Rebuilt motor, initial timing now 36 btc. New cam, timing chain, harmonic bal, distributor.   checked tdc on balencer -dead on.   rechecked timing chain marks on both gears 12:00.   put old distributor back on, still 24 off.  dont have degree wheel.  cant figure out?  Kyle802009-08-21 19:25:36

Well, I'm gonna ask the most obvious, and prolly silly question...are you sure you're on the #1 plug with your timing light? And...are you sure your timing light is accurate?
If it really has that much initial advance, it seems like it would be really hard to get it started, especially when hot.
It IS possible that the mechanical advance is stuck, but...you've got a ton of advance on two different distributors...
Are you checking with the vac. disconnected?
The '80 doesn't really have any electronic controls, other than just the HEI ignition set-up....
If you retard the timing back to where it should be, will it run?

are you making sure the idle is correct while youre doing this?  and of course vaccum disconnected.

Yes its on #1.  barrowed another timing light.  Put old dist back in- same.  Vac disconected.  When set around 12 wont run.  Dont have tac but at idle.  how critical is rpm, if at low idle should be good right.    Kyle802009-08-22 11:17:55

ON A SMALL BLOCK CHEVY THE TIMING GEAR MARKS ARE...GRANK GEAR AT 12 O'CLOCK....CAMSHAFT GEAR AT 6 O'CLOCK NOT 12 O'CLOCK, THE MARKS SHOULD BE FACING EACH OTHER , YOUR 180 OFF ON THE CAM 0R CRANK, SURPRISED IT RUNS. IF YOU HAVE A 3 KEYWAY SLOTS ON THE CRANK GEAR ROTATE THE MOTOR UNTIL THE CAM GEAR MARK IS AT 6 OCLOCK REMOVE THE CHAIN AND CRANK GEAR AND FIND THE SLOT THAT PUTS THE CRANK GEAR MARK AT 12 O'CLOCK AND FACING THE CAM GEAR MARK, IF YOU ONLY HAVE 1 SLOT IN THE CRANK GEAR BRING THE MARK TO 12 OCLOCK, REMOVE THE CHAIN AND ROTATE THE CAM AND SPROCKET TILL ITS AT 6 OCLOCK, INSTALL THE CHAIN.anips2009-08-22 12:41:22

You sure i thought they were both 12.  darn i called summit tech line to check & make sure, they said it was right- both 12.  have to check on that again.Kyle802009-08-22 12:59:22

Anips is right....Cam at 6 and Crank at 12. I also am surprised that it runs. I hope you haven't damaged anything.

Kyle802009-08-22 16:09:33

All my manuals from 1954 to 1997 all show that the STACTIC assembly of the camshaft and sprocket in relation to the crankshaft and sprocket is  at CAM at 6: crank at 12:, which according to your diagram is when # 6 is at TDC,  if I knew how to post the it out of my GM service manual which I don't I would post it, send me a PM with your email add. and I will scan and send it to you, like I said before, I'am sorry, get ready to roll your sleeves up.