I was on a trip to get my car dyno tuned today and along the way there I noticed that the motor developed a miss. I pulled the valve cover and saw 3 broken rocker studs (intake and exhaust on cylinder 1, and intake on cylinder 7). It has AFR 195 heads on it. What would cause these to break just driving the car down the road? The rocker arms on the studs that broke have like a dirty/sludge/carbon look to them too which I thought was odd. None of those pushrods were broke or bent either. Any ideas?

 

Pictures? What rocker arms? What lift cam?

If you have stock arms with short slots and running .500"+ lift, you could be running out of slot clearance. The higher cam lift could be rocking the arms into the stud.

 

Did you set up the valve train geometry with an adjustable PR?

 

Comp Cams magnum rocker arms. Lift is .566/.569" at 1.6 ratio. What is an adjustable PR?

 

Adjustable push rod.

If you have older AFRs the studs weren't the greatest. If you have newer AFRs with ARP studs, you have a clearance issue with the rocker somehow.

 

Yeah the correct pushrod height was checked for. I bought the AFR heads a year ago. Do the AFR's come with ARP studs? If not I was going to upgrade to them and possibly a stud girdle.

 

Curious, did you check for coil bind?

 

Never checked it. I just ran the recommended springs for my set up. It' just odd because I have been driving on this motor for 3 or 4 years now. They are the springs that come with the heads from the factory.

PAC Racing Spring 1.290" OD Hydraulic Roller Dual Valve Spring,
135 lbs on seat, .600" maximum lift, Max RPM 6300-6800

Would it be worth it for me to upgrade to the next step up spring that AFR offers since I am running close to that springs max lift number?

Upgrade Springs
PAC Racing Spring 1.270" OD Hydraulic Dual Valve Spring,
155 lbs. on seat, .650" maximum lift, Max RPM 7000-7200 (standard on competition head)

 

Rocker studs don't generally die, they are murdered.

Something's off with the rocker/pushrod geometry somewhere, perhaps. AFR heads won't work with stock length pushrods in most applications. They move things around on the head in subtle ways vs. stock.

Springs.... MAYBE. If you're almost using up everything a set of .600 lift springs can offer, I suspect you need something a bit more stout. Upgrading springs is NOT a substitute for confirming proper rocker geometry/pushrod length, however.

PAC racing springs.... hmmmm. It's possible the springs WERE OK when first installed, but not now. A bad batch of springs has been known to slip through from time to time.

 

That's what I don't get. The correct length pushrods were used. I just need to know why they broke all of a sudden and it anything else failed as well.

 

You bend any valves in the process?

 

Springs wear...they flutter as they get older, coupled with running near max lift...coils could have been binding. Continuing weakening of the studs.

One thing I am unsure on though, with a cam of that size, how could you get a "recommended" PR length...without checking the geometry?

Too many factors, but just because "XX" said use 7.71 PR's".."because I did", doesn't mean your geometry will be correct.

Sure, for a stock/mild build, off the shelf/etc is fine, but not (IMO) you case.

Edit:

Not binding, but "reverberating" into each other.

 

The engine was assembled by someone I know who has been assembling race engines for a very long time. He measured for pushrod length and chose the correct size. I don't believe any valves were bent. The odd part is that the rocker arms on all the ones that broke the rocker studs look like they came from a 200k mile motor with carbon/sludge looking build up on them. All the other rocker arms on the studs that are fine still look brand new. I have no idea about that part.

 

I see...I'd assumed you just put parts together based on input...

Personally, I'd ask the guy who uilt it what he thought...based on the way the studs broke, and inspection of the rest of the VT, he might beable to come up with a good answer, and solution for longevity.

 

Thanks. I appreciate all the responses. Does anybody have any idea about what could cause the fouled/dirty look of the rocker arms? I've had the valve covers off a lot recently and they never looked like that until now.

 

Were you getting on it when the failure occurred? I'm leaning towards it being a problem with the lifters.

 

My guess? What ever your root cause failure was, was creating excessive heat, which caused the oil on those rockers to oxidize.

How do the pushrod ends look on those cylinders (intake and exhaust on cylinder 1, and intake on cylinder 7)? The cups on the rockers?

 

I was just driving normally down the highway. The tip on one of the pushrods shows slight wear, not sure if that happened after the stud broke or not. The inside of the rockers show some wear from the rocker *****.

 

Sounds like some type of clearance or geometry issue
Not enough oil getting up there possible but unlikely id think

Best thing to do is mock it back up and carefully check everything twice
make sure you got at least .055 clearance from retainer to seal, rockers arent touching anything. Might just find the problem dont think well nail it from here
keep us posted

high lift cams with todays fast ramp cams can beat up a set of springs in a few yrs without a problem. Not saying thats your problem though