Leakdown results shady
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,586
Likes: 2
From: Bardstown Kentucky
Leakdown results shady
I did a leakdown on the 98 corvette that I have been working on. It came up with 60% on number 5 but when I pulled the head to see what was wrong I saw that it was not at top dead center. I know this will affect the results but what are your alls opinions? There is no smoke and all of the pistons look fine. I dont want to slap the heads back on to see I have bottom end problems. Just a quick fill in, the car had a twin turbo kit installed by a local piece of junk shop and it never worked right. The car knock retarded and made low power on the dyno. I figured it took a ring land or something out but so far so good. The cylinder walls even look fine. Any input would be great!
Safety Car
Joined: Apr 2004
Posts: 3,932
Likes: 8
From: Hayward California
not being TDC leaves risk that a valve wasn't fully seated. Ask yourself how long it would take to put the heads back on to redo and see if that time is worth it.
If the motor is still in the bay, I personally would retest.
Good Luck
If the motor is still in the bay, I personally would retest.
Good Luck
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,586
Likes: 2
From: Bardstown Kentucky
I actually tried it again with the rocker arms loose. It showed the same but I thought the piston being lower in the cylinder it may throw it off.
Melting Slicks
Joined: Nov 2004
Posts: 2,715
Likes: 0
From: Tinker till it blows... then back it off a notch, maybe!!
St. Jude Donor '08
Unless a valve is stuck open....I would say it's toast
if you already know this then disregard, but before tearing down...
when you do a leakdown, and it comes up bad, check for hissing
Out of exhaust = exhaust valve
out of intake = intake valve
out of oil cap = rings
rad = head gasket
throw some oil in spark plug hole and if it goes up, then rings/piston.
a little late for this, but that's how I've done it.
Piston being down in bore should have little effect, unless wear to cylinder is down low (unusual)
At this point, you could have a plate made and bolt it to the head mounting surface (seal it of course) . with threaded hole in middle of plate, apply air and check again.
A local machine shop could whack a plate out in little time...would save you from guessing, if you are not sure.
Was it only the one cylinder?
Good luck with it
if you already know this then disregard, but before tearing down...
when you do a leakdown, and it comes up bad, check for hissing
Out of exhaust = exhaust valve
out of intake = intake valve
out of oil cap = rings
rad = head gasket
throw some oil in spark plug hole and if it goes up, then rings/piston.
a little late for this, but that's how I've done it.
Piston being down in bore should have little effect, unless wear to cylinder is down low (unusual)
At this point, you could have a plate made and bolt it to the head mounting surface (seal it of course) . with threaded hole in middle of plate, apply air and check again.
A local machine shop could whack a plate out in little time...would save you from guessing, if you are not sure.
Was it only the one cylinder?
Good luck with it
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,586
Likes: 2
From: Bardstown Kentucky
Its just that cylinder and the weird thing is that there is no marks or anything in the cylinder wall. The top of the pistons look good as well.
Unless a valve is stuck open....I would say it's toast
if you already know this then disregard, but before tearing down...
when you do a leakdown, and it comes up bad, check for hissing
Out of exhaust = exhaust valve
out of intake = intake valve
out of oil cap = rings
rad = head gasket
throw some oil in spark plug hole and if it goes up, then rings/piston.
a little late for this, but that's how I've done it.
Piston being down in bore should have little effect, unless wear to cylinder is down low (unusual)
At this point, you could have a plate made and bolt it to the head mounting surface (seal it of course) . with threaded hole in middle of plate, apply air and check again.
A local machine shop could whack a plate out in little time...would save you from guessing, if you are not sure.
Was it only the one cylinder?
Good luck with it
if you already know this then disregard, but before tearing down...
when you do a leakdown, and it comes up bad, check for hissing
Out of exhaust = exhaust valve
out of intake = intake valve
out of oil cap = rings
rad = head gasket
throw some oil in spark plug hole and if it goes up, then rings/piston.
a little late for this, but that's how I've done it.
Piston being down in bore should have little effect, unless wear to cylinder is down low (unusual)
At this point, you could have a plate made and bolt it to the head mounting surface (seal it of course) . with threaded hole in middle of plate, apply air and check again.
