72 Chevy k20 350 won't start
 

Hello all. I'm having some trouble with a dump truck I just bought. It had a cracked exhaust manifold when I bought it so I replaced them with a set of headers. Well in the process I dented the d/s valve cover. I removed the cover and used a block of wood and a hammer to straighten it all out. Looked pretty good so I reinstalled the cover. Started the truck and had a tap, tap, tap then shut off. Tried to start again and it would only run for 2 or 3 seconds then shut off. Did that a hand full of times then said screw it and pushed the truck outside. I figured from the rockers hittin the cover it wasnt letting the valves open all the way hense the stalling out right away. It sat for about 10-14 days until I got a new cover.

So today I pulled the old cover and replaced with a new used cover. New cover is straight and true. Put the new one on and tried to start it and it just cranks.

The old cover there were 2 light rub marks no deep gouges or anything just rubbed smooth a lil. I'm praying it isn't a bent valve.

Any and all info is greatly appreciated. Would like to get her going cause thy are calling for some snow.
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Re: 72 Chevy k20 350 won't start
 

replace fuel filter inside the carb body if it's a quadrajet

Re: 72 Chevy k20 350 won't start
 

I think it is a quadrajet. Any link to how that is done or can anyone kinda walk me through it. Can I clean it?

I am pretty new to carbs. Not really sure what I'm looking for.
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Re: 72 Chevy k20 350 won't start
 

I don't think your dented valve cover has anything to do with it.. But maybe in the process of replacing it you had a coil wire come off? I would check for spark at the plugs... If none then check to see that you have voltage to the coil. And make sure your coil wire[ from coil to distributer]is making contact.
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Re: 72 Chevy k20 350 won't start
 

follow fuel line to front of carb, remove the nut and slide the line and filter out. clean or replace and install again. Have you checked to see if you are getting spark? When it turns over can you smell fuel? More info needed so the members can help

Re: 72 Chevy k20 350 won't start
 

During the header install I replaced all plugs and wires. Started no prob. But then shut off. I made sure all plug wires were tight at the distributor but still no start. If I manually play wit the carb I can watch fuel spit out but when I'm cranking it inside the cab I do not smell fuel. I will check for spark and try the carb filter.

Ok. There is spark. It is getting fuel.

Gave it a spray of ether and it wouldn't even run on that.
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Re: 72 Chevy k20 350 won't start
 

When you replaced the wires did you do it one at a time? If not, start with #1 and follow the firing order around the cap clockwise to make sure they are on the right plug. Driver's side staring at the front has cylinders 1,3,5,7. Passenger side starting at the front has 2, 4, 6, 8. Firing order is cast in on the top of your intake manifold. Make sure the cap is on square if you had it off, and make sure you didn't break the rotor if it wasn't on straight.

Re: 72 Chevy k20 350 won't start
 

Maybe from the short run time you may have flooded it? Pull one of the plugs to see if it is wet.

Re: 72 Chevy k20 350 won't start
 

x2 check the plug. did you mess with the timing at all. gotta be something simple since it was running when you shut it off. look for the obvious first

Re: 72 Chevy k20 350 won't start
 

I didnt replace them one at a time no. But I did go by a diagram when putting them back on. I will recheck them tomarrow. The plugs are not wet and I didn't mess with the timing at all.

Could a push rod be bent? There are 2 shiney spots on the old valve cover from where they were hitting/rubbing.
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Re: 72 Chevy k20 350 won't start
 

Ok. Sorry for the time lapse I have been busy and finally got back around to working on the 72 Chevy 350.
So I found out that in the process of denting the valve cover I must have stuck one of the rockers. The 3rd cyl back on the drivers side (#5 i think) the rocker closest to cyl #3 only moves maybe a 1/4"-1/2". With the cover off and cranking the motor I can watch all the rockers moving lets say with 1" of travel up and down with the exception of that rocker. It's the 4th one in from the firewall making it the 1st rocker/valve(front to back) on the #5 cyl.

Any and all help greatly appreciated.
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Re: 72 Chevy k20 350 won't start
 

This is just spitballin, and may not help at all, but make sure the spring for that rocker isn't busted. I had this happen on my 65 Impala. The spring cracked in half, but the break was on the rear where i couldn't really see it initially. Being a complete newbie at the time, I overtightened that rocker and bent the crap out of the lifter. I lucked out and just had to replace the lifter and spring and it ran like a champ.

