Brand New Engine Troubles....Poor Quality Control!

[tabascom16]

Well I have probably less than 500 miles on my new 408 and all hell broke loose under the engine compartment today. I've never even taken it past 4000RPM. All of a sudden today it started backfiring badly. I took the valve covers off tonight and there was a retaining nut and rocker laying just laying there. The rocker stud snapped off at the retaining nut.

Now this thing just has a mild hyraulic cam. There is no reason one of these rocker studs should just snap off. The heads were completely assembled from AFR. Anyone know where they get there rocker studs? I think I'm going to give them a call tomorrow and see if they can at least send me a free rocker stud.

Nothing else looks damaged. I was just down the street from my house when this happened so i should be able to put it all back together with no worries.

 

[honkey84]

My freinds 89 mustang did the same thing, but his retaining nuts backed off the studs. This was on cylinders 1,2, and 4. He then went to Harland Sharp rockers and didn't have a problem. He did over rev it when this happend, but you would think from just one over rev wouldn't hurt anything. He had Comp Cams full roller rockers if that makes a difference.



EDIT: Were these 185CFM heads by chance. Never mind saw that in your sig. My buddy had the same head as you too ?:? ?:? .

 

[cmud]

What kind of springs do you have, double, triple? That's a stange one, I'm sure they'll send you another stud, good luck.

 

[tabascom16]

Same heads...maybe same rockers too...the Promagnums??...all stainless with the really big trunyans?


I'm just pisssed that this could have happened a long way from home because I do a lot of traveling to and from school.

But there is no hog wild cam or really bad RPM's to put extreme stress on the rocker stud. When it did break is was only at about 2300RPM's while I was coming up the hill to my house.

Its just the dual spring setup from AFR. No high spring pressures there.

 

[Broncobowsher]

Friends 351 with roush heads did the same on the highway. We knew the quality control wasn't that great when the heads showed up and in the bag of parts was a stud with no threads on it.

When I did my latest engine (hope it runs by the end of the year) I just went ahead and speced out a full set of ARP studs and bolts.

 

[bmc69]

Friends 351 with roush heads did the same on the highway. We knew the quality control wasn't that great when the heads showed up and in the bag of parts was a stud with no threads on it.

When I did my latest engine (hope it runs by the end of the year) I just went ahead and speced out a full set of ARP studs and bolts.

I wonder what AFR is using for studs too..there are a LOT of options out there but I stick with the ARPs and have never broken one..ever. The 302 in my motorcross/TT truck sees 8000 RPM on a very regular basis and is still going strong after 6 sesaons of racing.

The weird thing is it snapping at the nut..there should not be any significant bending stress there, only tension. ???

 

[tabascom16]

From the look of the break it definately snapped under tension...right at the ends of the thread in the locknut that holds the rocker down.

 

[bmc69]

Take a close-up pic and post it if you can or fell like it. Somebody in the engineering outfit I work for could probably make an educated guess on failure cause(s) if we had a close look at the fracture zone.

 

[RIbronco]

Off the top of my head I can think of a few reasons why they break right under the nut, where the treads start.

-There is a stress riser where the stud transitions from the stud body to the treaded section. (think of the thread profile like a score line on a piece of glass or tile).
-The cross section of the stud is much less where the threads are cut/rolled into it.
-On the style stud that the pivot nut is just tightened down to X torque. The transition spot is under more tension than the rest of the stud (tension from bolt torque + spring seat pressure)
-Studs where the valve lash is adjusted by removing slack then turning nut X number of degrees. The transition spot has the most leverage, of the threaded section, being acted uppon it.

Sorry for the above. (schooled in mechanical engineering)
Bottom line, it's the most stress spot which results in the stud breaking there.

 

[tabascom16]

I'm an engineer too, industrial though, but I've had my fair share of mechanical courses. Only 6 more credit hours until I have my degree.

I knew it was a good place for it to break but it still should have not broken under the conditions the engine is set up. Like I said before, the fracture is definately characteristic of failure in tension.

 

[Skuzzlebutt]

I had a stud brake in the same spot, where the theads began. There was less than 1k on the rebuild and I was cruising at a steady 25 mph, in a school zone. The engine had sat in my garage for 'bout a year before being installed, so I guessed maybe something had fallen on it, weakening that stud. Or maybe there is just poor QC in the stud industry and one out of sixteen being bad is the norm.

 

[iwlbcnu]

AFR wss using Pioneer parts, an OEM supplier. Anyway I bought a set a few yrs ago and started hearing alot of stories of them breaking, AFR sent me another set of studs but I still have never fired the motor.

My Edelbrock heads didn't have hardened shims and I am still pulling shims out of the oil pan.

Basically when you buy an assembled head, they skimped somewhere.

 

[tabascom16]

Thanks for the info iwlbcnu. AFR has gotten back to me that they will send me another stud. If it happens again I will just break down and buy an APR set.

It being christmas time I'm almost thinking it might be a good safe investment to even do it now.

 

[Bronchopper]

just to state the obvious here, you did check to be sure that there is no coil bind or retainers hitting the seals at full lift right?