MBrennan Posted January 24, 2016 Share Posted January 24, 2016 So i noticed a rough idle and when cranking to start i could tell a cylinder was missing compression. So after a compression test the #4 cylinder was only 50psi. The other cylinders are 130. I might have 5k since rebuild. Heads were done. Link to comment Share on other sites More sharing options...
BDII Posted January 24, 2016 Share Posted January 24, 2016 Leak down? Need forum help? Private Message legGTLT Link to comment Share on other sites More sharing options...
xxBLOOD88SHOTxx Posted January 24, 2016 Share Posted January 24, 2016 Where did you get the short block? Link to comment Share on other sites More sharing options...
MBrennan Posted January 24, 2016 Author Share Posted January 24, 2016 No i didnt do a leak down. Im limited on what i can do in the driveway Subaru short block. The reason i had to have the overhaul was a top portion of the #4 piston broke off and rattled around in the cylinder. The machine shop said the head would be fine after after they looked it over. Link to comment Share on other sites More sharing options...
xxBLOOD88SHOTxx Posted January 24, 2016 Share Posted January 24, 2016 So they didn't touch the heads at all? Leak down is your next step IMO good sir. Link to comment Share on other sites More sharing options...
MTBwrench Posted January 24, 2016 Share Posted January 24, 2016 I would definitely get a leakdown test done. Something is broken in cylinder 4. Let us know what they say... The factory shortblocks have incredibly tight ring gaps from the factory, sometimes that leads to ringland issues. Could be a burnt valve due to bad tune or improper bucket sizing as well. For example, the guy that built my engine actually almost doubled the ring gaps from what they were. MTBwrench's Stage 3 5EAT #racewagon 266awhp/255awtq @17.5psi, Tuned By Graham of Boosted Performance Everyone knows what I taste like. Link to comment Share on other sites More sharing options...
MBrennan Posted January 24, 2016 Author Share Posted January 24, 2016 So they didn't touch the heads at all? Leak down is your next step IMO good sir. A complete head job was done Link to comment Share on other sites More sharing options...
MBrennan Posted January 24, 2016 Author Share Posted January 24, 2016 I would definitely get a leakdown test done. Something is broken in cylinder 4. Let us know what they say... The factory shortblocks have incredibly tight ring gaps from the factory, sometimes that leads to ringland issues. Could be a burnt valve due to bad tune or improper bucket sizing as well. For example, the guy that built my engine actually almost doubled the ring gaps from what they were. i doubt they would have checked the ring gap. its a factory tune and with 5000+- mile i cant imagine it burnt a valve Link to comment Share on other sites More sharing options...
MTBwrench Posted January 24, 2016 Share Posted January 24, 2016 i doubt they would have checked the ring gap. its a factory tune and with 5000+- mile i cant imagine it burnt a valve Do you have an Accessport or Tactrix cable to monitor IAM/DAM? If the buckets weren't sized properly two things could've happened: 1)an exhaust valve didn't seat properly, and after enough knocking, it burnt to the point where there was a real(i.e.-noticeable) loss of compression 2)after breaking in the valve stretched a bit causing it to not fully seat anymore. There's also the possibility that something caused very high cylinder temps, which can easily lead to a cracked ringland, or valve issues. I'm led to think it's more piston than valve related as I share your opinion that a bad valve is much less likely assuming the tune and engine build were okay. MTBwrench's Stage 3 5EAT #racewagon 266awhp/255awtq @17.5psi, Tuned By Graham of Boosted Performance Everyone knows what I taste like. Link to comment Share on other sites More sharing options...
MBrennan Posted January 24, 2016 Author Share Posted January 24, 2016 Do you have an Accessport or Tactrix cable to monitor IAM/DAM? If the buckets weren't sized properly two things could've happened: 1)an exhaust valve didn't seat properly, and after enough knocking, it burnt to the point where there was a real(i.e.-noticeable) loss of compression 2)after breaking in the valve stretched a bit causing it to not fully seat anymore. There's also the possibility that something caused very high cylinder temps, which can easily lead to a cracked ringland, or valve issues. I'm led to think it's more piston than valve related as I share your opinion that a bad valve is much less likely assuming the tune and engine build were okay. I dont have either to do any logs Link to comment Share on other sites More sharing options...
MTBwrench Posted January 25, 2016 Share Posted January 25, 2016 May be worth the investment! Sent from my iPhone using Tapatalk MTBwrench's Stage 3 5EAT #racewagon 266awhp/255awtq @17.5psi, Tuned By Graham of Boosted Performance Everyone knows what I taste like. Link to comment Share on other sites More sharing options...
MBrennan Posted January 25, 2016 Author Share Posted January 25, 2016 May be worth the investment! Sent from my iPhone using Tapatalk Yeah. I was hesitant to dump anymore money into this car until I knew things were going to last. 4+- months ago when I had the new short block done the drivers side head did have some pitting where piston pieces rattled around but I was assured they were cosmetic and the head was fine. Until a leak down test is done I wont know for sure whether its a head or piston issue. Hopefully the place where I had this rebuilt will stand behind their work or the machine shops work. Its wasn't done at a Subaru dealer Link to comment Share on other sites More sharing options...
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