Changing valve springs..TDC?
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Instructor
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Changing valve springs..TDC?
I’m replacing all the valve springs in my procharged c6 z06. Put the compressed air in but it seems to be escaping. Realized I didn’t do TDC. Could that be the issue? If so, how do I do it as I have all the rockers off from the drivers side ..
also, how do I rotate the motor as there’s no room to get to the harmonic balancer. I tried with the alternator bolt but the belt seems to be spinning 😵💫 (all plugs are out).
I’d really appreciate any help with the TDC..
thank you in advance.
also, how do I rotate the motor as there’s no room to get to the harmonic balancer. I tried with the alternator bolt but the belt seems to be spinning 😵💫 (all plugs are out).
I’d really appreciate any help with the TDC..
thank you in advance.
Race Director
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From: SW Florida
2021 C6 of the Year Finalist - Modified
If you want to rotate the engine, pull the relay shown in the photo below. Then get a paper clip and bend it so you can touch the two pins shown in the other photo.
The engine will rotate without a fuel pressure or spark to worry about.
The engine will rotate without a fuel pressure or spark to worry about.
Thread Starter
Instructor
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thanks so much! I’ll give this a go tomorrow after work.
now as mentioned the rockers are off..how do I tell when it’s at TDC?
now as mentioned the rockers are off..how do I tell when it’s at TDC?
Race Director
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From: SW Florida
2021 C6 of the Year Finalist - Modified
Once you remove all the rocker arms, the valve spring pressure will keep all the valves closed ... then pressurize the cylinder and remove the valve springs in that cylinder. All that pressure in the cylinder will keep both the intake and exhaust valves closed on that cylinder no matter whether or not the piston is down or up in the cylinder bore.
Got to have the cylinder pressurized before removing that cylinder's valve springs so the valves don't drop.
____________________________
Maybe you don't have a big enough air compressor ?
Got to have the cylinder pressurized before removing that cylinder's valve springs so the valves don't drop.
____________________________
Maybe you don't have a big enough air compressor ?
Le Mans Master
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From: Austin Tx
Even if you put the engine at TDC, once you connect the air hose, it's going to spin the motor. It's going to leak a little air passed the rings, that's normal. Make sure both rockers for each cylinder are removed.
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I only removed all the drivers side rockers, removed the plugs, put the fitting in cylinder #1 to pressurize the cylinder and started to compress the valve spring, heard the cylinder loosing/escaping pressure and I stopped.
am I doing something wrong?
am I doing something wrong?
Once you remove all the rocker arms, the valve spring pressure will keep all the valves closed ... then pressurize the cylinder and remove the valve springs in that cylinder. All that pressure in the cylinder will keep both the intake and exhaust valves closed on that cylinder no matter whether or not the piston is down or up in the cylinder bore.
Got to have the cylinder pressurized before removing that cylinder's valve springs so the valves don't drop.
____________________________
Maybe you don't have a big enough air compressor ?
Got to have the cylinder pressurized before removing that cylinder's valve springs so the valves don't drop.
____________________________
Maybe you don't have a big enough air compressor ?
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I found that it's not really the HP of the compressor that is that important, but you need a compressor with a pretty big tank (you need more air volume)
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I actually had my heads done 2years back 8000miles ago. Moldstar90 guides, PAC1207x springs along with the stem seals.
2 days back while driving home I noticed a tapping noise that would get worse when accelerating. A local shop told me the inner springs sometimes break and so I decided to change them all out while pulling them out to inspect. Visually I don’t see anything so far but I haven’t pulled them..
hoping nothing is damaged 😣
2 days back while driving home I noticed a tapping noise that would get worse when accelerating. A local shop told me the inner springs sometimes break and so I decided to change them all out while pulling them out to inspect. Visually I don’t see anything so far but I haven’t pulled them..
hoping nothing is damaged 😣
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I’m replacing all the valve springs in my procharged c6 z06. Put the compressed air in but it seems to be escaping. Realized I didn’t do TDC. Could that be the issue? If so, how do I do it as I have all the rockers off from the drivers side ..
also, how do I rotate the motor as there’s no room to get to the harmonic balancer. I tried with the alternator bolt but the belt seems to be spinning 😵💫 (all plugs are out).
I’d really appreciate any help with the TDC..
thank you in advance.
also, how do I rotate the motor as there’s no room to get to the harmonic balancer. I tried with the alternator bolt but the belt seems to be spinning 😵💫 (all plugs are out).
I’d really appreciate any help with the TDC..
thank you in advance.
What has worked for me in the past is that with the rocker arms off, take a deep socket that is slightly smaller than the diameter of the retainer and give it a good smack or two with a hammer.
When you start compressing the spring you're trying to push the retainer down far enough for the locks to come loose allowing you to remove them and the valve spring. If the springs have been on the car for a while, tapping them with a socket will loosen everything up enough so that the downward push of the retainer as you're compressing the spring doesn't exceed the opposing force of the air in the cylinder trying to keep the valve in place.
