#14 Build I'm going 9's or bust!

[Barnes]

The thing that confuses me is the fatigue life. Almost all aluminum I've ever heard of has no infinite fatigue life. However I've seen certain exotic aluminum alloys have infinite fatigue life. Which if this is the case, and these rods are made of that, the argument goes out the window.

Other thing that gets me thinking are the comments about torque specs. Are you guys using torque wrenches to do this? Or are you using stretch to determine how pre-tensioned the bolt is? I ask because as far as I know torque wrenches have fairly low accuracy.

 

I personally use an $800 snap on digital torque wrench. Most of the studs/bolts that do not use toque specs but rather tight plus a 1/4 turn are throw away one time use. There are a ton of aerospace grades of aluminum out there. Aluminum connecting rods are kind of like 7071 but each rod maker has their own secret blend. Connecting rods are subject to great loads, rpm and heat cycles. There is no infinite fatigue life aluminum connecting rods. Generally the small ends will go out of round or wear or if you have a really old rod it will usually crack in the bolt holes and travel up the beam. When you machine the rod and put threads in it you create a sharp edge/stress riser.

 

[Brianawd]

Quote:
I personally use an $800 snap on digital torque wrench. Most of the studs/bolts that do not use toque specs but rather tight plus a 1/4 turn are throw away one time use. There are a ton of aerospace grades of aluminum out there. Aluminum connecting rods are kind of like 7071 but each rod maker has their own secret blend. Connecting rods are subject to great loads, rpm and heat cycles. There is no infinite fatigue life aluminum connecting rods. Generally the small ends will go out of round or wear or if you have a really old rod it will usually crack in the bolt holes and travel up the beam. When you machine the rod and put threads in it you create a sharp edge/stress riser.




Why does evey thing I read of yours sound like you just pulled it off the net and posted it up.

 

Sorry but our shop builds race cars that is all we do. I am not some kid throwing together parts.I built my own engine as well as spec'ing out all the parts. We started doing 4G63 last year and have had the luck to work on some of the fastest cars around. It is my job to know what is going on, sorry i am good at it. I have to know the specs on all the parts we sell. What works, what doesn't, what's best for street, strip. I pay attention to little details as soon as you said 50ft/lbs with oil on an ARP2000 i knew your torque spec was wrong it is just experience. As for knowing the aluminum alloys i use to weld for the USDOE at a lab i know a lot about different alloys. I also talk to Mike at R&R he told me they use a 7000 series type alloy but he would have to kill me if he told me what it was exactly

 

[Barnes]

Quoting ryno529:
I personally use an $800 snap on digital torque wrench. Most of the studs/bolts that do not use toque specs but rather tight plus a 1/4 turn are throw away one time use.



Now you are confusing me. /ubbthreads/images/graemlins/frown.gif So what is 'tight' when you say tight plus 1/4? Do you turn the nut by hand until it stops, then turn the nut a fixed number of times? I ask because pre-tensioning a bolt using the number of turns versus torque-to-yield are two different things. I also don't think an $800 torque wrench, or any torque wrench for that matter, can overcome the inherent inaccuracy of using torque to pre-tension fasteners. I only bring this up because I find it strange to get picking about torque values when the entire method is only so accurate. But it seems to work for others, so perhaps I'm wasting my breath on an academic pursuit.


Quoting ryno529:
There are a ton of aerospace grades of aluminum out there. Aluminum connecting rods are kind of like 7071 but each rod maker has their own secret blend. Connecting rods are subject to great loads, rpm and heat cycles. There is no infinite fatigue life aluminum connecting rods. Generally the small ends will go out of round or wear or if you have a really old rod it will usually crack in the bolt holes and travel up the beam. When you machine the rod and put threads in it you create a sharp edge/stress riser.



Well, looking into it more I am finding there is no true fatigue limit (infinite fatigue) for aluminum. However Matweb list the fatigue strength of 7071 at 21,800psi @ 500,000,000 cycles. So even though that isn't an infinite limit, it sure is way the hell up there in cycles.

 

[cheekychimp]

What is a 'cycle' though? At 10,000 rpms that equates to just 50,000 minutes which actually isn't that long but I'm not sure if it is as simple as that.

 

When ARP designs their bolts they are designed to be used woith a torque wrench they are the ones who come up with the measurements based off the tools we have to use in the auto industry. Torque wrenches are not accurate in small icrements but are within a lb that is why we send them out for recalibration. Take an aluminum rod that is supposed to be torqued at 40ft lbs w moly and measure the bore it will be with in spec now crank it down another 10ft lbs the bore will distort. To compare a lab number on aluminum is ok but that is usally done in tensile strength(pulling) and at a given temperature (room). A connecting rod has forces from all direction and goes through heat cycles and when you are talking about a heat treated alloy that is not good.

