y5mgisi
1 ton status
Yea for sure. I just wanted to verify that i at least had something going on. Just need to find a leak down tester to borrow!
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Thinking of doing the unthinkable... *Rotor to cap gap. Normal?*
- Thread starter y5mgisi
- Start date
y5mgisi
1 ton status
So when i track down the leak down tester, how do i figure out what component is bad If I have excessive leakage? as far as it being rings, valves or head gasket?
A leakdown test is good. I don't think you're going to find bad rings or valves based upon what you've reported so far. BUT, it will take this test off the list of things to do and help narrow the search.
It seems like the issue is somehow going to be related to a couple plugs (cylinders) running rich, and a few not firing or somehow not getting any fuel. Or an erratic issue causing these problems.
It seems like the issue is somehow going to be related to a couple plugs (cylinders) running rich, and a few not firing or somehow not getting any fuel. Or an erratic issue causing these problems.
read the instructions.. TDC for whatever cylinder your testing, WOT and pull the oil fill cap..... decent cylinders will normally be 85 to 95%... they should have the same 10% difference your looking for in a compression test....
if a cylinder is low, you will hear it leaking/hissing from either the intake (bad intake valve/seat), the crankcase (oil fill hole, ring issue) or the exhaust (exhaust valve).. obviously the exhaust one is usually not a hearable one.. but sometimes you can hang a piece of paper over the exhaust pipe to see it depending on how low the % is..
it's critical that the piston be at TDC... for 2 reasons.. if not the motor will try to turn over from the air pressure... and also it verifies the valve timing is in the ballpark...
if a cylinder is low, you will hear it leaking/hissing from either the intake (bad intake valve/seat), the crankcase (oil fill hole, ring issue) or the exhaust (exhaust valve).. obviously the exhaust one is usually not a hearable one.. but sometimes you can hang a piece of paper over the exhaust pipe to see it depending on how low the % is..
it's critical that the piston be at TDC... for 2 reasons.. if not the motor will try to turn over from the air pressure... and also it verifies the valve timing is in the ballpark...
A leakdown test is good. I don't think you're going to find bad rings or valves based upon what you've reported so far. BUT, it will take this test off the list of things to do and help narrow the search.
It seems like the issue is somehow going to be related to a couple plugs (cylinders) running rich, and a few not firing or somehow not getting any fuel. Or an erratic issue causing these problems.
I'm trying to verify his valve timing is ok...
$60..... pretty freakin cheap for a vital diagnostic tool imo...
http://www.google.com/products/cata...sa=X&ei=GTzLToaCEOLh0QHq0dww&ved=0CIYBEPMCMAA
http://www.google.com/products/cata...sa=X&ei=GTzLToaCEOLh0QHq0dww&ved=0CIYBEPMCMAA
y5mgisi
1 ton status
Ok gotcha. Now, how do i find TDC on number 2 for example? Watch the rockers as i rotate the motor?
y5mgisi
1 ton status
I'll break down and buy one if i have to, but in the next day or two im going to try and find a one to borrow.
y5mgisi
1 ton status
Can i just back off all the rockers?
y5mgisi
1 ton status
Maybe if this thing is still around after christmas i should just do a swap? Who knows. Depends on if i can really convince myself to spend the money on a 5.3 swap or not.
http://portland.craigslist.org/clk/pts/2713496443.html
http://portland.craigslist.org/clk/pts/2713496443.html
Yes you could you just wouldn't be testing the cam at all, which you already degreed so it should be fine. Also, a compression test is better for testing the cam I think because it tests the whole cycle. A leakdown test you are trying to see whether the valves or rings leak, or the head gasket, so loosening the rockers so they are loose during the test would be fine.
Also, I have found, and maybe it's just me, that whenever I try to leave it at TDC, the air pressure just pushes the piston down in the bore, because at 100 psi in a 4" bore that's over 1200 lbs of force pushing down on the piston, and most of the time I dont get it exact so it goes one way or the other when I apply pressure.
However, being at TDC still changes the leakdown slightly, because the cylinder has more volume then so the leakdown percentage may change. Just try to do them all the same way.
Also, leakdown wet/warm vs dry/cold is a big difference.
I always adjust the regulator so the input gauge is 100 psi so there is no math, the leakdown pressure is the percentage then.
y5mgisi
1 ton status
So do you suppose that 100 ish psi will for sure push the piston down? Or is it just that there is a chance it will? Cause if it will for sure then i think it will be ok cause it will make them all test the same. But if it won't, then that's probably not the best way to do it. So to get tdc on all cylinders, could i get #1 tdc and then rotate the crank 90* and then test the next cylinder in the firing order and repeat?
when the intake valve closes, the next time the piston is at the top, it's TDC for any cylinder... if the piston is at true TDC, the top of the crank stroke, it wont spin the motor over.. i use a long piece of bent wire to feel the piston reach TDC... something like a 8" piece of coathangar with a very slight bend at the end would be similar.. once the valve closes, use the wire to feel it reaching the top, being carefully to make sure it stays free and away from the cylinder walls...
if the motor is turning over, just reset the piston height... we call it kickback because you'll usually have a longhandled ratchet on the crank that starts fighting ya... every once in a while i'll rush and get one that wants to spin over, but usually i can do a whole motor with no plugs in and it wont turn over.. just gotta have that crank at the top of its rotation..
i missed the bit about the cam being degreed, but i did see some talk about questioning the cam mark lineup... that, in conjunction with the plugs, has me questioning the valve timing..
if the motor is turning over, just reset the piston height... we call it kickback because you'll usually have a longhandled ratchet on the crank that starts fighting ya... every once in a while i'll rush and get one that wants to spin over, but usually i can do a whole motor with no plugs in and it wont turn over.. just gotta have that crank at the top of its rotation..
i missed the bit about the cam being degreed, but i did see some talk about questioning the cam mark lineup... that, in conjunction with the plugs, has me questioning the valve timing..
Just to bring you up to speed without having to read the whole thread, vacuum has never been good, nor compression.
He got a degree wheel, and found it way off with the marks lined up. He eventually moved it one tooth, which put it real close, improved the vacuum and compression.
I had a wild theory that the crank gear might have been put on backwards and someone made a mark to keep from having to reverse it, and missed.
Someone else chimed in with the idea that some rebuilders do that on purpose to modify the cam timing.
The cam timing is not perfect I don't think, but its very close now.
The degree wheel part is not too far back, if you need the exact specs.
He got a degree wheel, and found it way off with the marks lined up. He eventually moved it one tooth, which put it real close, improved the vacuum and compression.
I had a wild theory that the crank gear might have been put on backwards and someone made a mark to keep from having to reverse it, and missed.
Someone else chimed in with the idea that some rebuilders do that on purpose to modify the cam timing.
The cam timing is not perfect I don't think, but its very close now.
The degree wheel part is not too far back, if you need the exact specs.
I agree with Ryoken, it will more likely push the piston down if its not directly at TDC, and even then I have had them want to turn over on me. And yes, you can get #1 at TDC, then turn it 90 degrees and test #8, etc. Just be sure you are on the compression stroke, and not the exhaust stroke otherwise one/both valves may be slightly open which wold most likely produce very bad results.
y5mgisi
1 ton status
So yay or nay on just loosening all the rockers and doing it without rotating the motor?
nay....
You are going to have to rotate the motor anyway then to re-set all the rockers, so you might as well do it while leaktesting and leave the rockers alone.
But if you are curious, do it both ways and see how much of a difference it makes. I think if there is really a problem it's going to show up either way. But if you were testing a race motor to see how good the seal is and the consistency, then you better do it perfectly and at TDC.
But if you are curious, do it both ways and see how much of a difference it makes. I think if there is really a problem it's going to show up either way. But if you were testing a race motor to see how good the seal is and the consistency, then you better do it perfectly and at TDC.
y5mgisi
1 ton status
Ok done deal. I will do it the TDC method.
