compression???

[S13 240SX]

I"m rying to look for compression numbers what they should be for the sohc ka.... this is all i could fine...

Measurement of Compression Pressure

1. Warm up engine.2. Turn ignition switch off.3. Release fuel pressure (See How to Change Fuel Filter)4. Remove all spark plugs.5. Disconnect distributor center cable.6. Attach a compression tester to No. 1 cylinder.7. Depress accelerator pedal fully to keep throttle valve wide open.8. Crank engine and record highest gauge indication.9. Repeat the measurement on each cylinder as shown above.Note: Always use a fully charged battery to obtain specific engine revolution.

Compression Pressure kPa (kg/cm2, psi) / RPMStandard = 1,236 (12.6, 179) / 300Minimum = 1,040 (10.6, 151) / 300Difference limit between cylinders = 98 (1.0, 14) / 300

10. If cylinder compression in one or more cylinders is low, pour a small amount of engine oil into the cylinders through the spark plug hole and re-test compression.

* If adding oil helps compression, piston rings may be worn or damaged. If so, replace piston rings after checking piston.

* If pressure stays low, a valve may be sticking or seating improperly. Inspect and repair valve and valve seat.

* If compression in any two adjacent cylinders is low and if oil does not help compression, there is a leak past the gasket surface. If so, replace cylinder head gasket.

+++++++++++++++++++++++++++++++++++++++++++++++++++i found that off 240sx.org/faq but it was on a dohc so i'm just checking if the same steps and numbers are the same for the sohc

[Skidmark]

Compression Pressure kPa (kg/cm2, psi) / RPMStandard = 1,236 (12.6, 179) / 300Minimum = 1,040 (10.6, 151) / 300Difference limit between cylinders = 98 (1.0, 14) / 300

151-179psi according to that info which is accurate. Pretty good explanation of the low readings, too.

[S13 240SX]

okay thanks.. i just wanted to check sure if it was the same for the sohc. thanks a lot i'm gonna have to test mine tomorrow.

[Skidmark]

most all engines fall within or close to that range so if you're anywhere in that ballpark then you're good to go.

[Chezedik]

Anyone know what it should be on an un-run rebuild?

[Skidmark]

Well, assuming your vavle timing is correct, and your crank, rods, and pistons are all in good shape, then it would be impossible for your compression to be "too high". I would say the 179psi is the optimum "everything is perfect" number, but I wouldn't trust your readings until after the motor is out of it's break-in period and the rings have seated properly.

[Chezedik]

Right, but the engine has never been ran to seat the rings, and I am getting low numbers. I thought it was a cam timing problem at first, but changing it is giving me lower numbers, so I hope I didn't bend a valve. I am going to take the cams out and check compression again. If it is low, then I will put oil in the cyl and check compression again, if it is still low, then I guess I bent a valve. Is there any truth to the idea that compression may be brutally low before the rings seat, but will pick up as the engine runs?

[Skidmark]

How exactly are you testing your compression? What kind of numbers are you getting, and on which cylinders? That will help determine where to start looking first...

[S13 240SX]

yo guys, i did my compression test on my ka24e sohc... here are my numbers...

cylinder 1... 160cylinder 2... 150cylinder 3... 160cylinder 4. ..155

are those respectable numbers? motor has almost 90k i plan on turboing, upgradeing the fuel system, and boosting 7psi, think I should do it who those numbers of compression?

[Chezedik]

I have been screwing in the compression tester, and cranking the starter for about ten seconds. I am reading (at best) 85lbs across all cyls (give or take two lbs). So compression is even, but low. Of course, I cannot get the engine hot since it won't run, and I know you are supposed to check it hot. But I assume I was doing it right otherwise.

As far as those being respectable numbers, it depends on what year and what model the SOHC is from.

[S13 240SX]

it came from a 90

[Chezedik]

240sx I assume? Which means your stock ratio should be 9.1:1, which I would think means you are probably good. I know the DE at 9.5:1 is good at 179+/-14lbs.

[TrueSlide]

Your numbers look fine.

