push rod length check question
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,087
Likes: 4
From: granville mass
push rod length check question
I changed the cam to a pretty mild Pat G recommended EPS cam and did the heads on my LS7, and have been trying to find my way to the right PR length. Right now I'm short based on the turns to torque method when on the base circle of the cam. I can't use that method to determine the correct length because I'm near zero preload when the rocker torques down.
I bought a PR length checker, thinking it was marked, but it's not, it's just a jack screw in the middle.
My understanding is that PR are not measured end to end, but from a gage diameter on the spherical ends. So if I use the checker, get to a length I want, how do I turn it into PR length?
I bought a PR length checker, thinking it was marked, but it's not, it's just a jack screw in the middle.
My understanding is that PR are not measured end to end, but from a gage diameter on the spherical ends. So if I use the checker, get to a length I want, how do I turn it into PR length?
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,087
Likes: 4
From: granville mass
Melting Slicks
Joined: Jun 2006
Posts: 2,497
Likes: 261
From: Miami Florida
If you only change the cam and did not milled the heads your push rod length should not have change, if you want to know the lash to push rod binding, install a rocker arm and tight it down as usual then with the valve in close position use a leverage arm of some kind to push down the rocker with a dial indicator on top of the rocker arm tip just above the valve stem to see how mush the rocker travel till binding.
If you have 0.020 or more you are good.
The length is measure from tip to tip or overall length.
I use a 12" dial caliper to correctly measure push rod length.
An adjustable push rod is best used in conjunction with a soft spring sold for this purpose although is not necessary if you can get a leverage arm some how made for this purpose.
If you have 0.020 or more you are good.
The length is measure from tip to tip or overall length.
I use a 12" dial caliper to correctly measure push rod length.
An adjustable push rod is best used in conjunction with a soft spring sold for this purpose although is not necessary if you can get a leverage arm some how made for this purpose.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,087
Likes: 4
From: granville mass
for the length checkers that are not marked in turns or with a specific beginning length, like the one I have, Comp Cams technical line said take .033" off the overall length.
Guess I'll give that a try, not feeling great about it though.
Anyone else?
Guess I'll give that a try, not feeling great about it though.
Anyone else?
Melting Slicks
Joined: Aug 2000
Posts: 2,327
Likes: 44
From: Sacramento CA
If you only change the cam and did not milled the heads your push rod length should not have change, if you want to know the lash to push rod binding, install a rocker arm and tight it down as usual then with the valve in close position use a leverage arm of some kind to push down the rocker with a dial indicator on top of the rocker arm tip just above the valve stem to see how mush the rocker travel till binding.
If you have 0.020 or more you are good.
The length is measure from tip to tip or overall length.
I use a 12" dial caliper to correctly measure push rod length.
An adjustable push rod is best used in conjunction with a soft spring sold for this purpose although is not necessary if you can get a leverage arm some how made for this purpose.
If you have 0.020 or more you are good.
The length is measure from tip to tip or overall length.
I use a 12" dial caliper to correctly measure push rod length.
An adjustable push rod is best used in conjunction with a soft spring sold for this purpose although is not necessary if you can get a leverage arm some how made for this purpose.
If the new cam has a different base circle than the OEM, wouldn't that require a different PR length??
TIA
Melting Slicks
Joined: Jun 2006
Posts: 2,497
Likes: 261
From: Miami Florida
Interesting>>>>
So a pretty mild cam from Pat G- and what in wonderland is the real chance of an altered base circle on a mild cam?
Ah by the way the lifters don't ride on the base circle but on the cam lobes and these cam lobes are design to replace ls engine cam with ls cam lobes characteristics, so yeah it should be the correct base circle.
Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,087
Likes: 4
From: granville mass
So a pretty mild cam from Pat G- and what in wonderland is the real chance of an altered base circle on a mild cam?
Ah by the way the lifters don't ride on the base circle but on the cam lobes and these cam lobes are design to replace ls engine cam with ls cam lobes characteristics, so yeah it should be the correct base circle.
Ah by the way the lifters don't ride on the base circle but on the cam lobes and these cam lobes are design to replace ls engine cam with ls cam lobes characteristics, so yeah it should be the correct base circle.
I am very clear that I need to make pushrod measurements on the base circle. Measuring on TDC may work for some cams but will not work for others, including mine, which measured different at TDC than at the EO/IC method.
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Thread Starter
Melting Slicks
Joined: Feb 2005
Posts: 2,087
Likes: 4
From: granville mass
Wisdom is that if you change the cam, lifters, have your valves reseated (read this everyone who has had their guides done), or milled the heads, you should check PR length.
In my case I had the guides redone, which requires the valves to be reseated and sinks them into the head, the head was then milled to adjust the chamber volume, and of course I have a new cam.
