Make.....................nissanModel....................240sxYear......................1991Engine size............2.4Egine code.............KA24DEMiles......................170,XXXTransmition............5sp. manual
Question:...........im going to get a cylinder compresion test tomarrow,and i need to know what numbers i should be expecting to see, ive done a search and came up empty.so i need to know what is good compresion, and what is good compresion for the year and amount of miles it has.all usual maint. has been kept up, and the car is a toy every other week end, if that gives you a good idea of the condition of the engine.all info is greatly appritiated..............thanx Ryan
what is good compresion #s
Re: (Chezedik)
not in my book! thanx!Chezedik wrote: Now is it bad that I have that memorized?
Re: (Chezedik)
85! that sounds bad if 179 is good... and what is variance??yep , im a newbie."need input!..mmmm...need input!....no disassemble!"(short circut)Chezedik wrote: but my engine still only makes about 85psi w/ 3 psi variance. But then again, just rebuilt.
85 isn't that bad yet. When the engine warms up for the first time the rings will wear to the walls and allow it to seal better. I expect there to be in the neighborhood of 185lbs when they finally do set. Variance is the difference of pressure between the cyls. Let's say, these are the following pressures from cyl 1 to 4: 176, 177, 164, 180. You notice how all four cyls do not have the same compression pressures. This is very common. So common in fact that it takes a lot of trouble and expense to balance these numbers out to perfection, and involves race preparation. Anyway, you will notice that #3 is out of spec. This could be a bad valve sealing condition or a valve not closing, or a worn or broken compression ring. Then the other thing to watch is to see how fast the compression is lost in the cyl. When checking compression the other important diagnostic factor is leakdown. Since there is no such thing as a perfect seal, some of that compressed air will leak into the crankcase or valve cover. This happens when you have bad valve sealing or a worn or broken ring. All engines will have leakdown, the question is how much, or more appropriately how quickly. Hold the pressure on each cylinder for about a minute, and you should not lose more than about 10% (at worst), about 4% is normal. Such racing tricks as multi-angle valve seals or gapless top piston rings help reduce this. Anything else you need to know?
Re: (Chezedik)
wow!.... lots of good info, but (respectivly) i talked to a gm certified mechanic about compresion and he was telling me that i would be lucky to see 120 lb , and something about brand new motors mainly see 180 lb, so does this mean i will more than likely see my compresion in the 100 range ? and is this a good reading ?
No, that would be a bad compression reading, and with all due respect, that is because he is a GM mechanic. I do not mean that as an insult (at least outside of my own head), but they use cast iron rings rather than Chrome Moly like we do. The first thing about chrome moly is that they do not quickly set, but they are much harder. This could be detrimental to maintaining compression if the rings used spring tension to seal, like they do commonly in GM engines. But cast iron is less damaging to a block when cast iron are used. Long story short, we do not have (as) sprung rings, for better emissions. This gives longer ring and cyl wall life. Also, many of your small blocks (including GM 3.x and 4.3 liter) motors have low compression ratios. As low as 8:1, but not often above 9:1. Ours is at 9.5:1, this may not seem like much, but it really is. Look, my suggestion to you would be, if you are worried, or would like a second opinion you should find the FSM online. I know for a fact it is downloadable on PDF. And you should know that an engine would hardly run or want to start with compression that low. You would have to advance the crap out of it, and probably still use starting fluid. Just my $.02.
Re: (Chezedik)
wow!....lots of good info.how does one go about retaining all this info you have stored nice and neatly in your head?....see i know somethin about cars, but i cant seem to remember things in order. its like knowing the ABCs and trying to say them , only to have them come out A B C.. I M AN I D I O T . well you get the picture. so did you go to school for it, or is it all just knowlage built up over time and expieriance? ide like to go to school to be a mechanic, but ide end up building a motor upside down ok, so i should be lookin to see 170s and no lower than 151, right?thanx dude! ....................Ryan
chezedik, Nice replies man, right on the money with numbers too. Nice to see accurate info posted.
Learning this stuff does not happen over night. It takes years of experiance to learn the ins and outs. To get a feel for the in between that schools dont teach. Schools dont cover a third of what it takes to be good in the automotive trade. Schools teach both ends of the scale but hardly touch where most failures occur. They teach you about complete failure and fully functioning. When working on a car that has a problem 85% of the time it is neither , it is usually somewhere in between. The diagnostic requires you to test many components to find the one that is not where it is expected to be as compared to other components reactions to input.
Learning this stuff does not happen over night. It takes years of experiance to learn the ins and outs. To get a feel for the in between that schools dont teach. Schools dont cover a third of what it takes to be good in the automotive trade. Schools teach both ends of the scale but hardly touch where most failures occur. They teach you about complete failure and fully functioning. When working on a car that has a problem 85% of the time it is neither , it is usually somewhere in between. The diagnostic requires you to test many components to find the one that is not where it is expected to be as compared to other components reactions to input.
Re: (Chezedik)
results:#1..................170#2..................169#3..................168#4..................170
thanx for all the help chezedik!!!!
thanx for all the help chezedik!!!!
Re: (Chezedik)
as far as the bearings go, i dont hear any noise from them so they better stay put!! i plan on tradeing this car off next month, but i have full confidence in the engine, the next owner is sure to have fun with this car!