I have a 5.3 LM7 with a swapped in LS6 cam with stock heads were shaved .02" Question is with the stock pushrods it looks like they are too long. Bolted the intake & exhaust #1 cyl rockers & pushrods, cycled the crank and the valves don't completely close. Its about 3/4 turn of the rocker hold down screw from zero lash on the base circle till the rocker is completely seated by which point the valve is open.
My question is 1-pushrods are too long or 2-hydraulic lifters are jammed and do not compress. If someone has done a similar setup did you end up having to get shorter pushrods? Looking for advice on where the issue is, the pushrods or the lifters.
OK so I've measured the intake & exhaust pushrod length on multiple cylinders and I keep coming up with at zero lash is 7.3". Final length would need to include the pre-load which I think is 0.03" which would make final length 7.33"
I used a pushrod length checker and ultimately confirmed it with the below method. My friend suggested this and thinking back, I've done this way for years.
Bring cylinder 1 to top dead center, put the push rods in and rockers on. Tighten rocker bolt until they touch pushrods and you can barely spin rods with your fingers. That's zero clearance and no preload. Tighten rocker arms at normal preload specs they should bottom out at 1-1.5 revolutions. If your outside of 1-1.5 you need different pushrods.
Is it possible the cam is installed improperly?
__________________ 2002 TT 911, Switzer Performance L1 500 HP
Why are you only wanting to run .030 preload. Stock engines run around .080 I believe and I have had great success with running .060-.080 on the engines I've assembled. So 7.300 + say .075 gets you a 7.375 pushrod. Sounds right to me since stocks pushrods are about 7.390 and you shaved .020 off your heads so stock 7.390 - what you milled .020 = 7.370. Simple
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I wanted to add my bit to this. I added a z06 cam to my LQ9 with L92 heads. I was told 7.425 also. I think or thought the heads were not milled (bought used). after using the comp cam magnum checker. I got .15 to .12 shorter (checked all the drivers side lengths will tool) then my 7.4 pushrod. So 7.25 to 7.28 before preload. I added .080 preload and bought 7.35.
__________________ 2000 2wd Jimmy LQ9, L92 heads, 224/230 cam and 2010 Camaro intake! build thread
Dyno'd 374/372' old cam