Connecting rods that crack by design

[jumpinjan]

http://www.allbusiness.com/professional-scientific/scientific-research-development/155655-1.html

They aren't kidding. I'm rebuilding a 2004 GM-Daewoo engine and here's a picture of a cracked rod. Its impossible to put the rod cap on backwards
Jan

 

[twospeed]

Alot of machine parts and bearings are done like this---machine a piece and break it in half. Saves on labor.

 

[Bill Blue]

Alot of machine parts and bearings are done like this---machine a piece and break it in half. Saves on labor.

It also makes it impossible for the part to be installed incorrectly, it lines up perfectly every time and the force to misalign the part after assembly is probably great enough to cause component failure. Not only a cheaper, but in all ways, better way.

Bill

 

[RootesRacer]

It also makes it impossible for the part to be installed incorrectly, it lines up perfectly every time and the force to misalign the part after assembly is probably great enough to cause component failure. Not only a cheaper, but in all ways, better way.

Bill

I wouldnt say better in all ways.

This trick can only be done with iron rods.

Better for iron rods (than 2 piece and journal sizing), but since many OEMs come this way (modular ford V8 most notable), the aftermarket steel rod support still uses conventional wisdom and machining.

 

[Bill Blue]

I wouldnt say better in all ways.

This trick can only be done with iron rods.

Better for iron rods (than 2 piece and journal sizing), but since many OEMs come this way (modular ford V8 most notable), the aftermarket steel rod support still uses conventional wisdom and machining.

Okay, conventional construction enables the assembling mechanic to adjust bearing crush and in general, play with journal size and resizing. What other advantage does conventional construction have? I just don't see any.

Bill

 

[V6 JOSE]

Does it need any more advantages? I personally do not like the cracked rods, because they are a one way, one use rod. They can´t be rebuilt conventionally. The factories use them because they are cheaper to make, and all they care about is cost.

Jose

 

[Bill Blue]

Jose, what makes them one use? Yes, they are cheaper, but when the engine lasts 500,000 miles, who cares if the rods can be rebuilt? Are you denying the cracking process produces a rod cap that CANNOT be incorrectly installed or slip out of alignment?

Your talking like the old timers who used to say the old engines were better because they were handcrafted, when engines made on machines run by unskilled (or perhaps semi skilled) labor made engines ten times the quality. Or how about the fine old greaseable water pumps with adjustable glands that had to be repacked. Why would you get rid of one of those jewels for a pump with a sealed bearing? Get with the times, my friend.

Bill

 

[V6 JOSE]

Bill,

If a guy can get a rod cap on backward as he´s asembling the engine, and not know it, he doesn´t have any business trying to build engines. The fact that a cracked rod can only be assembled one way, is about the silliest reason to crack them.

As far as any gas engine going 500,000 miles before rebuilding, I have to see it to believe it.

Where do you come up with me saying that the old engines were better. The cracking of the rods was made simply to save the factory money, just like GM designing the rear axles to be the inner race of the axle bearing, so when the bearing goes bad, you have to buy another axle. All that was done so GM could save a few bucks on each car. The poor sucker that bought the car, was the one who had to deal with having to replace the axle when just the wheel bearing went south.

You will never convince me that cracked rods have any real advantage over regular rods, other then saving a few pennies for the car company.

Jose

 

[Bill Blue]

Okay, so I won't try. Just remember, "cheaper" does not mean "not as good" as evidenced by the thinwall rod and main bearings.

Bill

 

[Ken Ellis]

I always thought cracking a bearing surface like that was to get a high tolerance bearing surface -- not for mechanic-proof reassembly. But that impression comes from a memory of a conversation 25 years ago...

Ken

 

[Bill Blue]

I always thought cracking a bearing surface like that was to get a high tolerance bearing surface -- not for mechanic-proof reassembly. But that impression comes from a memory of a conversation 25 years ago...

Ken

Ken, thanks for that. I seem to remember working on a 2 stroke snow blower engine that had a cracked rod cap, but sometimes it is difficult to distinguish between a good memory and a good imagination. That just pushed me in the direction of a good memory.

Bill

 

[RootesRacer]

I always thought cracking a bearing surface like that was to get a high tolerance bearing surface -- not for mechanic-proof reassembly. But that impression comes from a memory of a conversation 25 years ago...

Ken

Keeps the caps from walking for sure.

The metallurgical disadvantage of the material is pretty evident though.

 

[V6 JOSE]

My complaint about these cracked rods, is that they are a throw away item, if the engine ever has to be rebuilt. That contributes to our disposable society. The rods can´t be rebuilt, period.

As Jarid said, the material is inferior to the forged steel rods that most engines use. They are made from powdered iron, so can not be as strong.

Jose

Okay, so I won't try. Just remember, "cheaper" does not mean "not as good" as evidenced by the thinwall rod and main bearings.

Bill

 

[Bill Blue]

Hey guys - the OEM rod does not have to be the best. It just has to be good enough to never fail. Until someone comes up with a spate of OEM powdered metal rod failures, I will make the argument that criteria has been met.

Jose, why do you have to throw away a cracked rod during rebuild? It appears Jan didn't.
Just because it is used does not mean it is out of spec.
Bill

 

[MikeH]

How about you two just agree to disagree.

 

[RootesRacer]

Hey guys - the OEM rod does not have to be the best. It just has to be good enough to never fail. Until someone comes up with a spate of OEM powdered metal rod failures, I will make the argument that criteria has been met.

Jose, why do you have to throw away a cracked rod during rebuild? It appears Jan didn't.
Just because it is used does not mean it is out of spec.
Bill

The "cracked" rods can be reused if they are still round at teardown (they cant be resized).

For stock engine applications, the rods will withstand the rigors for what they are designed. Upon any application of power adders, particularly additional RPMs, it is well known to replace these little gems with steel rods.
The 4.6 and 5.4 (and V10) fords are well known to eat these rods if they are hotted up (strong aftermarket), also the supercharged motors in this line get steelies.

For many applications they are plenty fine, the dealership however will not take a chance on them and will replace the rods should the engine get a teardown.

 

[V6 JOSE]

Bill,

As Jarid just stated, the dealers don´t use them when rebuilding an engine. They don´t want to have to warranty an engine because the owner hammers it and breaks a rod. Just because a powdered metal rod will work, doesn´t mean that it is ideal. I repeat, these rods were invented, just to save money. If you want to use them, that´s your choice, but they are not as good as a forged steel rod.

If I were going to rebuild any of these engines that use them, I would pop for steel ones. Nothing like peace of mind when you are having fun with your car.

Jose

 

[jumpinjan]

Jose, why do you have to throw away a cracked rod during rebuild? It appears Jan didn't.

This engine had only 50k miles, and it had a huge amount of sludge inside, and a lot of corrosion on the bare aluminum exterior. So, it had to come apart, and get cleaned. So, I'm just freshening it up with new bearing shells & rings.
This engine has aluminum bores, and a chrome top ring. Pretty interesting stuff
Jan

 

[Bill Blue]

Here is the result of a very quick (first hit) second Google search. Pretty interesting.

http://www.superchevy.com/technical/engines_drivetrain/shortblock/1510sc_howards/index.html

Bill

 

[V6 JOSE]

Notice they are forged, not just powderd metal. I don´t know how they forge powdered rods, but there is a difference between these rods and those found in a stock factory engine application.

Jose