do both rod bolts at the same time so you can torque them down together, place the gauge on the other rod bolt and instead of zeroing out the gauge move the black marker over to the second bolts zero position.

2) Follow ARP's instructions for tightening down the rod bolts. I can't say much more because I used Carrillo rods with their bolts and measured with a micrometer.

3) To check the amount of stretch, place the gauge back on the bolt and note the displacement of the needle from your zero position. Make sure to use the correct zero position for that given bolt if you are doing both at the same time. Keep in mind that torque is very susceptible to mating surface condition, so be sure to follow the installation instructions carefully when it comes to using assembly lube or not. If the installation torque you used varies a little from what ARP specified, that's ok, refer to your stretch measurements. Carrillo told me to easily go up another 7-10 lb-ft since my stretch measurements came in under spec.

[boyt911sc]

Trakrat,

To set the stretch gauge to ZERO, there should be no bolt at the gauge. See picture below.


If the pointer does not go to ZERO, rotate the dial CW or CCW and set to ZERO.

The small dial has 0.10” increment and my gauge is set @ 0.50”. The dial has to make two (2) revolutions to register a 0.10”. The very first line or mark after ZERO is 0.001+”. Let say the pointer is between 1st. & 2nd. lines (0.001+) or could be read as 0.0015”. The 4th digit is a little bit tricky because you have to estimate the reading between 0.0001~0.0009.

You have to do some practice measurements using old or new connecting rod bolts. You are using a STRETCH GAUGE and measuring the difference before and after. And if you are familiar with the Excel program, computation would be very convenient.

Lastly, I used and saved a CONTROL bolt to check and confirm that the stretch gauge has not changed its setting. So if you get the same value for the CONTROL after the end the job, you could be assured that stretch gauge has not been compromised. Example, if you dropped the gauge during the process, it might change the setting. To verify, use the control bolt.

Time to start your practice measurements.

Tony

[boyt911sc]

Trakrat,

I found last night an old data sheet dated March 23, 2012. This might help you understand my previous post.



Control bolt is optional. I just find it helpful to confirm after the installation that the ARP Stretch Gauge has not been compromised or altered. Also take note that both torque and stretch methods were done for this job.

Tony

[jons911]

Well scratch my comment. You should definitely listen to the person who has the same dial indicator and bolts as you do.

[gtc]

I used the same stretch gauge. I found that it was important to make certain that the pins were fully seated in the dimples at the end of the bolt before you take your measurements. The bull-nose pin on the gauge end was a bit too large and did not seat well.

[Jeff Alton]

To measure the actual stretch, Zero the gauge once installed on the bolt and fully seated. NO point zeroing it while it has nothing to measure.

[boyt911sc]

Originally Posted by Jeff Alton

To measure the actual stretch, Zero the gauge once installed on the bolt and fully seated. NO point zeroing it while it has nothing to measure.

Jeff,

Then how do you calculate the stretch value if you set it to ZERO without saving the initial value for multiple measurements? As shown in the calculation sheet, you need the finial value minus the initial value. The difference is the STRETCH value.

Tony

[TimT]

To measure the actual stretch, Zero the gauge once installed on the bolt and fully seated. NO point zeroing it while it has nothing to measure.

Thats it in a nutshell, the stretch is the difference between a relaxed bolt vs. a tensioned bolt.

Knowing the overall length of the bolt before hand isn't really necessary. Though I've had to prepare reports for agencies that require all sorts of extraneous info (I've used extensometers on an industrial scale, Think every bolt on every cable band on a suspension bridge)

Zero the gauge, tension the bolt, reapply the gauge, and note the "absolute" reading disregarding signs. That number is the stretch

Rinse repeat 11 more bolts..

Lets do this on the Williamsburg Bridge now....120 cable bands/cable, min 8 bolts/band, 4 cables...We know the change in length of 3840 bolts from untensioned to tensioned.

[boyt911sc]

Originally Posted by TimT

Thats it in a nutshell, the stretch is the difference between a relaxed bolt vs. a tensioned bolt.

Knowing the overall length of the bolt before hand isn't really necessary. Though I've had to prepare reports for agencies that require all sorts of extraneous info (I've used extensometers on an industrial scale, Think every bolt on every cable band on a suspension bridge)

Zero the gauge, tension the bolt, reapply the gauge, and note the "absolute" reading disregarding signs. That number is the stretch

Rinse repeat 11 more bolts..

Lets do this on the Williamsburg Bridge now....120 cable bands/cable, min 8 bolts/band, 4 cables...We know the change in length of 3840 bolts from untensioned to tensioned.

Tim,

After doing the 12 bolts, how do you go back and recheck your work? With your method, once you moved to the next bolt and re-zero it, the data for previous bolt is erased and lost. So you would have no way of re-checking your measurements. And would hope that everything was done perfectly. That is not metrology.

Tony

[burgermeister]

I added a light spring to my gage so it clamps more tightly. Had to lightly round off the points so they would register properly in the bolt. In that configuration, it stays put on the rod bolt.

I then use an 11mm 12 point wrench and some conduit as an extension handle, and torque the rod bolt with the gage hanging off it. Avoids the error from re-seating the gage, and also avoids the tighten / check / tighten / check cycle. Downside is you clamp one end down while the other is just lightly tightened. I don't see that as an issue, but others probably do.

[Walt Fricke]

Well, I've always zeroed my gauge against the appropriate length rod-like piece used to check micrometers. If a 2" block, zero is 2", relaxed measurement is 2" + what is measured, etc. Yes, you have to do a little arithmetic, but so what. So it is repeatable. And the blocks aren't quite as suitable for dial indicator points as for micrometer flats, but you can work at it until you get a minimum. No need to reset things.

[Jeff Alton]

Originally Posted by boyt911sc

Jeff,

Then how do you calculate the stretch value if you set it to ZERO without saving the initial value for multiple measurements? As shown in the calculation sheet, you need the finial value minus the initial value. The difference is the STRETCH value.

Tony

We are using a stretch gauge, not a micrometer. It measures, via a dial indicator, the actual elongation of the fastener. The gauge makes the actual numerical value of the length of the bolt irrelevant for the measurement. You can't measure the length of the bolt with a stretch gauge.

[stownsen914]

Is there a reason why a suitably sized outside micrometer can't be used to measure stretch on rod bolts? I get the convenience of a stretch gauge, but I'm a DIYer and build motors periodically (hopefully!)

['78 SC]

Originally Posted by stownsen914

Is there a reason why a suitably sized outside micrometer can't be used to measure stretch on rod bolts? I get the convenience of a stretch gauge, but I'm a DIYer and build motors periodically (hopefully!)

A micrometer works fine. You can get tips (McMaster Carr) that will fit into the dimples on the bolts to help center the micrometer (some Raceware hardware does not have dimples and works with regular micrometer anvils).

[burgermeister]

The ARP bolts I used had a little bit of burr on their tips... prevented a repeatable length measurement. Just a light pass on a 400 grit belt sander took off the burr, and then the bolt measured repeatable across the flats. I think that would work just fine to measure stretch.

I measured all of mine to see - next time the motor comes apart - if I yielded a bolt. Seems like the motors always do come apart, eventually, unless I don't drive the confounded things. Somehow the mythical 250K mile never touched air cooled motor has eluded me.