Shocked With My Compression Test !

[andy95'R33GTR]

1 - 100

2 - 165

3 - 165

4 - 165

5 - 95

6 - 160

what happened??? piston rings dead???

[r33niko]

looks like it

[andy95'R33GTR]

ok... i need to prepare parts for this...what do i need? 2 sets piston rings? head gaskets??

[NYTSKY]

Leave it to a well known and trusted mechanic. They will let you know what has to be done.

[blind_elk]

You need to do a "wet" compression test as well (bit of oil in each cylinder). If compression increases, then rings are the likely culprit.

You should replace all 6 sets of rings.

[Duncan]

but its more likely you have a damaged piston.

assuming the tst was accurate (and i guess there were other symptoms anyway....) just get the motor pulled down. there is no chance its ok with that compression and we are all just guessing at the cause

[tridentt150v]

But if a wet test doesn't make any difference then you have head gasket, valve or valve guide problems. I'd do this before ordering any rings, just to be sure.

[rob82]

Do a leak down test - that will tell you where the pressure is going.

[andy95'R33GTR]

hmmm... running full boost before...could be a blown gasket....

i will fix this myself...no good mechanic in our area... il post pictures

Edited March 28, 2010 by andy95'R33GTR

[skyline4lifer32]

best to pull it down before buying part's, no point buying a set of ring's if the bore is damaged and need to oversize it,

i rebuilt my rb20det about 2 years ago because i had compression differences of about 30psi, turned out to be a number of thing's from melted piston's, stuck rings, leaking valve's, If its the head gasket you will hear it, if it's blown into a coolant gallery you will see lot's of bubble's in you radiator when you idle it with the cap off,

When you find out what's wrong, the first thing to do is find out why, It turned out my Fuel pump was stuffed and could only deliver 35psi max, causeing the melt down of the RB, now running an bosch 044 at 85psi fuel pressure via sard rising rate reg, Now put's out a healthy 209rwkw on 14psi at 85%duty cycle on the stock injector's,

Hope you don't find to much damage, good luck

[The Mafia]

hmmm... running full boost before...

This is probably why it is dead..

Define "full boost" and what kind of turbo you have.

[andy95'R33GTR]

got a stock turbos, i have a vaccum problem, my wastegates won't open, until i relocated my hoses to stock piping, and i got a .7 boost..

[skyline4lifer32]

got a stock turbos, i have a vaccum problem, my wastegates won't open, until i relocated my hoses to stock piping, and i got a .7 boost..

.7 boost, is that on that factory gauge? my factory boost gauge read's +7 even when im running 14psi, and still read +7 when i split a wastegate vac line, when it boosted out to 23psi

[andy95'R33GTR]

.7 boost, is that on that factory gauge? my factory boost gauge read's +7 even when im running 14psi, and still read +7 when i split a wastegate vac line, when it boosted out to 23psi

that is from my apexi avcr gauge..

[andy95'R33GTR]

could a leaky injector cause the pressure to drop?

[skyline4lifer32]

could a leaky injector cause the pressure to drop?

No a leaking injector will not effect the compression, will only make that cylinder run a bit richer, the easiest way i've found is check the colour of your spark plug's and make sure they are running all the same colour,

If you avcr is reading .7 your waste gate's must be working fine, if they wern't you would get alot more boost on stock turbo's,

i did notice with my stuffed fuel pump was holding my turbo back, when i replaced it my boost went from 13psi to about 19psi without touching the boost controller

[RBJETT]

no, as that doesnt change the way the cylinder seals, the rings valves and gasket do that.

edit: looks like someone got in before me

[andy95'R33GTR]

ok guys... thanx for the help, what i do now is to wet test the low compression cylinders..and if pressure doesn't change il remove the cylinder header.. so i won't pull out the engine if its only the cylinder head removal right? or i still need to pull out the engine?

all spark plugs same color, brown..

Edited March 28, 2010 by andy95'R33GTR

[skyline4lifer32]

If the comp doesn't change with the oil test then you could just remove the head with the motor still in, just be sure you do the oil test properly, with enough oil to ensure it get's around the whole piston, and not to much or this will give you false higher psi reading's, the other way to check is to presurize the cylinder with a fitting that screw's into the spark plug hole, with both intake and exhaust valve's closed on the power stroke, then listen for leak's through the intake manifold and exhaust manifold to verify a faulty valve, test each cylinder and see if their is more hissing on the cylinder's with the low compression, just remember to rotate the crack each time to get the cylinder your testing on the power stroke to ensure the cam's arn't holding the valve's open slightly,

could also be worn valve seat's causeing low compression because the gtr's run solid lifter's they need shimming to change the valve clearance, but with rb20- rb25's use hydrolic lifter's so they never need touching until one shit's it's self, or you get sick of the 10 seconds of tapping every now on start up and then and replace the f-ing thing,

If it was me i would pull the motor and check the piston's and bearing's and fit new one's anyway while you doing open heart surgery on your RB, then you know it's going to be a healthy rb, for a couple of hundred extra it's worth doing now rather than later,

You need to know how to gauge clearances for your bearing's, if your not confident doing this then leave the motor in the car and just do the head, if you get the clearance wrong it could throw a big end bearing and end the fun,

I found the ACL bigend bearing's to have a enough varience to swap and change until i had all 6 with the spec's i wanted, to the point where the thickest bearing would lock the crank up when i fitted it to one cylinder, if i had just put the bearings in any which way, the motor wouldn't have lasted 5 minute's, It's still going strong 2 year's 25,000km later with abuse all the time, shit that means another service is due on my rb,

Hope this helps out a bit,

Glad i started on an rb20, will not be so worried if i can pick up a cheap gtr with compression problem's

[andy95'R33GTR]

If the comp doesn't change with the oil test then you could just remove the head with the motor still in, just be sure you do the oil test properly, with enough oil to ensure it get's around the whole piston, and not to much or this will give you false higher psi reading's, the other way to check is to presurize the cylinder with a fitting that screw's into the spark plug hole, with both intake and exhaust valve's closed on the power stroke, then listen for leak's through the intake manifold and exhaust manifold to verify a faulty valve, test each cylinder and see if their is more hissing on the cylinder's with the low compression, just remember to rotate the crack each time to get the cylinder your testing on the power stroke to ensure the cam's arn't holding the valve's open slightly,

could also be worn valve seat's causeing low compression because the gtr's run solid lifter's they need shimming to change the valve clearance, but with rb20- rb25's use hydrolic lifter's so they never need touching until one shit's it's self, or you get sick of the 10 seconds of tapping every now on start up and then and replace the f-ing thing,

If it was me i would pull the motor and check the piston's and bearing's and fit new one's anyway while you doing open heart surgery on your RB, then you know it's going to be a healthy rb, for a couple of hundred extra it's worth doing now rather than later,

You need to know how to gauge clearances for your bearing's, if your not confident doing this then leave the motor in the car and just do the head, if you get the clearance wrong it could throw a big end bearing and end the fun,

I found the ACL bigend bearing's to have a enough varience to swap and change until i had all 6 with the spec's i wanted, to the point where the thickest bearing would lock the crank up when i fitted it to one cylinder, if i had just put the bearings in any which way, the motor wouldn't have lasted 5 minute's, It's still going strong 2 year's 25,000km later with abuse all the time, shit that means another service is due on my rb,

Hope this helps out a bit,

Glad i started on an rb20, will not be so worried if i can pick up a cheap gtr with compression problem's

thanx... im not confident on change the main bearings..., i will only fix the low compression problem... ok i understand the oil test...to verify the problem..thanx