1966 GMC. I fixed it...but still don't know what I fixed?

[Kentchristensen08]

Okay, let's see if anybody on here can give me some insight about a 66 GMC pickup truck .. It was in really rough shape, it turned over and started everytime and I could drive it for 2 or 3 minutes and then would lock up and die. And for the short time it would drive it ran horribly. I rebuilt everything just hoping something would work or give me some insight. The transmission, the steering column, the clutch the carburetor. Redid the wiring, new HEI distributor, new carburetor... Still no luck. Then decided to put a new intake manifold, after that it wouldn't even start. I almost gave up and just put in a 454 that was in my motorhome. With one last grasp, I went to start rebuilding the engine. The first thing I did was try to take off the harmonic balancer. It turned a little bit and then stopped and couldn't turn anymore. I grabbed a pry bar and crank down on it. It broke free with a loud pop. I thought I either just broke my engine or fixed it so I put the harmonic balancer and crankcase back on and tried to start. It fired right up and has been running great since. I've asked a few good mechanics what could have happened? They basically don't believe that that's the sequence of events or don't know what it possibly could have been. Any ideas or preferably the answer?

[geezer#99]

I’m with the few good mechanics.
Hard to believe what you describe.
However, perhaps it’s your terminology. The word crankcase for example. It’s not something you can put on like an oil pan or timing cover.
A couple of things to help.
What motor?
What intake, distributor, carb etc.
What transmission?

How did you get the balancer off?
What puller did you use?

And pics help a lot.

[Warrens69GMC]

Did it sit for a long time? You may have a ring of rust in one cylinder.

[Kentchristensen08]

Oh ****...sorry, "crank case" was a typo. Supposed to be *crank case timing chain cover.

[geezer#99]

Gotcha!
And the answers to my other questions are———

[Kentchristensen08]

It could have ring rest in just one cylinder and still crank and start? If so, that is probably what it was. And it's a V8 305, was sitting for a long time, had a Rochester two barrel on it but upgraded to a aftermarket intake manifold and four barrel quadrajet, aftermarket HEI distributor, rebuilt munchen 3 speed transmission.

[Kentchristensen08]

And right now "since it's been running really good "since I fixed it" I put on new long tube headers, and working on the rest of exhaust now. So kind of follow-up question, I did what any self-respecting man would do to put new headers on his 66 GMC. I started it and drove it with only the long tube headers on. It sounded great "loud", but didn't run that well, no low-end power. Is that just because I hadn't put exhaust from the header back? I can't assume a couple more exhaust pipes will make that big a difference?

[geezer#99]

No power!
First thing always check timing.

Do you have pics of your motor?

[gmtech68]

You need a collector on the headers to get the low end. Might need to experiment with length but start long and trim if that's what you are after.

[1971 GMC SHORTY]

Need To put Complete Exhaust System To Have Correct Back Presser mine did Same Thing, when I Put A 500 CFM Holly Incredible Power Next I need to Install The Hei I Just Made Bushing for distributor