rods too soft ?

[flyingwedge]

Name brand, 4340 billet rods. No need to name names, just yet. What would be minimum acceptable rc. hardness ? I was thinking about 36rc. ? Thanks, flyingwedge.

[The Radius Kid]

These guys seem to agree:

http://www.interlloy.com.au/our-product ... ile-steel/

[PackardV8]

Just asking, why the concern? In all these years, I've never considered Rockwell hardness as a real determining factor in connecting rod durability.

Think about aluminum rods in Top Fuel. They're not particularly hard, but that rod will handle several thousand horsepower or run a hundred thousand miles in a street engine.

[wbclassics]

Name brand, 4340 billet rods. No need to name names, just yet. What would be minimum acceptable rc. hardness ? I was thinking about 36rc. ? Thanks, flyingwedge.

35-38HRC for MOST aftermarket 4340 rods. Even the good Chinese rods are in this range, some mediocre Chinese rods also are in that range.

42-45HRC for top tier 4340 rods, and I only know of two manufacturers getting into that range (including Carrillo).

The ground face of the thrust cheeks on the big end of the rod (preferably at the 12o'clock position, with the rod held perfectly upright) is a nice convenient spot to check the hardness if you're curious.

Kai @ WBC

[MadBill]

The spec I was given by Carrillo 35 years ago was RC 38.

[Stef]

Name brand, 4340 billet rods. No need to name names, just yet. What would be minimum acceptable rc. hardness ? I was thinking about 36rc. ? Thanks, flyingwedge.

35-38HRC for MOST aftermarket 4340 rods. Even the good Chinese rods are in this range, some mediocre Chinese rods also are in that range.

42-45HRC for top tier 4340 rods, and I only know of two manufacturers getting into that range (including Carrillo).

The ground face of the thrust cheeks on the big end of the rod (preferably at the 12o'clock position, with the rod held perfectly upright) is a nice convenient spot to check the hardness if you're curious.

Kai @ WBC

Good post.

To the OP; Make sure you test on a machined area as stated above. Testing on the other surfaces of the rod will show a higher hardness reading due to the work hardening of the rod surface from shot peening.
Going up to the higher hardness region ~45HRC (approx 200,000psi UTS) makes the material more notch sensitive and places greater emphasis on cleanliness of the steel which adds to the cost of the product.

[Dan Timberlake]

Just asking, why the concern? In all these years, I've never considered Rockwell hardness as a real determining factor in connecting rod durability.

............

Real Basic strength of materials info predicts the endurance/fatigue strength of steel is ~ 0.5 of the ultimate (tensile) strength.
page 7 here -
http://www.egr.msu.edu/classes/me471/th ... atigue.pdf

For steel the UTS generally follows hardness.
pages 139 and 140 here -
http://www.timken.com/en-us/Knowledge/e ... rgists.pdf

So, very generally speaking, increased hardness is likely to raise UTS and along with it the endurance/fatigue limit.

I want all the hard working engine parts to have a stress level below the endurance/fatigue limit because Under repetitive loading ( 1000s of load cycles) Cracks only initiate when the resulting stress is higher than the endurance/fatigue limit.

If I'm designing a new part, or an existing part is failing due to fatigue cracking in service, First I modify the geometry so the stress at any local region is not un-necessarily high.
Then I will pick a material and process it so it's endurance fatigue/limit is higher than the max stress.

Hardness testing a busted part, or one caught early by a good inspection schedule and merely showing "indications", would help determine if the part was made of the right stuff in the first place.

[flyingwedge]

I never understood why the Romans would send a messenger to the front lines of a battle, and kill him if brought back bad news. Now I understand ! First test, (4) different places "said" 12-13 rc. Pretty soft, not likely to be 4340 material. Next test 52c. Moral of the story, even if the test is "free", might not be a bargain ! What now ?? flyingwedge

[flyingwedge]

Just asking, why the concern? In all these years, I've never considered Rockwell hardness as a real determining factor in connecting rod durability.

Think about aluminum rods in Top Fuel. They're not particularly hard, but that rod will handle several thousand horsepower or run a hundred thousand miles in a street engine.

>>Not to argue-but what aluminum rod application runs 100k miles, on the street ? Aluminum rods are the sacrificial lambs/shock absorbers, for high maintenance drag motors. Where else are they used successfully ? I'm not a pro engine builder, but for serious motors, I always want to know the rod material, and its hardness = strength of the rods/ bolts. Buying a rod, simply by the brand name, doesn't work for me. Your results may vary. flyingwedge

[PackardV8]

>>Not to argue-but what aluminum rod application runs 100k miles, on the street ? Aluminum rods are the sacrificial lambs/shock absorbers, for high maintenance drag motors. Where else are they used successfully ?

