sr20 compression results and questions

[rmsj1]

Hello Zilvia,
just tested my redtop sr20det.

tried a compression test, each cylinder was
150
149
150
120

worried about the last cylinder i tried to put a bendy straw worth of oil in that cylinder, no change.

2 more bendy straws later my compression on the cylinder with 120 went up to 150.

so i suppose my rings are giving?

if i got 150 then that only leaves the rings right?

[jspaeth]

at first i thought maybe the intake or exhaust valves where stuck open from a lack of oil, but if i got 150 then that only leaves the rings right?


Generally, if adding oil increases compression, it's rings.

Not sure how a lack of oil would "keep the valves stuck open"...

The amount of oil has nothing to do with the fact that the cams mechanically force the valves open or closed...

[nickauger]

Leak test is way better to tell you the life of your engine.

[rmsj1]

i dont have access to a leak down tester unfortunately.

should i probably be prepared to rebuild at most, and at the least replace the rings on that piston??

[nickauger]

Most people that rebuild their engine themselves don't do long time after rebuild...cause most people don't know about specification, clearance, etc.

[rmsj1]

Most people that rebuild their engine themselves don't do long time after rebuild...cause most people don't know about specification, clearance, etc.

i do understand everything needs to be measured in the least and everything needs to be torqued right. i was not suggesting rebuilding myself however, because i dont trust myself to do that anyway.

sucks bad because i sold my perfect spare short block a few months back. :smash::duh:

[jspaeth]

i dont have access to a leak down tester unfortunately.

should i probably be prepared to rebuild at most, and at the least replace the rings on that piston??


I'm no expert at all, but even though 120 is significantly off from the other 3, it is not THAT low....it's not like you have NO compression.

People frequently post on here with compression numbers in the sub-60 psi range.....

[jr_ss]

I believe anything under 128, factory suggests a rebuild and greatest deviation between cylinders is like 10-12%.

[rmsj1]

well, everything is ready for car to run so i guess ill take it around the block once then try the test again. couldnt hurt.

if anythings messed up i swear im parting this car out...its been a huge headache, its not even fun anymore.

[Davidna2fi]

put fluid in the cylinder and let it sit overnight, if it drops a lot, its the cylinder rings, put the piston at TDC and fill with enough oil so you can take something to measure the depth of change when the fluid dropped. if the change is greater, pull the block out, if not, just remove the head and give the head a valve job, possible leaky valve.

[jr_ss]

put fluid in the cylinder and let it sit overnight, if it drops a lot, its the cylinder rings, put the piston at TDC and fill with enough oil so you can take something to measure the depth of change when the fluid dropped. if the change is greater, pull the block out, if not, just remove the head and give the head a valve job, possible leaky valve.

That is the most useless information I have ever heard. Any motor with good or bad compression will drop the fluid level over a given time. It'll wick down between the ring gaps no matter what. Leak down and compression tests are the only way to figure out what's going on internally with an engine without pulling it apart to look at cylinder walls, rings or ringlands.

[Davidna2fi]

That is the most useless information I have ever heard. Any motor with good or bad compression will drop the fluid level over a given time. It'll wick down between the ring gaps no matter what. Leak down and compression tests are the only way to figure out what's going on internally with an engine without pulling it apart to look at cylinder walls, rings or ringlands.

Have you tried it? I have, and it's not a true measurement, but the fluid will not drain as quickly as you think, and it will show the difference, and let him know if it is rings or a valve. Over 4 days for the cylinders to get dry again after sitting dripping with only fluid about 1/2 inch above the piston top. If the level does not drop as much as the others, then it'll be the valves. If you think it's useless you have not tried it. For someone who states they don't have tools, this is a pretty good indicator test. So don't knock something until you've tried it, also try reading more posts from the OP before you bash something.

[240sx123$]

Heres what i'd do, if you decide the rings on that cylinder are blown. If youre just a "normal guy," like me (aka you dont have your own shop or unlimited resources), this is what Id do. Im going on the assumption that your one cylinder has bad rings. 120psi is not THAT low. Its definitely still driveable. I wouldnt advice taking it to the track, but if its youre daily driver, you can definitely pull another couple months out of it. That being said, Youre fortunate in regards to the ability to prepare for downtime. If the car is your daily, youre kinda fucked unless you have a 2nd motor, or have a shop fix yours- if you want the car back in a reasonable amount of time. My advice would be to pick up a 2nd SR shortblock (or longblock) and rebuild it while this one is dying. The alternative is pull that one, rebuild it, and drop it back in. From a realistic point of view, youre probably lookin at a month or more of downtime, depending on your funds and how quickly you work.

If i was in your situation, id find an sr with a spun bearing for like $300, and rebuild it while that ones still running well.

[jr_ss]

Have you tried it? I have, and it's not a true measurement, but the fluid will not drain as quickly as you think, and it will show the difference, and let him know if it is rings or a valve. Over 4 days for the cylinders to get dry again after sitting dripping with only fluid about 1/2 inch above the piston top. If the level does not drop as much as the others, then it'll be the valves. If you think it's useless you have not tried it. For someone who states they don't have tools, this is a pretty good indicator test. So don't knock something until you've tried it, also try reading more posts from the OP before you bash something.

Regardless, he stated that he added "3 bendy straws" worth of oil to the cylinder. I'm no genius, but adding oil to the cylinder doesn't help seal valves... Obviously, if compression increases in the cylinder after adding oil to it, the rings are either going out or are out, not his valves. It would be safe to assume that if he had ringland problems, he'd have lower compression than he already does.

[Couped_up'd]

Just drive it. That is not to bad.