 

[Barnes]

From my understanding a cycle is from peak to peak of tensile load. So the rod is under max compressive load during the power stroke, and is under max tension during the intake stroke (I think). I think these would be the highest/lowest situations. A cycle would be each time this situation occurs. I'm just not sure all the forces on the rod so I could only speculate. I *think* that a cycle would occur once per every two revolutions, a complete cycle. If that is the case it would take 100,000 mins @ 10k rpm to reach that point. That would be the equivalent of running constant 10k rpm at load for 70 days straight. Of course all of this assumes that fatigue strength I listed is even strong enough for the loads the engine will experience.

 

[cheekychimp]

Yeah that was kind of how I took it, I had it at 34 days continuous on the basis of just a single revolution. I guess you are right though. The lower your rpms in a constant driving situation (lets say between 2500 and 5000 rpms) the longer that period becomes. Unless you are covering miles like a long distance truck driver there is probably a fair few years quota of driving hours in there.

 

[Barnes]

Quoting ryno529:
When ARP designs their bolts they are designed to be used woith a torque wrench they are the ones who come up with the measurements based off the tools we have to use in the auto industry. Torque wrenches are not accurate in small icrements but are within a lb that is why we send them out for recalibration. Take an aluminum rod that is supposed to be torqued at 40ft lbs w moly and measure the bore it will be with in spec now crank it down another 10ft lbs the bore will distort.



Like I said, I'm probably getting into an academic exercise. I suppose if more accurate pre-tension was needed ARP would tell customers to do so. However you are not understanding me. I'm not talking about torque wrench accuracy, I'm talking about the inherent accuracy of the torque method for fasteners. Using the torque applied to a nut/bolt only infers the actual pre-tension on the fastener. To measure the actual pre-tension you have to use a method that examines the actual fastener, e.x. stretch measurements or strain gauges etc. However torquing is probably the best when it comes to price vs. accuracy.

Quoting ryno529:
To compare a lab number on aluminum is ok but that is usally done in tensile strength(pulling) and at a given temperature (room). A connecting rod has forces from all direction and goes through heat cycles and when you are talking about a heat treated alloy that is not good.



Well, the fatigue strength value I listed is also used for calculations of fatigue in shear. I think fatigue calculations are fairly accurate if you can characterize you object of analysis well. That might be a bit hard with a rod, e.x. threading. As for temperature, I don't know what kind of creep characteristics aluminum rods have. Also, I'd be surprised if the rods got hot enough inside the engine to alter the heat treatment of the rod. Again, I'm not familiar with all the temps involved and how a particular heat treatment reacts.

 

[thecman02]

Quoting BarnesMobile:
From my understanding a cycle is from peak to peak of tensile load. So the rod is under max compressive load during the power stroke, and is under max tension during the intake stroke (I think). I think these would be the highest/lowest situations. A cycle would be each time this situation occurs. I'm just not sure all the forces on the rod so I could only speculate. I *think* that a cycle would occur once per every two revolutions, a complete cycle. If that is the case it would take 100,000 mins @ 10k rpm to reach that point. That would be the equivalent of running constant 10k rpm at load for 70 days straight. Of course all of this assumes that fatigue strength I listed is even strong enough for the loads the engine will experience.



I have a question about this logic though. That life would be a worst case scenario of hitting that tensile or compressive stress on every cycle. The less horsepower or cylinder pressure the longer that rod is going to last as well. So that would mean that they would most definitely be suitable for the street assuming the engine builder uses the correct fasteners and torque on the fasteners.

 

Talked to Mike at R&R he said the limit for the 4G63 for a street application is between 15-20,000 miles. I was like i thought the rods can only take so many heat cylcles. They grow around .010 from start up to operating temperature. The aluminum fatigues over time due to the heat cyles not from the load placed upon them. In a NA application they will last longer but on a small turbo 4 cylinder this is the limit. Also spoke with ARP about the torque rating. They say using a torque wrench on a dry bolt is very inaccurate there is a lot of friction, oil will help and give a better reading but with the moly lube you get a near perfect reading that is why the torque spec for a bolt with moly vs oil is so different the moly will give you a true reading.

 

[Barnes]

Quoting thecman02:
Quoting BarnesMobile:
From my understanding a cycle is from peak to peak of tensile load. So the rod is under max compressive load during the power stroke, and is under max tension during the intake stroke (I think). I think these would be the highest/lowest situations. A cycle would be each time this situation occurs. I'm just not sure all the forces on the rod so I could only speculate. I *think* that a cycle would occur once per every two revolutions, a complete cycle. If that is the case it would take 100,000 mins @ 10k rpm to reach that point. That would be the equivalent of running constant 10k rpm at load for 70 days straight. Of course all of this assumes that fatigue strength I listed is even strong enough for the loads the engine will experience.



I have a question about this logic though. That life would be a worst case scenario of hitting that tensile or compressive stress on every cycle. The less horsepower or cylinder pressure the longer that rod is going to last as well. So that would mean that they would most definitely be suitable for the street assuming the engine builder uses the correct fasteners and torque on the fasteners.



Very true, this would be the worst case scenario. The min/max stresses would occur at the same point, but the load would be greatly reduced over many cycles. Idle, or low load cruising.

