Compression #'s = non running motor?

[1973Guppie]

Hi,

some background on this thread here:
https://forum.ih8mud.com/40-55-series-tech/485158-pertronix-ignitor.html

so I finally got spark at all the plugs and wires. My points were not adjusted correctly, thanks POSER! appreciate your help and everyone's else.

Well, it still won't fire though. Engine cranks over well and I have spark at each wire and fuel spraying into the carb.

So, I decided to do a dry/wet compression test. Pic shows the results.

I think there is a break between 3 and 4 cylinders in the head gasket.

What I am wondering though is would this cause the engine not to fire at all? I used to have an F engine and I had a bad HG but it still ran, albeit it roughly. So, wondering if anyone can comment on whether a 0 reading on 3 and 4 would cause the engine not to fire at al? All I get right now is backfiring through the carb.

I have replaced: points, condensor, cap, rotor, wires, coil. I set the bb to the pointer and confirmed TDC by looking at the #1 cylinder and making sure it was topped off (tapped with screwdriver). Dropped the disty in with the rotor pointed to #4 spark plug and #1 on the cap.

Appreciate any help / comments / suggestions!

Noah

 

[1973Guppie]

Well, spoke to my father in law, he is old school and was a machinist, used to build engines. He says the fact that I have 0 in 3/4 means that most likely the engine is farting the fuel back out through the carb before it can fire. I am getting a big puff back out through the carb when cranking. Makes sense. Looks like I will be pulling the head tomm.

Noah

 

[inkpot]

Yup, makes good sense. Fuel is drawn into and then blown out of those two cylinders. Did you go thru the valve train to make sure you don't have broken/bent/stuck/burned valves that are preventing compression? John

 

[orangefj45]

definetly check your valves first.......

 

[1973Guppie]

well, I plan to pull the head and take it to a local machine shop that I trust. They should be able to tell me if there is anything wrong with the valves, correct? I plan to have them do a full workup on the head, valve job, and check the integrity of the head completely.

For the most part the bottom of the engine should be ok, right? seems to me the #'s say that this is a bad HG.

Noah

 

[hedgehog23]

have you had the valve cover off to take a look yet? thats a good first step. when i bought my fj/2f the cam was worn flat on a few lobs and a few push rods were toast.

 

[cjgoode]

Pull the valve cover off and watch the valves move while someone cranks the engine before pulling the head. I do not think a blown headgasket would cause 0 compression in 3/4. I think the only way you can have 0 compression is a hole in the piston, hole in the cylinder wall, or the valves not closing. Like others said it does sound like valves not closing at all.

 

[Pighead]

was there just a week ago...130 PSI in 1, 2, 5 & 6. 0 PSI in 3 & 4...could still start and drive though.

 

[1973Guppie]

the engine seems to turn over well, so I hope you are wrong about something being wrong with the bottom end of the engine. what should I be looking for when I watch the valves open and close?

 

[1973Guppie]

Pull the valve cover off and watch the valves move while someone cranks the engine before pulling the head. I do not think a blown headgasket would cause 0 compression in 3/4. I think the only way you can have 0 compression is a hole in the piston, hole in the cylinder wall, or the valves not closing. Like others said it does sound like valves not closing at all.

I had all the plugs out when I was testing the compression, so wouldn't it make sense that there was 0 compression in those 2 cylinders if there is a break in the HG between 3/4? meaning, that any compression would simply push back out through the other cylinder.

pulling the head and will post some more pics today. Thanks for all your help guys! Hope I didn't screw myself by buying this piece of crap.

Noah

 

[Pighead]

, so wouldn't it make sense that there was 0 compression in those 2 cylinders if there is a break in the HG between 3/4? meaning, that any compression would simply push back out through the other cylinder.

Yes. See if you put a plug back in either 3 or 4 if your compression goes up a bit...
Mine would go up to about 30PSI if I did that.

 

[1973Guppie]

guys, here's a link, looks like the rockers are not even compressing the valves in 3/4? are my valves just grossly adjusted? IE: need to be readjusted? that's what it looks like to me. I am thinking of readjusting them per the fsm and then trying to get it to fire.

video: YouTube - ‪Valves‬‏


thanks,

Noah

 

[1973Guppie]

Yes. See if you put a plug back in either 3 or 4 if your compression goes up a bit...
Mine would go up to about 30PSI if I did that.

actually did that and the compression was still 0 ?

 

[Pighead]

Bent pushrods? almost looks like it in the video...

 

[1973Guppie]

just readjusting valves after verifying tdc, they were WAY OUT OF WACK. I did this somehow when I adjusted them before, no idea how. Embarrasing for sure. Anyhow, hoping it will fire now, putting back together now.

Noah

 

[Spike Strip]

I see no movement at all on the #4 intake ... Was it just that far out ?

 

[cjgoode]

I have had gaskets blow on a boat engine and we had to drive it back to the dock. The gasket and part of the head and block had melted away from running it that way. It still had some compression, 10 or 20 if I remember correctly. The piston compressed the air quicker then it could escape into the next cylinder. But still check the valves before pulling the head, it is easier to see that they are moving prior to pulling the head.

 

[1973Guppie]

all back together and it noticeably turns over better, valves were so out of wack that 3 and 4 were not even moving. Still can't get her to fire though. Any ideas? checked spark at the plugs, ok. Carb is getting fuel. I guess I will do another compression check now that the valves are adjusted properly.

 

[Pighead]

Gotta re-check timing now...

 

[inkpot]

You could always use the old starter fluid/spray test. If ya got spark at the right time, then shoot the intake full of starter spray. If that don't at least cause some fire/misfire in the cylinders, then ya got a much bigger problem. John