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What is the diameter of the base circle of the OEM LS1 cam in comparison to the OEM LM7? I installed an LS1 cam in my 5.3L rebuild. I intended to use the factory length pushrods. Maybe I am just not using my Comp pushrod length tester correctly but I can shorten the length checker to almost 1/4" less than the stock pushrods and there is no slop in the rocker when I torque it down.
Yeah. That's what I thought too. Maybe I'm using the tool wrong. I really wish it could be adjusted in place in lieu of having to take the rocker off over and over.
Step 1: Bring the No.1 cylinder up to TDC and Install pushrod length checking tool onto the lifter for the intake
Step 2: Install rocker onto the pedestal and tighten hand tight.
Step 3: Turning the pushrod length checking tool adjuster out and bring it all the way up into the rocker arm to remove all the play which is known as zero lash.
Step 4: Carefully remove the rocker arm and pushrod length checking tool and measure the overall length with a caliper gauge and write this measurement down.
Step5: Repeat steps 2-4 for the exhaust.
This measurement should be fairly close to the same measurement as the intake but once your satisfied in your measurements then you add the proper amount of preload desired and order that length of pushrod. Be sure to state this is the overall length.needed.
If you don't want to determine TDC then use the EOIC method to determine pushrod length.
EO=Exhaust opening "Once you see the exhaust valve begin to open then you know the intake valve for that cylinder is on the base circle of the cam.
IC=Intake closing "Once you see the intake valve begin to start closing then you know the exhaust valve for the cylinder is on the base circle of the cam.
Step 1: Bring the No.1 cylinder up to TDC and Install pushrod length checking tool onto the lifter for the intake
Step 2: Install rocker onto the pedestal and tighten hand tight.
Step 3: Turning the pushrod length checking tool adjuster out and bring it all the way up into the rocker arm to remove all the play which is known as zero lash.
Step 4: Carefully remove the rocker arm and pushrod length checking tool and measure the overall length with a caliper gauge and write this measurement down.
Step5: Repeat steps 2-4 for the exhaust.
This measurement should be fairly close to the same measurement as the intake but once your satisfied in your measurements then you add the proper amount of preload desired and order that length of pushrod. Be sure to state this is the overall length.needed.
If you don't want to determine TDC then use the EOIC method to determine pushrod length.
EO=Exhaust opening "Once you see the exhaust valve begin to open then you know the intake valve for that cylinder is on the base circle of the cam.
IC=Intake closing "Once you see the intake valve begin to start closing then you know the exhaust valve for the cylinder is on the base circle of the cam.
Hope this helps!
It can't be done as far as I can tell. #1 is at TDC. I left it there when I put the heads on. My fingers cannot fit under the rocker well enough to spin it. And when I do spin it the whole tool turns. There is nothing to stop the body of the tool from spinning with the upper portion.
Yeah it is kinda tricky but I was able to take my left index finger to hold the base of the tool while taking my other thumb or index to move the adjuster.
Its important to make sure the rocker arm is fully seated in the pedestal before determining PR length. The LS1 lifters like between 0.08 to 0.10 of preload so if my math serves me right and your using the Comp Cams 7702 PR length checker that is 6.80 fully closed you should be at zero lash and fully seated on the rocker pedestal with 10 turns out on the adjuster. Assuming that 7.40 is the correct length needed.
Yes, that is the tool I'm using. There are a handful of different articles on how to measure the length. They go back and forth on the best way to accomplish it. The book I'm using as a reference to rebuild the engine calls for 0.060" of preload
TDC is NOT the place to have the engine at for measuring for push rod length.
The EOIC method is MUCH better.
DO NOT use the "twist the push rod" method of finding zero lash. Your measurement will be wrong EVERY TIME.
