Need some help, measuring PTVC!
09-07-2008, 06:25 PM
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Need some help, measuring PTVC! Ok guys I am in the middle of installing my TEA stg 2 LS6 heads, they have a 2.04I and 1.57E valve and have been milled .020, I am using a stock MLS gasket and as of right now I have about .050 clearance on the exhaust valve (I have not measured the Intake valve yet) BUT I am using the 7.425 pushrods I was using when I was cam only, my question is should I be using STOCK length pushrods to check this instead? Also I am measuring all this using my Yella Terra UL roller rockers.
09-07-2008, 07:25 PM
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Ok guys I am in the middle of installing my TEA stg 2 LS6 heads, they have a 2.04I and 1.57E valve and have been milled .020, I am using a stock MLS gasket and as of right now I have about .050 clearance on the exhaust valve (I have not measured the Intake valve yet) BUT I am using the 7.425 pushrods I was using when I was cam only, my question is should I be using STOCK length pushrods to check this instead? Also I am measuring all this using my Yella Terra UL roller rockers.
09-07-2008, 09:46 PM
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09-07-2008, 09:49 PM
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How are you getting it to zero lash? If you just tighten the rocker down all the way, whatever preload you had is transmitted to the valve side (x1.7 rocker ratio) when using checking springs. You can either tighten the rocker to zero lash (it will be sloppy side-to-side) or use an adjustable length pushrod to get it as close to zero lash/zero preload as possible. You have to set the 0 lash/ 0 preload on the basecircle of the cam, which is the TDC opposite of overlap's TDC (where PtoV is measured).
If your rotating the engine over by hand and have rockers installed, the basecircle of the cam starts after the intake valve closes as the piston is traveling back up, turn the crank until that particular cylinder's piston is at TDC, that's where you can set the rockers up at for zero preload. One more crank revolution from that is overlap (10 degrees before and after TDC) As a side note that's a perfect spot to check lifter preload after you get your PtoV measurements. The feeler gauge method will work fine.
With the YT rockers, it might help to do one at a time if you keep those pushrods and just tighten it down enough to take out the slack. If the valve moves as your tightening it, its too much and will skew your measurements.
One more tip that might help if you have the timing cover off anyway and are checking cylinder #1; Cam dot at 12 is #1 TDC firing position (base circle), with the cam dot at 6, its close to where PtoV is checked (overlap). Although a degree wheel would help too...
If your rotating the engine over by hand and have rockers installed, the basecircle of the cam starts after the intake valve closes as the piston is traveling back up, turn the crank until that particular cylinder's piston is at TDC, that's where you can set the rockers up at for zero preload. One more crank revolution from that is overlap (10 degrees before and after TDC) As a side note that's a perfect spot to check lifter preload after you get your PtoV measurements. The feeler gauge method will work fine.
With the YT rockers, it might help to do one at a time if you keep those pushrods and just tighten it down enough to take out the slack. If the valve moves as your tightening it, its too much and will skew your measurements.
One more tip that might help if you have the timing cover off anyway and are checking cylinder #1; Cam dot at 12 is #1 TDC firing position (base circle), with the cam dot at 6, its close to where PtoV is checked (overlap). Although a degree wheel would help too...
09-08-2008, 08:04 AM
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How are you getting it to zero lash? If you just tighten the rocker down all the way, whatever preload you had is transmitted to the valve side (x1.7 rocker ratio) when using checking springs. You can either tighten the rocker to zero lash (it will be sloppy side-to-side) or use an adjustable length pushrod to get it as close to zero lash/zero preload as possible. You have to set the 0 lash/ 0 preload on the basecircle of the cam, which is the TDC opposite of overlap's TDC (where PtoV is measured).
If your rotating the engine over by hand and have rockers installed, the basecircle of the cam starts after the intake valve closes as the piston is traveling back up, turn the crank until that particular cylinder's piston is at TDC, that's where you can set the rockers up at for zero preload. One more crank revolution from that is overlap (10 degrees before and after TDC) As a side note that's a perfect spot to check lifter preload after you get your PtoV measurements. The feeler gauge method will work fine.
With the YT rockers, it might help to do one at a time if you keep those pushrods and just tighten it down enough to take out the slack. If the valve moves as your tightening it, its too much and will skew your measurements.
One more tip that might help if you have the timing cover off anyway and are checking cylinder #1; Cam dot at 12 is #1 TDC firing position (base circle), with the cam dot at 6, its close to where PtoV is checked (overlap). Although a degree wheel would help too...
If your rotating the engine over by hand and have rockers installed, the basecircle of the cam starts after the intake valve closes as the piston is traveling back up, turn the crank until that particular cylinder's piston is at TDC, that's where you can set the rockers up at for zero preload. One more crank revolution from that is overlap (10 degrees before and after TDC) As a side note that's a perfect spot to check lifter preload after you get your PtoV measurements. The feeler gauge method will work fine.
With the YT rockers, it might help to do one at a time if you keep those pushrods and just tighten it down enough to take out the slack. If the valve moves as your tightening it, its too much and will skew your measurements.
One more tip that might help if you have the timing cover off anyway and are checking cylinder #1; Cam dot at 12 is #1 TDC firing position (base circle), with the cam dot at 6, its close to where PtoV is checked (overlap). Although a degree wheel would help too...
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09-08-2008, 08:46 AM
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Well I just went out there to check again before I leave and I adjusted the YT rocker to zero lash by turning the rocker bolt till I could barely turn the pedestal any and checked it again about ~20 deg before and after tdc and I am getting about .107 on the intake and .085 on the exhaust, does that sound right with a 233/239 112 lsa cam and heads milled .020 with those big valves? I think I should clay too just to be sure.
09-08-2008, 08:16 PM
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The exhaust is right at .080 (no flycut) and the intake is now at .080 after flycutting. Do you guys think the exhaust is ok to run or should I flycut the exhaust side now?
09-08-2008, 08:19 PM
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Unfortunately two things are at work here. One is most people won't say its OK as it is really up to you if you want to run that close. Second, I am willing to bet a lot of guys here, even those with big cams, are running closer and don't know it. In the end, its really your call.
09-09-2008, 08:23 AM
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Unfortunately two things are at work here. One is most people won't say its OK as it is really up to you if you want to run that close. Second, I am willing to bet a lot of guys here, even those with big cams, are running closer and don't know it. In the end, its really your call.
