Compression Test - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

slamed_s13 · 10-15-2008, 10:06 AM

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 · 10-15-2008, 10:18 AM

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

soldiaboy · 10-15-2008, 10:22 AM

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

Sileighty_85 · 10-15-2008, 11:00 AM

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 · 10-15-2008, 11:15 AM

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 · 10-16-2008, 07:10 AM

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 · 10-16-2008, 07:48 AM

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 · 10-16-2008, 01:30 PM

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 · 10-16-2008, 01:59 PM

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 · 10-16-2008, 03:57 PM

SoguRacing ..... 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
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 · 10-16-2008, 10:40 PM

Quote:

Originally Posted by Sileighty_85

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 · 10-17-2008, 12:15 AM

Quote:

Originally Posted by Saskacer

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 · 10-17-2008, 07:28 AM

Quote:

Originally Posted by Saskacer

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 · 10-17-2008, 05:29 PM

Quote:

Originally Posted by SoguRacing

that is what sleeving is.

Yeah that's what I thought.

Quote:

Originally Posted by Sileighty_85

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

importdude · 10-17-2008, 05:58 PM

Quote:

Originally Posted by Saskacer

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

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

there is a piston/wall clearance

Saskacer · 10-18-2008, 02:37 PM

Quote:

Originally Posted by importdude

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

10-15-2008, 11:15 AM	#5
SoguRacing Post Whore! Join Date: Nov 2007 Location: (714) Age: 35 Posts: 2,967 Trader Rating: (23) Rides Gallery: SoguRacing Feedback Score: 23 reviews	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 __________________ Pre Tune Checkup! Compression,LeakDown,Vacuum Test $80. Cams Install: $180

10-16-2008, 07:48 AM	#7
SoguRacing Post Whore! Join Date: Nov 2007 Location: (714) Age: 35 Posts: 2,967 Trader Rating: (23) Rides Gallery: SoguRacing Feedback Score: 23 reviews	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. __________________ Pre Tune Checkup! Compression,LeakDown,Vacuum Test $80. Cams Install: $180

10-16-2008, 01:59 PM	#9
Sileighty_85 Post Whore! Join Date: Dec 2006 Location: Misawa, Japan Posts: 6,815 Trader Rating: (8) Feedback Score: 8 reviews	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. __________________ 後輪駆動車１番 1989 Built SR GT2871R -363whp 1998 S14 W/RB25- 250ish (For Now) 1986 SR86 - 200ish 1990 R32 GTR - 320hp Don't Buy Engines from JDM-Online http://zilvia.net/f/businesses/207457-jdm-online.html Don't Buy XS-Power or SSAC Shit

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10-15-2008, 10:06 AM	#1
slamed_s13 Leaky Injector Join Date: Oct 2008 Location: San Antonio TX Age: 32 Posts: 140 Trader Rating: (4) Feedback Score: 4 reviews	Compression Test 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 Last edited by slamed_s13; 10-16-2008 at 01:32 PM..

10-15-2008, 10:18 AM	#2
1slowS13 Zilvia Junkie Join Date: Jan 2008 Location: Las Vegas, NV Age: 32 Posts: 466 Trader Rating: (6) Feedback Score: 6 reviews	did you do the test while in operating temperature, and WOT?

10-15-2008, 10:22 AM	#3
soldiaboy Zilvia Member Join Date: Jun 2007 Location: Miami Age: 36 Posts: 232 Trader Rating: (2) Feedback Score: 2 reviews	seems kinda low to me. I dunno whats the average for sr's but my ka had 190 on all four

10-15-2008, 11:00 AM	#4
Sileighty_85 Post Whore! Join Date: Dec 2006 Location: Misawa, Japan Posts: 6,815 Trader Rating: (8) Feedback Score: 8 reviews	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 __________________ 後輪駆動車１番 1989 Built SR GT2871R -363whp 1998 S14 W/RB25- 250ish (For Now) 1986 SR86 - 200ish 1990 R32 GTR - 320hp Don't Buy Engines from JDM-Online http://zilvia.net/f/businesses/207457-jdm-online.html Don't Buy XS-Power or SSAC Shit

10-16-2008, 07:10 AM	#6
mifesto Zilvia Member Join Date: Jul 2007 Location: NJ Posts: 209 Trader Rating: (2) Feedback Score: 2 reviews	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.

10-16-2008, 01:30 PM	#8
slamed_s13 Leaky Injector Join Date: Oct 2008 Location: San Antonio TX Age: 32 Posts: 140 Trader Rating: (4) Feedback Score: 4 reviews	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?

10-16-2008, 03:57 PM	#10
mifesto Zilvia Member Join Date: Jul 2007 Location: NJ Posts: 209 Trader Rating: (2) Feedback Score: 2 reviews	SoguRacing ..... 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 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