Rebuilt motor low compression

[Szlaga]

I recently bought a rebuilt 6 bolt block and head, both had zero miles on the rebuild. Basically just a stock rebuild with 1g rods and 2g pistons. The rebuild was done by a shop that has done hundreds of DSM and Evo engine builds and I have never heard of any issues with their work. I installed GSC S2 cams, Mitsubishi MLS headgasket, and L19s before installing the engine. I did the Motoman break in (http://www.mototuneusa.com/break_in_secrets.htm) as most people here recommended that. I have about 900 miles and decided to check compression. My readings were from (1-4) 120-120-140-150. When i add a little bit of oil to the cylinders I get around 20 more per cylinder. Just for peace of mind I retorqued the ARPs and then checked again with the same readings. I do not have a leak down tester so have not yet performed that. Im pretty sure the rings are to blame but am looking to see if maybe I missed something. Is there a chance the rings are still not fully seated? I have been using conventional 10w30 and have changed the oil after 20 minutes, at 20 miles, at 200 miles, at 500 miles, and now at 900 miles. Any opinions on why I am seeing such low and differing numbers?

 

[2gmitsueclipse]

Leak down test is the next step to determine if your issue is the rings.

 

[Szlaga]

Thanks, that's what i figured, anything else is just guessing at this point. Sucks because it's going to the shootout and i wasted too much time to not run it.

 

[Jacolu3]

Man that sucks. Good luck and hopefully it's something easy to fix.

 

[Szlaga]

Thank you, decided against running it this weekend but can finally get to the leak down test. Will post results tonight.

 

[97_AWD_GSX]

Man that sucks about your car, especially after all that work, a leak down test will definitely help you determine where the compression is going.. If it was a reputable shop that did the build hopefully the cleaned the cylinders properly and checked ring end gaps.. Also if they didn't seat the valves properly.. Just do a leak down test and use a hollowed stethoscope to pin point leak.. Hope you find the problem..

 

[Szlaga]

I did the leakdown and am seeing around 20-25% out of each cylinder. I can feel a small amount of air coming from dipstick tube so im pretty positive its the rings. It drove perfectly all the way to the shootout and back which was 600 miles and didnt loose any oil. With rings leaking this bad shouldnt i be consuming more oil?

 

[97_AWD_GSX]

That's a pretty reasonable percentage for a leak.. Not necessarily more oil consumption but definitely more blow-by.. Have you notice a loss in power? How much boost are you running?

 

[Szlaga]

I have not been able to tell if there is a loss of power or not because it is now a full 6bolt longblock with gsc s2s vs my stock 2g longblock. The turbo only saw a few hundred miles on my old setup at only 10 psi. Im at 21psi, spool is a few 100 rpms slower (maybe 500-600) im assuming that is due to the cams and 1g head... before boost there is almost no power at all but it feels good once im in my powerband (5-7.5k)

 

[97_AWD_GSX]

I would just double check my timing and make sure everything lines up.. You already did your compression and leak down test so if you dont find anything with the timing then you got ring problems or glazed cylinder walls.. What's size injectors are u running? A washed out cylinder will also loose compression..

 

[Szlaga]

I will try to recheck the timing tonight. I'm pretty positive everything is lined up right but wont hurt to check again. Currently I am just running 560s til I get everything sorted out.

 

[tay97gst]

I know this sounds stupid but do you know how reliable the conpression gauge you were using is? I got really low readings from a harbor freight compression tester once, and bought one from autozone just to double check and the harbor freight one was about 40 psi lower than the autozone one.
Although 20-25% leakdown does seem a bit excessive to me. Just a thought.

 

[Szlaga]

Doesn't sound stupid at all i have had 3 different gauges give 3 slightly different reading but all similar, i was hoping it was the gauge too. My biggest question would be is it normal for all for cylinders to fail at once or is this just a sign of poor machine work/assembly?

 

[1twistdtalon]

How many miles do you have on it now ? And what oil did you use for break in?

 

[Szlaga]

put over 600 on it this weekend so im around 1600 miles. I've used 10w30 conventional oil from walmart

 

[Jared Johnson]

I'm having the same issue
I have a "rebuilt" 6 bolt Ross pistons arps Manley rods and have extremely low compression. I've put 350-400 miles on it so far and have had a sluggish start everytime I've went to start it. Compression results read (1)85psi (2)70psi (3) I gave up on cylinder two. <---(4). No smoke on startup I don't hear any weird noises really from the motor. Ughhhh. Tooo muchhh moneyyyy