Low Compression #3&4 cylinder

[1g4g63t]

I have a brand new motor (turbo) with maybe two hours on it. I checked compression before start up and had 100lbs. per cylinder. I drove it around the block trying to begin to tune it and it was just not right. I then started to get a mild overheating problem and again checked compression to find 60 lbs in 3&4 and 95 in 1&2. Took the head off replaced the head gasket and gave a visual to the valves and cylinder walls all looked good. Put it back together and fired it up, sounde like crap. Re checked compression 1&2 95 lbs. and 3&4 barely 30. Put oil in cylinder and re checked,,got worse. Cranked over with out plug and blew oil out. Checked number 4 about 5 different times and 1st time 90 lbs. second time 15 lbs. third time 15 and fourth time 65 and last time 40. I do not believe it is a head gasket and none of the valves looked bent. It has a brand new valve job and re built lifters (it also needs a new front window as I punched it). I do not want to pull the head again and I just replaced it with a composite head gasket, arp studs and torqued to 80 ft. lbs. Can any one help me here? I'm lost!!!!!!!!!
Nick

 

[92awddsm]

You had problems to begin with. Even a fresh motor with 0 miles and 0 runtime should be well over 135 psi compression. My guess at this moment would be bent valves. If the head was surfaced after the valves were reinstalled, Im sure it hurt the intake valves. They stick into the combustion chamber enough that they can be damaged from a resurface.

And if that isnt the case, did you ever set the head down on the deck side? If so, you can and most likely will bend valves that way also. Do a leak down test and see where the air is leaking from. My guess is that it is coming back through the intake manifold.

 

[1g4g63t]

You had problems to begin with. Even a fresh motor with 0 miles and 0 runtime should be well over 135 psi compression. My guess at this moment would be bent valves. If the head was surfaced after the valves were reinstalled, Im sure it hurt the intake valves. They stick into the combustion chamber enough that they can be damaged from a resurface.

And if that isnt the case, did you ever set the head down on the deck side? If so, you can and most likely will bend valves that way also. Do a leak down test and see where the air is leaking from. My guess is that it is coming back through the intake manifold.

when i had the head resurfaced the valves were out..all of them..so thats not the problem..and when i had the timing done it was done right so i dont see how the valves could be bent...i can drive the car and it runs but it runs shitty..

maybe sticky lifters ? not letting the valves close all the way maybe ?

when i first did a compression test on it when i had my 1st head gasket on it the car read 125 across the board..and then after that thats where it got shitty...then i changed the head gasket...and its torqued to 80 ft lbs and it still reads like crap..

let me know asap !!

 

[92awddsm]

I am assuming that the head was torqued to 80 ft/lbs using the supplied moly lube on the threads and nut to washer mating surfaces, right?

Also, remove the lifters and bleed the pressure and try a compression test again. I see you said rebuilt lifters but there is no such thing. Either they were cleand and reinstalled or they were replaced with new but no one rebuilds lifters. There arent even replacement parts available for them to be rebuilt.

And again, if the head was ever set down on its deck surface, it can bend the valves. Just because the timing was done properly doesnt mean that the valves couldnt get bent before hand.

Like I said, take your compression testor and hook an air hose to where the guage would normally be hooked to and pressurize the cylinders. Now listen and see where the escaping air is coming from. This will pinpoint where your compression is going.

 

[1g4g63t]

I am assuming that the head was torqued to 80 ft/lbs using the supplied moly lube on the threads and nut to washer mating surfaces, right?

Also, remove the lifters and bleed the pressure and try a compression test again. I see you said rebuilt lifters but there is no such thing. Either they were cleand and reinstalled or they were replaced with new but no one rebuilds lifters. There arent even replacement parts available for them to be rebuilt.

And again, if the head was ever set down on its deck surface, it can bend the valves. Just because the timing was done properly doesnt mean that the valves couldnt get bent before hand.

Like I said, take your compression testor and hook an air hose to where the guage would normally be hooked to and pressurize the cylinders. Now listen and see where the escaping air is coming from. This will pinpoint where your compression is going.

I assume that the shop must have cleaned them. Can a lifter stick and cause a valve to hold open enough to leak down compression on the compression stroke. I also have Crower Stage 2 cams with a stock turbo motor

 

[92awddsm]

I assume that the shop must have cleaned them. Can a lifter stick and cause a valve to hold open enough to leak down compression on the compression stroke. I also have Crower Stage 2 cams with a stock turbo motor

If a lifter is removed from the head and not bled before reinstall, it will definately hold the valve open resulting in loss of compression.

 

[1g4g63t]

If a lifter is removed from the head and not bled before reinstall, it will definately hold the valve open resulting in loss of compression.

would it be a wise choice just to go and by the 3rd gen lifters and install them and see what happens ?

 

[92awddsm]

would it be a wise choice just to go and by the 3rd gen lifters and install them and see what happens ?

That would be a wise decision but I would wait until I find and solve the problem before I spent $ on trial and error parts.

Try this before you spend any more $. http://www.vfaq.com/mods/lifters.html

 

[K_Hill]

I was having the same problems as you a few days ago after i built my motor... All I had to do was get the cams degreed in right.. Is your timing correct??? Try and mess with your degree on your cams and see if that helps.