Re: 72 Chevy k20 350 won't start
 

To check for this do I still need to pull the head or can I check while it's still on the truck?
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Re: 72 Chevy k20 350 won't start
 

Was it a running driver when you bought it? If it had been sitting for a while the gas could be bad also check the points if it still has them I believe the gap should be .030 use a small file and gap them and make sure the file or emery and feeler gauge is clean no oil residue. Re trace your steps, check the coil for cracks where the wire goes in or if oil leaking from it or inside it. Your spark should be a bright blue if it’s orange you have a weak coil.

As far as the spring look and feel real close for a broken spring but it should still run with one bad cylinder, there is a fitting you can get at the parts store that you can put an air fitting in and pressurize the cylinder with both valves closed to see if the valve is all the way up, if the spring is broke with the valve all the way up it will be loose.

I would stick with ignition and gas, one other thing did you pull the starter? Check the wires on the starter if original you should have 2 wires, the out side one is for the ignition and the inside one is for the solenoid you could of possibly put them on backwards which would let it start while you crank it and shut off when you let the key go I know I did it and it drove me crazy. You could of also nicked or broken the wire while installing the headers.
Here is the wiring diagram.

Re: 72 Chevy k20 350 won't start
 

Yes it was running when I bought it. The top coil where the 2 wires connect are def oily. I don't rem the color of the spark but I did install new plugs and wires. I gapped the plugs correctly. If the spark is weak will it not fire? I didn't touch the starter. Just removed the main power wire to install the headers.

After the header install it fired right up but only ran for about 20 seconds. After that it would only fire up and run for 3 seconds. I know I screwed up the plug wires the first time and it's prob still out of time but we are having a hell of a time getting it in time.
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Re: 72 Chevy k20 350 won't start
 

Full disclosure: I'm a crappy mechanic. But the broken spring is just one of those things I've run into and worked through on my own. And one of the few things that turned out to be GOOD news as it was a really easy fix!

You just need to pull the valve cover to check the individual springs. Not sure if this has anything to do with it running then dying, but without the pressure of the full spring pulling the valve upward, that valve will fully seat and that cylinder has no compression. I actually found the broken spring on mine after I'd done a compression check and had no pressure at all on that cylinder. The broken spring made that valve pretty darn noisy. Again, no clue if this is even the right track, but if you have the valve cover off it isn't hard to take a second and look all the springs over just in case.

Re: 72 Chevy k20 350 won't start
 

Based on your description, I still think it is either spark plug wiring and timing or fuel issue. Even if you bent a pushrod (why don't you remove that rocker and check the pushrod and rocker and spring) the engine should run on 7 cylinders easily if it has fuel and correctly timed spark. Start over from scratch - put it on TDC on number 1 with both valves closed, make sure your rotor is pointing at number 1 on the cap when the cap is seated on the distributor and follow the firing order clockwise insuring that the wires go to the right cylinders. It ran before you changed the plugs and wires right? If so, start there. Good luck

Re: 72 Chevy k20 350 won't start
 

I agree that is should run on 7 cylinders. I certainly don't think the spring would be the ONLY issue, as mine was still running (rough) with no compression on #6. The other symptoms just sounded painfully familiar so I thought I'd put it out there to at least take a look at them.

It does sound more like an ignition / timing issue with it only running briefly. I actually had THAT issue with my 69 GMC last spring. Fought it and fought it between cold weather spells, and finally determined it was combination of EXTREMELY advanced timing, and poorly gapped (and eventually fouled) plugs. I eventually started from scratch, pulled and reseated the dizzy, set TDC on number 1, gapped and replaced the plugs, and it started right up on the first tap of the starter. It has started with little to no effort ever since, even in single degree temps.

I've definitely made a lot of mistakes playing with my rigs, but eventually you learn something when you fight your way through it (and do a lot of reading on the forums!).

Re: 72 Chevy k20 350 won't start
 

Thanks everyone for your all your input thus far. Greatly appreciated.

When I am finding tdc on comp stroke my thumb is being blown off the sparkplug hole on #1 cyl. Correct? As soon as that happens I then check the distributor. The rotor(little metal tab) is pointing almost directly at the drivers seat. Standing at the front of the motor it's pointing like 1 o'clock. Is that correct? So now i put my #1 plug wire in that spot on the distributor cap and follow the firing order clockwise. Also I noticed there is a groove/line on the harmonic balancer and that line is about 2" past the timing tab.

