compression check showed 60psi in 2 cyl?

[stephen4785]

I bought this stang from a friend of a friend and hes said that he had the motor rebuilt but he didnt install it because he got shiped off to Korea before he couldinstall it. I put the motor in the car and it has never ran like it was suppost to.I tried everything and my friend did a compression check on it and it showed like 55-60 on 2 cyl(i dont know which ones). Iv heard of people having a hard time getting the rings to seal after a motor rebuild.Does this sound like what it is?Any good waya to get them to seal or should I just tear it down?Thanks for any help.

 

[90mustangGT]

70psi is minimal for combustion. Was the engine warm? Even a cold engine should read better than that. Try dropping a little oil in the combustion chamber and retest, if it makes a big difference, it's the rings. If it doesn't, it is probally a valve or head gasket issue.

A valve hung open even a little would cause it to run like crap and would thow off the compression readings.

 

[jerry beach]

That sounds real low, what did the others read? I think a leak down test would provide more info before tearing into it. Need to know if its top or bottom end leaking. Mine read around 170 on all.

 

[Blandnuts]

Anyways, if the rings are on backwards or if the compression one isn't in the right spot it will still read more then 60 psi. I think I was still getting 150-170. Now this is a wet test (oil in the cylinders).

Is the car consuming oil? How do the plugs look? Does the car smoke on start up if it has been sitting? Who adjusted the rockers?

If there isn't an oil problem then I'm leaning towards a valve train problem... Like what 90mustangGT said.

 

[stephen4785]

Well once I first got it running it smoked a little.I dorve it and had to refill the tranny and smoked real bad(bad vacum modulator).I replaced it and it got better then when the V.M. went out.Ever since I got it running it hasnt ran right.Its seems to always have a miss. I pulled some wires off to see if it made a difference and 2 of the clyinders that I pulled them off of werent making any difference.Im assuming that these are the same casue my friend did the comp test at his shop and i dont know exactly which ones were the 50psi.Im going up there tomorrow to do the oil in the cylinder test.I didnt even think about the valves being imprperly adjusted.Im hoping that its just something with the heads.At least that way Id have to buy some better heads to cure the problem .But if there just improperley adjusted then Ill just adjust them and be happy for now.The only kind of test that Ive done to check wether or not its the valves or rings is when I was messin with the intake I ran the car with out the PCV or the tranny vacum line but plug the holes on the carb and I got blow by and smoke.Would it do that casue the PCV was just not hooked up.The blow by want real bad but I could hold my hand over the oil fill hole and let it up after a few seconds and hear a hiss like air was excaping.Any ideas.Im going up there this morning to try and figure something out.

 

[wildstang347]

if both cylinders showing the 60psi are side by side it could very well be bleeding pressure into the ajoining cylinder wich a friend of mine has encountered after he rebuilt the engine neglecting to have head surface checked 2 see if still within allowable warpage specs. as far as the blowby issue, some is common but hard to determine without actually seeing the vehicle wether if its excessive.
what are the pressures of the other cylinders?
leakdown test would actually be quite helpful as stated earlier.
as far as adjustment goes on rockers of bad cyl. back off adjustment all the way till free play in pushrod and retighten spinning pushrod with fingers till contact is felt with plunger noteing were position of torque wrench is, and if 3/4 turn or more is required after torqued 2 spec a shim kit is required.