Rebuilt Motor Backfiring No Start

[heyitzjoel]

I just dropped a sbc 350 long block in my 1998 Chevy K1500 made sure the intake valve was closed all the way and the line on my harmonic balancer lined up with the timing chain cover. I could feel the top of the piston through the #1 spark plug hole. I set the distributor to the #1 spark plug and when I crank the key I hear the fuel pump and then POP it backfires. I've done this twice and I'm breaking my head trynna figure this one out. I tried to turn the distributor and advance/retard the timing and still backfiring, no start. I used all brand new spark plugs, I have a new rotor and cap on my distributor. I need a second opinion.

 

[Schurkey]

First Guess: Distributor 180 degrees off. The intake valve was closed because the lifter had bled-down, the cam is actually on overlap--TDC-Exhaust instead of TDC-Compression.

Second Guess: If this is a Vortec 350, there's a special procedure for setting the distributor in place, based on markings molded-into the distributor itself. Download the service manual set for your vehicle, follow the instructions for dropping the distributor in place, and then final-adjust with a scan tool. Turning the distributor on a Vortec does NOT change the timing, although if you turn it far enough the spark may jump to the wrong distributor cap terminal.

 

[HawkDsl]

Yes, if SBC, your 180 out. double tripple check you got the right wires going to the right plugs.

 

[heyitzjoel]

Okay so I went ahead and took the distributor out and set to TDC once more and it is still backfiring out of the exhaust on the drivers side. Is it possible that I tightened my rocker arms a little too much? This is what I'll check for when I get some more light tomorrow.

 

[PlayingWithTBI]

Okay so I went ahead and took the distributor out and set to TDC once more and it is still backfiring out of the exhaust on the drivers side.

Check your firing order and plug wires 1-8-4-3-6-5-7-2

 

[Connorpod]

Okay so I went ahead and took the distributor out and set to TDC once more and it is still backfiring out of the exhaust on the drivers side. Is it possible that I tightened my rocker arms a little too much? This is what I'll check for when I get some more light tomorrow.

MY guess is that it is not the rocker arms. If they were too tight, the engine would turn over easily and there would be no compression because all the valves would be open. Learned that the hard way. Quite scary to see happen! Happy I did not bend a rod!

 

[scott2093]

Okay so I went ahead and took the distributor out and set to TDC once more and it is still backfiring out of the exhaust on the drivers side. Is it possible that I tightened my rocker arms a little too much? This is what I'll check for when I get some more light tomorrow.

I'd say it's possible you tightened them too much but couldn't say that's what's causing your backfire. But there seems to be info out there correlating too much preload and backfiring . Not sure if that's relevant to your truck.

 

[Schurkey]

I went ahead and took the distributor out and set to TDC once more

WHICH "TDC"??? TDC-Compression, or TDC-Exhaust?

Is it possible that I tightened my rocker arms a little too much?

Sure.



Is this a Vortec distributor? Did you follow the service manual procedure for aligning the rotor with the molded-in markings on the distributor housing?

 

[heyitzjoel]

WHICH "TDC"??? TDC-Compression, or TDC-Exhaust?

TDC-Compression, atleast that's what I think. I rotated the engine with the valve covers off until the #1 intake valve opened and closed. The first time I did this it was backfiring out the intake now it's backfiring out of the exhaust.

Is this a Vortec distributor? Did you follow the service manual procedure for aligning the rotor with the molded-in markings on the distributor housing?

Yeah this is Vortec distributor, I lined the dimples up with the paint marking and dropped it in so that the rotor is facing the "8" embossed on the distributor housing. The distributor lined up parallel to the intake manifold.

Tmrw I'll take the valve covers off again and turn the engine again to confirm that everything is lining up properly before I start loosening rocker arms.

 

[Vikingdude]

With cylinder #1 at TDC, you need to line up the marks on the distributor housing, and the part that rotates and drop it in. The confusing part is, when it settles in place, the marks will no longer be lined up. To get your cam-crank correlation the ball-park,
Same distributor as it had in it before the rebuild? What kind of shape is the gear in? Stock camshaft?