Life of roller rocker arms? Only 20-30K?

[DartByU]

I've never ran any but I was reading the new Summit catalog and Professer Overdrive says that aluminum rocker arms only last 20-30,000 miles in a street engine. What part wears out? I was going to use some when I put my new 360 stroker in my Dart but now I might rethink that and keep my plain adjustable ones. I'll be driving it mostly on the street so I want something that will last.

[sanborn]

There are lots of different kinds of rocker arms out there. The needle bearing fulcrum rocker arms usually wears out first(the shafts arn't hard enough) especially with high spring pressure. The Crane type shaft rockers(no bushings) have a short life due to aluminum rubbing on steel shaft. Norris Stainless will last practically forever since they use the stock Mopar shafts and have bronze bushings. Roller tips last well as long as the springs are well lubricated. The Crane rockers would probably last well if they had bronze bushings.

[Hybridized]

Originally posted by sanborn
The Crane type shaft rockers(no bushings) have a short life due to aluminum rubbing on steel shaft.

If that was the case, then the steel piston pin that hold the aluminum piston would wear out in a hurry also. Not the case

Usually when you have two similar metals rubbing on each other, there will be a short life for the parts.

Aluminum fatigues after cyclic loading. Steel will "weaken" to it's ultimate strength (I believe it is called that) and no more.

[sanborn]

Hybridized, you are correct in theory. But, aluminum/steel is not a good combination because aluminum galls easily under high pressure/loose fits. Lubrication helps but it needs to be pressurized lubrication which does not occur in Mopar rocker shafts. The bronze bushings are more compatible with steel shafts and don't depend upon oiling as much as aluminum would. You are correct about piston/pins as well but the tolerances are so much tighter and angular movement is not near as great as would be experienced with a rocker. And still under race conditions, pistons gall in a very short time unless oiled very well. That's the reason even some race race engines are put together without full float pins.

[sanborn]

Disregard the last sentence in previous post. For some reason, I can't edit it.

[MoparBilly G]

Talking to Ken Lazzeri of Indy cyl. head at St. Louis, and my brother and I voiced concerns about some racers breaking the offset Indy rockers. He said, "Well, aluminum rockers are much the same as aluminum rods... they fatigue after a certain amount of time and you throw them away!

I was shocked but it makes sense..I'm staying with my ductile iron adjustables!!!!!

[DartGT66]

It has a lot to do with the usage, valve spring pressures etc. In my car the life span seems to be about 4 years. Still two left.