ARP Rod Bolt Stretching, on the Crank with Bearing or Not?

[Determined]

When performing ARP's recommended procedure for stretching the bolts to specification, should this be done while on the crank with the bearing or on a vise without bearing in place?

Thanks for your support!

Alex

[davidppp]

Hello, Alex.

If we do the rods up nice an tight in a vice, won't it be kinda hard to get the rods onto the crank?

Seriously....you really need to work with and alongside someone who has a bit of background in engine building if you need to ask this..its great to see guys with The Force to go for it, but the 911 motor is not a suitable motor to learn the basics on..

The purpose of the bolt stretch measurement is simply to ensure the bolts are under the correct strain when assembled, and will not come loose, or allow fretting....not to permanently stretch them.


It is a much superior method to torque settings, which result in wide variations in fitted strain.

Kind regards
David

[Jeff Jagusch]

Hi Alex,

I assume that you are referring to the instructions that say to tighten and loosen them a couple times.

For this, I would assume that they do not need to be on the crank.
The process is to get the bolt and nut comfortable with each other
(for lack of a more technical explanation).

This reduces the variation in bolt stretch when you are using a torque wrench for the final assembly.

The ideal method is to measure the stretch of each rod bolt when assembled on the crank.

Hope that answers your question?

Jeff

[Determined]

Thanks Jeff and David,

I found a few more forums on this subject and it looks like it can be done in a vise since the objective is to stretch the bolts first before final assembly and torqueing. Thank you both for your time. Oh, I'm not new to engine rebuilding but only new to using ARP rod bolts.

Best Regards,

Alex

[chancecasey]

No - it's not to stretch the bolts prior to final assembly. NOT. It's to burnish the nut and rod cap surfaces to reduce friction during final assembly, giving a somewhat more accurate result when using the torque method. Do not use the torque method if you have a stretch gauge. Use the stretch method.

Put the rods and bearings and assembly lube (between crank and bearing) on and, using a stretch guage, stretch the bolts the prescribed amount (mine were .012" IIRC, yours may be different.) You are now finished. Wasn't that easy?

If you have a stretch gauge, you are wasting your time assembling things more than once.

The stretch is elastic, they will "shrink" back mostly once you unload them. Permanently stretching them, multiple times, is not a good thing imho, although ARP claims they can be reused after permanent stretching. But how many times is undefined AFIK - I mean obviously there's a breaking point.

Use the stretch gauge, assembly ONCE, stretching the indicated amount. There's also a GREAT thread here about how to do this with the crank still in the case.

[Determined]

Thank you Chance, I really appreciate your comments and time to clarify this procedure. I will perform the stretch method. I assume you gradually stretch each one until you reach the desired stretch, my instructions included with the ARP rods call out .0117" to .012". Do you alternate until the stretch is reached or stretch one then do the other?

Thanks again!

Alex

[chancecasey]

No problemo! I learned a lot about these the HARD way.

1. torque both nuts to 5 foot pounds (this will not stretch the bolts at all)

2. Put on your stretch gauge and do one at a time - the full stretch.

You will likely be turning each about 135 degrees after the initial 5 foot pound snug-up.


P.S. - you'll need more than just a small box end wrench to get the full .012" - can be as much as 50 foot pounds sometimes - so get a big ratchet or something - small box end won't cut it.

[ken180]

Might read this.

Ken

http://www.arp-bolts.com/Tech/TechInstall.html
http://www.arp-bolts.com/Tech/TechTorque.html

[snowman]

A stretch guage is a dial indicator arranged in something that looks like a C clamp, one end goes on the head of the bolt and the other on the end of the bolt. If the overall length of the bolt changes it will register on the dial indicator. The rod and bearings are loosly assembled on the crankshaft, the stretch guage is connected to one of the rod bolts. That same bolt is tightened, using a high quality box end wrench with a pipe or something for an extension (the wrench is usually to short to get enough torque on it), while observing the dial indicator. Once you see the desired stretch,, say 0.012", you are DONE with that bolt, go on to the next one. An alternate method is to measure the bolt length, when it is loose, using a micrometer. Tighten in very small increments untill the bolt is 0.012" longer or whatever the desired stretch is, much more time consuming, but it works. Rember, the bolt is in place, on the rod and bearing, on the crankshaft. This is the FINAL assembly.

