so can anyone tell me why my compression is 95 across the board?

[wild_maxx]

well my motor is really pissing me off. its freshly rebuilt and now the compresison is at 95 psi across all 4 cylinders. i did the test correct so dont think that is the problem. could it be a head gasket? there is no smoke at all, no coolant mixing with oil. all new internals except rods, only boosting 7 psi, jwt ecu, cleaned/balanced/flow tested injectors, change the oil after the first 20 miles then again at 75 miles. did the compression test and the results are making me sick. all 95 the spark plugs were loose when i did the compression test as if they just worked themselves out of the holes and yes i torqued them down. any clues?

[virus77]

if its 95 across the board then it might be a faulty gauge giving a low reading? how does the car run?

[wild_maxx]

it idles fine, but wont even boost past 5 psi. do you think since the plugs were loose that the piston rings havent really had a change to break in? not enouf load on them? god i hope so cause i will ****y my pants if this motor is ****ed up.

[trackslut240]

the spark plugs were loose when i did the compression test as if they just worked themselves out of the holes and yes i torqued them down. any clues?



i did a comp test this way, disable fuel(pull out injector connectors, pull out fuel pump fuse), disable spark(pull out coil connection), crank the car wide open throttle with all the plugs out, and the compression testor tight on one plug hole, so i am confused about the plugs being loose, if it was close to this then virus77 is correct, try with another gauge,

[crzycav86]

What is the CR of the pistons you put in?

[klattr1]

test done cold? test done warm? who assembled the top end? (cams, timing chain, all the alignment, etc)

[Kenrik]

Dam those are some ****ty numbers Sorry man hope your engine is not ****ed

The fact that it's 95 on all of them makes me think it's something like the head gasket because you should have some variation otherwise.

[PalmerWMD]

test done dry or cold hot or wet?

I am leaning more to a problem with your testing ,as a shot motors very nearly always show <different> compression #'s at cylinders, never all spot on (albeit low)

[PapaSmurf2k3]

have you tried pouring a small ammount of oil down the hole onto the piston and re-checking it to verify bad ring seals?

[rn240sx]

95 psi has got to be a bad gauge or motor was not put together very well especially if they just rebuilt it....!!!

I guess we will have to wait on him to let us know how he did this compression test..

[fiznat]

Need to know if the motor was warm or not when you did the test.

Also, how many miles are on this motor since it was built? The rings do need a chance to wear in...

[nismofly]

i thought the number didnt matter as long as they were all within a few psi of each other

does that only apply when its a little more or less than normal?

if so then id have to say its something test related

[Kenrik]

ummm yeah but normal is 175-185 PSI.... under 140 is BAD! mine was 155,155,155,155 but I checked it just after putting is some really light weight 5w 30 synthetic oil. I figure I lost a few PSI from that... 95 though... and across all four is so strange!

[wild_maxx]

ok, the test was done with the motor at operating temp. it was idleing then i pulled the fuel pump fuse and it dies off like it should. cranked it over to get any fuel out of the cylinders then took out all spark plugs, WOT the did the test. that is correct way. i had the bottom end assembled by at the maching shop then i did the timing chain and head install my self. this is on a kae by the way. i set the timing at 15*. when i installed the timing chain i made sure everything at correct, crank at TDC key on cam wat @12 and dot on sproket was at 3 o'clock then lined up silver links. made sure to crank it by hand to make sure no valves were hitting. the motor now has 75 miles on it. the head was rebuilt as well, new valve stems cleaned new cam installed. is it possible that the rings just havent had a chance to wear in all the way?

[wild_maxx]

also, my boost/vac gauge was reading 17 vac at idle, now it reads about 10 meaning i have a leak somewhere, i will track it down in the morning. could that make such a huge differnece in the testing? i am running 8:1 comp supertech pistons.

[Craving4Boost]

your base timing is set to 15?

[wild_maxx]

yes, this is a ka24E

[:: orion ::]

Cam a tooth off, maybe?

Not likely, but it could cause an even-across-the-board, low compression scenario.

- Brian

[wild_maxx]

ok i bought a new gauge today and the results are better. i am getting about 130ish across the board now. I drove it about 10 miles before i did this compression test so maybe the rings are still wearing in. i will drive it more and get another test tonight. hopefully it keeps goin up. dont buy cheap compression gauges. they suck balls

[wild_maxx]

heres a weird question, why can i boost to 7 psi with no load on the engine? i can rev it up and the boost gauge will read 7 psi. this is weird.

[:: orion ::]

Are you sure the timing is correct?

Did you set it per the FSM?

- Brian

[wild_maxx]

yes, i made sure it was on the compression stroke when i installed the dist and oil pump. then aligned them together.

[nissanfanatic]

LOL too funny your pic. I even had to post a comment in the picture gallery.haha I have the same kind of gauge and it works well. They crap out over time.

How about ignition timing?

[wild_maxx]

ok so i pulled the timing cover off today to double check the timing setup. here you can see that the silver link are lined up with the dots on the cam and crank sproket. the timing is at TDC on the compression stroke. this is correct? I also discovered that i forgot to torque down my chain tensioner bolts so i fixed that. only one of them were out. i am going to reset the timing tomorrow and do a boost leak test.

[Mikoriad]

75 miles on it huh.... hmmm sounds to me like the rings still have some work to do. I'd say break in a little longer. Don't be easy on it, need some hard accleration (not to red line), then long in gear engine braking. Get a few more miles and recheck.

[wild_maxx]

i think i found the problem. got a timing light and discovered that the base timing was -5* BTDC when i should be at 15* BTDC. the first time i set the base timing i had a safcII wired into the ecu and had the setting all messed up. well i set the timing to 15* then but didnt check it again till tonight ( i removed the safc) and saw that the timing was so far retarted. also, the car would be at full operating temp in about 3 minutes of idleing, is this related to timing? my a/r ratio was never bad in boost but i did have some knock from the engine. hopefully nothing is ruined.

[NateDogg]

also, the car would be at full operating temp in about 3 minutes of idleing, is this related to timing?

Decreasing the timing results in increased exhaust temperatures, so yes I would say this would have an impact on how fast the motor warms up.. Obviously it also depends on the ambient temp, your coolant system setup (electric fans or mechanical clutch fan, stock shroud or no shroud..), the operating RPM and the fuel ratios.

I hope you are running high octane gas. Sometimes if timing is so far off like that it can cause funny things to happen, like pre-detonation.

As far as your compression is concerned, I would say 130psi is nothing to cry about for a new built motor with 8:1 pistons. I would say it should be around 140-150psi when fully "broken in".

Good luck boosting!

[wild_maxx]

thanx, i will fill everyone in tomorrow when i get it back together.