 

[Barnes]

Quoting ryno529:
Talked to Mike at R&R he said the limit for the 4G63 for a street application is between 15-20,000 miles. I was like i thought the rods can only take so many heat cylcles. They grow around .010 from start up to operating temperature. The aluminum fatigues over time due to the heat cyles not from the load placed upon them. In a NA application they will last longer but on a small turbo 4 cylinder this is the limit. Also spoke with ARP about the torque rating. They say using a torque wrench on a dry bolt is very inaccurate there is a lot of friction, oil will help and give a better reading but with the moly lube you get a near perfect reading that is why the torque spec for a bolt with moly vs oil is so different the moly will give you a true reading.



So you are saying that the highest fatigue stress is from the aluminum expanding and becoming more highly loaded against the bolts since they have a smaller CTE? I could see that being the case. Although that would be a fraction of the cycles induced due to all the other forces. I wonder if that 15-20k mile figure is partially dependent on how many times you run the car.

Well, I was not privy to your conversation with ARP. I still don't think you are following what I'm saying. I also was under the impression that the reason the torque values are different with different lube is not due to accuracy of reading, but because the decrease in friction means you need less torque to get the same pre-tension load. Although I could see lubrication helping with more consistency among fasteners.

 

The numbers Mike gave me were for a street/strip car. The aluminum is plenty strong but the heat cycling destroys it. Lost me on the bolts i think you are over analyzing it. If you were torquing say a 1mm bolt you would be in trouble with a 1/2 inch torque wrench as for 10, 11,12 + size bolts you are safe this has been proven for years. ARP knows what the stretch is on a bolt torqued to certain ft/lbs. I would feel a lot safer with a bolt torqued with a wrnech than a torque to yield bolt like many of the auto manufacturers use.One time use and a lot faster to install at an auto factory.

 

[Gordian79]

That car blows lol.Ryan gimme a call asap i lost all my contacts.

 

[Brianawd]

Taken from ARP'S website.


Engaged Thread

An additional factor must be taken into account in defining the bolt configuration: the length of engaged thread. If too few threads are engaged, the threads will shear at loads that are lower than the strength of the bolt. As a practical matter, the thread length is always selected so that the thread shear strength is -significantly greater than the bolt tension strength.

This problem is especially important in bolts used in aluminum rods because of the fact that the shear strength of aluminum is much lower than the shear strength of steel.

Grodens instructions


R&R instructions



Taken from MGP website
Technical Advice
Torque Procedures and Specifications

The method need to achieve proper torque and fastener stretch will be identical for all connecting rods manufactured within our facility. The torque rating will be dictated by the number designated on the head of the fastener. Compare the number on the had of the fastener with the list below for proper torque specifications.

Before assembly in the engine takes place the connecting rods must be taken apart, cleansed and dried with compressed air. It is imperative that the serrations on the rod cap and rod body be free of dirt, oil and debris. Utilize extra caution when handling the cap and body, as the serrations must remain undamaged for proper assembly. Once in the engine place the rod cap on the rod body. Lubricate the threads of each fastener liberally with fifty(50) weight motor oil and thread the fastener into connecting rod until the head of the fastener just contacts the washer assembly. The use of fifty(50) weight motor oil is critical, as the use of any other lubricant will lead to improper fastener stretch. Using a slow and steady pass with the wrench torque each rod bolt. The "Step-Torque" method is an IMPROPER technique DO NOT USE this technique it will lead to improper fastener stretch. The use of a stretch gauge can be used to guarantee proper fastener torque and stretch.

Fastener #1003: 105/ft/lbs Fastener Stretch: 0.007"-0.0075"

Fastener #1004: 85/ft/lbs Fastener Stretch: 0.007"-0.0075"

Fastener #1008: 65/ft/lbs Fastener Stretch: 0.006"-0.0065"

Fastener #1009: 105/ft/lbs Fastener Stretch: 0.007"-0.0075"
Clearances

Per our recommendation the vertical clearance on rods for drag racing use should be .003-.0035" and the side clearance should be a minimum of .015" and maximum of .020". These specifications are for naturally aspirated engines for endurance applications. We have seen no advantage to opening up clearances beyond recommendations.

For nitrous-oxide applications our recommendations are the same as for naturally aspirated engines.
More Assistance

If we may be of assistance in answering any other questions please do not hesitate to contact us at 719-219-3017 or fax 719-219-3078. We are very happy to help in any way possible.

 

Grodens new instructions also come with torque specs for moly it is 38ft/lbs. Mike torques his rods at 47lbs with moly. You will still not get the proper stretch at 50ft/lbs with oil on an ARP2000 bolt. Could also be why Keith does not like to offer rod bolt upgrades on his standard rods? We can go back and fourth on this but i have yet to have a Groden fail the way we do it, but like i said I don't really like his rod compared to R&R and yes the Groden does not offer thread engagement like the R&R. Sorry you had a problem with your rods : ( Also my rod is a little different than others heck i have small block chevy wrist pins in this thing.