Why Rockers off for Leak Down test?
Sep 19, 2017, 01:35 PM
#1
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Why Rockers off for Leak Down test?
I'm reading around and noticing some posts (even from buschur himself) that all rockers must be popped off to perform a proper leakdown test, but I haven't really gotten any info as to why. Wouldn't being at TDC close the valves completely? If not, does that mean that the valves stay slightly open during normal operation?
I'm about to do a leakdown test but not sure if I have to undo the timing and remove the cams to remove the rockers before doing it
I'm about to do a leakdown test but not sure if I have to undo the timing and remove the cams to remove the rockers before doing it
Sep 19, 2017, 01:44 PM
#2
EvoM Guru
iTrader: (1)
Just need to be at TDC of the compression stroke of the cylinder you're testing.
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TheRealDirtyDan (Sep 19, 2017)
Sep 19, 2017, 02:05 PM
#3
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Sep 19, 2017, 11:19 PM
#4
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Why do you want to do a leakdown test?
You want to pressurise the cylinder to find a leak?
But what problem are you trying to find.
Leakdown tests usually don't work due to the post above.
If it's leaking in the cylinder past the rings , it's probably NOT going to leak when the piston is at the top and it's probably NOT going to leak when the piston's at the bottom.
If there's bore damage then most of it is going to be about half way.
Removing the rockers is one way because then the valves will be closed.
But if you take the piston to TDC with both valves closed (firing position) then rotate another 90 deg, the valves are still closed and the piston is about half way down.
You've just got to put it into top gear (brake on) to stop the crank turning when you add pressure.
Obviously wrong.
You want to pressurise the cylinder to find a leak?
But what problem are you trying to find.
Leakdown tests usually don't work due to the post above.
If it's leaking in the cylinder past the rings , it's probably NOT going to leak when the piston is at the top and it's probably NOT going to leak when the piston's at the bottom.
If there's bore damage then most of it is going to be about half way.
Removing the rockers is one way because then the valves will be closed.
But if you take the piston to TDC with both valves closed (firing position) then rotate another 90 deg, the valves are still closed and the piston is about half way down.
You've just got to put it into top gear (brake on) to stop the crank turning when you add pressure.
Obviously wrong.
Sep 20, 2017, 12:07 PM
#7
EvoM Guru
iTrader: (1)
Why do you want to do a leakdown test?
You want to pressurise the cylinder to find a leak?
But what problem are you trying to find.
Leakdown tests usually don't work due to the post above.
If it's leaking in the cylinder past the rings , it's probably NOT going to leak when the piston is at the top and it's probably NOT going to leak when the piston's at the bottom.
If there's bore damage then most of it is going to be about half way.
Removing the rockers is one way because then the valves will be closed.
But if you take the piston to TDC with both valves closed (firing position) then rotate another 90 deg, the valves are still closed and the piston is about half way down.
You've just got to put it into top gear (brake on) to stop the crank turning when you add pressure.
Obviously wrong.
You want to pressurise the cylinder to find a leak?
But what problem are you trying to find.
Leakdown tests usually don't work due to the post above.
If it's leaking in the cylinder past the rings , it's probably NOT going to leak when the piston is at the top and it's probably NOT going to leak when the piston's at the bottom.
If there's bore damage then most of it is going to be about half way.
Removing the rockers is one way because then the valves will be closed.
But if you take the piston to TDC with both valves closed (firing position) then rotate another 90 deg, the valves are still closed and the piston is about half way down.
You've just got to put it into top gear (brake on) to stop the crank turning when you add pressure.
Obviously wrong.
No, its not wrong. If the cylinder is damaged like you suggest, the rings will also be damaged due to go over the damaged cylinder wall and not seal correctly on the undamaged portion of the cylinder wall. I've never had an engine test good for leak down and compression, only to be pulled apart and have damaged cylinder walls half way up.
Last edited by letsgetthisdone; Sep 20, 2017 at 12:17 PM.
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Sep 20, 2017, 12:09 PM
#8
EvoM Guru
iTrader: (1)
How new? have you given it some time to seat the rings?
Like the other guy stated, to check for valve seal issues, you'll need to pull the manifolds off to look for oil in the ports.
