I must have done something wrong.
Don't put your tools back until after the test drive.
Did I put the gasket on before I bolted up the short pan?
Your experience or boner moment?
Built up an overhead motor from bare block all the way through and transmission. Put the head on last and dropped in push rods...they fell in too deep. I had installed the cam with no lifters thinking the push rods ran off the cam.
Well, being somewhat new to the hobby (owned my car since 2013), I can say I haven't had time to make too many mistakes yet. My biggest mistake was using wire to tie the bands together when completing a lining change. I didn't realize how dumb this was until one day my magneto didn't work any more... luckily the errant wire had lodged against the bendix and didn't cause any damage, but it did take me a long time to figure out what was going on.
My biggest, uh-oh was to leave a rag in the trans when changing bands. It requires a complete teardown of the engine, to get all the shredded pieces out after grinding the rag to shreds. Now the rags are counted going in, and counted coming out. I also write down the number of rags going in, and compare that number to the number coming out. (just in case my memory fails me)
A local guy put an engine together, then saw the inside oil tube in the parts box. Tear down time.
Years ago I heard of a local shop that had done a valve and ring job on a flathead V-8, after putting it all back together and starting it up it was making odd rattling noises, when they pulled the intake manifold to take a look they found a ball pein hammer that had been left in the valley.
(Message edited by Ken_Todd on August 07, 2015)
Got every thing together ready to install the next day then remembered the next morning that I had not put the cotter pin in the clutch drum lock screw.
I pulled the intake manifold off my 312ci Ford and found my lost 9/16 socket in the valve passage in the head. Just recently I cut a new carb gasket for my '24 T and after installation the car wouldn't run. Three days later I sat up in bed and remembered I hadn't cut the hole for the fuel passage!!! Don.