Checked piston to valve clearance. Having issues
Thread Starter
Launching!
Joined: Nov 2008
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From: Pembroke pines FL
Checked piston to valve clearance. Having issues So I'm swapping a cam into my 2002 z06. The cam is supposed to be 228/230 .571/.573 112 LSA. I mocked the stock heads to check piston to valve clearance and they seem to be touching. There are small visible marks on the piston let alone the clay was cut. This was worrying me but then I remembered that the valves on the 02 z06 are supposedly 0.6mm taller(about .024") to compensate the lower base circle on ls6 cam. I have an adjustable pushrod but am not sure what length it should be. My questions are for those of you who have done cam on a 02-04 ls6, what length pushrod did u use? Also does this sound right? Am I overlooking something? I wouldent think that the 0.6mm would cause ptv issues with this relatively small cam.
I did use a weak toilet paper roll spring to hold up the valves so the hydro pic lifter won't be collapsing, could this be an issue?
I did use a weak toilet paper roll spring to hold up the valves so the hydro pic lifter won't be collapsing, could this be an issue?
I prefer to measure the PTV with check springs and a dial indicator. However, a solid lifter also should be used as stated above to ensure you are not depressing the plunger at all which will skew the results. Adjustable is set to zero lash.
Are you installing a head gasket during the measurement? Re-use the original if you are using the GM replacements. If you are using Cometic 0.040" gaskets, then remove one of the thin layers from the original GM MLS gasket and that should give you close to 0.040" of gasket thickness.
Are you installing a head gasket during the measurement? Re-use the original if you are using the GM replacements. If you are using Cometic 0.040" gaskets, then remove one of the thin layers from the original GM MLS gasket and that should give you close to 0.040" of gasket thickness.
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
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From: Pembroke pines FL
I am using the head gasket that came out of the car. I havent checked the thickness against the GM MLS gasket. As I said before, im not using the valvesprings when checking. I am using a very weak spring out of a toilet paper roll holder thing. I doubt that could be depressing the lifter and if it were then it should mask the piston to valve clearance issue.
I am starting to think if it could be that my timing set is off, but I am certain that the dots lined up right. if it were off, can they even line up? this is a picture that I took when I did it. Im starting to think maybe the previous owner milled the head. I took one of the pushrods out of the car to measure to see if its shorter because if it is it could mean the heads were milled.
but again its confusing because most people believed this cam should clear a .030 milled head...
I am starting to think if it could be that my timing set is off, but I am certain that the dots lined up right. if it were off, can they even line up? this is a picture that I took when I did it. Im starting to think maybe the previous owner milled the head. I took one of the pushrods out of the car to measure to see if its shorter because if it is it could mean the heads were milled.
but again its confusing because most people believed this cam should clear a .030 milled head...
Are you turning the car over with the clay and it's touching the piston? You shouldn't be unless your pushrods are really far off and holding the valve open. If you have a dial indicator, you can install on the retainer, zero it out, depress the valve and measure the distance til you hit the valve as you turn the motor over slowly. A degree wheel would be handy there so you can check at 1 degree intervals from 10 BTDC through 10 ATDC.
Btw, you're dot-to-dot is closer than mine... but that means nothing. I degreed mine and I was off half a degree on IVC. 107.5 vs the stated 108 of the cam.
Btw, you're dot-to-dot is closer than mine... but that means nothing. I degreed mine and I was off half a degree on IVC. 107.5 vs the stated 108 of the cam.
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
Are you turning the car over with the clay and it's touching the piston? You shouldn't be unless your pushrods are really far off and holding the valve open. If you have a dial indicator, you can install on the retainer, zero it out, depress the valve and measure the distance til you hit the valve as you turn the motor over slowly. A degree wheel would be handy there so you can check at 1 degree intervals from 10 BTDC through 10 ATDC.
Btw, you're dot-to-dot is closer than mine... but that means nothing. I degreed mine and I was off half a degree on IVC. 107.5 vs the stated 108 of the cam.
Btw, you're dot-to-dot is closer than mine... but that means nothing. I degreed mine and I was off half a degree on IVC. 107.5 vs the stated 108 of the cam.
this may be a dumb question but when its dot to dot it should also be top dead center correct? shouldent the cam be on the base circle of both intake and exhaust at that point, because it looks like its about to open the two.
If I recall correctly, Cylinder 6 and 1 are both at TDC when the Crank is at 12 o'clock and either on the compression or exhaust stroke relative to the camshaft gear position (6 o'clock means exhaust stroke for Cyl 1 and compression for 6 and vice versa). So Cylinder 6 would be on the base circle, since both valves should be shut on the compression stroke.
Last edited by JakeFusion; Nov 13, 2013 at 09:26 AM.
