Unexpected preload measurments on LS7
07-14-2013, 03:16 PM
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Unexpected preload measurments on LS7 I have an LS7 that is basically stock internally except for the cam and valve springs. The cam has .655" lift with stock rockers and PSI springs. The pushrods, lifters, and rockers are all stock. The cam is supposed to have .030" smaller base cir (.015" less on the radius). Based on the smaller base circle, I was expecting to have too little preload. I've been told that stock is about .060" preload so I was expecting about .045" preload. Instead I am measuring about .100" to .110" preload on all valves. Anyone have an idea of what is going on here? The pushrod checker I am using has the same 5/16" ball as the stockers and it has the stock 7.8" pushrods installed. Engine runs fine, but does have a little bit of the sewing machine sound. Nothing real loud though.
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07-14-2013, 03:45 PM
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Stock preload on my bone stock LS7 is about .125 - .130 so the numbers you're getting sound perfect.
Edited to clarify: I checked the same way you did... measured pushrod checker, compared to OEM pushrod. I know of another gent that checked his stock cammed LS7 via calculating the rocker bolt thread pitch, he came up with about .142 preload. GM apparently runs them pretty deep. As a hobbyist, and not a pro, I'd be happy with the .100 that you're getting.
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Edited to clarify: I checked the same way you did... measured pushrod checker, compared to OEM pushrod. I know of another gent that checked his stock cammed LS7 via calculating the rocker bolt thread pitch, he came up with about .142 preload. GM apparently runs them pretty deep. As a hobbyist, and not a pro, I'd be happy with the .100 that you're getting.
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Last edited by Mark200; 07-14-2013 at 05:06 PM.
07-15-2013, 07:09 PM
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Stock preload on my bone stock LS7 is about .125 - .130 so the numbers you're getting sound perfect.
Edited to clarify: I checked the same way you did... measured pushrod checker, compared to OEM pushrod. I know of another gent that checked his stock cammed LS7 via calculating the rocker bolt thread pitch, he came up with about .142 preload. GM apparently runs them pretty deep. As a hobbyist, and not a pro, I'd be happy with the .100 that you're getting.
.
Edited to clarify: I checked the same way you did... measured pushrod checker, compared to OEM pushrod. I know of another gent that checked his stock cammed LS7 via calculating the rocker bolt thread pitch, he came up with about .142 preload. GM apparently runs them pretty deep. As a hobbyist, and not a pro, I'd be happy with the .100 that you're getting.
.