I did go back to the youtube video, to make absolutely sure I saw what I saw. The video is from TurboKraft, certainly a well known builder of uber expensive high power Porsche motors. The tech is explaining that they torque the ARP fasters in 3 stages. They didn't show any stretch gauge. They are building 600-900hp motors...

Also, with a stretch gauge, isn't the point to keep it on the bolt while tightening? No one ever does that, as everyone is using a torque wrench to put it on necessitating removal of the dial indicator...

Everytime you remove the dial indicator, you introduce room for error...

That said, being anal, I will probably still buy a new tool to measure bolt length...

Another question... many assembly books recommend Loctite on the rod bolt to prevent it from coming loose... do folks on here do that???

Yep, I work in manufacturing and have to limp along these folks.

No, that's not the method I used.

I used a long reach box end wrench and never took it off the bolt. Just slowly turned the nut until I read 0.0105"????

Not sure on actual stretch, but I believe something like 0.010"?

https://media.tenor.com/images/54451...d53c/tenor.gif

There is a much more intelligent and informative discussion of ARP rod bolts in this thread:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/890139-can-i-reuse-arp-rod-bolts.html

The goal when assembling rods is to preload the rod bolts to a certain point, and measuring stretch is inarguably more accurate than measuring torque.

^Except you can only measure bolt stretch on short bolts like rod bolts, and other fasteners you can get to the back of.

For every other of the dozens of fasteners on the motor you'll need to use either torque or angle or both.

My question to all the bolt stretch champions is what do you guys do on those?

Not knocking the concept, All I am saying is I have built dozens of engines and I make the cases. Reality needs to take hold here on the religiousness of the bolt stretch topic. If you have a gauge, great, use it.

If all you have is a torque wrench, you'll be fine.

Can't say I have seen a failure where one method was used over another.... That said, we do have stretch gauges and we do use them on rod bolts that specify a stretch value. However, we also use digital torque wrenches with angle function where fasteners call for that as well (factory rod bolts). We use the specified method for the rod bolt because we are equiped to do so. Not every builder has this stuff at his disposal.

We have seen a varied torque range when comparing to stretch, but like said above, never seen a failure attributable to the method...

Take a typical click type torque wrench. It clicks, how much more force did you apply after the click? When we first got our digital wrenches we were surprised. They give you plenty of warning through a series of lights and a readout when you are getting close to the specified value. After they beep, flash and vibrate in your hand they tell you the actual torque applied. It is amazingly easy to torque way beyond your goal even with the best equipment.

Put it this way. Think about how many engines have been built that required a rod bolt be torqued to a niminal value, then rotated a specified number of degrees one or more times. How many times did the builder not have a digital readout tell him the exact number of degrees? "That looks like about 90 degrees" has been used plenty of times I am sure.... Do you think most home builders of non failed engines had expensive digital torque wrenches or stretch gaugues that read accurate stetch, torque and degrees?


Just throwing it out their for thought....

"If all you have is a torque wrench, you'll be fine."

Yeah, Harbor Freight has one for 19.99, what could go wrong?

Stretch eliminates both the improper use of a torque wrench by the user plus the possible inaccuracy of the torque wrench itself.

Sure it does, on rod bolts. What do you do for the other bolts?

Don't answer, we already know.

I have four torque wrenches, all good ones and I send them out for a calibration check. I use the stretch gauge on the rod bolts because it is the most accurate way to do it, period. I don't understand why someone is willing to spend several thousand on parts and machine work and then not spend the money req'd to get the right tool for the job. Do you also use "maybe-gauge" for checking the clearances?

Agreed. Bolt stretch gauge eliminates any torque wrench error.

And, if you use a torque wrench at its lower or upper 15% of range, they get inaccurate.

Again, it is ONE manufacturer's "suggested" practice that a stretch gauge be used. That manufacturer is ARP, and I am a dealer for them.

All my torque wrenches are Snap On digitals, they are accurate to 3%. I have probably 3K alone in torque wrenches.

Porsche themselves have never specified a stretch gauge for their rod bolts in any WSM I am aware of.

What I am trying to do is dispel the notion that you NEED a stretch gauge to do this job so some novice reading this won't get the wrong idea. Not even ARP claims you need one.

Depending on the lube or lack thereof used on the bolts, torque variance will be exhibited.

Stretch gauges eliminate this variance 100%.

That's why I'm using one, and I know the bolt is stretched perfectly to manufacturers specs.

Even NASCAR uses stretch, that's where I personally learned this technique from.

^ and what does one do on a factory rod bolt? Is there even a stretch spec?

That's a controlled environment where the same techniques, equipment, and quality checks are used.

Not so much in our garages where folks use Harbor Freight torque wrenches, put 30wt motor oil on the bolt and nut, or their kid threw the torque wrench in the toolbox like a toy (exaggerating, but you get my point). ;)

There's virtually no variability in strecthing.

But that's the thing, Tip, as pro engine builder posted a few posts ago on this thread, plenty of people have done just what you are saying without a failure. I am not defending it, but across the country, hundreds of engines are rebuilt annually by diligent shade tree, non pro mechanics who buy the Porsche bolts, download the WSM, and torque them to spec with their harbor freight wrench.

To my knowledge, there has never been a failure of factory rod bolts when treated with loctite and torqued to spec as per the manual.

I am not speaking about the factory, I am talking about what actually happens in garages and shops every day of the week.

Few people (including yourself apparently) own a stretch gauge and even fewer know how to use them.

Oh, and I do want to acknowledge that you are 100% right in saying stretch is more accurate.

My beef is with the sentiment that failure will occur if stretch is not used.

I 100% understand, I just sleep better knowing I used the stretch method. :)

Wasn't sure anyone stated failure was eminent?

I'd definitely used a calibrated torque wrench if using that method!

Nobody in this thread has put forth such a claim.

You seem to be arguing with your own imagination.

:rolleyes:

For what it is worth, we used to send one of our ARP gauge to members on this forum. We took a deposit, and sent it out. We stopped when we did not get it back one time. For anyone intersted, we would consider doing this again. We have a couple and never have more than one in use at a time.

Cheers