Stud bolt got loose

Rocker stud bolt got loose. This is the second time it hapened. first time it was an "intake" stud and now it was an "exhaust". Any ideas why this occurred?

AFD heads, solid flat tapped cam.650 lift, very, very low milage on engine.

Anyone out there knowing if there is any shaft mounted roller rockers that would fit these heads???
Rocker stud bolt got loose. This is the second time it hapened. first time it was an "intake" stud and now it was an "exhaust". Any ideas why this occurred?

AFD heads, solid flat tapped cam.650 lift, very, very low milage on engine.

Anyone out there knowing if there is any shaft mounted roller rockers that would fit these heads???

Two things come to mind, one is valve spring coil bind and the second is have you used a decent thread lock on the studs?

I had a similar experience with Edelbrock RPM Performer heads on a Ford 302/331 at 200 miles mileage: one intake stud fully unscrewed and the side one found loose...
By chance, no damage ...

I made a complete disassembly of all studs on both heads and found erratic torque levels and no thread lock on several units !

I reinstalled everything at the right torque , with blue Loctite;no problem so far ...

So, the main first advice would be : check everything : springs, studs, thread lock etc ...and reinstall very properly at the supplier specifications ...

To answer you; yes I used thread lock but I don't remember brand. When I removed the rocker stud there was some stiff leftovers on the threads. There is no coilbind, measured during assembly.
Thank you so far
If you have checked the valve spring installed height and used a thread lock you are down to a duff thread in the head or valves touching pistons. Both need checking. A duff thread could be fixed with an insert, it may be worth checking the whole lot. They are made at the same factory in China that make the pro comp head, they too are a bit hit and miss.


Randy V

Staff member
Lifetime Supporter
.650" lift on an engine used for the road is a LOT of lift.. A good .100" more than I would chose - but that's beside the point.
I presume your heads are AFR and not AFD (which I have no knowledge of)..
As the others have pointed out, a good thread locker should be used on clean threads for assembly. Red Stud-Loc is the stuff I use. You must use a pretty good amount of heat from a propane torch to re-liquify for removal.
The only other thing I can think of that is not mentioned is the pushrod tolerance in the guide plates which may allow the rocker arms to skew slightly. When that happens it puts forces at different and varying angles to the stud which will work them loose. Also possible is interference from the undercut side of the rocker arm and the valve spring retainer..

For what it's worth, I learned my lesson the hard way on buying and installing factory prepped cylinder heads. I had some sticking exhaust valves as they did not hone the guides properly. When I tore the engine down, I also found that the valves were not seating properly as they had not been ground properly..Now all heads get broken down completely for inspection and valve lapping etc..
Anders has been down this road before, check his other posts. The motor is a Fontana Block with AFD Cleveland style Alloy heads. These heads are essentially an alloy version of the 4v Iron Cleveland heads. The Fontana block is essentially an alloy 351w, but with Cleveland crank/cam centreline distance to allow longer stroke combinations.
Remember that Cleveland rocker ratio is 1.73.
Both Jesel & Yella Terra make shaft mount rocker systems for these heads, perhaps the big advantage of both systems is the valve lash adjustment is done at the pushrod end of rockers, NO Posi-locks and NO guide plates for pushrods.

With reference to Randy's post and sticking valves etc, we found many of the early SVO alloy heads had some casting shift after the first few heat cycles and required rework of valve seats etc to improve sealing, at the time I had some very good contacts with some engine builders and they were removing heads after the first race or dyno runs to reseat and also using torque plates while doing that work. Suggestion at the time was the 100+ ft lb head torque might also have been a factor on the alloy heads moving around a bit when installed and heat cycled, I know the outer row of head bolts by exhaust ports would 'sink' into the alloy casting in use and washers/steel strips used in some cases to deter that.
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I would say the heads are not fit for purpose, if it needs that much attention its way beyond the capabilities of the average enthusiast. The heat cycle and machining should be done prior to retailing.

The heads are equipped with insert threads, helicoil.
I have to go through them all. Maybe I go for shaft mounted rockers and skip the guideplates, one problem less, I hope...


Lifetime Supporter
In addition to the other comments already posted, since an alloy block and solid cam was mentioned, one other thought would be your lash setting. Are you setting lash hot or cold and how much? If you are setting it hot and fairly tight, the growth in aluminum block/head pushrod engine can result very low lash at cold. That would certainly pose the potential to create the problem. For a couple hundred degrees F temperature difference the change can be as much as .015”. Alloy engines can loosen up quite a bit as they warm up but with that kind of growth potential it’s easy to understand why they can tend to be set up in a manner that would make them very tight cold. Always advisable to be gentle with such engines on start up until they are brought to full temperature. Many similar race engines have preheating systems to help with such issues.

The lash is set to .022" cold on both

Is that the recommended hot valve lash? In my experience that 0.022" cold lash would grow to around 0.033 hot and running if not more on that block/head combination. The easiest way I have found to work out what your 'cold' lash settings should be is to 'choose' an initial base setting of say 0.010" cold, then run the engine up to full running temperature, stop it and quickly check the valve lash when hot, if it is now 0.022" then you know your cold lash should be 0.010". if it had opened up to 0.026" then you should choose 0.006" cold lash...hope you understand that! The taller the block and head combo the greater difference between hot & cold settings.

With the wider lash settings you currently have the cam follower contacts the lobe above the 'ramp' area and induces a lot more shock loading to the valve train which is likely to cause the type of problems you have.
Hi Anders
I run a Fontana with CHI heads and a solid roller cam similar set up. My running clearance is 0.018 intake and 0.020 exhaust. I set mine cold at 0.008 on both to maintain that clearance hot.
The cam manufacturer spec's should be followed because cam profiles are all different. the transition between the base circle, the accelerating ramp and the opening ramp help determine the lash setting. As Jac said if your setting is to loose you can damage your valve train.
I suspect your setting at 0.022 is hot.
Follow up
This is what I have come up with
1 When I set up the valve spring and checked for coilbind I have to change springs and go for offset locks. This would result in less open spring preassure...
2 I have probably set the lash hot on cold. Since I have an engine with both the block and heads in aluminium the hot lash would have been .034 hot...
3 Or a combination of both

Now I have set the lash cold to .014 which will theoretically give .026 hot (target), right?

Roller rockers suggestion?
I think I will go for a new set of rockers though those I have don't feel ok at the roller tip.
Steel or aluminium rockers.

As described above about open pressure;
Is there any advantage to change valve locks with zero offset to reach a higher open preassure and go for a rocker with less gearing, 1:6 insted of 1:73?

No damage on the valve stems and retainers.

Suggestion is appreciated
Do you have the installation instructions that came with the Camshaft, might help us to read that, 0.650" is quite a bit of lift for a flat tappet, depending on how your using the car- road or race?
Cam spec.
Bullet solid flat tapped 292/300, lash hot I/E .026, dur.050 I 259 E 267,
lift 1.7 I .636 E .661 lobe seperation 108

Randy V

Staff member
Lifetime Supporter
You might be surprised at how much fum your car could really be on the street if it were detuned via a milder camshaft profile.. Cams with lift like yours have typically got a torque profile which has a large spike in it rather than a long and flat climb..
My $.02 worth at any rate..