low compression? or somthing else?

[talon187]

ok for some reason ive got 120 compression across the board isnt that low? this is what my motor has
eagle rods
arp rod bolts
apr mains
arp head studs
.20
wesco pistions 9:1 compression
o ring block
stock head
mitsu 4 layer metal headgasket

i picked the motor up for a nice deal it had under 3k on it and i was told was in working order i beileve when i put it in i did a compression test and it had 130ish this was in june
i had the motor over heat once or twice but it never got to the H side it got between the h and the normal mark when it happened but the thing is on that my stock gauge is incorrect if the car runs for 3mins with 180 thermostat in it. the gauge says its up to temp but if you go under the hood u can touch the radator and all that stuff and its still cold any input would be helpful thanks

 

[eagletalonjohn]

does your battery got a good charge?

 

[awdtalon21]

put a cap full of oil down the cylinders and then check the compression. post the results if you can.

 

[rrussell]

Are you using the same compression gauge?

 

[talon187]

battery is good its opt red top yes im using the same gauge. ill try and do another compressipon test somtime this weekend if i can if not sunday ill do one on monday...just curious if i didnt have the throttle at woot when i did the test how much could it throw it off ?

 

[awdtalon21]

battery is good its opt red top yes im using the same gauge. ill try and do another compressipon test somtime this weekend if i can if not sunday ill do one on monday...just curious if i didnt have the throttle at woot when i did the test how much could it throw it off ?

probably not much if any, dont forget the oil too

 

[talon187]

i will im just dont see how it could be all 4 in one shot like that but its possible ill try and do it tomrrow after work

 

[1gDSM4g63]

It doesn't mean that there is anything wrong with you car. As long as all four cylinders are within 5 psi of each other it's fine. Just because you have 9:1 pistons doesn't mean that you have to have high compressions. But it you think there is something wrong it is best to do a leak-down test.

 

[rrussell]

battery is good its opt red top yes im using the same gauge. ill try and do another compressipon test somtime this weekend if i can if not sunday ill do one on monday...just curious if i didnt have the throttle at woot when i did the test how much could it throw it off ?

Having the throttle open verses close i have seen as much as a 8psi difference.

 

[eagletalonjohn]

i heard about the oil trick. i think you dump a cap full of oil in each cylinder and re-due your compression check it will raise the compression?? if so the rings are going. i dont remember.tell me about that lil trick.

 

[TunaTalon]

i picked the motor up for a nice deal it had under 3k on it and i was told was in working order i beileve when i put it in i did a compression test and it had 130ish this was in june

Was the engine at the same temperature for this test as last June? Google is showing 33 degrees in Connecticut right now.

A cold engine will remove the heat of compression and cause lower readings.

Early tomorrow morning when Defiant logs on he will extol the virtues of a leak down test over a compression test.

 

[talon187]

yeah i think the engine was a tad cold so im going to see when i shovel the car out later im going to make sure the battery has a good charge and im going to get her warmed up and see if theres a change in the compression or not i just figured since the motor is like brand new i should have more compression then 120

 

[eagletalonjohn]

what should a motor have compression wise??? i think a good reading is 150 but i am not sure. i just did a test after reading this thread and thats what i got.

 

[talon187]

yeah 150 is good

 

[talon187]

a thought had just come acorss my mind when i bought the motor i was told it was built for nos and a small gap between the pistions and the cyclinder walls i was also told the rings were gaped with alittle space as well....would that make my compression lower then normal?

 

[awdtalon21]

i heard about the oil trick. i think you dump a cap full of oil in each cylinder and re-due your compression check it will raise the compression?? if so the rings are going. i dont remember.tell me about that lil trick.

A wet compression test should be used when cylinder pressure reads below the manufacturer's specifications. It helps you to determine what engine parts are causing the problem. Pour approximately 1 tablespoon of 30-weight motor oil into the cylinder through the spark plug or injector opening, then retest the compression pressure.

If the compression reading goes up with oil in the cylinder, the piston rings and cylinders may be worn and leaking pressure. The oil will temporarily coat and seal bad compression rings to increase pressure; however, if the compression reading stays about the same, then engine valves or head gaskets may be leaking. The engine oil seals the rings, but does not seal a burned valve or a blown head gasket. In this way, a wet compression test helps diagnose low-compression problems.

Do not put too much oil into the cylinder during a wet compression test or a false reading may result. With excessive oil in the cylinder, compression readings go up even if the compression rings and cylinders are in good condition.