Rod Stretch Bolts

[lv2race]

I’m installing Carrillo bolts onto Carrillo rods and using the Carrillo stretch bolt gauge. Spec is .005” to .0065” of stretch.

The first two rods I torqued to 38 ft-lbs which stretched the bolts .003”. When I torqued to 40 ft-lbs the bolts stretched to .009” in both cases. I’m using a Snap-On torque wrench.

Has anyone else seen this?

Thanks,

Rob

[Harpo]

Is that stretch specification for lubed or dry bolts?

David

[lv2race]

Originally Posted by Harpo

Is that stretch specification for lubed or dry bolts?

David

Lubed I believe.

[stownsen914]

To be clear, the increment of from 38 ft-lbs to 40 yielded the additional .006" of stretch?

[lv2race]

Yes, that’s what I’m seeing.

[Neil Harvey]

Here is a suggestion of how to.

First, before you even install the bolt, number them and measure their free length before fitting. This way you can always check if they return to their free length after stretching. If they don't, throw them away.

Second, lube the threads and under the head of the bolt.

It doesn't matter what torque wrench you are using if you are using the stretch method.

Third, if you have to add more stretch, always loosen first, then add more turning radius or torque. It takes more effort to over come the friction on a bolt that is already in tension. If you did not do this, loosen the bolt, then re torque the bolt to 40 ft/lbs.

But first make sure the bolt has not stretched past its yield. The only way is to know what it measured before you installed it.

[lv2race]

Thanks, I didn’t measure the overall length before I tried the first two rods but that’s a good suggestion.

I’ll order new bolts just to be safe.

Thanks for the suggested procedure.

Rob

[Neil Harvey]

Originally Posted by lv2race

Thanks, I didn’t measure the overall length before I tried the first two rods but that’s a good suggestion.

I’ll order new bolts just to be safe.

Thanks for the suggested procedure.

Rob

Glad you understand.

Once you have numbered all the bolts, measured their free lengths, assign them to a rod in your records. Lube them with whatever anti friction grease you are using, under the heads as well, install them and torque each bolt to 15-20 lbs. Pick a value, it doesn't matter, all you are doing is seating the cap to the beam. Make sure before hand the parting lines are clean.

Undo one bolt at a time and do your angle or torque making sure you do it in one single movement. Once one bolt is to the correct value, undo the other bolt and repeat.

[lv2race]

I’ve been using bolts that I will throw out to seat the beam to the cap (I have plenty at this point). Then I take one of the bolts out and install a new lubed bolt. I can tell if it retains its original length after I torque it by loosening it and seeing if the gauge homes back to zero. I’m getting about 2-3 good torques out of a bolt before it starts to deviate from the home reading of zero (by about .005”).

After much trial and error, with increasing torque by 2 lbs at a time, I finally got a bolt to reach the minimum spec of .005”, first try with the bolt torqued in one motion. The value on the torque wrench is 60 ft-lbs to achieve this. I would prefer to be in the center of the spec though at around.00575”.

I’m assuming the whole purpose of measuring the stretch is that you will get a more precise reading than by using a torque wrench which I would have just torqued to 40 ft-lbs in the past.

I’m certainly sensitive to the measurement having thrown a rod at Watkins Glen. At the time I was using stock rods and stock bolts.

Thanks again.

Rob

[Neil Harvey]

Originally Posted by lv2race

I’ve been using bolts that I will throw out to seat the beam to the cap (I have plenty at this point). Then I take one of the bolts out and install a new lubed bolt. I can tell if it retains its original length after I torque it by loosening it and seeing if the gauge homes back to zero. I’m getting about 2-3 good torques out of a bolt before it starts to deviate from the home reading of zero (by about .005”).

After much trial and error, with increasing torque by 2 lbs at a time, I finally got a bolt to reach the minimum spec of .005”, first try with the bolt torqued in one motion. The value on the torque wrench is 60 ft-lbs to achieve this. I would prefer to be in the center of the spec though at around.00575”.

I’m assuming the whole purpose of measuring the stretch is that you will get a more precise reading than by using a torque wrench which I would have just torqued to 40 ft-lbs in the past.

I’m certainly sensitive to the measurement having thrown a rod at Watkins Glen. At the time I was using stock rods and stock bolts.

Thanks again.

Rob

Good job!!

By measuring the stretch you eliminate the friction factor.