rb25 cylinder 5 bad compression - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

davidg01234 · 06-13-2012, 06:57 PM

I just decided to do a compression test and I saw that all cylinders were about 150 except number 5 , it was about 75psi. I dropped oil there and it went up. BUT before I call it the rings let me also say that its smoking whitidh blue quite a bit through exhaust but there is no mixing of oil and coolant in the engine or radiator?? There is oil coming from the back of the motor around the cylinder 5&6 area. I can't tell if its coming from directly between head and block but it does kinda looks like it. Could it still be a bad hg? Could putting oil in cylinder and making the compression go up be a sign of a bad hg? Or is that only for rings?

*fliprayzin240sx* · 06-13-2012, 07:15 PM

If the compression jumped after dropping oil in there, its the rings. If you dropped oil and it didnt jump, then its something else like the HG or the valves.

davidg01234 · 06-13-2012, 07:20 PM

[QUOTE=fliprayzin240sx;4746123]If the compression jumped after dropping oil in there, its the rings. If you dropped oil and it didnt jump, then its something else like the HG or the valves.[/QUO

The rings could also be the reason for the smoke? Oil getting past rings?

*fliprayzin240sx* · 06-13-2012, 09:30 PM

Yup yup...

davidg01234 · 06-13-2012, 09:34 PM

Quote:

Originally Posted by fliprayzin240sx

Yup yup...

Damn was hoping it was the hg or valve lol. So can I just put some new rings on the pistons and put them back in with new main and rod bearings? No need to overbore unless the walls are fucked right?

*fliprayzin240sx* · 06-13-2012, 09:48 PM

Correcto...most of the time, if the cross hatching is still there, you dont have to re bore it. Just make sure theres no nick in the cylinder. But 75psi on 1 cylinder when everything else is at 150psi, it might even be a cracked ring land.

davidg01234 · 06-13-2012, 09:53 PM

Quote:

Originally Posted by fliprayzin240sx

Correcto...most of the time, if the cross hatching is still there, you dont have to re bore it. Just make sure theres no nick in the cylinder. But 75psi on 1 cylinder when everything else is at 150psi, it might even be a cracked ring land.

Well the thing is that it still runs good and pulls pretty hard so I'm gonna guess its just the rings and not the Piston or walls (hopefully). If the walls need reboring, that means I can't use the OEM pistons right? I would have to buy after market ones to match the bore size correct? Please correct me if I'm wrong man lol

Miguelone · 06-14-2012, 12:01 PM

Quote:

Originally Posted by davidg01234

Well the thing is that it still runs good and pulls pretty hard so I'm gonna guess its just the rings and not the Piston or walls (hopefully). If the walls need reboring, that means I can't use the OEM pistons right? I would have to buy after market ones to match the bore size correct? Please correct me if I'm wrong man lol

Nissan do pistons in 86.5mm

davidg01234 · 06-14-2012, 12:03 PM

Quote:

Originally Posted by Miguelone

Nissan do pistons in 86.5mm

What do u mean

Miguelone · 06-14-2012, 12:19 PM

Quote:

Originally Posted by davidg01234

What do u mean

Quote:

Originally Posted by davidg01234

If the walls need reboring, that means I can't use the OEM pistons right? I would have to buy after market ones to match the bore size correct? Please correct me if I'm wrong man lol

Original pistons are 86mm. .5 overbore allows you to use OEM 86.5mm pistons.

greenwood · 06-14-2012, 12:09 PM

You did a bad compression test the 1st time around. Retest again to make sure it's ok now. Lucky you

locoluna825 · 06-14-2012, 12:13 PM

Or you did it cold the first time.

davidg01234 · 06-14-2012, 12:22 PM

Quote:

Originally Posted by locoluna825

Or you did it cold the first time.

Ni it warmed up. But even if I did, one shouldn't be that much lower than the other

Miguelone · 06-15-2012, 05:56 AM

Just replace em, ACL race series are good cheap insurance.

davidg01234 · 06-15-2012, 08:32 AM

Quote:

Originally Posted by Miguelone

Just replace em, ACL race series are good cheap insurance.

