Hi all,

I had an incident while on the way back from Moab this last weekend.
I had just gotten my cruise control working before the trip (which was great to have!) but there were a few issues with it still, such as the brake pedal not fully disengaging it. If you don't push the brake hard enough, it'll resume as soon as you let go. Normally not a big deal, since it kinda came in handy from time to time.

However, my wife was driving, and was pulling off to a gas station. She pressed the brake to turn off the cruise and then pushed in the clutch and released the brake, to coast up to the stop sign.
The cruise reengaged and, since the clutch was in, raced the engine trying to maintain speed. Before she could figure out what had just happened, the tach was BURIED (it stops at 6,000 RPMs), so I have no idea how fast it spun.
I shouted to hit the brake. She did and it shut off the cruise, and the engine dropped down to idle.

So far, the engine seems okay. It was idling fine after that, and we drove it another 250 miles home on the interstate at 75. I've also been driving it to work the last few days.
However, something just seems "off". It is a little harder to start, and it sounds ever so slightly different to my discerning ear. Not sure if it's my imagination, or if something's up.

What can happen from over revving an engine, when it's not catastrophic?
I know this engine is built up quite a bit, with stronger valve springs, etc. and the camshaft is rated to about 5,000 RPMs.
Again though, I have no idea how fast it spun, but I'm guessing 6000 - 7000 RPM.
Fortunately, there was no load on it, but still.

Also, I know the 300 is normally a non-interference engine, but with my block shaved to zero deck, is that still the case?

Thoughts? Ideas? Things to check?

 

I feel like being there was no load it should be fine.

Maybe check compression? I would think your only issues would be possible valve float, and something breaking? since nothing broke just make sure rings and valves are still sealing?

 

Good call on the compression check. I'll run one.
I think considering how it's running, at worst case I either very slightly bent a valve or a pushrod, but not much more. However, I definitely want to be sure, as I wouldn't want something like that to continue running.

 

X2 to what KO76 said. Maybe pull the valve cover and check for broken springs and bent pushrod(s) or a sucked retainer, depending on how far away from coil bind you were with the springs you got in your modified head..
Normally a 300 in stock form is pretty much unbreakable. I've heard of guys putting a brick on the gas pedal in an attempt to blow up the engine with no success. At TDC the valve seats are about .300 away from the piston tops so even at TDC in the overlap phase you still have plenty of margin-of-error. A stocker will free rev and just start missing and sputtering until the revs come back down and the valves stop "floating". Likely there might be a little paranoia built in to your worries (BTDT) about damage but I'd check things out anyway.

Later versions of cruise control disengage when either clutch or brake pedal is engaged. I've had a similar occurrence as you on my old Pinto. Didn't hurt nuthin tho (2.3 OHC). Good luck.

 

Thanks guys, that definitely puts my mind at ease.

Yeah, the cruise is stock, but the Bronco was originally an automatic, so there's no shut-off for the clutch pedal. I'm working on one, but it's not implemented yet.

Good to know on the 0.300" of space. I only have 0.032" shaved off, so sounds like there's PLENTY of error room between valves and pistons. A quarter inch of tolerance left is a lot.

These are the specs on my springs:

Installed height: 1.700" (105 ft/lbs)
Compressed Height: 1.196" (285 ft/lbs)
Coil Bind: 1.026"


Sounds like things are probably alright, and I am being paranoid. But, better safe than sorry.
Thanks