Can't seem to adjust timing correctly

[champ9_QC]

Hi, so I've got a bit of an issue here. I rebuilt my vortec 350 and I can't make it run correctly. It only works when the timing is off by 180, idle sounds great but as soon as I give a lot of throttle the carb is spitting. Also the timing mark on the damper doesn't align with the timing cover, it's almost 90* off. I added a Comp Cams xtreme 4x4 ( 08-414-8 ) cam in it but I'm a bit skeptical about it. I set valve lash on cyl. 1 then when I turn the engine the exhaust immediately starts to open, which is pretty weird. To be fair I'm about to pull the engine out and buy a new stock cam, any ideas what I could do before doing all that?

Thanks.

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[GoToGuy]

Is your harmonic balancer in correct index? Could the outer ring have moved?
I go back a verify all static, ( the index parts that are fixed position for assembly ) are assembled correctly.
No. 1 at TDC, and you watched the intake close, the timing mark is at what? All together now. " O " Zero degrees.
Yes it will involve some disassembly but that's how visually eliminate machined errors. Now you have zero point to continue. That's what I would do, and have done it. Good luck.

 

[Road Trip]

Hi, so I've got a bit of an issue here. I rebuilt my vortec 350 and I can't make it run correctly. It only works when the timing is off by 180, idle sounds great but as soon as I give a lot of throttle the carb is spitting. Also the timing mark on the damper doesn't align with the timing cover, it's almost 90* off. I added a Comp Cams xtreme 4x4 ( 08-414-8 ) cam in it but I'm a bit skeptical about it. I set valve lash on cyl. 1 then when I turn the engine the exhaust immediately starts to open, which is pretty weird. To be fair I'm about to pull the engine out and buy a new stock cam, any ideas what I could do before doing all that?

Thanks.

What a lot of people don't realize is that the timing marks have been moved at least
(3) different times on the SBC over the years. The reason given for moving the pointer
on both the stamped pointer on the front cover AND the mark on the balancer was
that when they relocated the belt-driven accessories on the front of the engine this
would block the mechanic's vision of the timing marks, so the marks had to be moved
in order to give the mechanic a clear line of sight for his timing light flash.

Check out the 3 different locations for the marks over the years:

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(Credit: Grumpy'sperformance.com -- LINK)

Once upon a time you could mix & match all this stuff and (thanks to the legendary Chevy compatibility)
you never had to question how stuff lined up. But this is 2023, and my first question would be
have you ever seen this front cover AND this damper ever work together before?

And a good cross-check would be to (temporarily) insert a positive stop device in the #1 spark plug hole,
turn the crank clockwise until it stops, and mark the damper. Then, turn the crank counter-clockwise almost
the full 360° until it stops again, and mark the balancer again. In the perfect world, the machined mark on
your balancer will be exactly in the middle between your 2 marks. IF not, then you will need to mark the
correct TDC (Top Dead Center) on your balancer equidistant between your 2 marks. (NOTE: I find that the
brightest red fingernail polish to work well.)

And now with your 'proven accurate' TDC pointer on your damper, is it in agreement with your front cover
or not? Once we get your true TDC figured out, only then can we try to figure out if your cam is installed
correctly phased to the crank or not.

Let us know what you find. Pics would be very helpful, good or bad. Good luck!

 

[Erik the Awful]

I rebuilt my vortec 350 and I can't make it run correctly. It only works when the timing is off by 180

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[Schurkey]

vortec 350

How much of the stock ignition system is still on the engine?

The Vortec 350 ignition system cannot be timed by moving the distributor. The timing is not adjustable, it's controlled by the crank sensor and ECM/programming. Turning the distributor does not change the timing, it changes the synchronization between the crank sensor signal, and the cam sensor signal (which also changes the alignment between the rotor tip and the distributor cap terminals so the spark doesn't jum to the wrong terminal.)

Aligning the distributor is a process detailed in the service manual, you should download the service manual set for your engine from the links on this web site.

From there, you need a scan tool to determine the distributor offset. Spec is + or - 2 degrees at 1100-ish RPM.