Please don't flame me...
 

I did something very stupid due to impatience. after a top end rebuild and refreshment of my 68 912 engine I reinstalled it today and when I started it, it was wildly backfiring :confused: so I shut it off after running it for around ten seconds and just pondered. this wasn't your average hickup backfiring, it was consistant. finally after a couple hours I realized it was because I was missing a valve adjustment nut. --enter brute critisism here-- so my question is, do I just shrug it off and stick the valve adj. nut on, or do I drop the motor again to check for damages?? what is the worst that could've happened? anyway.. I know I'm Dumb. no need to tell me. :(

I think I'd pull the plugs and do a valve adjustment paying close attention to how hard it is to turn the motor over by hand.
Once the valves are adjusted and you're sure there's no bent valve I'd crank it, without the plugs in, using the starter. If all sounded good I'd then put the plugs in and give it a shot.
912's are tough little engines, I don't think 10 seconds is going to kill it.
(I had a '67 912 Sunroof coupe before getting my SC)

And maybe before that, one fine glass of bourbon/wine/beer/your choice and go a little easy on yourself. We're all human.

Congrats on the rebuild.

Dumb things
 

I have done many more dumb things than I will ever admit.

EPS

I'll surely do that before I fire it up again. No alcohol for me though...underage. By the way scott, I'm located in OC as well! Thanks for the advice!

Don't think that nut would cause it to backfire, Double check that your plug wires are on correctly.

Good thought. The missing nut would only let the valve not open fully when the rocker became loose. You would hear a lot of clicking, but no real damage. And, in 10 seconds, the rocker would not become that loose.

I go with Pete 100%.

I'll be sure to double check that too! Thanks milt&pete!

I'm a little slow: Did you forget the nut, or did it back off and end up in the motor somewhere?

I accidently left it out because I was going to replace it, the threads were bad. My mental note wasn't good enough to remind me though. The whole reason I had to do a rebuild was because the previous owner dropped a tin screw in the cylinder so frankly I'm sick of things being stuck in my engine. it was simply forgotten.

If the adjuster went loose then no worries. so long as the rocker and cam are not damaged from the extra lash there is pretty much no way anything south of the valve got damaged. I wouldn't think that an adjustment screw would go tighter in that situation.

I doubt very seriously you have any engine damage. With the nut missing, the valve simply not open far enough to hit anything. I would be more concerned with the foot of the rocker damaging the cam lobe by "smacking" against it. You sure didn't run it long enough to do that. If the nut in question was left off the exhaust valve it will surly backfire since the cylinder would not be able to fully empty itself during the exhaust stroke. I would install the nut, check all your valve clearances, check your firing order and hit the switch.

When I missed my shift a couple of years ago, the impact of the exhaust valves spun three of the adjuster nuts off, a common occurence. One of them looked like a pretzel, but surprisingly did no damage in it's travels around the drive train. I did replace the adjuster screws as those 3 did get a slight bend.

As mentioned above, consistent, repeatable misfiring is often the result of switched plug leads.

too young to drink. huh, he's got a lot of years left to do more stupid stuff that most of us have already done:D

we have all done stupid things, whats bad is when you do it twice.