Well, I know you will all make fun of me for being so old fashioned. But I have always used a torque wrench to install rod bolts in the past. With these new super-duper Oliver rods and fancy rod bolts I decided to try the "stretch" method. I can't see how you could use anything other than an end wrench to do this (while keeping the indicator on the bolt). I can't get enough leverage with an end wrench to stretch the bolts enough. Do you use a ratchet a little at a time? Or do all of you have much stronger arms and hands than I do? Do I need to look for a long, tall end wrench? Or what?

I think I will break out the old, trusty Snap-On torque wrench and just forget the stretch method

Rich Krause

 

Interesting, I've never heard of this method.

I have a feeling it has something to do with achieving proper torque
versus strechting the bolt to a predetermined length to ensure
proper loading.

My guess is that other factors preventing a torque wrench from
applying proper torque to the bolt are eliminated with the stretch
method (dirty bores, lack of lube, etc) ?

Don't mind me...I'm just thinking out loud. I have no idea what
you're talking about, but I'll look damn good if I'm correct.

 

Good question.

Here's ARP's take on it:
Here's a link to the catalogue showing the stretch gauge (ARP Part# 100-9941): http://www.arp-bolts.com/media/pdf_files/TO_65-66.pdf

Couldn't find the direct link, but here's a quote from ARP's online catalogue (looks like a micrometer would be fine... and you can alternate tightening / measuring until you get the proper stretch):


If you give up, here's their conversion chart for torque specs (depending on what lubricant you utilize): http://www.arp-bolts.com/pages/tech/images/fasttorq.pdf

 

This is not exaclty correct but what I do is set my torque wrench about 10 ft-lbs shy of what ARP says is the proper torque spec using their lube and stuff. Then measure the bolt loose with the stretch gage and write it down. Then torque the bolt to the preset torque reading. Then measure the bolt again. if no change increase by 5 ft lbs and remeasure until you get the .001 stretch or whatever your bolts are to be streached to, also make sure you looking at the right bolts on the chart ARP sells lots of different alloy rod bolts and the ones Oliver and the like use aren't always the default ones listed for a SBC.

Once I have the torque setting that yeilds the desired strecth I'll measure all the bolts and torque them all down. check afterwards to make sure they are +\-.001 of the desired reading. I think most are to be streched like .002 to .003.

you don't have tighten these down with the stretch gage in place but if you really want to you could get one of those wrenches with the hole in the middle and hope it has a really long handle and can take the torque setting.

 

I know the stretch guage method is the best but I've never done it myself. I'm still old tech and torque them 3 times.

Torque to yield is only really good if you can measure the untorqued bolts to see if they're stretched to begin with.

Head bolts on a Cummins N14 are first checked against a length guage to see if any are stretched (never found one yet). They're then torqued down to 220 pounds in a progressive sequence. They're then tightened an additional 1/4 turn. I have no idea what that final torque is but I would guess it's in the 400 pound range. You have to figure that the head bolt must stretch a lot in that final stage. The specs don't give an actual final torque so they'll vary from bolt to bolt unless you do a perfect 90* every time.

With the rod bolts if torque varies by a few pounds, it shouldn't make very much of a difference. Remember before clicker torque wrenches were around people used a spring bar torque wrench and those things couldn't do 2 bolts the same for accuracy.

As for using a box end wrench on the rod bolt, if you need more leverage you could always double wrench it.

I always liked the 3 torque method. First torque sets the bolts and does an initial crush of the bearing. Second torque cleans the threads. Third torque is the final set.

 

Excellent question rich.

Excellent response Steve in Seattle.

At one time I saw, but never had, a funny looking adapter that went over the rod nut like a box wrench, but bent around over the stretch dial indicator and had another 1/2 square end (aligned with the rod centerline) where you could insert torque wrench.

Just torque, measure, increase torque a few lb-ft and remeasure stretch. Assuming you lube correctly, per APR's recommendation, you'll be able to come very close to your final stretch value by staying a few lb-ft below what you found on the first bolt. This will minimize the number of stretch measurements you need to take. A 3/8-24 stretches about .0001 per degree you move the nut when you get into the stretch zone, so getting the last .004 or so stretch is only about 35-40 degrees of rotation.

Many good rod bolts have centers, or machined conical depressions in the center of both ends to locate the stretch gage or pointed-end micrometers. Otherwise you need a ground flat on each end of the bolts to accurately measure.

Depending on the diameter, material and bolt length, stretch varies from about .005 to .007 on rod bolts we might use but a specific bolt stretch should be held a close as you can get it.

IMO, you need a dial indicator with a minimum of .0005 readings because stretch tolerances are .0004 to .0005. A .0001 dial indicator might be better. It only needs about .010 travel if you set it with an unstretched bolt. Some bolt stretch gages come with a .001 indicator. See Arrow Precision's discussion here, some of which is from ARP:

http://www.arrowprecision.co.uk/assets/arod_care.pdf

Page 6 has a nice chart.

If you are using titanium rods (is that next, rich?), note the lube procedures.

Everyone first torques/stretches their assembled rod/bearings with the rods out of the engine, right? Also note the recommendation to torque/stretch new bolts 5 times to minimize the friction factor if bolts cannot be measured for stretch in the assembled rod. Not a bad idea for all new rod bolts, IMO.

Remember you are not "torquing to yield" rod bolts. You are staying below the yield point because the rod bolts get cycling loads, as was pointed out. If you measure and record the free length of new bolts, and remeasure after the engine is torn down for rebuild, and you find the bolt has permanently stretched as much as .001, it's time to replace the bolts. If you don't have that data, and you are rebuilding a highly stressed engine, replacing the rod bolts is a good idea.


