A Mystery If Anyone Dares
 

This may be a thread that many of you will scratch your head at and move on but here goes. I owned a 79 L82 with a replaced engine (block 3970010) that I wanted to start doing lots of mods to. It ran fine with no problems until I started my top end rebuild. I installed 2.02 camel hump heads, new hei dist, new cam, gear drive, and new intake package. I timed the engine "straight up" w/TDC comp stroke and double checked everything was correct, set dist on #1 cylinder and started car to break in cam. When I went to start car it just turned over and didn't want to "catch". I moved dist from the flush and even position (meaning it wasn't turned to the right or left to advance or retard timing) to advance the timing and car started right up and ran thru cam break in. When I turned it off and tried to restart it, the motor turned over and then "kicked back" (don't know any other way to describe it but engine reversed its turning) and made a very loud screech/bang. I tried this several times and then figured I had it timed wrong. I took out dist, made sure #1 was at TDC comp stroke and reinstalled dist flush and even, same problem, advanced it, same kick back and noise. Figured cam was installed wrong. Took everything apart, reinstalled, tried again, same outcome. Thought maybe cam or gear drive was bad. Bought new Comp cam, put in timing chain, timed 'straight up". tried starting, same problem, this time the starter broke by engine kicking back, bought high torque starter, same issue. I was able to play with the dist to move timing right to the point where car would start but ran like crap with timing way retarded. Had no power unless I advanced timing and car ran great, then the "kick back" occurred while starting. Anyone have any ideas on what I could have done? My guess is still timing, but although I am not the coldest beer in the fridge I do know how to time a SBC. Thanks for any input.

Your valves could be to tight or several are loose as a goose. This will make it act like timing or timing chain.

Hmm, the valve train never crossed my mind. I used 1.6 rollers and followed the manufactures instructions while setting them. I suppose one or more could have hung open causing the problem while they got whacked by the piston. But does that explain the car starting without kicking back when ignition timing was retarded?

My thoughts keep coming back to timing as well. It sounds to me like the weights in the distributor are stuck in one position and not giving you the advance when it starts. If you could try leaving the hold down nut just loose enough to allow you to move it as you start then you could test this theory. Set the timing in the position it likes to start. Have someone start it and when it fires, give it a little throttle and manually advance the distributor as it revs up. If it runs smoother as you do that then you know somethings wrong with the internals of the distributor. But I have a feeling you might not be able to try this, as one of your opening lines is, "I OWNED a 79..." Did you send it down the road?

Possibly a stupid question... But do you have all of your plugs routed in the proper firing order?

This crossed my mind as well.

I once had a mis-marked timing set. It was a brand name.

I always use the dial indicator and the big timing wheel now.

Have you actually set the timing with a timing light? If not, that's your first step.

Fireball, not a stupid question at all. That was my first thought when I was trying to figure this out. I triple checked the firing order and wires. Sadly I did "send it down the road". I posted this because this problem has bugged me for 10 years. It got to the point where I would start it with timing retarded, then go out loosen dist, advance it and drive.

This is interesting. So to be clear, the same issue has been happening for the last 10 years ? Was the issue the same before and after you changed the cam and made your modifications?

Has it been like this since you owned the car? Was there a point that it was running correct but then something changed?

Send it down the road = sold car?

This isn't a stupid question either but you haven't answered it.

BK, I didn't have a timing light back then, I was old school, I set timing by ear which usually was 12BTDC. I know some will pull your hair out at that but that was how I rolled back in the day. Just to clear to everyone reading this, this was an old issue I had with my very first corvette. I no longer own the car. I have done a few other cam swaps and never had a problem like this before or since. Hence the "mystery."

Did you line the marks up right on the cam and crank pulley's? 12 o'clock and 6 o'clock? Did you turn the crank 360 degrees before dropping in the distributor? Sounds like you may be out 180 degrees?

As suggested the valves maybe way to tight as well.

You've supported my earlier theory... Starting it in one position and moving it to another to drive it = locked up distributor internals. Non working mechanical or vacuum advance.

Sounds a lot like the problems I had with a BBC.
I had done a cam swap and installed an aftermarket ignition box, coil, and a different distributor (used).

After much of the same frustration, it turned out mine was a bad distributor. IIRC, it was the vacuum advance canister.

The game is afoot, Dr. Watson!:lol:

Scott

i had the same problem with a chevy pick up truck , mechanical advance was stuck in the full advance position , easy fix once I figured it out

If it fired and ran good for 20 minutes for the cam break in, the motor is fine but you have a distributor problem.
Question; how did you verify TDC? If you just turned the balancer to the mark is not good enough. Many times on old balancers the timing mark shifts on the balancer.

Hmm, the distributor was the one thing I did not look at or even think of looking at. It was brand new so I assumed it was fine. I thought about it being 180 out, however I quad checked the timing marks and TDC firing stroke, and when the dist was advanced after starting the car ran super. Thanks for all the answers!!!!:cheers:

This may be old school, but I use to determine TDC by using a wood dowel. After I was sure #1 was on the compression stroke, I would gently insert a 1/4 in. wood dowel into the plug hole, and gently "rock" the crank back and forth watching the dowel rise and fall. :rock::rock: