low compression on all cylinders after hg replaced...need help

RPSil13

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#1
its a used jdm engine, have never heard it run

i opened it up to inspect it and replace the hg (used a stock one)

torqued the head to 75 ft/lb

havent been able to start it

has spark and fuel

figured i should check the spark plugs, all old brown and oily

while i had all the spark plugs out i decided to check the compression

got 75 -80 psi all across the board

im confused as to what i did wrong or if my compression tester is busted

any ideas or suggestions would be greatly appreciated

thanks
 

suprajztwenty

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#2
what do the compression numbers do with a teaspoon of oil down the holes? if your numbers get dramatically higher then you have bad rings.

you "could" have leaking valves in the head, or maybe someone did a bad valve clearance job. the way to check this is with a leakdown test (compression test in reverse...you actually pump air into the cyl with the valves closed on that cyl) and listen for leaks in the oil fill hole/dipstick and intake/exhaust manifolds and wherever the sound is strongest thatll tell you where air is escaping.

goodluck man
 

CyFi6

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#3
Double check your cam timing by making sure the crank pulley is lined up with 0 when both cam gear notches are strait up. Also make sure you inserted the pin into the center hole of the cam and installed the gears with the pin in the center hole. Are you holding the throttle wide open when you crank during the compression test?
 

BryanDyer

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#4
what do the compression numbers do with a teaspoon of oil down the holes? if your numbers get dramatically higher then you have bad rings.

you "could" have leaking valves in the head, or maybe someone did a bad valve clearance job. the way to check this is with a leakdown test (compression test in reverse...you actually pump air into the cyl with the valves closed on that cyl) and listen for leaks in the oil fill hole/dipstick and intake/exhaust manifolds and wherever the sound is strongest thatll tell you where air is escaping.

goodluck man
This was actually the recent problem with mine. I had low compression in cylinder 6 added, added oil and didnt notice much so I moved on to a leakdown. Results were a horribly bad leaking intake valve. I mean, they were done. The previous owner didnt take to good of care so I took the head off got a new head with a full valve job, comp springs, and got everything back on and she runs like a champ:)
 

RPSil13

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#5
ok, so i checked today

i put a splash of oil in there and the compression jumped up to a little over 100

i guess its safe to assumes its the rings?
 

RPSil13

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#7
ok cool, i will do a leakdown test before tearing it apart

thanks for the input,

will report back over the weekend
 

Suprapowaz!(2)

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#10
Yes, check that timing.

Also, when you do your leakdown test listen to where your leakage is coming from. Listen and feel for air from the throttle body, pcv ports, uncap radiator and look for bubbles, or the back of the turbo (disconnect turbo elbow).
 

Backlash2032

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#11
maybe its just me, but imo a 20psi jump isnt so normal.
Oil will ALWAYS increase compression numbers. Simply because its a fluid and therefore cannot be compressed.

That's atleast the way I look at it. If someone knows more definitely correct me. I can always know more!

Sent from my HTC Droid DNA
 

RPSil13

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#12
Did you ever check the cam timing and that the Balancer hasn't slipped giving an incorrect TDC?
i checked that the cam markings lined up when it was at tdc, but now that the plugs are out, i will double check that its actually at tdc and that the balancer isnt worn/incorrect
 

suprajztwenty

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#13
Oil will ALWAYS increase compression numbers. Simply because its a fluid and therefore cannot be compressed.

That's atleast the way I look at it. If someone knows more definitely correct me. I can always know more!

Sent from my HTC Droid DNA
i didnt mean to make this a pissing contest. ofcourse oil will help seal the rings and increase the number. but when you see a 20psi jump all im saying is i wouldnt rule out the rings being bad.
 

RPSil13

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#15
sorry for taking so long, have been in the process of moving

i just bought the compression tester and am picking up a new compressor tonight,

just have a question in the meantime.

would bad valve stem seals/low compression keep the car from starting?

when checking everything, it had spark, the fuel pump worked, no cel,

any ideas if there is anything else i should have also checked,

thanks
 

Nick M

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#17
i put a splash of oil in there and the compression jumped up to a little over 100

i guess its safe to assumes its the rings?
No, it isn't safe to assume. You were across the board and the gain was minimal.

Simply because its a fluid and therefore cannot be compressed.
The oil creates a much better seal in the cross hatch, that is where low compression would be if rings were worn. Since you took the head off, my best guess is that the engine/cam is out of time giving you ridiculous low compression numbers. Or the test was done wrong.

The combustion triangle is not air/fuel/spark. It is air fuel ratio/ spark timing/ compression.
 

RPSil13

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#18
first of all i just want to thank everyone for their input, this is why i love this community

i went out and bought a new compressor and then before doing the compression check, i figured i should triple check the initial timing

turns out both the intake and exhaust cam were 4 teeth off,

20 min later tdc and timing set compression jumped to 150 across the board

threw on some new plugs and it started right up

THANKS!!

 

super51fan

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#19
Thanks for sharing the cause of the no start. And the picture is also a great help. These cars can be tricky, however it usually is the basic things that cause problems.