The timing tab is around the 2 o clock position and the line falls after the tab around the 3 o clock position. I dont know if that needs to at a certain spot.

I never pulled the distributor out. Just changed the wires. I don't know about previous owners but I havent removed it.
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Re: 72 Chevy k20 350 won't start
 

here

Re: 72 Chevy k20 350 won't start
 

Im not an expert just know enough to get in trouble :lol:

I usually stick my finger over the hole soon as i feel it blow it off i turn the harmonic balancer clockwise until I line up the balancer mark on the 0 on the timing tab

Should be #1 tdc compression

Re: 72 Chevy k20 350 won't start
 

The above diagram is for an HEI distributor where there is no "points adjustment door" and number 1 is at the 5:30 position as you look back at the distributor. If you have a points distributor, Number 1 is the first one on the cap to the left of the point adjusting door as you are standing in front of the truck looking at the distributor on a points distributor.
Here is a diagram for a points distributor and there is an article that it is from that will help you for either a points or HEI distributor:
http://www.classiccarauto.com/impala...istributor.png

Here is the article:
http://www.classiccarauto.com/impala...ng_order.shtml

If you have the valve cover off, click the engine over until the timing mark on the crank balancer lines up with the 0 TDC mark on the timing tab on the timing chain cover. Look at and feel both rocker arms for the number 1 cylinder - both should be fully up with no pressure on them. The piston is at the top on both the compression stroke (what you want) and the exhaust stroke (the exhaust valve would be open What you don't want). If your distributor is in correctly, the rotor should be pointing at the number 1 on the cap. Your vacuum advance if it is a points distributor should be pointing at about 8:00 o'clock for initial starting.

If your rotor (assuming a points distributor) is pointing at 1:00 o'clock instead of 7:00 - 7:30 it is one of two things - you were on the exhaust stroke not the compression or your distributor was put in 180 degrees off.

Re: 72 Chevy k20 350 won't start
 

Where is 0 on my timing tab. I can't see any numbers it just has like 5 teeth. Would it be in the middle? It is the factory timing tab if that helps at all
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Re: 72 Chevy k20 350 won't start
 

I looked at the one on my Blazer and it has 7 teeth with 0 (TDC) being the middle one. There is writing on the tabs - usually "before" and "after" and numbers like 2, 4, 6, etc. Clean it off real well and you will see them. Mark 0 with some chalk along with the timing mark on the crank balancer.

Re: 72 Chevy k20 350 won't start
 

Did'nt see wher you said if it were an HEI dizzy or not but if you do have points the gap should be .017 not .030 If you were to use a dwell meter to check the points the dwell should be set to 30
from what I have read here about your problem its sounding like a ignition problem, if it wont start on starting fluid it is probably not a getting spark.
good luck

Re: 72 Chevy k20 350 won't start
 

I knew 30 was in there but was tryin to remember from back in the day. :confused: Still have a Dell Meter and an allen wrench on a flexable shaft for adjusting the points while it is running so you know I'm old:lol:

Re: 72 Chevy k20 350 won't start
 

Ok so I tapped te key until both valves on #1 cyl were all the way up and the mark on the harmonic balancer was about an inch or 2 past the timing tab so I turned it back to 0(dead center on the timing tab). I could sorta wiggle both rockers so i knew they were both closed on comp stoke. I pulled the distributor cap and the rotor metal tab piece thing was pointing at 7 o clock. So I pulled all of my plug wires are started over with #1 wire going on the 7 o clock position on the cap. I followed the firing order starting with 1 and went in a clockwise rotation. I thought this is it here we go and nothing just cranks. So I pulled the #1 plug and had someone crank it while I check the spark. It is def yellow. So I assume I have a weak coil. So if my coil is weak and that is the problem why won't the spark it is giving off ignite? Is it getting to the cyl late and exhaust stroke already sucked out all the fuel vapors?
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Re: 72 Chevy k20 350 won't start
 

Everywhere I looked sparkplug gap with points(what I have) should be .030-.035. Mine are gapped at .030.
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Re: 72 Chevy k20 350 won't start
 