Sep 20, 2017, 02:15 PM
#10
Newbie
Thread Starter
500 miles in. It burned 1 quart in 500 miles. Blue smoke on a cold start, but goes away ( no blue smoke under idle ) no blue smoke under boost or vacuum.
Sep 21, 2017, 01:01 AM
#11
Account Disabled
That's not going to help either.
If you remove the exhaust manifold and see oil, it could be coming from the intake seals, the rings or maybe the exhaust seals.
Some engines don't have seals on the exhaust valves, they're not needed as they don't get vacuum.......they don't usually leak.
Pulling the intake manifold, you'll see nothing.
For VSS issues, you remove the valve cover and take a look.
If it's a new build they should be new.
But if it's got an aftermarket cam (high lift) which was fitted without measuring properly, they might be destroyed.
But if you're looking for an oil burning issue, a leakdown test might find faulty rings but it won't find a bore that's been honed wrong.
No, its not wrong. If the cylinder is damaged like you suggest, the rings will also be damaged due to go over the damaged cylinder wall and not seal correctly on the undamaged portion of the cylinder wall. I've never had an engine test good for leak down and compression, only to be pulled apart and have damaged cylinder walls half way up.
Still wrong.
Not in this case but with an old engine that's tuned wrong, it's common to break the ring lands (detonation), the owner doesn't know and keeps driving, the only sign is too much smoke. One ring no longer rotates in the bore and the end of it wears a groove down the bore.
The other ring still seals so ..........you'll only find the problem with the piston half way down. It leaks where there's a groove in the bore.
Last edited by RightSaid fred; Sep 21, 2017 at 01:09 AM.
Sep 21, 2017, 05:54 AM
#12
Newbie
Thread Starter
That's not going to help either.
If you remove the exhaust manifold and see oil, it could be coming from the intake seals, the rings or maybe the exhaust seals.
Some engines don't have seals on the exhaust valves, they're not needed as they don't get vacuum.......they don't usually leak.
Pulling the intake manifold, you'll see nothing.
For VSS issues, you remove the valve cover and take a look.
If it's a new build they should be new.
But if it's got an aftermarket cam (high lift) which was fitted without measuring properly, they might be destroyed.
But if you're looking for an oil burning issue, a leakdown test might find faulty rings but it won't find a bore that's been honed wrong.
Still wrong.
Not in this case but with an old engine that's tuned wrong, it's common to break the ring lands (detonation), the owner doesn't know and keeps driving, the only sign is too much smoke. One ring no longer rotates in the bore and the end of it wears a groove down the bore.
The other ring still seals so ..........you'll only find the problem with the piston half way down. It leaks where there's a groove in the bore.
If you remove the exhaust manifold and see oil, it could be coming from the intake seals, the rings or maybe the exhaust seals.
Some engines don't have seals on the exhaust valves, they're not needed as they don't get vacuum.......they don't usually leak.
Pulling the intake manifold, you'll see nothing.
For VSS issues, you remove the valve cover and take a look.
If it's a new build they should be new.
But if it's got an aftermarket cam (high lift) which was fitted without measuring properly, they might be destroyed.
But if you're looking for an oil burning issue, a leakdown test might find faulty rings but it won't find a bore that's been honed wrong.
Still wrong.
Not in this case but with an old engine that's tuned wrong, it's common to break the ring lands (detonation), the owner doesn't know and keeps driving, the only sign is too much smoke. One ring no longer rotates in the bore and the end of it wears a groove down the bore.
The other ring still seals so ..........you'll only find the problem with the piston half way down. It leaks where there's a groove in the bore.
That leaves the rings and valve seals / guides. The rings would normally smoke under acceleration correct? I don’t see smoke under acceleration. I also don’t see smoke under deceleration. The only visible smoke I see is for 2-3 seconds on a cold start. But I don’t think that would cause me to burn 1 complete quart in 500 miles. I have double and triple checked under the car and every cranny, there’s no leaks. This oil is being burned.
Sep 21, 2017, 10:10 PM
#13
Account Disabled
If there's signs of oil in the intake side of the turbo, it's usually coming from blowby.
That means the rings aren't sealing properly.
You won't find the problem without pulling it apart.
That means the rings aren't sealing properly.
You won't find the problem without pulling it apart.
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