I prefer OEM but my question is, CAN I reuse them if they're good

sterlinge · 06-15-2012, 09:20 AM

You are already in there. Replace them.

davidg01234 · 06-15-2012, 09:22 AM

Quote:

Originally Posted by sterlinge

You are already in there. Replace them.

How do I know which ones to get?

sterlinge · 06-15-2012, 09:50 AM

Look up fsm crank specs, rent a mircometer/caliper only takes maybe. 20-30 minutes to go over it. Chances are its all original still and you need standard size.

Miguelone · 06-16-2012, 01:55 AM

davidg01234 · 06-16-2012, 02:17 AM

Quote:

Originally Posted by Miguelone

Awesome!! Thanks man your alot of help! Now does the angle of the gaps have to be that perfect or is it OK as long as theyre pretty eye close?

Miguelone · 06-16-2012, 02:20 AM

No worries, judging it by eye should do fine.

davidg01234 · 06-16-2012, 02:23 AM

Quote:

Originally Posted by Miguelone

No worries, judging it by eye should do fine.

OK thanks so much man! Everything is alot clearer now and I now know exactly what I need to do and what I need to order

Miguelone · 06-16-2012, 02:25 AM

While you're at it you may as well get some ARP rod studs. The stockers are the weak link in the bottom end.

davidg01234 · 06-16-2012, 08:14 AM

Quote:

Originally Posted by Miguelone

While you're at it you may as well get some ARP rod studs. The stockers are the weak link in the bottom end.

Great suggestion but no I'm keeping it all stock. Besides as long as the stocks can hold my 400bhp goal, I'm happy

Miguelone · 06-17-2012, 12:34 AM

All the torque settings are at the end. Right before the index.

davidg01234 · 06-17-2012, 11:02 AM

Quote:

Originally Posted by Miguelone

All the torque settings are at the end. Right before the index.

i just decided to tighten them by feel, they dont really seem like something that requires a specific torque. thanks though man!!

JKL1031 · 06-18-2012, 08:31 AM

Mann Zilvia spoon feeding?!

davidg01234 · 06-18-2012, 07:47 PM

Quote:

Originally Posted by JKL1031

Mann Zilvia spoon feeding?!

lol sorry its my first time going this far into an engine

*fliprayzin240sx* · 06-18-2012, 08:08 PM

Quote:

Originally Posted by JKL1031

Mann Zilvia spoon feeding?!

Just cuz this shit is actually techinical...not asking whether or not my damn 9j +42 wheels will fit or what's better, SR or KA-T?

greenwood · 06-18-2012, 08:23 PM

I've been reading up on this thread it's good stuff. I will be building a RB20 in my living room very soon.

06-13-2012, 06:57 PM	#1
davidg01234 Zilvia Member Join Date: Feb 2011 Location: Fort Worth,TX Posts: 179 Trader Rating: (3) Feedback Score: 3 reviews	rb25 cylinder 5 bad compression I just decided to do a compression test and I saw that all cylinders were about 150 except number 5 , it was about 75psi. I dropped oil there and it went up. BUT before I call it the rings let me also say that its smoking whitidh blue quite a bit through exhaust but there is no mixing of oil and coolant in the engine or radiator?? There is oil coming from the back of the motor around the cylinder 5&6 area. I can't tell if its coming from directly between head and block but it does kinda looks like it. Could it still be a bad hg? Could putting oil in cylinder and making the compression go up be a sign of a bad hg? Or is that only for rings?

06-13-2012, 07:15 PM	#2
fliprayzin240sx Man w/ CTSV & a Car Seat Join Date: Aug 2002 Location: Tampa Posts: 17,998 Trader Rating: (19) Rides Gallery: fliprayzin240sx Feedback Score: 19 reviews	If the compression jumped after dropping oil in there, its the rings. If you dropped oil and it didnt jump, then its something else like the HG or the valves. __________________ If you think Zilvia has too many assholes... CLICK HERE!!!

06-13-2012, 09:30 PM	#4
fliprayzin240sx Man w/ CTSV & a Car Seat Join Date: Aug 2002 Location: Tampa Posts: 17,998 Trader Rating: (19) Rides Gallery: fliprayzin240sx Feedback Score: 19 reviews	Yup yup... __________________ If you think Zilvia has too many assholes... CLICK HERE!!!

