I've almost completed the installation and assembly of the A12 GX motor.

I just did a compression test and got 148,145,140,140 across cyl 1,2,3,4.

Is this a fairly normal result? There seems to be a spread of about 3-4% between results. From memory a motor is fair when there is a 10% variance from the middle number.

Seems pretty good to me. They all seem close - it can depend on the quality of your compression guage also - screw in ones are definately better than the cheaper hold in ones. Should be good.

Yeah it was a cheap gauge but it's a screw in type.

I did 4-5 pulses on the gauge with wide open throttle and recorded the max result.

Sounds alright then. Just make sure to double check the valve clearances also if its a fresh motor if you havent already done it.

Yeah, this sounds good. Low compression engines are usually around 120-140, and high compression engines can be much higher.

The key is that they should be consistent, like yours, all right around 145 lbs +- 5 lbs is good.

I just found out that compression tests should be done on hot motors to allow for expansion of all metals etc.

I've always done mine on completely cold motors. I wonder how much difference it will make.

Does anyone else have compression results they can share with me for an A12 GX?

Compression warm throttle open all plugs removed 5 pulses should be 180-190 Psi.
Check cam timing. Also noise could be slinger on wrong way.
Good luck

All the books say it should be done with the throttle fully open, however I've never seen a significant difference when leaving it closed.

All Nissan manuals say to
1. Warm engine to normal temp
2. Remove all plugs
3. depress acellerator fully
4. crank engine at 350 rpm
5. measure comp as quick as posssible.
Pressure should be 192 Psi. (Minimum 178 Psi)
If you dont open the throttle the cylinder is not able to fill fully due to flow resistance past buterfly if idle speed is set low. If idle is set high it would make less difference.

If you are checking against specs do it the way the manual says I reckon..

192psi. woow that's incredibly high. I thought I was doing o.k. when I got 145.

The motor was cold - so I'll do it again when at operating temp.

Somehow I doubt though that I'll get it to jump all the way up to 192 though.

My other car (a 6cyl triumph) is 9.5:1 and it averages about 165psi across the cylinders - but I've only ever checked that one cold too.