Low Compression on 1600 mile Rebuild

[Dark_Horse]

I know everyone and their mom asks about low compression, but here it goes anyway.
The engine in my car is a 91 6 bolt rebuilt 1600 miles ago with new pistons, rods, rings etc. Did a compression test a few days ago and my results were:
Dry:
Cyl 1 - 125
Cyl 2 - 125
Cyl 3 - 130
Cyl 4 - 135

Wet:
Cyl 1 ~ 180
Cyl 2 ~ 180
Cyl 3 ~ 180
Cyl 4 ~ 180

Question is when I rebuild, since the rest of the internals are new, can I just re-use them? Timing belt, tensioner, pistons, rods etc as long as they're in good shape...

 

[SpeedFreak03]

Did you use stock parts when you rebuilt it? Because 125-135 is pretty low, considering the lowest it can be is 121. Sounds like your rings are beat because the compression jumps up when you add oil. If you do rebuild it again, replace the piston rings for sure, and just inspect all the other parts and use your best judgement. They will probably be fine since they are pretty new. Why is the compression so low after so soon? It sounds like the rings never seated properly. Also don't reuse the timing belt, always replace it with a new one. That is one thing you don't wanna cut corners on.

 

[2g6boltTsi]

Your rings probably haven't fully seated yet. drive another 1000, and do lots of engine braking, and I bet your numbers will go up. by the way, your not breaking that motor in with synthetic oil are you?

 

[Dark_Horse]

Used good ol' dyno oil for the 1st thousand, the next 600 miles were with Mobil 1 synthetic 10-30. After 1600 miles can the piston rings really not be seated?

Also did a leakdown test a few days ago. Cyl # 1 & 2 were leaking out the piston rings & exhaust valves. Cyl 3 & 4 were only leaking out the piston rings.

 

[AWDPSI]

well your rings sound shot.....i wonder if the gap was set correctly. Sorry bro that stinks

 

[burldude]

You have got to be kidding ,The rings have not even seated yet and will not do so for at least 5000 miles maybe ten . These rings are a lower tension than many and the block being of high nickle content they have not set. Did you have the throttle open and was it warm or hot ? Dont start pulling it apart becuase somone here says to, bad advice is everywhere!!!! If your motor runs cooler than most hovering around 170 it could take as many as 20,000 miles to break the rings in . the only way around this is to use a ck hone with torque plate or make sure your running at 210 f and even then it can take 20,000. I personaly have recorded 135 psi on a rebuilt motor, torque plate honed with 135 psi . 5000 miles later I checked again and it was hitting 180 . No kidding !!!!! If the throttle was closed you can add ten psi and if it was warm add another 15 . A cold test will tell you if the motor is breaking in proper . As it heats oil will thin , as you prpably know . If you check it while it is hot the oil will not fill in the slight voids in the cylinder walls and cause your psi to be lower . the rings will eventually seat and cause your compression to skyrocket . I dont think there is anything wrong with your motor since compression is fairly even across all of them . Run it in and you will be happy !!!!

 

[Dark_Horse]

The car pours out blue smoke constantly and goes through about a quart of oil every 2 weeks. Is that normal with a rebuild?

I did the comp test when the car was hot, and held the throttle open to come up with the #'s above. I've still got to pull the head off since I have burned exhaust valves in Cyl#1 & 2.

 

[SpeedFreak03]

I would agree with burldude's thinking, but can you say that it's normal for a new engine to burn oil? No! I am convinced that they are the wrong rings or something like that, because they are leaking mad oil into the combustion chamber.

 

[Dark_Horse]

Talk about raising a thread from the dead
I know when I read this forum, I always wonder if the people posting ever solved their problem. So here's an update.

Anyway, after a year, I finally tore the engine out of the car and had a mechanic friend of mine take it apart. Turns out that the rings would have never seated because the brilliant people that built this engine bored the cylinders much larger than they needed for 20 over pistons. On top of that, they only used 2 wrist pins instead of the 4 required to hold the piston to the rod. Plus the crank is scored and most likely can't be turned again since it's at the limit.
Then lets see...On a 1500 mile engine, is it strange to have the copper showing on some of the bearings? I sure as hell think so.

So...To sum up, new crank, pistons, mabe rods etc. What a crappy day!