Ok, I have a 65 stang with a straight six. Heres the deal: I did a compression test on all cylinders- #4 was bad with almost none. Then I soaked it with oil- still none. Then I did a pressure test AFTER I took off the valve cover and removed the pushrods (valves will/should seal) I get air leaking from the vaccum tube coming from the intake manafold. No air coming from the carb, pcv or exhaust.
Here is the tricky thing. The motor was rebuild years ago and never driven. During the storage time, the freeze plug popped out. I took the head off and can not see any cracks or sign of damage so I dont know if the freeze plug being popped is even an issue...
Anyone have any ideas on how this air is leaking though the vaccum hookup on the intake manafold and if teh intake valve is not seating right, why is it not leaking from the carb- it shouldnt be leaking cuz it was machined when the motor was rebuilt?
Thanks in advance

 

was there no antifreeze up in it?

Were the push rods moving before you took them off as in did you see the valves traveling up and down and did they stay in contact with the rocker? One could be stuck open.

-Gun

 

Ya, I took the valve cover off and turned the motor over. Everything looked like it was moving as it should.... besides, during the pressure test, wouldnt there be air coming from the carb if the intake valve were leaking uibstead of the intake vaccum hookup?

 

oh, I'm not sure of teh antifreeze... I would assume so... but even if there were, it doesnt seem like it was the right mixture if it froze and popped a freezeplug

 

Don't know if this will be much help but, I'll try. Which hose are you talking about that it is blowing through? It is strange that it leaks through the intake but not thru the carb. Were the throttle plates open? You can check to see if the valve is stuck open since you have the head off, flip it over and fill the comb chamber with something (water?) and see if it runs past the valve. Was the piston up top when you did press test or at the bottom. I would look for a crack in the cylinder wall.

Another place to look when you do a pressure test is to pull the radiator cap and watch for bubbles coming thru there.

 

i agree with stepman, look for cracks in the cyl wall, probably starting at the water jacket.

 

ok, I looked real hard.. saw nothing. The cylinders are fresh with crosshatch since the motor was just rebuilt. I saw no cracks in the head or cylinder, I even relapped the intake valve and it didnt look too bad. Could the crack be small enough not to see by looking at it but give it NO compression?

I'm starting to think that who ever rebuilt the motor had the wrong pushrod to valve clearance... the valve could ahve been working fine but never closed cuz of wrong rocker clearance... the only thing that gets me is that the guy who owns the car, said it started and ran fine before... thats what he says anyway... ? Maybe he didnt notice once a cylinder not firing?

Any other guesses or advice?

Thanks

 

no fluid since... Im assuming the freeze plug froze popped out a while ago...
Right below the carb on the intake manfold there is a vaccum line connection. it seems to be blowing out of there on teh pressure test no matter where the throddle plate is, open or closed... I'm at a loss but I hate to put the thought of waisting a head gasket to try it out... check out my other replay for more info
and thanks

 

Could be the head gasket itself. If you still have the head off, lay a straight edge on the gasket sealing surface and make sure it's flat. It is possible to have cracks that you can't see but I have never seen an engine not make at least some compression even with cracks you COULD see. Since it froze hard enough to push out a freeze plug, if it were mine I would pull the motor and tear it down and have it magnafluxed to make sure it's not cracked at all. If it's not all you are out is the cost of a gasket set, the cost of having it magnafluxed, and some time. Pretty cheap insurance to guarantee that you aren't going to have any problems after you do get it running.

 

I would think it is either a head sealing issue or a valve seat issue. Either way, I think you need to pull the head.