pushrod question
pushrod question Im a newb to the lsx stuff, im used to setting lash on SBC's so bear with me. Everyone talks about setting the lash using the pushrod length which makes sense to me, but the amount of change seems excessive. With older small block chevy's as im sure most of you know, stock length PR's is fine more often than not as long as the valve train geometry stays good and you aren't using a small base circle cam, shaved heads and decked block or angled valves ect....you get the point.
Why do these lsx motors require adjustment with even the smallest aftermarket cam...or am i wrong in saying that? How large a cam can i go using stock (length) pushrods.
I have searched and cant really find anything on the topic, id appreciate it if someone could shed a little light on the subject.
Why do these lsx motors require adjustment with even the smallest aftermarket cam...or am i wrong in saying that? How large a cam can i go using stock (length) pushrods.
I have searched and cant really find anything on the topic, id appreciate it if someone could shed a little light on the subject.
Registered User
Joined: Mar 2004
Posts: 199
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From: Austin, Texas
If you don't change heads, machine your heads or block you shouldn't have to change pushrod length just because you go with a bigger cam.
The problems start when you switch heads or machine the deck surface of the heads or block. Basically if you change the height between the rocker arm pedestal and the base circle of the cam you will have to change pushrod length, more than likely. Unlike the SBC the LSx motors have non-adjustable rocker arm. The rocker arm bolt torques to the head, the only way to adjust it is to shim it.
Which is why you need to get the correct rocker arm geometry by shimming the rocker arm then measure for pushrod length. Just make sure you have the correct preload on the lifters you're running.
The problems start when you switch heads or machine the deck surface of the heads or block. Basically if you change the height between the rocker arm pedestal and the base circle of the cam you will have to change pushrod length, more than likely. Unlike the SBC the LSx motors have non-adjustable rocker arm. The rocker arm bolt torques to the head, the only way to adjust it is to shim it.
Which is why you need to get the correct rocker arm geometry by shimming the rocker arm then measure for pushrod length. Just make sure you have the correct preload on the lifters you're running.
TECH Resident
Joined: Jan 2003
Posts: 855
Likes: 0
From: AUSTIN TX
On the older SBC, you used the rocker nut to adjust your lifter preload/valve lash and only used different length pushrods to change your geometry (swipe pattern). Now with the LSX's you no longer have an adjustable valvetrain so we use different length pushrods as a way of adjusting our valvetrain (setting preload). This works more often than not but it is still a good idea to check your swipe pattern to be sure you have not altered it too much. If so then you end up shimming the rockers along with using different length pushrods to get it right.
As a result, the valvetrain geometry changes and the lifter preload is reduced (if you use stock length pushrods). To correct this, you increase the pushrod length, generally to 7.425 or 7.450 to get the proper lifter preload.
If you don't have proper length pushrods, you probably won't have catastrophic engine failure, but most people get a "sewing machine" sound that is pretty annoying.
alright, so its just as i thought. All the same factors affect it as they do on older motors like im used to.
I guess i was just a little taken back by reading all the posts and threads about people using different length PR's. It was always a given to check it with our old motors but nobody really talked about it, it just seemed like a bigger deal with these lsx motors.
Thanks for the insight, it cleared up a few misconseptions i had.
I guess i was just a little taken back by reading all the posts and threads about people using different length PR's. It was always a given to check it with our old motors but nobody really talked about it, it just seemed like a bigger deal with these lsx motors.
Thanks for the insight, it cleared up a few misconseptions i had.
