I will have the machine shop test them when I take the engine down for new bearings. Thanks, Pete

 

I just checked the difference of the two sets of springs and the AFR springs are just 20 # more at the seat. I do not think that is even an issue. Now the oneness is back on the cam, which now looks to be the culprit. I won't know for sure until it comes back from the lab...

 

That sucks, that is a major component failure!

Spring pressure would have been my guess but it looks like that is not the issue

I can say +1 for Bullet cams, their billet cams are great, I have owned 3 so far, no issues with gear wear etc.

 

Now that we're getting more details, broken studs, I'm looking at a geometry problem.

Not spring pressure, not a bad cam core; instead binding/interference somewhere in the valvetrain.

Studs don't just break; pushrods don't just bend/break; cams don't just break; there's a geometry issue at work here.

Jake

 

I can't believe it didn't break anything else...

 

Talk to me about the geometry problem, ie binding, interferance. I have had no pushrod problems, and have had no more studs breaking after going to the larger studs. Need some help here because I sure dont want it to happen again, so tell me what I am looking for. New
AFR heads, measured and purchased new pushrods that I guarantee are the proper length. So where would I look for binding.

 

In the mid 80's (kind of the tail end of the Pro-Street craze) I saw 3 broken cams like that. All 3 were from engines with gear drives - as Pete had mentioned before. 2 were Iskys and one was a Crane, and this was LONG before the cheap chinese parts were comming over here.

I also had a friend with a 383 Road Runner snap a crank in the same way. His was a balance issue, but the engine ran that way for 7 years before the crank snapped.

Is that a roller (billet) cam? Looks like it from the pics. If so, I would call it HIGHLY unusual, HOWEVER any part can fail - face it, stuff happens. Good thing it didn't happen when you were getting on it merging with heavy traffic or something.

 

Was the pushrod length determined on the assembled motor by observing rocker arm sweep on the valve tip?
You said the AFR springs were 20lb more on the seat, how much more at max lift?

 

This is how you determine the push rod length,,, look at the wear mark on the top of the valve, is the wear spot on center? I use an adjustable push rod and a sharpie to mark the top of the valve to determine push rod length

http://www.compcams.com/Products/CC-'Pushrods'-0.aspx

 

Like I said it is not the pushrods, the wear patterens are dead on center.

 

Grasp at a straw: Could spring coil bind be a factor here?

 

When we broke the firt 3/8 stud, the first place we checked was the geometry on the rockers and on the pushrods. We could find no wear patterens on the inside of the rockers where they might hit the stud, and thought it might be a fluke, then we broke another. I called AFR and they said to change to 7/16ths. At that point we also changed roller rockers. The wear patterns on the valve stems were dead on then and still are. If there were a chance that the rockers were hitting, how do I stop it, or which rockers should I buy that won't hit. Lastly, once I get the cam back from the lab I may know if it was the cam.

But for all of you whothink it may be geomtry, step in side and lay some answers on me..

 

.600 lift is a lot, but maybe the lobe ramp up itself was a little on the steep side. I'd consider trying a different profile or another brand all together. It seems like you checked all the usual things to check. My gut feeling is that the profile was too fast.

 

You said the AFR springs were 20lb more on the seat, how much more at max lift?

 

When you broke two studs that should have been a BIG Red Flag Warning that something was drastically amiss. Think about the amount of force needed to actually break a stud. Whatever that was going on it had to be applying a tremendous amount of side loading on the stud in order to break it. Clamp one in a bench vice and see how much force it would take to break it. I'll bet you'll give up before the stud does.

There are several areas that require checking for the proper minimum clearances. Retainer to valve stem seal, retainer to valve guide, pushrod to head, valve spring coil bind, piston to valve, retainer to rocker arm, trunnion to stud and probably some others I can't recall. You can check the sites of the major cam companies for a more complete listing.

Some of the geometry issues can be corrected by changing the length of the pushrods; others can't. For instance, a different pushrod length may well improve the side loading of the valve stem in the valve guide but don't address retainer to guide binding or piston to valve clearance.

I strongly suspect the valve train failures you've experienced are the result of an accumulation of stress to a part over time. Each time/cycle the part is exposed to excessive stress until the part finally fails - sort of like bending a coat hangar back and forth, over and over, until it finally breaks.

Now, one could initially suspect a defect in the cam OR a defect in the studs (two of them ???), but when you combine those two things, broken studs and a broken cam, to me, the under-lying cause definitely points to binding/interference somewhere in the valve train.

Just as an example, right now there are at least two guys on this and one other Forum experiencing valve train failures due to insufficient piston to valve clearance.

The more I think about it the more suspicious I become of a valve train geometry problem.

Jake

 

Jake, When we installed the new heads, we measured and intalled a new length pushrod. When looking at the valve stems the roller marks are dead center. (should I dismiss that as the problem). The next issue you address is posibbly the heads hitting the valve. The motor is out of the car and I would have to pull the heads, is this what you suggest. My salesman for AFR had a long call with them today and they seemed to think that the 3/8s studs were to small for the 650 lift springs. Your thoughts? The third issue could be the roller rockers, this is a question, Could the rockers be a problem. Looking for guidence as I am inclined to think like you..

 

Jake, just a quick update, I have just pulled the heads, there are no marks of anykind on the valves, pistons, rod ends, clean, clean.. So with no geometry issues, no pistions hitting the valves, I am back to waiting for the tests on the cam. In talking with a bunch of industry people, I think we can call the cam very suspect at this time. Thanks for the help..

 

If you are interested, Ive got a Lunati VooDoo 60101LK still in the box that I was going to use for my 85 L98 build but I decided to go to a 383 and that cam wont work for me now. Cam and lifters with cam lube included.

 

I completely agree! TOTAL

I also believe the '3/8" studs aren't strong enough so you need 7/16" studs' is too. I don't believe any of that foolishness. I'm amazed that someone at AFR would actually say something like that. That's in addition to what cuisinartvette pointed out above.

How about listing the specific parts you're running; all the specific, detailed specifications of your valve train parts.

Start with the camshaft and work your way Up. Devil's in the Details.

Tell us what specific method you used to determine the correct pushrod length.

Tell is what specific method you used to set the lifter preload.

Tell us everything in the valve train you measured for the correct minimum clearance and what those clearances were. You did write down all those clearances, right? If not, now's the perfect time to do it.

If you need to know what to check and what the minimum clearances should be check the Tech Articles on CompCams and/or Crane/Lunati, etc., websites. I wouldn't leave this for someone else to do; look where that's got you so far.

Short, general comments won't cut it. Did I mention specific and detailed? Please, don't make it like pulling teeth, making it necessary for us to come back and ask a lot of questions because you left info out. LOTS of paragraphs (as in contrast to LOTS of sentences).

These kinds of failure don't just happen; something's causing it. You didn't just happen to get two defective studs AND a defective camshaft core. The law of probability against that happening must go through the roof!

If you don't find what's causing these failures they're bound to recur.

Jake

 

I will be back to you in a couple of days....