Help with camshaft degree walk through, please.
Thread Starter
Teching In
Joined: Jun 2021
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From: TX Y'all!!
Help with camshaft degree walk through, please. I'm learning on a 03 4.8 LR4 with roughly 90XXX miles. The head is off on the odd bank which im practicing on. I have the wheel zeroed out on tdc. I was able to verify max lobe lift on both intake and exhaust for cylinder #1 going off of the available gm specs but I was a few thousands shy which im guessing is due to wear.
Now where I'm getting lost is verifying the 190/191. Do I get to max lobe lift, zero the gage and go down .050 on both sides? Or do I zero the gage on base circle and get my .050 reading after base on both sides?
I appreciate any help.
Now where I'm getting lost is verifying the 190/191. Do I get to max lobe lift, zero the gage and go down .050 on both sides? Or do I zero the gage on base circle and get my .050 reading after base on both sides?
I appreciate any help.
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Joined: May 2008
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From: Carnation, WA
The second way, zero the base circle and go in one direction to pick up .050" off the circle both going up and coming down. If you take two measurements from peak lift, you have more chance for errors/inprecisions to stack up... twice as many measurements, twice as much error or chance for it.
Finding the true TDC is critical. How did you determine TDC? I use a piston stop. The post before mine is the way I would do it, not at max lift. If you have the intake opening spec, say it for *****/giggles, it opens at 30° ATDC (meaning the valve lift is .050" off the seat@30° ATDC, that's what I'd use. However, most people, myself included, consider the intake closing spec most important. If you have that spec, where they give the intake closing spec .050" from the seat@80°BTDC, you can use that, and let the intake opening fall where it may. I'm not trying to confuse you, and my degree specs were just for discussion. Just trying to help. GM usually doesn't provide a lot of detail in ther cam specs, so you may have to go with the intake opening spec@.050 lift. This would be a great time for an aftermarket cam. Hope this helps....
Thread Starter
Teching In
Joined: Jun 2021
Posts: 41
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From: TX Y'all!!
The second way, zero the base circle and go in one direction to pick up .050" off the circle both going up and coming down. If you take two measurements from peak lift, you have more chance for errors/inprecisions to stack up... twice as many measurements, twice as much error or chance for it.
Finding the true TDC is critical. How did you determine TDC? I use a piston stop. The post before mine is the way I would do it, not at max lift. If you have the intake opening spec, say it for *****/giggles, it opens at 30° ATDC (meaning the valve lift is .050" off the seat@30° ATDC, that's what I'd use. However, most people, myself included, consider the intake closing spec most important. If you have that spec, where they give the intake closing spec .050" from the seat@80°BTDC, you can use that, and let the intake opening fall where it may. I'm not trying to confuse you, and my degree specs were just for discussion. Just trying to help. GM usually doesn't provide a lot of detail in ther cam specs, so you may have to go with the intake opening spec@.050 lift. This would be a great time for an aftermarket cam. Hope this helps....
Thanks guys, I'll find tdc again with the stopper this time and try the second method.
Thread Starter
Teching In
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From: TX Y'all!!
Just finished trying it this way and I was able to verify the 190/191 @ .050 on some of the cylinders on the driver side. Number one continuously came back 170 170ish on both intake and exhaust. The others were within a few thousands. I did use the same lifters for each cylinder so it couldn't be a damaged lifter. Maybe im still doing wrong for #1?
The even side head is still on but the rockers and pushrods are out. So that rules out the lifters still inside possibly messing with the reading right?
Anybody else seen seen a factory non vvt cam possibly worn like that before?
The even side head is still on but the rockers and pushrods are out. So that rules out the lifters still inside possibly messing with the reading right?
Anybody else seen seen a factory non vvt cam possibly worn like that before?
Seems odd to me that you don't have consistent readings accross all the lobes of the camshaft. Are you using a solid lifter to check this or lightweight checking springs on the hydraulic lifters?
Thread Starter
Teching In
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From: TX Y'all!!
I have the dial indicator on the edge of the lifter body and ill keep pressure with my finger to ensure the lifter doesn't hang.
