compression test before / after first start?

[1Gina2G]

Would it be a good idea to do a compression test before I try to start my engine up for the first time? This is a completley new rebuild, just slighlly nervous about starting it up right away without going over a few things, was wondering if the compression test would still be accurate if the piston rings haven't had anytime to really seal/ expand?

would it be a better idea to do the compression test afterwards? Or should I do 1 before and after? I just picked up a new compression testing tool from the store, I can't think of anything else to check after fixing some fluid leaks, and doing a boost leak test.

 

[92AWDHX40]

I didnt i just fired it up, why do you want to do a compression test before you start the car?

 

[mattasi]

I would just fire it up. I can't see how the compression test before starting would tell you anything except that there is a piston in there. I would put some miles onto it then test it. I have 709miles on my new motor and still haven't checked mine. I better do that soon haha...

 

[BogusSVO]

If you want to do one, it will be fine.

Pull all the spark plugs. Hold the TB wide open, disable FUEL!! and spark

Basicly, you will just be priming the engine with oil, and no/minamal load on the piston.

Keep a Notebook, with the before, then try taking readings at like 100miles, 500 and 1000 miles and you should see an increase in compression till the rings fully seal and you get peak readings.

 

[BIG boost tech]

Would it be a good idea to do a compression test before I try to start my engine up for the first time? This is a completley new rebuild, just slighlly nervous about starting it up right away without going over a few things, was wondering if the compression test would still be accurate if the piston rings haven't had anytime to really seal/ expand?

would it be a better idea to do the compression test afterwards? Or should I do 1 before and after? I just picked up a new compression testing tool from the store, I can't think of anything else to check after fixing some fluid leaks, and doing a boost leak test.

In my line of work I have had to run a compression test before engine start-up after a inframe. This is information that the OEM sometimes wants during warranty rebuilds. The compression will be low for the first few hundred miles (500ish). If you can turn it over by hand & everything was tightened to spec it will be fine. Hook up a oil pressure gauge & fire her up!

 

[1Gina2G]

thanks for the help everyone, still slightly confused on what is meant by priming the engine. I really thought there was atleast a few more tests I should do before the first start up, just to be on the safe side.

I feel if anything's going to keep me from starting it'd be something electrical.

is there anywhere on this site that shows the locations of all the grounding connections in the engine bay? I think my alternator might not be grounded, not sure how many ground wires there even are though.

how long should I let the motor run for atleast, saying there's no leaks?

 

[zcoh2gdsm]

priming the engine is disabling the fuel and spark and cranking the motor to get the oil to start flowing through the parts without starting the engine.