Crane Ductile Iron Rocker Stress Limit

Hello all. I recently had an issue with a broken ductile rocker arm in our N/SS car's engine. That failure also bent the push-rod and pushed the roller lifter out of the bore, eliminating all oil pressure. I pulled the engine and checked all the bearings which look fine.

The engine is a 413 + .060". It runs a .680 lift, solid roller cam. The rockers are 1.5:1 ratio. This engine has run for roughly 250 passes. It ran 10.82 @ 123 as a best et. We typically shift at 6500 RPM and see 6800 at the stripe.

I am wondering if the rockers are not suitable for this combination, given the high spring pressure associated with the cam shaft. It would be easy to replace the broken rocker and bent push rods and put it back together. Do you think I'm asking for trouble?

This car has Mopar Performance steel max wedge heads, and uses a standard rocker shaft assembly. As a side note, I run the same rockers in my street car. That engine is a 496" RB with a Comp Cams Street Roller Cam (.575" lift). Should I consider replacing the rockers on both cars?? Thanks in advance.

2 things break those rockers (that I know of) and that is age (just met it's cyclical limit) and lash. I will tell you that I have never found a case where lash gets tighter when the engine is hot. So as a rule I set all CI stuff .002-.004 tight cold, AL/CI stuff .006-.008 tight cold and all aluminum engines .010-.012 tight cold and then adjust that so my hot lash is what the cam card calls for, with this exception. I never lash a cam over .020 HOT. EVER. I have found no reason to do this. If you take a cam that calls for .028/.032 HOT lash and you do it like most, you are going to be .030/.032-.034/.036 running HOT. You are just beating the crap out of it. You can add a bit more with aluminum heads and an all AL engine can have another .006-.008 on top of that. It's just stupid.

The one other thing I've seen break a rocker was harmonics. That usually happens when you are using too small a wheel on the lifter for your RPM or lift or both. But that will break ANY rocker. Crane Cams cost me THOUSANDS of dollars because of their crap .750 wheel cheap [censored] lifters.

Thank you for the reply. Keep in mind, these are not roller rockers. They are the ductile iron ones that are adjustable, but have no roller tip. I have also had problems with Crane's gold, aluminum roller rockers.

The current cam calls for .026 lash. I run cast iron (CI) heads on a steel block. That being said, I was adjusting the lash cold, and to spec. It's very possible that the lash loosened up a bit, if your advise above is correct. If what I am reading is correct, I should be setting the lash at .022-.024 cold? What are the ramifications of a lash that is set too tight? I always thought that dead on was perfect, but loose was safer than tight. Is that incorrect thinking?? Tom

Tight is dangerous if the valve is not fully seated.

As long as they have running clearance that's all you need. I would go tighter cold. Probably go .020 cold and then check a couple hot and see where they are. I think .026 is too loose. I would try to end up at .020 hot and set them cold at whatever gets you there.

I can tell you thatI have never seen an egine that didn't pick up RPM and even some HP with tighter lash. There are limits for sure. My new cam is to lash .016/.018 HOT. So I'm at .010/.012 cold to start.

The only way to know how tight is too tight is to test. I do know that wide lash is a parts eater.

It's really quite refreshing to read another builders opinion on the ridiculous wide lash specs from cam grinders recommendations I've been building engines produced from all corners of the globe and I have yet to see a manufacturer with more than .014 lash I set all my solids at .008/.010, iron block alloy head. My engines run quiet and don't beat the valve train parts up.

Gus

Sounds like your running a MP cam.. I have one
of the rollers in my 416 right now... I set the
lash at .018/.018 cold.. I run it as a street/strip
car... even when I pull the covers hot and check it..
its .014 with W-2 (iron heads) with alum roller rockers

Thanks to all that commented. I'm excited to test these ideas at the track. As far as testing to see what's too tight...how will I know? Will the performance drop? Will the valve train fail? I'm not running a heads up class. I don't need every nano-second of et for any reason other than to say it went faster. I'm guessing that most of the issues I've had with adjustable rockers has come from adjusting the lash cold and to the manufacturer's specs...thus ending up with too much play and beating the valve train up.

Can you enlighten me on why a manufacturer would suggest .026 lash when others use .012 or so? I'm not an engine builder, but I've set the lash on all my engines. My thought process is that the lash is the clearance between dead-tight and acceptable clearance. Tommy

There are 2 style cams.. one is referred to as a
tight lash cam.. its the way they make the ramps
but I havent had any issues with the tighter lash
on the old style big lash cams.. the one in my 416
is a old roundy round roller with .028/.032 lash
(thats what it calls for on the cam card).. for one
thing it was super noisy with all that lash and second
my engine likes the larger lift with the tighter lash

Lash is a spec from the cam grinder based on the ramp design. You really don't want to be changing the lash from the cam card spec unless you've mapped the ramp and you know what you're doing. The cam card says what it says for a reason.

As for your rocker arm failure it is hard to say. Those rockers are probably old so perhaps it just fatigue. I will say that a good quality steel rocker arm will last a lot longer than an aluminum rocker arm given the same level of stress. But with your setup you should be able to get an aluminum rocker arm to last a long time also.

Are you around 600 lbs on the nose? If so you might want to step up to a more robust rocker arm. The entry level rocker arms usually start to have problems once you get past the 600 lb mark.

for a cam that size, 240 seat/550-600 open would be pretty normal pressures.......and thats quite a bit more than i would run with those rockers.

for a cam that size i'd probably use HS rockers.

As far as tightening up the lash and knowing when to stop is try .002 to .004 tighter and look at the time slips. If the motor likes the tighter lash try some more, a little at a time until it stops gaining HP and MPH . If it goes from .026 hot to .016 hot and is still going faster I would probally stop thier and think about buying a bigger cam with better lobes. If it goes slower with tighter lash try loosening it up a little and see what that does
Good luck.