Low compression on fresh rebuilt engine

I did my first rebuild on an 89 1.6L Sidekick and have compression problems. I bought a rebuilt head for it, and it has new .50mm over pistons and rings.

Compression is 85-89 psi on all cylinders, goes up to 135-140 on wet test. Book says 170-199 is the normal range. Engine started and ran OK, but has very little power on test drive. I tried seating the rings with accelerations and decelerations but dry compression was still the same. Didn't start a day later and I suspected it was due to the low compression. When cranking slowly with a socket and the valve cover off, I easily hear air squeezing past the rings listening down the oil passages to the crank case. I heard nothing listening at the intake and exhaust ports with manifolds off.

I checked the ring gap during assembly and it was .020-.025" (over the limit), but a note in the manual said ring gap is not critical unless .040" or more. I suspected the machine shop messed up the bore and pulled the engine and tore it down again.

I don't have a great micrometer, just a dial caliper supposedly good to .001". It shows about .001" difference between the piston skirt and bore diameters, but hard to tell if it is accurate. Book says clearance should be .0008-.0014 but this is beyond the accuracy of my caliper. One thing that surprised me was the top of the pistons were .020" smaller than the skirts.

Any suggestions? Is it normal to hear ring leakage on a freshly rebuilt engine? Is the ring gap too wide?

i thought i replied to this guess not.

anyway it could be the shop messed up. take it back and see what they say. also i would suggest getting a digital caliper that has a bigger range then the one you have.also were the cylinders honed out before you installed the piston and rings. if not that could be one of the problems or they were honed too much.

Short answer, Yes, and Yes,

The ring gap is to big, which means the machine shop overbored the cylinders, or your rings/pistons are to small (for example if someone had honed the cylinders once already). Either way you need to be able to measure accurately and buy appropriate sized rings/pistons - your freshly rebuilt engine should have specs that are near/at OE new - not over the listed tolerance.

Good luck!