Should still run do your self a favor and get a new coil the gas today just don't burn like it did in the 70's

Re: 72 Chevy k20 350 won't start
 

Ok so I got a coil. Installed it with the wire coming from the distributor to the neg on the coil and the other wire (I'm assuming 12v) to the positive on the coil. Still nothing just cranks. Didn't get to pull a plug and look at the spark yet.
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Re: 72 Chevy k20 350 won't start
 

If the wires are correct and you are getting gas it should fire. Some thing happend when you installed the headers. Turn the key on and see if you have 12 volt to the coil then check the wire at the termanal block that has the small wire from the battery going to it and make sure it has 12V

Re: 72 Chevy k20 350 won't start
 

The truck fired after the install that's why I don't know why it won't now. Could I have collapsed a lifter? When the motor is cranking its not a smooth crank it almost sounds and kinda feels like something is rubbing somewhere.
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Re: 72 Chevy k20 350 won't start
 

even if you damaged something in the valve train on 1 cyl or even 2 it would still run.
It sounds like you have the dizzy and the plug wires correct. It will not start on starting fluid, still sounds like an ignition/spark problem. Did you check the voltage at the + term on the coil? Pull a plug wire off at the spark plug, then grab a spark plug and plug it into the wire, ground the plug to a good clean part of the engine or frame or a bracket, hit the starter and watch for a spark

Re: 72 Chevy k20 350 won't start
 

Did you ever get it running ? If so what did you find

Re: 72 Chevy k20 350 won't start
 

Maybe theres no gas in it. My 72 k2500 wouldnt start or crank even with ether. Turns out my trusty fuel gauge was very incorrect. It read 1/2 tank and was empty!

Re: 72 Chevy k20 350 won't start
 

Hate when that happens

Re: 72 Chevy k20 350 won't start
 

Just read this whole thread and now Im on the edge of my seat wondering what was wrong. If it didnt start just to throw in my 2 cents,if its a points distributer there should be 2 wires to the + side of the coil. 1 is from the ignition and the other comes from the starter and is a bypass to keep the coil voltage up while there is a starter draw. The starter cranking can drop the coil voltage down to 9 volts or less creating a weak spark in the start mode.Hence the second wire. If the ignition wire breaks the motor can start on the bypass but will die imediatly when you let go of the key. Hei is the way to go. Also if its points dont forget (everybody always forgets) the condenser can be bad and cause weak or aradick or no spark also. Hei is the way to go...sorry I think I already said that. Good luck and let us know what happend!

Re: 72 Chevy k20 350 won't start
 

Hey everyone. Thanks for all your input. I have been so busy I haven't had time to work on it. Latest update I got a new coil. I haven't had the chance to try and start it and look at a plug to see if the spark got stronger or stayed the same. Quick refresher on what I changed.
Plugs, wires and coil.

Do points distrib just go bad? I can't even figure out why it doesn't even sound like it wants to turn over.

I only have 2 wires to the coil. 1 to the + and 1 to the - . I wonder if in the header install process I broke the wire coming from the stater to the coil. I'm pretty sure 1 wire goes from coil to distrib and the other goes down to a wiring harness. I THINK. But i am positive I only have 2 wires hooked up.

The tank was on fumes before I did the headers so I ran to the gas station and put 5 gal in it. The gauge reads half and after I put the gas in I only drove it 3 miles MAX. When I lookin in the carb an work the throttle I can see fuel squirt in.

Tomorrow I'm going to hook up a multi meter to the coil and check the volts, also I will look to see if I can find that missing 2nd wire that is supposed to be on the coil.

Thanks again everyone and keep the ideas coming this truck ain't gonna fix itself. Lol.
Quick question. Hei distrib- what are some good ones preferably in the cheaper price range?
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Re: 72 Chevy k20 350 won't start
 

If your unsure about the coil wire you can always use a jumper right of the battery to the positive side of the coil,as a test. Just be careful because it will be wired hot and you wont be able to turn it off at the key with the wire on that way. As hei goes the factory ones are awsum and can usally be found at a resonable price. You might find one in the parts board here. Good luck keep us posted.

Re: 72 Chevy k20 350 won't start
 

If you are having trouble finding the wire go back to post 14 and check the wiring diagram the wires are color coded. If you have trouble reading it go to view at the top of your computer and go to zoom and hit 400%. Good luck