The alternate method ARP uses is to tighten and loosen the bolt several times to burnish the threads, and then torque to a final value. Unfortunatly this method may leave 20% or more of the clamping force on the table as a necessary safety factor. In my opinion, if you use this method, you might as well use factory torque to yield bolts. They are very good, cost less, and the tightening method is almost foolproof, as long as you NEVER reuse, retighten one.

A high quality rod,like Carrillo, requires the stretch method. The SPS multiphase bolts are up to 30% stronger than the best ARP. 320,000lbs vs 220,000lbs, 180,000lbs typ.. Of course cost is not an object. Bolts are $25 ea vs $4 ea. Note, these are NOT required on any streetable engine.

[JoeMag]

When i built my engine last year I found what the others are mentioning also, is that you leave some torque on the table if you use torque method. I'd also keep the initial lenght of bolts so you can tell in future dis-assembles if they have been permenantly stretched.

[BReyes]

'A stretch guage is a dial indicator arranged in something that looks like a C clamp"

Is the tool a separate tool or can use what use with a z-block e.g.?

[snowman]

A dial indicator is a dial indicator, about $10 at Harbor freight. The C clamp arrangement is about $120, including a dial indicator. Once you see one you can easily make your own, but if you want to you can buy one. I haven't looked lately but they should be available on line or check the links at ARP. Some may cost more, but there is no justification for it.

Here is one http://carshop.carshopinc.com/product_info.php/products_id/59234/CSRBSG

and another http://www.amazon.com/Proform-PRO-66788-Indicator-Adjustable-Capacity/dp/B000A8J5NA

I haven't used either one of these so I can't vouch for their quality, but it gives you the picture of what they look like.

http://www.arp-bolts.com/Catalog/Catalog.html page 88

[Determined]

Thank you Snowman, I appreciate your input and time.

Best Regards,

Alex

[armandodiaz]

I was wondering if it would be useful to use both methods. I would like to torque and loosen 3X to clean the threads as the insturtions state. But use the stretch method as the final install. What do you guys think?

[Determined]

Armando,

I'm doing the same, I performed the torque method and now I'm awaiting my stretch gauge tomorrow. I did premeasure my bolts before the torque approach and they did not grow. I also spoke with AL at ARP and he highly recommends the investment in the stretch gauge. I'm planning to take some pictures through out the process. I just didn't feel comfortable about the torque approach, good luck.

Alex

[eapcpa]

I recently borrowed a stretch guage from a fellow pelican. If you use ARP bolts use the stretch method. My bolts averaged 60 ftlbs before they began getting close to the stretch range. I think the torque spec was around 45 ft lbs. You WILL under torque your bolts even with the three step method ARP recommends. I will reiterate what has been said by others, If you are spending the money for ARP bolts use the stretch method otherwise just use stock Porsche bolts. To perform the stretch procedure, bolt the flywheel lightly on the crank and have a friend hold the crank upright with the flywheel resting on a sturdy bench. You will definitely need more leverage than you can apply with a 12mm box end wrench. I used my torque wrench set on 40lbs. and increased in 5lb increments until I achieved the proper stretch. I would check the stretch at each 5 lb setting. Time consuming but it works. Good luck with your motor and above all have fun.

[snowman]

Just remember, Torque can by off by as much as 50%!!!, Stretch is the only accurate method to tighten a bolt. PS constant tightening and retightening of bolts is not good for them. Tighten it ONCE, tighten it right, use stretch.

[cab83_750]

Guys,

I am starting my rebuild. Do we need to use loctite when using the stretch method?

[Determined]

Are you using ARP rod bolts, if so, you only need the lubricant they provide and no loctite. The bolts are stretched slowly and hold under tension. For factory bolts, I've read in books that it is used, maybe other will jump in.

Good luck, oh....do yourself a favor and use a stretch gage.

Best Regards,

alex

[cab83_750]

Alex,

Thanks for the response.

I am using ARP's. I searched and searched and it looks like I can use my micrometers. I started playing with it last night, and it is working. As a matter of fact, it looks like the torque as recommended by ARP (almost) equals to the stretch.

I thought it was pretty interesting.