Torque on the rocker bolt, and the point in the cycle that you torque it, is mostly IRRELEVANT. The entire bolt arrangement is metal to metal; there is no gasket crushing, metal bending, spring tension, or any of that. All that the torque does is seat the rocker trunnion in the rail. It's only that particular value to make sure the bolt is "tight enough" but not "too tight" (in fact it's just the "standard" torque for that hardware size, not some kind of special number), and the only reason for doing it at any particular point in the cycle is to make sure that the valve spring compression from an opening valve doesn't confound it, and make you leave it loose with the trunnion not seated. Don't get all hung up on it.
Instead, use the EO and IC method of locating the base circle (int is on the base when exh is just opening, and exh is on the base when int is just closing). Adjust your push rod to some convenient length that's close but virtually certain to be just a little too short; say, 7.25". Install it. Grease the rocker bolt threads. Install the rocker. Check for play in the ROCKER, not the push rod. If there is any, unbolt the rocker, lengthen the push rod .025" (that being the increment you can buy them in), which is exactly ½ turn, and try again. Or even, a full turn, if there's LOTS of play. (probably won't be) Keep doing that until you find the closest length you can buy (even .025" ½ turn increments) that almost takes up all the play. Add your desired preload to whatever length your adjustable is, and buy that length. I like to check both valves on 4 cylinders, at the corners; 1, 2, 7, & 8.
I use that same Comp tool. Can't even tell you how many engines I've built with it. Works great. It's 6.800" when screwed all the way in; then exactly .050" per turn from there. (its threads are ¼"-20) 7.25" is 8½ turns out. You don't even have to measure anything or know what the length or diameter of anything is; just count the turns.
A stock LS1 has approx .200 preload. Or whatever two full turns of the rocker bolt is past zero lash (I forgot the exact preload number). The other LS engines are the same.
You're gaining nothing by setting it differently.
A stock LS1 lifter has about .100" of plunger travel. It wants about .050" of preload.
A stock LS7 lifter (the most common one people buy these days) has around .150" of plunger travel. It wants about .075 - .080" preload.
I've never in all the engines I've ever built, seen a lifter that had .200" - almost A QUARTER OF AN INCH - of plunger travel, LET ALONE wanted that much preload.
2 turns on the rocker bolt doesn't sound right. The "turns of the bolt" deal has never been a particularly good way, for me, to measure push rod length to get the right lifter preload in a LS motor. I don't ever do it that way. But... the rocker bolt has a 1mm thread; 1mm is .03937" (call it .040" to keep it simple), 2 turns is .080" at the trunnion, which after the multiplication from the rocker ratio is about .125" on the push rod. That's too much. That would BURY the plunger in a LS1 lifter and then hang the valve open around .040". It would "work" on a LS7 lifter but would tend to pump up more than it should at high RPM.
I've got two ls1 cars that are bone stock. One with 118k miles one with 53k. They both go two turns past zero lash. One had the lifters changed under warranty at 16k. And four spare truck engines I have for future projects have the same 1 3/4 to 2 turns.
I know this because I ran into a problem during a build and checked every ls engine I own. I checked with that same pr length checker and a caliper and a dial indicator.
Like I said it's two turns. I have it wriiten down at home how many thousanths preload that is.
I also have a quote on this site where someone who works for a sponsor of this site thinks that one turn equals .047 which it doesn't. But he insists that he's done 3 or something cam swaps a week for years and turns the bolt 1.5 to 1.75 turns and no one has had a problem.
The numbers are the numbers. I don't have to "have a quote" or "look them up" or even "have them written down" (although I just did). I just gave them to you. They are what they are. :shrug: But I don't even bother trying to use the turns on the bolt method, I don't like it, I prefer to select the correct PR length by measuring directly as I described above, but that's just me, so go ahead and do whatever works for you.
Yes you can just install the rockers with whatever push rods you just happen to have, stock or otherwise, and not even bother checking their length, and yes that will work perfectly fine sometimes. But sometimes not. And if it doesn't, … then what? That's why meticulous people, especially those who understand numbers, always prefer to check these things first, and make them right so that there is no opportunity for error.
04-09-2020, 05:43 PM
LS1 vs. LM7 Cam Base Circle 
They have more tools than I do though. I'm jealous.