216 chevy 3 & 4 cylinder not fireing

Picked up a 1950 chevy deluxe . It has the strock 216 in it which idles a bit rough shakes pretty bad . I tried pulling of the plug wires to the cylinders one by one and cylinders 3&4 appear to be not fireing. Didnt get to compression tester yet was just curious what can be some things to look for to diagnose . Checked the plugs wires and cap have ruled them out. Thanks for any advice

 

so you are getting spark at #3 & #4?
are those valves opening?

 

Yea I have spark at 3&4 . There is no valve noise at all did not pop the valve cover yet

 

if you put your thumb over the sparkplug hole and spin it over do you get any compression?

 

Havent tried that yet . I do have a compression tester but its on loan for a few days lol

 

could be as simple as 2 fouled plugs.
or not

 

if you get enough pressure to blow your thumb off the hole- you should have enough for it to fire.

did you double check the firing order and wires and cap sequence?

hopefully some others will chime in- i am heading home for the day from work. will check in there.

 

At my job whenever I see cylinders next to each other not firing I first think blown headgasket.
That's why you gotta do all the silly little disgnostic checks to rule that out. Is firing order correct???

 

Fireing order is correct . Didn't get a chance to check the compression yet but thanks for all the tips .

 

With out an official compression gauge test .they do seem to have the same compression as the fireing cylinders using the magical thumb over the spark plug hole

 

Visible spark on#3 & #4 plugs?

Sent from my SGH-T989 using H.A.M.B. mobile app

 

Yes

 

Go and get you compression tester so there will be no guessing,are the two plugs fouled and have you removed the valve cover to see if any of the pushrods are still where they are supposed to be.

 

Good fat blue spark? Maybe swap a plug out with a cylinder that is firing.

Sent from my SGH-T989 using H.A.M.B. mobile app

 

also look for a vacuum leak at the center of the intake manifold.

 

Not sure I'm a big fan of that thumb test... seems to me any engine with enough compression to blow your thumb off, may also have enough vacuum to suck it in...

 

Will post the results of compression test in a few days . I have not popped the valve cover off yet.

 

my guess is bent pushrod or busted piston. have seen both do what you are talking about.
pull the valve cover and see what it looks like. do compression test soon as possible. both will tell you real quick how bad it is. good luck.

 

I guess I have really big thumbs.

 

any updates?

 

Will have the conpression results in a day or so did not forget lok

 

Well a few things i have found one its not a 216 it is a 235 . The vaccume advance on the distributor does not work .

Conpression is a even 145-150 pounds between all the cylinders .

 

I don't think it works that way. On a four-cycle engine there is a compression stroke, not a vacuum stroke. What would the vacuum be on an engine being cranked over with the starter? Maybe 5 pounds? I have never checked but pretty sure it isn't 145 psi.

Neal

 

very good chance that the distributer is blessed with worn bushings and shaft.

 

Triple check the wires, the two cylinders are close together, it's possible to cross them and not notice.
The vacuum leak is a good suggestion, 3 and 4 are on the same intake port.
Head gasket would be a possibility, too.
It would have to be two pistons shot to cause both to not fire, too much of a coincidence for me.
Possibly a stuck intake valve on one cylinder could act like a vacuum leak and cause the other cylinder on the same port to lean out enough to misfire.

 

I have to say my 53 has a 216 and it was acting "about" the same way but my vaccum pot was shot also...buy a new one for $40 at National Chevy and forget about it..problem solved..

 

I am going to test for vaccume leaks that seems like the most probable cause. The 2 cylinders defenetly are not firing like the others cylinder 3 has a very slight fire while 4 has completely no effect when i pull the wire . Also ordered the a new vaccume advance. Upon crunching casting numbers it is a 54-62 235 engine.

Thanks for all the tips i will keep you posted i dont get to work on the car daily.

 

If the vacuum advance doesn't work due to its diaphram leaking, follow the vacuum hose from it and see where it connects. Does it go to the intake manifold near the number 3 & 4 cylinders? Or does it connect to the carb where it would also be nearer to the two center cylinders?

 

It connects to the carb near those cylinders. Hopefully it is that let you lnow thanks

 

Easy enough to plug off the vacuum port and see if things improve. Or better yet, install a vacuum gauge there if it's a full manifold vacuum port and see if you can pull a decent, steady vacuum reading.