SBC fresh heads, not won't run - backfires

[dogsofwar]

Got an 85 K5, 305, had a blown head gasket, so I put on a fresh set of heads. It ran before I tore it down, just ran really rough. Got everything put back together today and tried to get it running, but it was backfiring out of the carb, wouldn't even run at all.

We checked the distributor several times, always starting at 1 top dead center. Double checked the plug wires several times. Even double checked the rockers. I used the same lifters, didn't pull them. Adjusted each rocker when the other was down, tightened until the pushrod had no up and down slack, then gave it another 1/2 turn.

This is the first time doing something like this, so I might not have done something quiet right, but I followed everyones advice on getting it setup initially. I figured I would have to time it and adjust the rockers after it was running, but it won't run at all. Backfires real bad when I crank it, won't go at all on its own.

Any advice on what to check next?

 

[British Slave]

Gotta be timing. 180* out.

 

[4X4HIGH]

Either distributor is 180* out or the valves are adjusted too tight. The valves should be adjusted when the piston for the particular cylinder being worked on is at TDC, remove all "slack" then 1/2 turn more. There usually will only be about 3-4 threads of the rocker stud visible above the rocker nut when they are adjusted properly.

 

[gopher_6_9]

Either distributor is 180* out or the valves are adjusted too tight. The valves should be adjusted when the piston for the particular cylinder being worked on is at TDC, remove all "slack" then 1/2 turn more. There usually will only be about 3-4 threads of the rocker stud visible above the rocker nut when they are adjusted properly.

Yep, yep, 1 of the two very common mistake.

 

[dogsofwar]

Its not 180 out, we thought that too, but its been checked and rechecked. Pulled the plug, waited until the piston was at the top, the timing mark was right at 0, set the rotor to a post and marked it as 1.

For the rockers, I adjusted each one while the other rocker was opening the valve to make sure the valve was closed all the way. Double checked them all while I had a friend turn the engine. There might be only 3-4 threads showing on each stud, maybe less but not more. And they all look pretty much the same, none of them are tightened down or too loose compared to the rest.

I've double check both multiple times and always come up the same way.

 

[dogsofwar]

Here's a pic of a couple of the rocker nuts, they all look about like this:

 

[bp71k5]

Read 4x4High's valve adjustment procedure again. He knows what he's talking about.

 

[ryoken]

Its not 180 out, we thought that too, but its been checked and rechecked. Pulled the plug, waited until the piston was at the top, the timing mark was right at 0, set the rotor to a post and marked it as 1.

For the rockers, I adjusted each one while the other rocker was opening the valve to make sure the valve was closed all the way. Double checked them all while I had a friend turn the engine. There might be only 3-4 threads showing on each stud, maybe less but not more. And they all look pretty much the same, none of them are tightened down or too loose compared to the rest.

I've double check both multiple times and always come up the same way.

both of those procedures "could" be wrong..

first, the piston being all the way up doesn't mean didley.. could very well be the exhaust stroke... watch the #1 valves, as soon as the intake closes, the next time up to 0 on the balancer is TDC...

you should only be turning the motor over 360 degrees when adjusting valves... TDC #1, set 1/2 the valves. TDC #6, 1/2 the valves...

http://www.centuryperformance.com/adjusting-valve-lash-spg-149.html

 

[blazinzuk]

I don't mean to hammer you but I think you 180 out too. I have had several freinds who have made this mistake. If you haven't messed with it since last time take the disty out turn it 180 and see if it works.

Is it kind of a chug backfire? Or more of a POP backfire?

 

[4X4HIGH]

Its not 180 out, we thought that too, but its been checked and rechecked. Pulled the plug, waited until the piston was at the top, the timing mark was right at 0, set the rotor to a post and marked it as 1.

For the rockers, I adjusted each one while the other rocker was opening the valve to make sure the valve was closed all the way. Double checked them all while I had a friend turn the engine. There might be only 3-4 threads showing on each stud, maybe less but not more. And they all look pretty much the same, none of them are tightened down or too loose compared to the rest.

I've double check both multiple times and always come up the same way.

The piston will come up to TDC of the compression stroke and also TDC of the exhaust stroke and each time the timing mark will line up with zero. Rockers look ok so i'm guessing 180*. Iit doesn't hurt to move it 180* to be 200% sure.

 

[dogsofwar]

fixed it

Yep, it was 180 out, once I fixed that it fired up.

Also, I adjusted all the rockers again, going through all the ones for the 1 at top dead center, and then all the ones at 6 top dead center. I still get a tap but its not until I raise the rpms, around idle I don't hear it(but it won't stay running at idle very long, might be carb issues, had that before too). It sounds just as it did before the head swap, could it be bad lifters?

 

[4X4HIGH]

Try adjusting the rockers with the engine running. Slowly loosen a rocker nut until it "clacks" at you then slowly tighten it back down until the "clack" goes away and then another 1/2 turn on the rocker nut. This is the best way of adjusting a hydraulic lifter.

A bad lifter or flat cam lobe will usually make noise all the time.

 

[Stomis]

Try adjusting the rockers with the engine running. Slowly loosen a rocker nut until it "clacks" at you then slowly tighten it back down until the "clack" goes away and then another 1/2 turn on the rocker nut. This is the best way of adjusting a hydraulic lifter.

A bad lifter or flat cam lobe will usually make noise all the time.

Yes do this. Especially with those nice valve covers ya wont get dirty.