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Thread Starter
Instructor
Joined: Jul 2008
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thank you I’ll try this!
As others have me mentioned the piston doesn't need to be at TDC. I've also done it several times before with a fairly small Harbor Freight compressor so I don't think that's the main culprit either.
What has worked for me in the past is that with the rocker arms off, take a deep socket that is slightly smaller than the diameter of the retainer and give it a good smack or two with a hammer.
When you start compressing the spring you're trying to push the retainer down far enough for the locks to come loose allowing you to remove them and the valve spring. If the springs have been on the car for a while, tapping them with a socket will loosen everything up enough so that the downward push of the retainer as you're compressing the spring doesn't exceed the opposing force of the air in the cylinder trying to keep the valve in place.
What has worked for me in the past is that with the rocker arms off, take a deep socket that is slightly smaller than the diameter of the retainer and give it a good smack or two with a hammer.
When you start compressing the spring you're trying to push the retainer down far enough for the locks to come loose allowing you to remove them and the valve spring. If the springs have been on the car for a while, tapping them with a socket will loosen everything up enough so that the downward push of the retainer as you're compressing the spring doesn't exceed the opposing force of the air in the cylinder trying to keep the valve in place.
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Now that I think of it, TDC is exactly where you don't want it to be.
The purpose of injecting air into the cylinder is to provide an opposing force to keep the valve in place. If the piston is at TDC it would greatly reduce the quantity of air in the cylinder, compared to having the cylinder completely filled if the piston is sitting at the very bottom (which is usually what happens anyway as soon as you start injecting air into it).
Either way, good luck and let us know when you finally get it sorted out.
The purpose of injecting air into the cylinder is to provide an opposing force to keep the valve in place. If the piston is at TDC it would greatly reduce the quantity of air in the cylinder, compared to having the cylinder completely filled if the piston is sitting at the very bottom (which is usually what happens anyway as soon as you start injecting air into it).
Either way, good luck and let us know when you finally get it sorted out.
Instructor
Joined: Aug 2012
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From: Griffin GA
In the past with an SBC, had used that rubber coated clothes line to change out valve springs.
Remove all spark plugs and remove rocker arms.
Then on a cool engine with the piston below TDC, insert clothes line into spark plug hole until you cannot push any more in (do not cut it). Then rotate engine by hand enough to lightly compress the line inside the cylinder so that it is up against the valves. You can then remove the springs without dropping the valves.
When finished, rotate the crankshaft counter clockwise to lower the piston and take pressure off the line, then pull the cord out through the spark plug hole; then on to the next cylinder.
This may sound hokey, but if you do not have an air compressor it works well, and the rubber coated line will not damage or leave any debris in your cylinders. Also do not need to be concerned with leaks or power outage.
Remove all spark plugs and remove rocker arms.
Then on a cool engine with the piston below TDC, insert clothes line into spark plug hole until you cannot push any more in (do not cut it). Then rotate engine by hand enough to lightly compress the line inside the cylinder so that it is up against the valves. You can then remove the springs without dropping the valves.
When finished, rotate the crankshaft counter clockwise to lower the piston and take pressure off the line, then pull the cord out through the spark plug hole; then on to the next cylinder.
This may sound hokey, but if you do not have an air compressor it works well, and the rubber coated line will not damage or leave any debris in your cylinders. Also do not need to be concerned with leaks or power outage.
Pro
Joined: Feb 2014
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From: England
Now that I think of it, TDC is exactly where you don't want it to be.
The purpose of injecting air into the cylinder is to provide an opposing force to keep the valve in place. If the piston is at TDC it would greatly reduce the quantity of air in the cylinder, compared to having the cylinder completely filled if the piston is sitting at the very bottom (which is usually what happens anyway as soon as you start injecting air into it).
Either way, good luck and let us know when you finally get it sorted out.
The purpose of injecting air into the cylinder is to provide an opposing force to keep the valve in place. If the piston is at TDC it would greatly reduce the quantity of air in the cylinder, compared to having the cylinder completely filled if the piston is sitting at the very bottom (which is usually what happens anyway as soon as you start injecting air into it).
Either way, good luck and let us know when you finally get it sorted out.
But as is said above the crank will spin regardless. If the car is on jack stands, put it in 4th gear and rotate the wheels to turn the engine over, slow and you may need 2 people to turn both rear wheels due to the diff.
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thanks for this tip. It worked finally.
however, turned out my springs are all intact. Now the troubleshooting begins 😣. Next I guess is to pull the heads off and inspect the lifters.
If anyone thats experienced could give their opinion on the engine noise in the video above? I’m hoping it’s not the bottom end..
Last edited by Vette2lo; Jun 10, 2022 at 09:51 PM.