Low Compression In Cyl 5 In Rb25det

[newdylan]

I am getting really low Compression in Cylinder 5 atm and am blowing heaps of Blue smoke from about 2000-3500rpm. The car lacks power and sounds similar to a WRX but is idling stable. Its been running a little rich due to the microtech tune (as they always do).....but i'm trying to figure out whether its the pistion/ring....or maybe a valve problem. Compresion test results are as follows....

Dry test                                                      Wet Test (5ml oil)

1.....124psi                                                  1......145psi

2.....119psi                                                  2......145psi

3.....125psi                                                  3......151psi

4.....125psi                                                  4......145psi

5.....28psi                                                               5......38psi   (49psi with 10ml of oil)

6.....125psi                                                  6......145psi

There is a heap of oil in the air intake and the catch can is filling up pretty quick cause I am also getting pretty high

pressure... Like 25psi at idle but

90 to 100psi at 4000+ rpm and about 55-60psi at very light cruising. Any help you guys can give would be great...

Thanks

Edited December 17, 2007 by newdylan

[abu]

Piston rings are gone.

I am fairly certain it works like this;

If you drop oil into the bore and retest, if compression rises it means the rings are gone (oil increases compression slightly, making more of a seal)

If compression doesn't rise and stays the same, even when dropping oil into the bore there is a problem with the head (dropped valve etc) as air is leaking out the head.

My cousin had the same problem few months ago, same sort of compression test results. Resulted in a cracked piston ring in cylinder 5.

Blue smoke means your blowing/burning oil which also means your ring/s are gone.

Edited December 17, 2007 by abu

[newdylan]

Yeah thats what I'm guessing too, but i was kinda hoping someone would say its just a valve or something. Im just not looking forward to pulling the motor out and doing a rebuild...

I can get access to a hoist and everything and am thinking of maybe just changing the rings first to see if that maybe fixes the problem. Does anyone know if r33's can be done with the sump and a few other bits off.....or does it have to be done with the motor out. I know its best to get it honed and everything, but if i can get a few more k's out of this motor i would rather at least try this as a temp fix.

[R34GTFOUR]

blue smoke = rings/melted piston

definately rebuild time

[newdylan]

Does anyone know why cylinder #5 is such a common problem in these engines?

I have read quite a few posts that have had a similar problem.

Edited December 17, 2007 by newdylan