My $.02

 

Thanks for the replies so far. Very informative! I think I am going to use the method that's worked for me in the past. Prestretch 5 times, then install using the specified lube and a good torque wrench. I may measure the bolts in order to be able to check on stretch at the next teardown. But this would be sort of academic as I replace them each time anyway. OTOH, maybe I don't need to if I check the stretch?

The bolts are ARP "WSP" 7/16" as supplied by Oliver. Funny that ARP doesn't seem to list "WSP" on their web site. Anyone know what material these actually are? When I talked to Oliver they indicated that the bolts would be fine for my application, so I took their word for it. I could have gotten the "L19" bolts but they (Oliver) implied these weren't ideal for a street motor due to possible corrosion and that they just weren't needed.

Rich Krause

 

There are a few things that i have done...

Although I haven't installed rods yet.. .but on the heads.. I take a pointer and a small hammer and tap all the screws after my last torque run... Then retorque again to the last specs.. Ive gotten out up to 180 degrees more turn at the same lbs of torque...

Now.. with rod bolts.. I do know this...

Some rod tightening sequences are TTY (torque to Yield) and can ONLY be torqued once since the bolt "streches" and its a use once type bolt...

The instructions are like this: Torque to xxx lbs then xx degrees more or whatever... when I get home I will check on my alldata... Most rod bolts are TTY... GM started using this from lt1s 96 and up engines...

Hope this helps.

 

Yes, GM uses angle torque readings for installing engine bolts, but that doesn't necessarily make them TTY bolts! I believe that if they are TTY, the instructions say to replace them after one use with NEW bolts, to quote the manual. LS1 shop manual does NOT say rod and main cap bolts are TTY and the only ones they suggest replacing are the main cap cross boltswith a bluilt in sealer in order "To prevent engine block oil leakage".

Rod bolts (LS1) are installed at 15 lb-ft then either 60 degrees more (1st design/single dimple) or 75 degrees more (2nd design/2 dimple). That's equivalent to the total stretch desired. More on the 2nd design because the bodies are slightly smaller diameter so they need to stretch more to get the same clamping load.

Both rod bolts and main cap boots get cycling loads, and IMO are NOT meant to be TTY. Head bolts, on the other hand need to clamp only. Combustion loads are not that high on the bolts, and would probably bend the head casting minutely before they loaded the bolts much more than they are during installation.

FWIW, if you got 180 more turn with a head bolt that had the proper clamping load due to the correct lube or sealant and torquing, you have seriously yielded those bolts. Just my opinion, but that's not something I'd recommend.

 

Its a trick my father taught me... he used to build 240z's engines back in the day...

180 was ONE bolt....

i tapped them lightly and then retorqued to 70 ft-lbs as the 3rd torque session indicated and I got 30-45 degrees on most and 180 on that one... it has worked so far... I will be using new bolts on my new head install

 

You might discuss that method with a tech @ ARP. They might have some advice.

Good luck.

I think I still have a '68 Datsun shop manual (L-16 here) somewhere in my collection.

 

I tend to follow his advice it has worked whenever I had followed it... unless i TOTALLY know.. that is old school in which case it still applies to many things...

But I will... THe purpose of tapping it is to beat the "friction" forces and thus have the correct clamping force...

 

Not to rag on the old Man, because I'm probably older than he, but the reason torque is used to apply load to a bolt is all about friction. If you properly (or don't) lube based on the manufacturer's instructions, a certain torque should result in a given amount of stretch and therefore the desired preload with the friction that exists in the nut/bolt interface with the specified lube or dry, if so specified. Using slipperier lube, or "relieving" the friction once torque is reached merely increases the possible bolt load/stretch you can achieve when you retorque to the spec, and can easily yield the bolt. Once you get much past the yield point, the load starts to drop off with more stretch. It looks a lot like a hp curve if you plot it, and you are operating well past hp peak.

FWIW: A lot of things in nature have that characteristic curve. Airplane wings with lift plotted against angle of attack, as well as tire side force when ploted against slip angle are a couple of examples. You certainly don't want to "stall" your bolt.

Using moly lube vs. motor oil in bolt threads changes the torque necessary to achieve the desired load. Same with lubed vs. dry. Some bolted applications are designed to be assembled dry, like wheel nuts, and some with lube or sealer like some SBC head bolts. It does make a big difference.

My $.02

 

ARP makes Eagles stuff too, and all bolts that are made for a certain manufacture ARP will not sell to you, you hav eto go to the company who makes the rods and get the botls thru them. In an industry as small as the high performance fasteners bussiness there are only a few companies in the world who do this.

L19 bolts are a pain in the ***, but in some instances they are needed. If I remember right MindGame said he was using them in his motor. The corrosion problem is called hydrogen embrittlement. It's from the material used in those bolts, and it can happen if you touch the bolts by hand and and get any sweat or oils or even any water on them. The bolt will only corrode after it is TQ'ed down and has a stretch on it, then it slowly fatugies and breaks. They can be used, and in some instances they should be used, but you have to handle them carefully. Once they are in a motor full of oil then you will be ok. A good place to use them is in a Eagle H beam when you plan on putting 750hp thru them. Good rod bolts are always a plus! but the L19's are not a noivce item.

I have to say that Oliver Rods are probably the best designed connecting rods out there.

Highlander,

About this tapping the bolt thing, I gotta say I would listen to my old man rather than yours. Once you break a bolt from doing this the $$$ lesson will be enough for you not to do it again.


Bret

 

Here's a good cross-reference thread that was just reactivated in LT1- Tech on just this subject.

http://web.camaross.com/forums/showt...hreadid=221187