[S13 240SX]

240sx I assume? Which means your stock ratio should be 9.1:1, which I would think means you are probably good. I know the DE at 9.5:1 is good at 179+/-14lbs.

actually i think the stock raito is 8.5.1 the de you are correct is 9.51. but i think all sohc ka's are 8.5.1

[Chezedik]

it was 8.5 in 89, in 90 it went to 9.1

[Chezedik]

Trueslide? I assume you are talking to S13, because mine are pretty low. Or is that okay on a not ran motor, because they will seat?

[TrueSlide]

Yes I was talking about s13.

I would def do a compression test after the rings get seated.

Did you do the rebuild yourself?

[Chezedik]

Yes, I did, and to be fair it was a **** rebuild. I did not hone the walls because I saw the factory scores on the walls. Now, I am worried about that. My friends tell me that the factory chrome-moly faced rings take some time to seat, but these numbers are really low. I am only getting about 85#s per cyl. I was waiting to get a spare to do the good rebuild. Will they seat (and raise compression) after the engine runs?

[Chezedik]

I would still be happy with any input, but good news for me. I was doing the test with the throttle closed, which I wouldn't think would make a difference, but apparently it does. From what I am reading, if we assume a manifold vacuum of 5" Hg (-10psi), then 10psi is entering the cyls (theoretically). This being the case and multiplied times 9.5 is 95. Added to 85 gets 180. So now I guess I need to check it with the throttle open, huh? Anyways, does anyone else have input on that? Does that seem right? Here is my source:http://www.misterfixit.com/dyncompr.htm

[S13 240SX]

heh yeah you need to check it with the throttle fully open i made the same mistake once with closed throttle.

follow these steps...

1. Warm up engine.2. Turn ignition switch off.3. Release fuel pressure (See How to Change Fuel Filter)4. Remove all spark plugs.5. Disconnect distributor center cable.6. Attach a compression tester to No. 1 cylinder.7. Depress accelerator pedal fully to keep throttle valve wide open.8. Crank engine and record highest gauge indication.9. Repeat the measurement on each cylinder as shown above.

[Chezedik]

I can't warm up the motor, since it won't start. Every thing else is done. This is just what it says in the FSM, I have the FSM, it doesn't tell me what I need to know.

[S13 240SX]

well **** man get the ****ing car started first... why wont it start? what's it doing?

[Chezedik]

That's what I am working on, I just resolved a fuel problem, and I am not altogether sure I don't have another. I will need to pull the injectors to check spray. I have spark, but I can't get fire on starting fluid. This tells me that either there is a cam timing problem or a lack of suitable compression. I will work on it next week. I am hoping that I do not need to open it back up, but if I do then I do. This is after a thorough (maybe not enough) rebuild and resto.

[S13 240SX]

yo my car wont start now either... i have spark too.. how are u checkingthe injectors for spary? so i can try that.

[Chezedik]

Well, I have a harness and injector tester. They both test correctly. But I am going to do it the unsafe way and remove the fuel rail, then turn the key to see if they are actually spraying. Afterall, the injectors are pulsing and the computer is telling them to pulse. But, if you want an easy way to test to see if your injectors are pulsing, remove the distributor. Put the key in the run position, then turn the distributor gear. You should hear the injectors clicking when you do this.

[S13 240SX]

i can hear the injectors clicking... i use a screwdriver on the injector and put the other end to my ear. i herd them.. but i have a damn injector leak.. its not an o-ring its the bushings.. I gotta go to the dealership tmorrow for them.

[Chezedik]

You can get them from Advance too. But they are the same price. That's good, I might work on mine tomorrow.

[S13 240SX]

no i can't get them at advance or auto i already asked. they only carry the o-rings there they don't carry the bushings for some gay reason.

[Chezedik]

Well they had them for me. I just returned a set as a matter of fact. At least those are the ones for the DOHC. But I would think the bushing is the same, try looking them up for the DOHC, have them show you a pic and see if it is the bushing you need. If it helps, they are made by Beck-Arnley.

[Chezedik]

I am sure you got a dumb-*** parts guy. Here is the BA part number for what you need:1580372. Just have them order that. It is $7.44 per injector.