i doubt the cam will be an issue unless you had one mega dodgey spring.
if the cam was the problem you would have smashed more valves in a much shorted period of time.

when you say the HLA was off centre, do you mean left or right (on the side of the rocker arm) or back to front (facing outwards or inwards to the end of the rocker arm)

The problem is those other guys have street cars that very rarely (comparatively speaking) see your kind of revs for any significant period of time. You really can't expect a street engine with street engine parts to do the job of a race engine.

hey don't know if this helps but....... i am in the middle of changing my HLA and have a friend who has done head work all his life....his main tip to me for this job was "make sure the retainers are in the right way, if not the oil will not drain from HLA they will lock up".......not sure what he means just yet, haven't cracked the top of it yet but yeah.....

i'd suggest it's an isolated incident, probably more so due to old valve springs at those sustained rpm's

we've used 4.0's in burnout cars, with various regrind cams and limiters set to upto 6200 rpm and havent had anything let go yet...

I might as well ask my question since it's related.

I did an EF engine rebuild and the installed a Wade 1673 with stock EF springs. There were no HLA noises and the engine was quiet. During a dyno run, the head started leaking so I fixed it with AU metal head gasket & Hylomar. I had to lift the head off by myself so I removed the rocker gear & cam. After reassembly, the HLAs started chattering and driving the car for 50km still didn't quieten them down. Since then I've:

1. Had the rocker gear on and off 5 times;
2. Bled the HLAs each time;
3. Installed brass restrictors in No. 1, 5 & 7 oil return holes in the block (to increase oil pressure in the rocker gear). This was suggested by an engine reconditioner.
4. Put in some new 10W30 oil (the running in oil was 10w mineral)
5. Installed new HLAs during on the 5th attempt
6. Replace two rockers that cracked around the HLAs
7. Tried adding a 0.5mm shim to the 2 shims in each rocker, but that made the engine run worse (valves not sealing)

Oil pressure is good.

Help, help, help! Can anyone think of anything else that might fix this?