S13 KA24de Compression check was low but auto shop sayes motor is good

[Carbonsnail]

I am the original owner of a 92 S13 coupe with a KA24de motor I wanted to check the condition of the engine, so I had a leak-down compression check performed. It was rebuilt 6yrs ago and is mildly driven the results were 140, 140, 130, 145 the mechanic said the engine checked out to be in good shape with no issues but I've seen posted here on this site that say that the correct numbers should be around 175psi or slightly lower what do you guys think? Thank you all for your help.

[Thursday7]

The 130psi cylinder would be my biggest concern as it is over 10% variance from the 145psi one. Other than that, they are on the low end of "acceptable", but if you're just driving the car around racking up miles (which is what I would be doing if I were the original owner of a stock example), I wouldn't pay much mind to it, just keep it maintained and see how long it goes.

[jedi03]

agreed...normally theres only a big issue with more than 10% variance as it shows extra wear normally or something wrong with that cylinder. if you are just daily driving it i also agree...just make sure to use quality fuel, change oil frequently etc for maintenance

[Kingtal0n]

1. always use different compression testers, never trust 1 tester
2. cranking speed, number of hits, throttle position, air temperature, cam profile, air filter restriction, and other factors influence compression, never take a number at its face value

The most important aspect of the test is the difference between cylinders. If you see a low or high cylinder(s) you should try some basic things to even them out. You can try de-carboning them (water injection or seafoam etc...) or remove the head and manually clean off carbon. You should wash the intake manifold and ports out because there is a chance that oil and carbon deposits in the manifold are causing changes to gas velocity which influences compression. Inspect the pcv system and replace the pcv valve and hoses. Old hard Oil or lots of aging liquid oil hanging out in the cylinder raises compression and causes detonation so washing out the cylinders is also applicable approach. I remove all plugs so it won't hydrolock and literally degreaser them with water and purple power for example. Then immediately re-oil them, pour oil and crank it over with plugs out to spread the oil rapidly so it doesnt rust. The fresh new oil isn't a danger as it lubricates the cylinders and prevents rust, its the old oil accumulating in the ring packs and deposits forming from old oil hydrocarbons that need to be removed.

Next, how do you know when compression is too low.
Answer: when the fuel economy of the engine is too low for your application.

For example say I have an engine that runs fine but it has low compression on every gauge. I tried cleaning out the carbon. I make sure the valves are all fully closing. I cleaned the pcv system and made sure PCV is working fully by measuring crankcase pressure so the engine doesn't smoke or have any cleanliness issues. But the fuel economy is much worse than it should be on the stock tune. Or maybe I tuned it and still the economy is very bad. Like 18mpg instead of 27mpg. Thats how you know maybe its time to get some new rings.

If the economy is good enough, compression is fairly even or at least then engine doesn't shake noticeably and seems to be runs fine, pcv is intact- then ignore the results no matter how low on a gauge. Heaven save us from people that rebuild their engines because a gauge told them to "oh no the gauge says its bad" worst thing you could do. Props to a mechanic that understands that. Results help you diagnose a problem and there is no problem with a perfectly running engine if you are satisfied with the economy.

[Carbonsnail]

Originally Posted by Kingtal0n

1. always use different compression testers, never trust 1 tester
2. cranking speed, number of hits, throttle position, air temperature, cam profile, air filter restriction, and other factors influence compression, never take a number at its face value

The most important aspect of the test is the difference between cylinders. If you see a low or high cylinder(s) you should try some basic things to even them out. You can try de-carboning them (water injection or seafoam etc...) or remove the head and manually clean off carbon. You should wash the intake manifold and ports out because there is a chance that oil and carbon deposits in the manifold are causing changes to gas velocity which influences compression. Inspect the pcv system and replace the pcv valve and hoses. Old hard Oil or lots of aging liquid oil hanging out in the cylinder raises compression and causes detonation so washing out the cylinders is also applicable approach. I remove all plugs so it won't hydrolock and literally degreaser them with water and purple power for example. Then immediately re-oil them, pour oil and crank it over with plugs out to spread the oil rapidly so it doesnt rust. The fresh new oil isn't a danger as it lubricates the cylinders and prevents rust, its the old oil accumulating in the ring packs and deposits forming from old oil hydrocarbons that need to be removed.

Next, how do you know when compression is too low.
Answer: when the fuel economy of the engine is too low for your application.

For example say I have an engine that runs fine but it has low compression on every gauge. I tried cleaning out the carbon. I make sure the valves are all fully closing. I cleaned the pcv system and made sure PCV is working fully by measuring crankcase pressure so the engine doesn't smoke or have any cleanliness issues. But the fuel economy is much worse than it should be on the stock tune. Or maybe I tuned it and still the economy is very bad. Like 18mpg instead of 27mpg. Thats how you know maybe its time to get some new rings.

If the economy is good enough, compression is fairly even or at least then engine doesn't shake noticeably and seems to be runs fine, pcv is intact- then ignore the results no matter how low on a gauge. Heaven save us from people that rebuild their engines because a gauge told them to "oh no the gauge says its bad" worst thing you could do. Props to a mechanic that understands that. Results help you diagnose a problem and there is no problem with a perfectly running engine if you are satisfied with the economy.

Thank you very much for taking the time to give me a detailed response.

[Carbonsnail]

Do you think that I should be preparing for an engine rebuild in the near future? On average, I use 3/4 or less a tank of gas monthly. Thank you.

[Kingtal0n]

If you are satisfied with economy no reason to do anything but maintain it. The rings wont break or fail if the engine is maintained. It won't influence longevity. No reason to prep for rebuild based on that. The things that generally kill engines are like, oil pump failure, loss of oil pressure, debris in the oil system, oil leaks which lead to low oil or dirt getting into the oil system, dropped valves, over-rev condition, broken timing chain due to age or over-rev, poor air filtration, aftermarket air filters that are poor quality, debris that gets past the air filter due to leaking intake, leaking seals, pressure leaks, stuff like that.

I think a good investment if the engine is old high mileage is a mechanical oil pressure gauge that you can see all the time easily but also in a place where it won't leak into your car. Or at least a warning light for low oil pressure besides the factory one.

[Carbonsnail]

Originally Posted by Kingtal0n

If you are satisfied with economy no reason to do anything but maintain it. The rings wont break or fail if the engine is maintained. It won't influence longevity. No reason to prep for rebuild based on that. The things that generally kill engines are like, oil pump failure, loss of oil pressure, debris in the oil system, oil leaks which lead to low oil or dirt getting into the oil system, dropped valves, over-rev condition, broken timing chain due to age or over-rev, poor air filtration, aftermarket air filters that are poor quality, debris that gets past the air filter due to leaking intake, leaking seals, pressure leaks, stuff like that.

I think a good investment if the engine is old high mileage is a mechanical oil pressure gauge that you can see all the time easily but also in a place where it won't leak into your car. Or at least a warning light for low oil pressure besides the factory one.

Thank you.

[Carbonsnail]

I was told that my stock KA24de requires a minor valve adjustment. Could someone give me an idea of what the auto shops cost maybe? Thank you.