Need compression check FAQs
02-20-12, 10:43 PM
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Need compression check FAQs
Im going to look at a motor this weekend. Owner states it has a rebuild on it. The motor is a long block. I don't have money for a rotary compression tester and going to use a pistion type tester. I know I have to use 19mm socket and spin the motor by hand. I read the motor needs to be warm to get an accurate reading but that's not an option for me.
So my questions are; Where should PSI be with a cold motor (S4T2) and do I put the tester in the leading or trailing plug holes? Does there need to be a spark plug in the plug hole I'm not using to get a more accurate reading? Anything else I need to know before I go look at this motor?
So my questions are; Where should PSI be with a cold motor (S4T2) and do I put the tester in the leading or trailing plug holes? Does there need to be a spark plug in the plug hole I'm not using to get a more accurate reading? Anything else I need to know before I go look at this motor?
02-21-12, 01:03 PM
#2
You can't do a comp test using a gauge while rotating the engine by hand. You can only listen for 6 pulses while spinning slowly by hand. To use a gauge and obtain a semi-accurate number, you MUST have the engine spinning 250rpm by using a starter. You're VERY limited in what you can discern by simply spinning it over by hand, and your gauge is useless that way.
02-21-12, 01:09 PM
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If I take a drill or impact with me will that work or should I take the starter he has hook it to the motor and give the starter power to spin the motor? Will spinning the engine @ 200RPM with no lube mess up anything. See I'm torn between getting an engine from JDMSOURCE or getting this engine from a guy in San Francisco. Price is about the same.
02-21-12, 01:15 PM
#4
You have to have a transmission bellhousing to install the starter in. And of course a battery to spin it.
A drill would certainly not have enough power to spin an engine over fast enough. An impact would spin the engine no faster than you could by hand. There is no other way to do this except with a starter and battery. Otherwise, you'll simply be chugging it over by hand and checking for 6 pulses in succession front-back-front-back-front-back with no skips or variations. You CAN NOT use a gauge while rotating by hand, you can't spin the engine fast enough to generate any significant compression.
Rotating an engine by hand or with the starter will not hurt anything. Even though there may be no oil in the oil pan, there is still residual oil in the rotors and on the bearings/gears, and that oil will last for quite a while. It takes 2-4 seconds for a standard engine to get oil from the pan pumped up when you first start it every day, it's that residual oil coating that protects the parts in the meantime.
A drill would certainly not have enough power to spin an engine over fast enough. An impact would spin the engine no faster than you could by hand. There is no other way to do this except with a starter and battery. Otherwise, you'll simply be chugging it over by hand and checking for 6 pulses in succession front-back-front-back-front-back with no skips or variations. You CAN NOT use a gauge while rotating by hand, you can't spin the engine fast enough to generate any significant compression.
Rotating an engine by hand or with the starter will not hurt anything. Even though there may be no oil in the oil pan, there is still residual oil in the rotors and on the bearings/gears, and that oil will last for quite a while. It takes 2-4 seconds for a standard engine to get oil from the pan pumped up when you first start it every day, it's that residual oil coating that protects the parts in the meantime.
Last edited by RotaryResurrection; 02-21-12 at 01:17 PM.
02-28-12, 05:47 PM
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Make sure you have a fully charged battery(engine must spin between 200-250rpm) engine needs to be warmed up (more accurate reading) remove fuse for fuel/ignition, make sure the check valve is out of te pistion type tester(removing the valve allows tester to read all three phases) Insert tester in leading plug hole, have someone open throttle all the way open and crank motor.
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03-03-12, 02:39 PM
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Okay so tomorrow is the day I go look at a motor. I have final questions.
Guy stated motor has no fluids. So do I need to ATF the rotor house before I spin the motor?
Also guy put aftermarket clutch and doesn't have the tool to line everything up. My question is does the clutch have to be attached in order to mate the trans to motor in order to hook up the starter to spin the motor?
Guy stated motor has no fluids. So do I need to ATF the rotor house before I spin the motor?
Also guy put aftermarket clutch and doesn't have the tool to line everything up. My question is does the clutch have to be attached in order to mate the trans to motor in order to hook up the starter to spin the motor?
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