Compression drop after 2 events

[ballinnmiami240sx]

I just rebuilt my Sr20 and the compression went from 155 all across to 90, 60, 60, and 60 after 2 events and less than 2000 miles. The engine was making good power, no smoke, and sounded great.

Specs on engine:

Honed, dipped, and deckedNew ACL race bearingsHead decked, cleaned New valve sealsValve recut to 45* and matted to headCometic gasketStock pistons and rodsNewer oil pump w/ s14 pick upGreddy panGreddy oil relocationS15 sr Gt28370 inj.stock ecu

I rebuilt the engine my self with no problems at all. i have rebuilt other engines. I kept the engine at stock psi 6-7 til I was sure the engine had enough miles to turn it up. Any ideas would be greatly appreciated. After getting a low initail compression test I added a cap full off synthetic oil to see if the compression would go up and nothing happend.

What do you guys think?

[hotrod240sx]

if you have added oil and the compression stayed the same, sounds like the rings are good which would mean a prob in the head, either head gasket, valves not seating properly, burned, etc, if you can run a leakdown test see what ya get

[liquid_cool]

if you deck'd the head or block...then you have changed the valve to piston clearences..you may have just slightly bent your valves..they way you can tell if this is the issue is you will see slight indentations on your pistons from the valves themselves...this will look like small lines or dents on the top of the piston where the valve sits over...its not hard to notice but you will need to pull it apart to check...if ya do have that issue..you can ajust it by a thicker head gasket or clearencing the pistons...good luck man..let us know what ya find.

[ballinnmiami240sx]

Ill be checking both today. I'm going to to buy t a leak down test kit today to see what I get. I have never used it, but it sounds fairly simple plus is another tool a man should own!!!!

I'll post up what I find and add pictures as well.

[ballinnmiami240sx]

This is the car in question



I went to HF and scored a $29.99 leak down tester...

Setting it up to use. Make sure that the leak down gauge reads 0 before you hook it up the the spark plug attachment. Also make sure the cylinder you are testing is at TDC.

After is set...make sure to lock it down

Then attach it to the spark plug connection

BOOOO...way to much leak down.When you do a leak down test you are testing a few things. You want to make sure that the cylinder block is holding pressure. You will lose a little, but it should be as drastic as mine.

When looking for a leaky intake valve disconnect your intake piping and listen for air leaking

When testing for leaky rings take oil your dip stick and listen for air coming out of it.

Take the radiator cap off to see if bubbles come out telling you that you have a bad HG.

To check exhaust valves leaking listen for air coming out of the exhaust. My readings where as follows. This was my first time using a leak down tester and it was kinda confusing at first. I recommend you look at a few videos online to give you an idea if you have never done this.

My readings:

Cylinder #1 = bubbles in rad, 40% leakdownCylinder #2 = Leak air out off #1 and #4 cylinder, 50% leakdown Cylinder #3 = Leak air out of all cylinders, 48% leakdownCylinder #4 = Leak air out of # 2 cylinder, 43% leakdown

As far as i under stand it is that I have a bad headgasket or even a not properly torqued down HG. I followed the FSM on this but I think the cometic HG might be the problem here. I will be ordering an OEM peice and I already have arp studs,

Thanks for looking,

Danny

Modified by ballinnmiami240sx at 4:27 PM 8/17/2009
Modified by ballinnmiami240sx at 4:32 PM 8/17/2009

[liquid_cool]

hay danny...check for valve impact on the pistons anyways..it would allso have the same simptoms as a headgasket as the force the valves impact the pistons is extreem..if you see sighns you have hit the pistons with the valves..but the valves dont look bent..you may be able to just get away with a thicker headgasket..good luck and take some snap shots of the pistons so we can all see whats up.

[ballinnmiami240sx]

I definetly will. I am pulling the motor out sometime this week to check a few things.

[1KleenS13]

You probably warped the head, When you take the head off lay a straight edge on top and run a feeler gauge along the head and see if its warped.