low compression in 2 cyl. need advice

[ANVIL]

a little bit of background in this thread, rb25det in s13

http://zilvia.net/f/showthread.php?t=601919

Short story of what happened.
-went out for street tune, felt boggy and misfire after a few pulls at 20-22psi. during session found valve cover vent tube blew off and oil leaking from valve covers
-found oil in ic piping. Found pcv to be bad. Leakying vc allowed spark plug galley for #5 to fikl almost completely with oil. Replaced and installed catch can. Also cleaned up all oil.
-still runs rough. Did compression test 1-4 @ ~155-165. 5 @ 90 6 @65

not sure what caused this. Leaky Pcv valve do enough to do this kind of damage? Or completely unrelated?

Prior to tune session it ran great at 18psi. i have a hypergear turbo upgrade which can stil make great power up to 24-26psi on my stock block/head. Was going to crank it up until this happened. All we really got to do was do a few pulls at 18psi to log and keep afr safe before adjusting ign timing. Did a pull at 20psi. Everything ok. 22psi pull is when it occured. I doubt the tune played a part in it, all we did was log abd adjust afr on the rich side.

sounds like rings ? Just old? Can i just get new rings and replace them for 5 & 6? Can valve seals cause this bad of a compression drop?

Now i need to decide on what to do and what is the next step to diag then fix this. All opinions and advise is apprcieciated

[Prok0]

If your VC vent tube blew off you most likely have a lot of crank case pressure making its way up to the head and pushing out, which may be caused by a cracked piston, worn rings, etc.

I would do a leak down test, see if you can establish where the air is going, or even just filling the cylinders with some air with all the valves closed. If you rotate the motor so that all valves are closed on a specific cylinder and fill the cylinder with air you will have it either start pushing out your intake manifold or exhaust manifold (Bent valves), or it will start to push out of your PCV system (issue in the bottom end, rings/piston/etc.)

Valve seals wouldnt cause that issue, as the head of the valve would be resting on the seat when the valve is closed, so no air should be making its way behind the head of the valve to even get close to the stem/seat/seal.

As for tuning, AFR is one component, if your timing was all jacked up it could have caused some issues.

I would recommend establishing where the compression is going (leak down or compressing cylinders) and then going from there. Your most likely going to have to yank the head off and pull the bottom end apart but at least you could get a good idea of what you may need to replace before you pull it all out.

With compression that low I would say you most likely damaged a piston. Depending upon what happened it could have caused some damage to the cylinder walls as well.

[ANVIL]

Do you know if pistons can be replaced with the motor still in an s13 or would that require it to be pulled?

I drove it home which was only about 3 miles away, can i mess it up more driving it? i dont plan to but just in case some situation needed me to or if i needed to get it somewhere to be looked at

[Prok0]

Originally Posted by ANVIL

Do you know if pistons can be replaced with the motor still in an s13 or would that require it to be pulled?

I drove it home which was only about 3 miles away, can i mess it up more driving it? i dont plan to but just in case some situation needed me to or if i needed to get it somewhere to be looked at

You most likely *COULD* replace it with the motor in, but I would not recommend it, as at minimum the cylinder wall will most likely have to be honed to get a good clean surface for the new piston/ring to go in. And you would need to drop the pan as well to get the rod out, really it would not be worth it and would ultimately be more of a hassle even if the cylinder walls appeared to be very clean.

Depending upon what was damaged, driving it further could further damage the cylinder wall. A lot of times if you melt a piston it will cause a bit of damage to the cylinder wall up at the top of the block right on the deck and will require the block to be bored over as well.

I would yank it out and tear it down and assess the damage and order the appropriate parts then.

[ANVIL]

Figured that would be the case. So damn tight fit in there.

pulling the head, i should be able to see what is damaged and what to fix right?

[Prok0]

Originally Posted by ANVIL

Figured that would be the case. So damn tight fit in there.

pulling the head, i should be able to see what is damaged and what to fix right?

Most likely yes, although if the ringland of the piston cracked you may not see that until you physically pull the piston out of the bore.
If you melted the corner of a piston you would clearly see it.

[ANVIL]

Ok. Thanks for your input and quick replies. appreciate that.

Super bummed about the situation. Having an rb has been a pain for me. Swapped back in 06 and the last 2.5 years has been the best ive had it running and longest. Always something. Sucks i never got to feel the full potential of my turbo upgrade.

Enjuku carry rb interals?

[Prok0]

Originally Posted by ANVIL

Ok. Thanks for your input and quick replies. appreciate that.

Super bummed about the situation. Having an rb has been a pain for me. Swapped back in 06 and the last 2.5 years has been the best ive had it running and longest. Always something. Sucks i never got to feel the full potential of my turbo upgrade.

Enjuku carry rb interals?

No worries man. And yes we do, CP, Wiseco, Supertech, Manley, Eagle, ACL, King, Clevite, Tomei just about anything. Give us a call or shoot me an e-mail once you find out what exactly needs replacing and I'll throw an estimate together for you!

[ANVIL]

Thinking about it, the timing was untouched from the basemap for that part of the map for that boost/throttle/rpm

What we did was just richen it all up to be safe before adjusting timing and never got to do any timing adjustments before the problem occured. Could the tune on there have caused this problem?

[Prok0]

Originally Posted by ANVIL

Thinking about it, the timing was untouched from the basemap for that part of the map for that boost/throttle/rpm

What we did was just richen it all up to be safe before adjusting timing and never got to do any timing adjustments before the problem occured. Could the tune on there have caused this problem?

Absolutely. What was the 'base map' for? If you didnt have the timing adjusted properly it could definitely cause some issues.

[ANVIL]

Originally Posted by Prok0

Absolutely. What was the 'base map' for? If you didnt have the timing adjusted properly it could definitely cause some issues.

Apex power fc rb25 basemap

[ANVIL]

I assumed base maps could be driven on then adjusted. Usually retarded timing and rich. If anyone wants to take a look a my map n see if they see anything i can send it.

Using FCedit for tuning