Compression Test

[slamed_s13]

I ran a compression test on my rebuilt sr and got some weird results:

#1-130
#2-130
#3-140
#4-130
is that normal? I think the numbers are kinna low......all I did was put new pistons and rings. I haven't really had the time to break the motor in but will the compression go up after I break it in? Any info will be appreciated. By the way, what's the proper way to break in the motor?

Thanks

[1slowS13]

did you do the test while in operating temperature, and WOT?

[soldiaboy]

seems kinda low to me. I dunno whats the average for sr's but my ka had 190 on all four

[Sileighty_85]

Brand new is 156 psi
Average is 150
Minimum is 139ish?

So yeah.....130 is not good

Warm up engine
Pull all the plugs
put a teaspoon oil in each cylinder and try again @ WOT
If the numbers shoot up when the oil is added then your piston rings

EDIT: Oh i see you replaced the rings, break it in so the rings will seat
Did you bore and hone the cylinders?? or just replace the piston rings in the stock bore?

For the break in there are many ways to do it just figuring out which one is "right" cuz there are so many ppl that contradict how to do it.

Me I just stayed low-med RPM's staying out of boost for 500miles

[SoguRacing]

how to do a compression test:

1 remove plugs
2 install gauge
3 disconnect ignition/fuel..one or the other..or both
4 prop open throttle body 100 percent
5 crank engine over 6 times while "noting" the first puff which should be at least 50 percent of the total psi...and the final puff on the gauge. Ex. 75psi would be 50 percent of 150psi of the final puff.
6 repeat for each cylinder and all final puffs should be within 10 percent of eachother. If not then you have a problem. On a rebuild engine your compression will be low at first until the rings seat. I wouldnt worry though i did my compression with 100 miles on a rebuild and my numbers were 155,160,155,155 with all other numbers within spec. s13 SR

[mifesto]

i dont agree on waiting for 6 ticks for each cylinder, as practices vary between each person you also cant 100% compare the result either... (kinda like dyno numbers, go figure hehe).

best practice is go ABOUT 6 ticks but can be more, basically wait until it tops off. first time i had my mechanic do a compression test it had semi low results at high 130's to low 140's. i was quite disappointed. then mechanic told me he only allowed 5 or 6 ticks because he felt it was "good enough". i made him go until it leveled off (about 8 ticks) and the results were high 140's to low 150's... MUCh better.

[SoguRacing]

i disagree with your answer. it shouldn't take that many "ticks" before you reach full compression on a warmed up engine. I actually did 5 ticks on my car and the numbers should be the same because the engines are the same. perhaps going with 8 ticks is giving you a false reading and a false perception that your engine is healthier than it actually is.

[slamed_s13]

Thanks for the info guys.

I just ran another compression test and all of them showed 130psi. Like I said, I just replaced the pistons and rings with stock boaring (for the first time, I'm so pround of myself, only 19 :) ) . So the low compression is normal from what I can tell from this thread. All I need to do is break it in. To be honest, I haven't even reached 100 miles yet, lol. What's the best way to break in the SR?

[Sileighty_85]

well thats probably one reason causing low compression

Your never suppose to just install rings on and old engine like that

Over time the cylinders walls become uneven like / \ or \ /
you need to bore and hone to make them look like this | |

just beause you still see the cross hatch doesnt mean they walls are still good.

[mifesto]

SoguRacing (http://zilvia.net/f/members/soguracing.html) ..... I have to flatly disagree. not because 8 or 6 is correct. simply theres too many variables to say what is correct. most compression tests are not meant to compare one result to another. the numbers vary HUGELY depending on operating temp, outside temp, quality of the tester etc.

for example How to do a compression test on your engine: 240sx Articles: Nissan Forums / Infiniti Forums - NICOclub (http://forums.nicoclub.com/zerothread/159838)
they say seven... you say 6, nissan says until it "levels off".... so whos right?


no one is.....except draining your battery, 8 ticks or 80 ticks its irrelevant. a seal around the pistons will hold a specific amount and thats it. its not going to hold more so stating 8 ticks instead of 6 is giving you false positive impression is crazy. compression test is to get a rough idea of it's health, nothing more. not a pissing contest of who has a healthier motor

[Saskacer]

Over time the cylinders walls become uneven like / \ or \ /
you need to bore and hone to make them look like this | |


So when do that you won't be able to get it back to stock bore will you? Is that what sleeving is, bringing it back to the OEM bore?

[SoguRacing]

So when do that you won't be able to get it back to stock bore will you? Is that what sleeving is, bringing it back to the OEM bore?

that is what sleeving is.

[Sileighty_85]

So when do that you won't be able to get it back to stock bore will you? Is that what sleeving is, bringing it back to the OEM bore?

You bore and hone the cylinders also having to buy oversized pistons and rings that will fit the new bore

[Saskacer]

that is what sleeving is.
Yeah that's what I thought.
You bore and hone the cylinders also having to buy oversized pistons and rings that will fit the new bore
Would you be able to use the same size pistons, but with bigger rings? Or would that not work. Sorry I am totally new to engine stuff:bigok:

[importdude]

Yeah that's what I thought.

Would you be able to use the same size pistons, but with bigger rings? Or would that not work. Sorry I am totally new to engine stuff:bigok:

no u cant just overbore and use stock sized pistons with bigger rings

there is a piston/wall clearance

[Saskacer]

no u cant just overbore and use stock sized pistons with bigger rings

there is a piston/wall clearance
Oh alright, thanks for the clarification