A local machine shop could whack a plate out in little time...would save you from guessing, if you are not sure.
Was it only the one cylinder?
Good luck with it
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,586
Likes: 2
From: Bardstown Kentucky
Since there are no markings in the wall can I pop that piston out the top and re-ring it? I am trying to not pull the engine. I really dont feel like doing that at this time.
Melting Slicks
Joined: Nov 2004
Posts: 2,715
Likes: 0
From: Tinker till it blows... then back it off a notch, maybe!!
St. Jude Donor '08
sounds like a challenge, but maybe..drop pan and whatever to get to it???
I can say this much...if rings in that cylinder are bad, the other are probably not far beehind, unless you can find out why JUST that cylinder is bad
Do you not have a plate that you can clamp to the head..with a drilled/tapped hole to make sure? That cn't take that much to do, and your question will be answered.
Otherwise, you may be chasing your tail on this one.
Sorry, i wish i had better answers.
I can say this much...if rings in that cylinder are bad, the other are probably not far beehind, unless you can find out why JUST that cylinder is bad
Do you not have a plate that you can clamp to the head..with a drilled/tapped hole to make sure? That cn't take that much to do, and your question will be answered.
Otherwise, you may be chasing your tail on this one.
Sorry, i wish i had better answers.
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Le Mans Master
Joined: Jan 2001
Posts: 5,786
Likes: 6
From: Lafayette Colorado
If you are worried that the valves are not closed all the way, take off the rocker arms on the intake and exhaust valves for that cylinder. That will make usre both valves are closed.
Keith
Keith
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,586
Likes: 2
From: Bardstown Kentucky
Le Mans Master
Joined: Oct 2005
Posts: 7,088
Likes: 1,829
From: Metro Detroit Michigan
Before going to the trouble of pulling the piston, why not see if the valves have a good seal since the head is already off? Yank the valves, have them checked for straightness and seating.
If you were correctly on the compression/firing tdc, being exactly at tdc shouldn't make a big difference. If you were very far from tdc the engine would have turned over from the air pressure.
If you were correctly on the compression/firing tdc, being exactly at tdc shouldn't make a big difference. If you were very far from tdc the engine would have turned over from the air pressure.
Heel & Toe
Joined: Feb 2005
Posts: 17
Likes: 0
Sorry to hear that Sabe. It sounds like you have hurt a piston ring land. I had a customers procharged car that was the exact same way. The piston and wall looked perfect from the top but leakdown was apparent. I even bolted the head back down to be sure and after tearing it down I found the problem.
If you took the rockers off it will not make that much of a difference on where the piston is in the bore. 60% is a problem.
Jessie
If you took the rockers off it will not make that much of a difference on where the piston is in the bore. 60% is a problem.
Jessie
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,586
Likes: 2
From: Bardstown Kentucky
Sorry to hear that Sabe. It sounds like you have hurt a piston ring land. I had a customers procharged car that was the exact same way. The piston and wall looked perfect from the top but leakdown was apparent. I even bolted the head back down to be sure and after tearing it down I found the problem.
If you took the rockers off it will not make that much of a difference on where the piston is in the bore. 60% is a problem.
Jessie
If you took the rockers off it will not make that much of a difference on where the piston is in the bore. 60% is a problem.
Jessie
Ah well, its all in good fun! At least we had a good time down there at your shop. Its good to see you on here finally. I know you will bring some good info to this board.
You guys need to stop in down there at Jessies shop if you get the chance, stand up guys down there! Not to mention Jessie got me over the 600RWHP mark!
I'm usually just a lurker though.
Thread Starter
Melting Slicks
Joined: Jul 2005
Posts: 2,586
Likes: 2
From: Bardstown Kentucky
With the quality work and the respect you pay your customers you need to stop lurking. I couldnt ask for better results than you gave us. I mean when you can walk out of a dyno shop with a blown ring and say, "man those guys are great", you know its a good shop. Even though we found problems you all made the day work out pretty good. We will be back, oh yes we will be back.