For the benefit of those who are planning to run ARP rod bolts (as well as other aftermarket rod bolts I imagine) you'll see in the accompaning literature the recommendation for using stretch rather than a torque reading.

Believe me, there is a BIG difference in the final clamping force between the two values; stretch Vs torque reading.

When I did my friend's 434, Carrillo rods with ARP bolts, I found that they required considerably more torque to achieve the recommended stretch.

Here's a diaster example:

Years ago, another friend of mine had his engie "professionally" done. He had a low 9 second Vega (quarter miler) with a single carbed 477 BB.

After a dozen or so passes, the engine let go in a big way; took out the block, both heads, valve train, etc.

I did the autopsy in his garage and I found a single rod nut in the bottom of the oil pan (what was left of the pan) that had absolutely NO thread damage. No sign of stripping, or wear. Of course, the rod it came from was mangled beyond belief (little over 7 grand when it let go), but the nut told the story.

Jerry, the engine building, had used torque not stretch and these were SPS 7/16ths bolts too. They were considered top of the line back then; probably are still comparable to ARPs, just not advertised as much.

So the nut loosened over time and finally disaster struck.

Conclusion; if you plan to keep her alive and like to play with those wonderous "R's", stretch is the key. A stretch gauge is relatively inexpensive too.

Just thought I'd pass this along.

Jake

 

:iagree:

ALWAYS stretch rod bolts...
-Jeb


[Modified by jburnett, 11:40 PM 1/8/2004]

 

Stretch is the only way to go! A good stretch gage is far cheaper than a wiped out motor!

 

:iagree:

 

The problem with using a torque value to determine preload is that it can be off by as much as 30%. It depends on factors like thread condition, lubrication, friction under the nut and more. The stretch method is much more accurate.

 

Exactly...even using the wrong kind of lube, such as Moly vs motor oil can make a difference. There are situations, however, where it is impossible to use stretch, such as mains. In those situations, I ONLY use the torque-and-angle method. If you know the stretch, but don't have a torque-and-angle spec, you can make one by setting up a fixture, torquing to a certain value (I usually use 40 lb-ft when creating a spec), and measuring the angle on the gauge until you get the required stretch.

 

I know bolts will have some stretch but never heard of a stretch gage. What does it look like and how do you use it? Is a stretch gage used mainly for rod bolts?

 

My exroomates Nissan BROKE a rod bolt, that was definitely some nastiness.

I used torque, but I'm so **** that I dropped the pan and retorqued(they didn't move) all of the bottom end bolts at 100 hours. :lol:

:seeya

 

Well, they come in different flavors, but generally they resemble a little horse-shoe shaped device with a point on one end and the dial indicator plunger on the other. The dial indicator attached to it registers how far apart the point/plunger is.

You place one point on each end of the rod bolt (most of the newer rod bolts have tiny dimples that the points of the gauge fit into).

You then begin tightening the nut and take readings from the dial indicator as to how much longer the bolt becomes as you torque it. When you're done the rod bolts will be longer that when you started because you stretched them. The amount of stretch differs depending on the specific bolts being used. The last engine I did called for .006 stretch.

Some gauges allow the readings to be taken without having to remove the stretch gauge from the rod bolt; others require the gauge to be removed in order to get the socket on the nut.

Yes, rod bolts are the ones stretch is used on. Rod bolts are the most stressed bolts in the engine too, so getting them tightened correctly is critical.

Using new rod bolts it's been my experience that I've had to exceed the numerical torque value by quite a lot to get the correct stretch; perhaps 15# or more.

I use a Snap-On dial type torque wrench and have it regularly calibrated by a friend who works in the aircraft jet engine shop for one of the major airlines - so I'll bet it's accurate. If not we had all better start taking the bus. lol

Jake

 

Jake: Thanks for the great explanition. Now I know what a stretch gage is and how its used. I knew all about torque but never new stretch was also used as a measurement although I knew the bolts streched. :cheers:

 

"Professional" engine builders don't know everything either. A Colorado hunting guide called me and asked if I could get him a 350 short block for less than he could locally. I checked and GM was having a short block sale and he had me freight it to him. His local garage that worked on his trucks installed it. He called me about a week later and said he picked up his truck and drove about 3 miles whereapon it threw a rod. He wanted me to find out if and how GM was going to stand behind this engine. I asked him if the garage ran the oil pump before installing the distributor and he said he watched them do that. Upon teardown they found loose connecting rod bolts. GM shipped the engine without torqueing all of the bolts and the garage assumed they were torqued by the factory. GM replaced the engine.

 

Good example of "You never know unless you check". The same thing applies to degreeing in a new camshaft.

Here's another, many, many years ago I bought a freshly built, never fired BB Chevy engine that had just come out of the machine shop and was built by them. Engine was complete, carb to oil pan, damper to flexplate.
I spent the next week or so installing it in a 80 Trans Am.

When I finally fired it, it blew enought smoke out the mufflers to kill every flying insect in the county. Called around and was told "Don't worry, the rings just need to seat".
Too it for a test drive to do just that down the Interstate and it blew so much smoke out the mufflers L couldn't see a single thing behind me.

Got about two miles down the road and the check oil light came on. When I checked, the five quart pan was emply. Climbed the embankment to a gs stationand bought six quarts of oil, dumped it in and headed back home.

As I was arrive, the light came on again, and, you guessed it, oil pan was empty.

Out with the engine for a tear down and I found ring end gap was almost 1/4" (.250) rather than the .020 or so that it should have been.

Further checking discovered the top compression ring on #7 was not in the piston groove and had put the nicest verticle deep scoring (requiring a sleeve for that hole) in the cylinder wall as you'd ever want to see.

Read a mag article saying that AFR shipped them a set of heads without the rocker studs being torqued.

Saw another post that had photos of an AFR head that was shipped and one of the rocker studs did NOT have any threads on it; How do you suppose the valve lash or lifter preload could be set without any threads on the stud?

The more things you inspect, the better you'll sleep at night; at least for me it works that way.

Jake