A guy I know just broke a rocker arm, don't know the whole story but when I saw this pic the first thing I noticed was what seems to me to be way too much thread showing on his adjusters. Thoughts?

That’s a geometry issue. He may have too many threads showing on the adjuster, but that didn’t cause the failure. Also, if he machined the spring pockets for clearance that will cause a failure. That goes back to incorrect geometry.

Have him go to b3racingengines.com and read all the tech threads and then have him order a geometry correction kit.

Thread count that matters: below the rocker, not above. It affects the rocker ratio, smallest thread count is generally higher ratio (not to mention less breakage).
Always check for relief clearance machined into bottom of the valve (long) lever where adjacent to spring collar. If you have to do this, after reaching minimum safe depth, radius & blend the relief into the parent body. If it catches your fingernail, that's where it will break.

Had similar situation happen many years ago. I neglected to check vs retainer to top of valve guide height clearance on all guides.It had iron adjustable rockers, so the adjusters and pushrods gave up first .Weaker links. Heads had to come off and and get machined, but at least no piston to valve clash. Let us know what you find. Bill

i'd say simple metal fatigue. high spring pressures/aggressive lobes take their toll on alum. those rockers came have the long adjusters. time to replace them and move on.

X2. I had a t&d rocker break just like that. Geometry was spot on. Rockers were 12 yrs old.

This.

Without seeing the underside of the rocker, everything is just a guess.....could be as simple as the pushrod was too long and adjuster stud was backed out far enough that the pushrod cup hit the underside of the rocker.

Yep.

I’m not at all sure of this, but I believe the “-02” on the rocker is the year of manufacture.

If so, we have a broken aluminum rocker that’s 18 years old.

Not really a surprise imo.

Edit- apparently the letters/symbols on the left indicate the year of manufacture, and the number on the right is the month.
So, if you don’t have the legend for the letters/symbols...... you don’t know when they were made.

Looks like at least two different years by the pic. “B” on some rockers, “#” on others.

What he said!

Aluminum rocker arms break when they reach their fatigue limit. Tell the guy that he should replace them all if they were installed as a set at the same time.

As said, aluminum will fail eventually. Steel can be run closer to its tensile limit (stretch is what breaks them, not power) and recover.
However: the calculation is complex. I'll leave out shape, metallurgy, heat treat, etc.
It's the number of cycles × some exponent of the highest RPM reached × spring pressure × some function of maximum incline angle × reciprocating load.
An aluminum rocker may last 50,000 miles turning 5,000 RPM, and explode if run to 8,000 even once.
Generally true for connecting rods also.

If you can't find a better answer to "what broke it", safest position: assume it's fatigue and replace all of them.
Once you get up on the learning curve you'll find that your vision works very well (shade tree FEA) in determining "there should be more metal here", and "that makes me nervous".

I run the blue MP rockers for a long time that were made by Crane, same as the Crane "gold" rockers shown here. I have a pile of broken rockers that are broke just like this one is. Starts at the oil hole and works its way to the edge, then fails, just like this one did. When the last one of mine failed, I had seen enough (or so I thought) and looked at the rest of mine. Looked OK until I got a bright light and a magnifing glass. That's when I found that 9 of the other 15 were cracked in varying degrees, in exactly the same place. Replaced them all at that time.

Brian

Hi Rich, yes I know but on my arms if I had that much thread on top, the cup would be inside the arm... I asked him when the motor was built, no idea yet if this is a recent build or has a lot of time on it...

Hopefully he'll answer tonight.

Thanks, everyone.

EDIT... Just heard from him,
1st: rockers are 20 year's old
2nd:"Had to get some long pushrods about 4 years ago so the adjusters didn't go so far down. The threaded part of the adjustment screw is in the the full body of the rocker. Had a problem before with the adjuster ball end being too low and the cup not receiving enough splash from the rocker oil hole to keep it lubricated, that's why we chose the longer pushrods a few years back."

Bad deal all around it sounds like...