[mrtleavitt]

This isn't a mustang but the engine will soon be swapped from my '69 F100 to my '67 Mustang.

So I was driving my truck from Salt Lake to Vegas to store for the winter at my dad's place and on the way the truck started missing. It drove good enough and drove the rest of the way home. I diagnosed it yesterday and did a compression test with one cylinder being about 100 psi while the others at 150. A squirt of oil did nothing with the low cylinder so that made me a bit happier. So I went ahead and took off the valve cover to find the rocker arm on cylinder 5 intake broken! The motor is a 428 with roller cam, solid roller lifters, and roller rocker arms- everything from comp cams (and everything recommended for my specific camshaft including valve springs)-(also the heads are Edelbrock aluminum CJ heads). The motor has about 3,000 miles on it and earlier this year I broke rocker arm #7 exhaust. Being an exhaust valve it would backfire from combustion but with this cylinder 5 intake, there were no major signals other than the misfire. I thought for sure the push rod would be thrown into my valve cover and I would hear the pinging but never happened.

1. With the rocker gone wouldn't there be enough force on the push rod to throw it all the way to the valve cover?

2. Also what damage could have been done with running an engine like that for 200 miles?

The rocker arm is aluminum and it was a clean break. The broken part was wedged between the head and the intake manifold so luckily no metal parts are unaccounted for. When the exhaust rocker arm broke I simply replaced the broken arm and everything ran great, I hope this one goes the same way. I must be running my lash too tight. Comp recommends .020" lash but maybe I need to back off a bit more to .025" or something. Any advice and input would be appreciated. Thanks