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Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
Can someone who has done a cam swap on an LS6 chime in? My understanding is that the base circle on the ls6 cam and an aftermarket cam should be the same, so wouldent the stock 7.4" pushrods be the correct size? or should it be shorter to compensate for the longer valve stem?
Also is there another way to tell if the heads were milled, and is it safe to assume when I measure the pushrods that came out of the engine, if they are shorter than 7.4 that the heads were milled? I havent measured them yet, need to get my hands on a 8" caliper
Also is there another way to tell if the heads were milled, and is it safe to assume when I measure the pushrods that came out of the engine, if they are shorter than 7.4 that the heads were milled? I havent measured them yet, need to get my hands on a 8" caliper
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
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From: Pembroke pines FL
When you say same length pushrod as LS1, do you mean stock LS1 length 7.4" or same as what an LS1 would use in a cam swap? what is typical for LS1 pushrod length on aftermarket cam? the LS6 valve stem is 0.6mm which is about .024" so that is considerable but I am not sure if that is the problem I am having.
What were you using when you checked it? Are you sure you were at 0 lash? If you use the stock pushrod and tighten down the rocker with checker springs you are opening the valve.
Lets say your setup will have .050 lifter preload. If you tighten the rocker arm with a checker spring it will open the valve .050...causing .050 less ptv clearance.
Lets say your setup will have .050 lifter preload. If you tighten the rocker arm with a checker spring it will open the valve .050...causing .050 less ptv clearance.
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
What were you using when you checked it? Are you sure you were at 0 lash? If you use the stock pushrod and tighten down the rocker with checker springs you are opening the valve.
Lets say your setup will have .050 lifter preload. If you tighten the rocker arm with a checker spring it will open the valve .050...causing .050 less ptv clearance.
Lets say your setup will have .050 lifter preload. If you tighten the rocker arm with a checker spring it will open the valve .050...causing .050 less ptv clearance.
FWIW i measured the stock pushrod and got 7.399 so yeah its basically stock 7.4 pushrod.
There's your problem. You're opening the valve. You need to only run the rocker arm bolt down until you have zero lash or use your pushrod length checker and adjust it until you have zero lash.
Thread Starter
Launching!
Joined: Nov 2008
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From: Pembroke pines FL
I have heard that the preload on the lifter is .050 before, so the idea here is, using the weak springs, the lifter is adding .050" to the lift?
Thread Starter
Launching!
Joined: Nov 2008
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From: Pembroke pines FL
should I be doing this on the base circle of the cam or at top dead center. As Jake Fusion said before and as I was suspecting, when its dot to dot, the cam for cylinder 1 are not on the base circle. I can clearly see the cam through the lifter holes so I can move it to a point where its on the base circle and conduct the test.
Zero lash is when you dont have any lash in the valvetrain. Thats means the lifter is touching the cam, the pushrod it touching the lifter, the rocker arm is touching the pushrod and the valve tip is touching the rocker arm. You just want to take out all the clearance. If you go past 0 lash something has to move and in this case its the valve.
The best way to do it is use the pr checker and adjust it to zero lash while on the base circle of the cam. For a quick check just run the bolt down until 0 lash. I've tried it both ways with no difference in the measurement.
To find the base circle of the an intake lobe I always turn the engine until the exhaust valve of the same cylinder just starts to open. For the exhaust lobe I turn the engine until the intake lobe is on the closing side.
The best way to do it is use the pr checker and adjust it to zero lash while on the base circle of the cam. For a quick check just run the bolt down until 0 lash. I've tried it both ways with no difference in the measurement.
To find the base circle of the an intake lobe I always turn the engine until the exhaust valve of the same cylinder just starts to open. For the exhaust lobe I turn the engine until the intake lobe is on the closing side.
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
Zero lash is when you dont have any lash in the valvetrain. Thats means the lifter is touching the cam, the pushrod it touching the lifter, the rocker arm is touching the pushrod and the valve tip is touching the rocker arm. You just want to take out all the clearance. If you go past 0 lash something has to move and in this case its the valve.
The best way to do it is use the pr checker and adjust it to zero lash while on the base circle of the cam. For a quick check just run the bolt down until 0 lash. I've tried it both ways with no difference in the measurement.
To find the base circle of the an intake lobe I always turn the engine until the exhaust valve of the same cylinder just starts to open. For the exhaust lobe I turn the engine until the intake lobe is on the closing side.
The best way to do it is use the pr checker and adjust it to zero lash while on the base circle of the cam. For a quick check just run the bolt down until 0 lash. I've tried it both ways with no difference in the measurement.
To find the base circle of the an intake lobe I always turn the engine until the exhaust valve of the same cylinder just starts to open. For the exhaust lobe I turn the engine until the intake lobe is on the closing side.
Some people will disagree but I think you would be fine just running the bolt down to zero lash. If you already have a pushrod checker just do the intake and exhaust one at a time. To get an accurate reading you should really use a solid lifter.