How do I measure my ARP rod bolts with my micrometer if they dont have points?

[JonT]

My ARP stretch gauge has points that fit into the ends of the rod bolts but my micrometer has flat ends that make contact with the part being measured. This lends itself to some variability in results due to the ends of the bolts being rounded. What can I do about this?

[TimT]

You dont need to know how long the bolt is before you tension it...

Assemble the rod on the crank, snug up the nuts, install the stretch gauge and zero it, then tighten the nut until you have the required stretch..

You can leave the stretch gauge on the bolt while doing this, or remove it, if you remove the stretch gauge, do not rotate the dial on the gauge or you will lose your zero...

tighten, reinstall gauge, wash rinse repeat...


Better to leave gauge in place so you don't risk losing your zero...

Good article with explanations..... We use stretch gauges on bolts up to 2" dia in some very critical applications, and sometimes use ultrasound to measure stretch when a physical gauge cannot be used...

How to Use Rod Bolt Stretch Tool Stretching Exercise - Car Craft Magazine

[JonT]

Thanks Tim but I was referring to ARP's recommendation to measure each bolt for future reference if needed. I have been practicing with the stretch gauge itself and have become familiar with it enough to start fastening my rods to the crank with the new ARP bolts.

[TimT]

Not sure what brand of mic you have, but you can get different tips for most of the big players.. get some ball tips and you can measure away....

McMAster

I wonder what the rationale is for knowing the original length of the bolt.. Does the bolt returns to the original number after it has been stretched and put through a few hundred thousand cycles..?

[JonT]

Per arp if the bolts measure more than .001 than their original length they have been permanently deformed and should be replaced.

Re the McMaster site...thanks for the tip on the tips.....

[gtc]

I used a pair of high quality calipers and measured the bolts end to end before and after. Worked just fine, and all of my caliper measurements were in line with my stretch gauge measurements.
Those tips are probably a better idea, though, if you are using a micrometer.

[wdfifteen]

Originally Posted by TimT

I wonder what the rationale is for knowing the original length of the bolt.. Does the bolt returns to the original number after it has been stretched and put through a few hundred thousand cycles..?

Hopefully, yes. But if you don't know the original length, how would you know?

[Gordo2]

Tim hit the nail on the head - a good mic has removable tips with a variety of tips you can buy.

Here's a thread on measuring with flat mic tips - didn't really work:

Measuring ARP Rod Bolt Stretch - Micrometer vs. Stretch Gauge

And here's a few thoughts on measuring stretch from my experience:

Summit Racing Rod Bolt Stretch Gauge Review

Good luck,

Gordo

[boyt911sc]

Originally Posted by JonT

Thanks Tim but I was referring to ARP's recommendation to measure each bolt for future reference if needed. I have been practicing with the stretch gauge itself and have become familiar with it enough to start fastening my rods to the crank with the new ARP bolts.

JonT,

You need to know the initial length of each bolt before installation and the final length after final torque. The difference before and after will determine if you achieved the correct "stretch". I've done a half dozen engines with ARP bolts and the tabulated data (Excel) show how reliable is your torque wrench versus stretch length.

Keep your ARP gauge set or calibrated with a control bolt. If you keep adjusting the ARP gauge each time you stretch a bolt, there will too many variable. This is how I do it and obtained very reliable and uniform data.

First I set the ARP gauge. Choose a convenient number and stick to it. Have a control bolt and measure it at room temperature. Save the bolt and its measurement in the box. Measure each ARP bolt and place it in a small zip lock bag with label. Do the rest.

If you are balancing the weights and have to use a certain bolt at a particular rod, the labeled bags would be very helpful. Apply the required torque and lubricant as suggested by the manufacturer and measure the bolt/s. If your torque wrench is well calibrated, the applied recommended torque would deliver the correct stretch value. Measure the bolts with the stretch gauge. Tabulated the data in an Excel format.

Make sure you don't exceed the stretched value. Since my torque wrench had been successful in the past, I used the recommended torque value and did the stretch gauge side by side. Your first time installation would be nerve wrecking, the following would be much fun and easier.

Tony

[gtc]

I strongly disagree with the post above.
Several people here (including myself) have noted that:
a) the suggested torque generally does not result in the suggested stretch
b) the torque required to achieve the suggested stretch is not even across all 12 bolts

Furthermore, that "control bolt" procedure is meaningless.

[boyt911sc]

Originally Posted by gtc

I strongly disagree with the post above.
Several people here (including myself) have noted that:
a) the suggested torque generally does not result in the suggested stretch
b) the torque required to achieve the suggested stretch is not even across all 12 bolts

Furthermore, that "control bolt" procedure is meaningless.

Graham,

I agree with items A & B. That is why you use the gauge to measure the stretch or elongation of the bolt/s. However, if you have a well calibrated torque wrench, the recommended torque would deliver a very close value of stretch.

A control bolt or gauge is meaningless to you until you accidentally drop the gauge and altered the calibration. I don't know if you have experience in metrology but in my previous life I used Angstron, nanometer, and electron microscope to measure things.

You must have misunderstood or misinterpreted my post because the stretch gauge was final test.

Tony

[Trackrash]

Perhaps my bolts, ARP for my 3,0, are different than some others? I had no problem using my standard mic to get reliable measurements of my bolts.
I chose this method because, as ARP states, the length of the bolts should not change if being reused. This requires documentation of each bolts length. It was not really a problem for me to mic each bolt before and after torquing.
I used generous amounts of ARP's supplied lube and found that after torquing each bolt the stretch was within range.

[IXjamesXI]

I think like others have mentioned you need to have ball tip anvils for your mic to make using a mic worthwhile. Another data point for the pile, i recently installed a set of the M10 arp hardware (3.0 crank) and did so in concert with a torque wrench. Ended up 5-10 lbs ft more than arp suggested 50# torque in order to get the stretch numbers in the specified range.

[KTL]

This can go off on all sorts of tangents, but some are certainly worth mentioning. One tangent that came to mind for me is the torque spec. vs. stretch length with respect to lubricant. In other words, your applied torque is VERY sensitive to what lubricant is being used. On the other hand, stretch is stretch regardless of how the threads are being lubricated.