Evanlovell24

Hey guys! I have a 1980 20r pickup that I just rebuilt the carb on. It started fine but then I replaced the oring on the distributor and it would only crank. I checked the timing and rotor position and it was off. I repositioned it but it will only crank and what sounds like a backfire from the engine bay. Any thoughts?

mwisham

sounds like the timing is still off.

Evanlovell24

tdc is aligned to the "0" and first cyl is on the top left of the dist?

slacker

iTrader: (1)

if your just looking a the 0 timing mark , there are 2 TDC/strokes .. compression and exhaust . you need to make sure your on compression @ " 0 * "
stab the distributor back in @ 90* , allowing the rotor to move back to # 1 .

your most likely on the exhaust stroke , so you need to rotate the crank 180*


.

Evanlovell24

What do you mean by "90*" exactly?

msane99

180°

Evanlovell24

What do you mean by rotating it 180*?

rowdy235

Basically your cam/distributor turns at half speed of the crank. So Cylinder 1 is actually at TDC twice per each turn of the distributor. Once when cylinder 1 is on compression (this is when it should be firing) and again when it is at the top of exhaust/beginning intake stroke (should NOT be firing). So just because your crank mark is at TDC doesn't necessarily mean you distributor needs to be pointing at #1. An easy way to test/fix this is to put crank at TDC/Distributor pointing towards #1. Then pull the distributor, turn the crank one revolution (until it is back at TDC), making sure you turn it only one revolution, and then put the distributor back in pointing towards #1. If it was 180* out, the engine should fire up.

If the same no start, I would check to see if #1 is on compression. There are various ways to do this but I like to turn the engine over by hand with my thumb over the plug hole (helps to have a buddy to turn the engine over and also pull all the plugs. When you feel compression, keep turning until the crank pulley reads TDC. That *should* be TDC on #1 compression stroke. The only reason it may not be is if your crank pulley or the marks are messed up, which happens on occasion. If you think this is the case you can use a straw or similar in the plug hole to locate TDC (turn crank each way until you find the top). Once you've got Cylinder 1 at TDC on compression stroke, set the distributor to #1.

If you're sure you've got the distributor pointed toward #1 on TDC compression and its still not starting, the only thing else I can suggest would be to have someone turn over the engine while you rotate the distributor both directions. Provided everything else is okay you should be able to get the engine to fire up at some point.

Of course, all of the above assumes you've verified you're getting good spark to the plugs and there are no air/fuel issues (try with starting fluid if in doubt). Another potential area for issues would be the distributor cap/plugs/wires, but since the engine was running before we can probably assume those are OK.

Hope this helps

mwisham

the surest way to tell if you are at TDC on the compression stroke is to remove the valve cover and check to see if both valves are closed on number one cylinder when the crank is at TDC. Both valve rockers on number one cylinder will be loose at TDC. If you are on the exhaust stroke, the exhaust valve will be open. Be very ,very careful spraying starting fluid in the engine!!! Too much can be disastrous.

msane99

might be able to set crank @ 0 pull #1 plug and shine small bright flashlight in hole and see top of piston, or small screwdriver like Craptsman #1 phillips with little tape wrapped around head should touch top of piston @ TDC ... if you dont feel or see anything the first time turn balancer 360 try again.

@ TDC rotor button should be just passing #1 on distributor cap. eye balling it.

I had a woodruff key sheer off the crank once and took me forever to figure out that was the problem. it keeps Harmonic Balancer in place.

msane99

If you are one tooth off distributor I think it may still run adjusted all the way in whichever direction its off. wont be right but should run if I remember right.