06-13-2012, 09:48 PM	#6
fliprayzin240sx Man w/ CTSV & a Car Seat Join Date: Aug 2002 Location: Tampa Posts: 17,998 Trader Rating: (19) Rides Gallery: fliprayzin240sx Feedback Score: 19 reviews	Correcto...most of the time, if the cross hatching is still there, you dont have to re bore it. Just make sure theres no nick in the cylinder. But 75psi on 1 cylinder when everything else is at 150psi, it might even be a cracked ring land. __________________ If you think Zilvia has too many assholes... CLICK HERE!!!

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06-13-2012, 07:20 PM	#3
davidg01234 Zilvia Member Join Date: Feb 2011 Location: Fort Worth,TX Posts: 179 Trader Rating: (3) Feedback Score: 3 reviews	[QUOTE=fliprayzin240sx;4746123]If the compression jumped after dropping oil in there, its the rings. If you dropped oil and it didnt jump, then its something else like the HG or the valves.[/QUO The rings could also be the reason for the smoke? Oil getting past rings?

06-14-2012, 12:09 PM	#11
greenwood Zilvia Addict Join Date: May 2011 Location: nc Posts: 618 Trader Rating: (5) Feedback Score: 5 reviews	You did a bad compression test the 1st time around. Retest again to make sure it's ok now. Lucky you

06-14-2012, 12:13 PM	#12
locoluna825 Zilvia Addict Join Date: Sep 2009 Location: Santa Ana Age: 30 Posts: 721 Trader Rating: (27) Feedback Score: 27 reviews	Or you did it cold the first time.

06-15-2012, 05:56 AM	#14
Miguelone Zilvia Member Join Date: Jun 2012 Location: Australia Age: 30 Posts: 215 Trader Rating: (0) Feedback Score: 0 reviews	Just replace em, ACL race series are good cheap insurance.

06-15-2012, 09:20 AM	#16
sterlinge Zilvia Addict Join Date: Apr 2008 Location: Austin, TX Age: 31 Posts: 857 Trader Rating: (15) Feedback Score: 15 reviews	You are already in there. Replace them.

06-15-2012, 09:50 AM	#18
sterlinge Zilvia Addict Join Date: Apr 2008 Location: Austin, TX Age: 31 Posts: 857 Trader Rating: (15) Feedback Score: 15 reviews	Look up fsm crank specs, rent a mircometer/caliper only takes maybe. 20-30 minutes to go over it. Chances are its all original still and you need standard size.

06-16-2012, 01:55 AM	#19
Miguelone Zilvia Member Join Date: Jun 2012 Location: Australia Age: 30 Posts: 215 Trader Rating: (0) Feedback Score: 0 reviews

06-16-2012, 02:20 AM	#21
Miguelone Zilvia Member Join Date: Jun 2012 Location: Australia Age: 30 Posts: 215 Trader Rating: (0) Feedback Score: 0 reviews	No worries, judging it by eye should do fine.

06-16-2012, 02:25 AM	#23
Miguelone Zilvia Member Join Date: Jun 2012 Location: Australia Age: 30 Posts: 215 Trader Rating: (0) Feedback Score: 0 reviews	While you're at it you may as well get some ARP rod studs. The stockers are the weak link in the bottom end.

06-17-2012, 12:34 AM	#25
Miguelone Zilvia Member Join Date: Jun 2012 Location: Australia Age: 30 Posts: 215 Trader Rating: (0) Feedback Score: 0 reviews	All the torque settings are at the end. Right before the index.

06-18-2012, 08:31 AM	#27
JKL1031 Zilvia Junkie Join Date: Nov 2010 Location: MS Posts: 427 Trader Rating: (1) Feedback Score: 1 reviews	Mann Zilvia spoon feeding?!

06-18-2012, 08:23 PM	#30
greenwood Zilvia Addict Join Date: May 2011 Location: nc Posts: 618 Trader Rating: (5) Feedback Score: 5 reviews	I've been reading up on this thread it's good stuff. I will be building a RB20 in my living room very soon.