LM7+LS6 cam+shaved heads pushrod question - LS1TECH



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LM7+LS6 cam+shaved heads pushrod question

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Old 01-03-2012, 04:31 PM   #1
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Default LM7+LS6 cam+shaved heads pushrod question

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.
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Old 01-03-2012, 04:37 PM   #2
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Obviously you didn't check with adj pushrod for the correct new length, will never be right till you do, or you can just keep guessing!!!! not!
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Old 01-03-2012, 08:05 PM   #3
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You need to measure. With unmilled heads you would have needed 7.425 pushrods with that cam. You cant guess once you mill heads.
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Old 01-03-2012, 10:08 PM   #4
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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"
right?
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Old 01-03-2012, 11:41 PM   #5
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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?
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Old 01-04-2012, 12:06 AM   #6
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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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Old 01-04-2012, 07:41 AM   #7
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The pre-load in my last post was more of a question, really wasnt sure about the 0.03" thanks for 0.06-0.08.
7.375" long push rod it is, nice that Summit has that exact length.
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Old 01-11-2012, 08:43 PM   #8
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did it work? what pushrods did you get? i am wanting to due the same cam swap in my lm7. any advice would help. thanks
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Old 01-11-2012, 11:48 PM   #9
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^^Measure.
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Old 01-12-2012, 12:12 AM   #10
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anyone used a trickflow pushrod checker? semms like adjusting nuts are too big for pushrod bore
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Old 01-12-2012, 12:26 AM   #11
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I Use one. I always have the heads off when I measure. Take the nut off and use it without it. Put some tape around it so it doesn't turn if it makes you feel better.
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Old 01-12-2012, 12:42 AM   #12
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how are you measuring pushrod length without having the heads on the motor? if there is a way, that would be much easier
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Old 02-05-2012, 08:33 AM   #13
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Quote:
Originally Posted by toez54 View Post
did it work? what pushrods did you get? i am wanting to due the same cam swap in my lm7. any advice would help. thanks
In the post previous to yours I state 7.375" that what I ended up with. Also my adjustable pushrod adjusting nuts fit the head no problem.
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Old 02-05-2012, 10:00 AM   #14
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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.
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