compression issues

[EsiGoneT-Esi]

Well I have been a member of this community for a very long time. I have been through about 5 different setups on my car and am no novice when it comes to building cars. I have ran into a problem that has me and all of my good friends/techs stumped. Im running a built 420a turbo. I recently assembled the engine. Prior to start up I did a compression check just to assure myself due to some prior bad luck. I got 155psi across the board, the rings were definitely not seated but the consistency was on point. The car started up wonderfully and ran great. I shut the car off to do an oil change after it reached operating temperature. I cranked the car after changing the oil and it sounded like a cylinder was down. I shut the car off and did a hot compression test. cylinder one had nothing, cylinder 2 had 75, cylinder 3 and 4 had 175. At this point I was ready to jump head first off a cliff. I pulled the v/c off and yanked the lifters out to ensure the valves were seated. I pressurized cylinder 1 and 2 to 100 psi regulated. I then used a stethoscope to listen inside the intake foor an air leak, got nothing. I pulled the turbo manifold off, nothing. The cylinders were holding pressure fine. I bled the lifters down completely and re assembled the head. I compression tested the motor with the lifters bled down. I got 175 across the board. I started the car and it ran great. I shut the car off feeling great. The next day I got to the shop and cranked the car. The same problem returned. I figured the the lifters were getting "over pumped" or stuck fully extended.. I replaced them with a brand new set of 2.4l lifters. same problem. I am at a complete loss right now. Has anyone ran into this before? All the valves are ss 1mm oversize valves and the head just left the machine shop!

the setup:
420a
crower 2 na cams, springs and retainers
pt lifters and rockers
ss 1mm oversized valves
je pistons, crower rods, mellings oil pump
arp everthing
amm intake manifold and exhaust manifold
precision pte 6766 turbo
ms1 v3.0
Injector dynamics 1000CC injectors
lots more but you guys get the point

 

[thirsty]

G'day.
I had a similar problem in a 4G63 Turbo rally engine for for about 4 years with number 2 cylinder always down on compression. After doing a rebuild, new pistons, rods, crank, lifters, it was still there. I had the head looked at and the engineer suggested the geometry of the lifter/rocker/valve was wrong. The cams were a Group 'A' grind and had washers under the lifters to take up the reduced diameter of the cams. I placed correct thickness machined washers under the lifters, same problem. Last desperate move was to place standard cams in the head, put the head back together and try it on the car. Eureka! Problem solved. Tighe Cams here in Brisbane checked the group 'A' cams with micrometers etc and found a small hum on the resting side of the intake cam at number 2 cylinder. It would just open the valve at 75% compression stroke to let the compression out into the intake manifold. I have fitted some EVO 3 cams and now have a sweet 175kw atw and 325nm torque atw.
It goes pretty hard.

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Cheers
Ross

 

[EsiGoneT-Esi]

Thanks for the input ross. I think you put me on the right track. Im going to pull the cams and contact crower to check them out

 

[bryanwheat]

Check the valve height. If the stem is too long on one of them than it could be hanging open a bit after the lifters get primed.

 

[EsiGoneT-Esi]

Im tearing into it in a couple hours. I will post up when i figure this out

 

[miliman13]

I have heard Bc is known for having their cams a Little off, and sometimes degreeing the cams don't remedy the situation. I currently have a compression problem myself, and run bc 272's. I have read that many have resolved this issue by going back to stock/oem cams, i hope you figure it out!

 

[EsiGoneT-Esi]

I just got done working on it. It was the crower 2 cams. I went to a local yard pulled a set of stockers and threw them in and the car ran fine. I will be calling crower on tuesday to see if they will stand up to their name. Thank you guys for the input! You all steered me in the right direction