Need some help from some experts on compression

[Mjag60e]

Hey guys, need some advice from the experts...seems as if I have a compression problem.

I am in the process of building a 4G63 motor on a 90 Eclipse, N/T.

After assembling the block, head, and transmission I mounted the motor in the car, hooked up a new battery and starter to test the compression. No Intake attached, only Exhaust Header. #4 Cylinder read 170 psi, #3 read 168, #2 read 170, and #1 read 100 !!!! I squirted a bit of oil in #1 and the pressure came up by 20 psi, indicating that I might have a ring problem. That sorta blew my mind because of the following work that I have done:

Block surface machined, bored .020" over, head surfaced, new 3 angle valve job, checked for cracks (pressure), new Crower Cams, new seals, etc. This work was done from a very dependable machine shop. I also have new forged pistons and rods (thinking of adding a bit of laughing gas! ), new crank.

So off with the head. I checked EVERYTHING on the block...bore size, piston size, compression ring end gap, compression ring slot clearance, piston clearance...everything was perfect! So here is my delima... If the head has been surfaced, and completely reworked, and the block checks out dimensionally where is the leak coming from. Should I take my head to another shop and re-check it, could there be a problem with my new head gasket? And by chance if when I inserted the new piston in the beginning and somehow the gaps in the two compression rings were not opposed could that be enough to lower the compression that much?

HELP...I'm stuck and I consider myself to be a pretty good mechanic!

Thanks for any assistance and thanks for the space!

 

[hose101772]

Comp around 90-100 sounds like headgasket to me.Now way off in left field-could be lifter stuck.

 

[98TsiAWD]

Do a leakdown test on it

 

[4g63mightymax]

Definitely do a leakdown test before you tear the engine apart again, make sure the piston in that cylinder is at BDC and pressurize the cylinder (dont go crazy with the psi, you are just finding a leak). Then listen to the exhaust, the intake, and the oil cap and see where the air is leaking through. It has to be going someplace. Good luck!
Jeremy