Not entirely true; many have been used on the street. Back when custom steel rods were prohibitively expensive for certain applications or just weren't available, we ran Bill Miller aluminum rods on the street. I personally know of several engines which have done many thousands of street miles. One Pontiac has never been apart after 20+ years, more than 50,000 street miles and several drag strip passes each summer.

The Only Streetable Aluminum Rod

Urban legends abound in the gearhead community. One is: aluminum connecting rods don't work in street engines. Prior to the mid-'70s, that might have been true, however, introduction of the Bill Miller Engineering Forged Aluminum Connecting Rod in 1975 provided an exception to that myth.

The BME Rod has great durability in high-end, high-power, street/strip or hot street engines because it is die-forged, rather than cut out of a plate. Bill Miller Engineering's unique, aluminum alloy further enhances fatigue strength such that the durability of BME Rod rivals that of many forged steel rods and exceeds that of a few.

About 20 years ago, a few resourceful engine builders, led by H-O Racing's, Ken Crocie, began using BME Rods in very-high-performance street engines. Crocie, a racing and street/strip Pontiac V8 specialist, faced with a shortage of acceptable steel rods for Pontiacs, began to use BME Aluminum Rods. While a few other engine builders followed Crocie's lead, admittedly, use of the Bill MIller Engineering Rod in street engines has not been widespread, but that's only because of its higher cost and the stubborn belief that any aluminum rod is unsuitable for street use.

"In a street application, using the aluminum rod is a no brainer," BME President, Bill Miller, recently said in an interview with an automotive magazine. "I don't know how the myth that aluminum rods can't be used on the street got started, but I'll guess that, back in the 60s and early-70s, they weren't making them using the process we're using, today. With the material we've got and they way we manufacture the connecting rods, they'll live a couple hundred thousand miles on the street because a street application is, for the most part, low load. Our basic Aluminum Rod is made for 10,000 rpm and 800-hp. The design criteria for the connecting rod is way overkill for what it's going see on the street. We been running aluminum rods on the street for 20 years."

To read the whole story, go here http://www.bmeltd.com/rods.htm

jack vines

[wbclassics]

I never understood why the Romans would send a messenger to the front lines of a battle, and kill him if brought back bad news. Now I understand ! First test, (4) different places "said" 12-13 rc. Pretty soft, not likely to be 4340 material. Next test 52c. Moral of the story, even if the test is "free", might not be a bargain ! What now ?? flyingwedge

What kind of equipment was used to do the testing? One of those cheapo rebound hardness testers will not work for something that has less than 5kg of mass (like a rod).

If you're doing it properly on a Wilson Rockwell type stationary indention hardness tester (120 degree diamond tip brale, 150kg test load), how large was your mounting pedestal, and was the rod well supported so that it couldn't change position as the major test load was applied. Supporting the part being tested is critical to getting an accurate hardness test reading. Sometimes it is very difficult to mount odd shaped automotive parts in a manner that allows consistent and accurate testing.

Considering the wide range between 12HRC and 52HRC, after test site #5 gave you the high number I would have grabbed a certified test block and double checked testing accuracy on the test block.

Kai @ WBC

[Dan Timberlake]

In addition to the pitfalls mentioned by others, Sometimes soft readings happen when the test is made too close to an edge.

Sometimes carburized parts have soft stripes if they sat on a grill in the nitridiing bath.

http://store6.geomerx.com/olivebranch/g ... %20cws.jpg

[flyingwedge]

I think bottom line is, I can't trust "any" of the (8) test. Pretty unlikely, a well known/respected rod mfgr., sent them out at 52c, or 12c. So, where to get checked again, in So Cal. ? Thanks for the responses, flyingwedge.

[ptuomov]

Do connecting rods get tempered after quenching or not? I guess not. Axles I would temper after quenching. But then again, I didn’t go to engineering school.

[falcongeorge]

Just asking, why the concern? In all these years, I've never considered Rockwell hardness as a real determining factor in connecting rod durability.

Think about aluminum rods in Top Fuel. They're not particularly hard, but that rod will handle several thousand horsepower or run a hundred thousand miles in a street engine.

>>Not to argue-but what aluminum rod application runs 100k miles, on the street ? Aluminum rods are the sacrificial lambs/shock absorbers, for high maintenance drag motors. Where else are they used successfully ? I'm not a pro engine builder, but for serious motors, I always want to know the rod material, and its hardness = strength of the rods/ bolts. Buying a rod, simply by the brand name, doesn't work for me. Your results may vary. flyingwedge

I don't know about 100,000, as I didn't do quite THAT much mileage, but I have put substantial street miles on BME aluminum rods, in a big HP, frequently raced street driven BBC.My first-hand experience dovetails with what Jack Vines is saying, and I would do it again IN A HEARTBEAT. LOVE those rods. Of course, internet hearsay trumps first-hand experience every time, so...