I am about to install an MS4 cam into my ls1 with 243 heads and i dont know what the length of the pushrods would be

 

For that cam you should be checking for ptv clearence first off. Let's say on stock un modded heads you may stand a chance of going with the recommend size that TSP gives. In the end due to the type of rocker you run the pushrod length becomes very important.

 

MEASURE How many times do we have to repeat that same thing.

 

Every time a newbie picks up a cam, it seems...

 

These threads do come up alot, yes. But are you really helping the guy out by just telling him to measure. It's pretty safe to assume that most know measuring is the best way to go. Truth is though there are alot of guys out there running similar combos and if someone can share what they learned on their setup with someone so be it. It could be kind of a PITA to order everything you need for doing a cam swap in a afternoon and then having to stop in the middle of it and order new pushrods now making your one afternoon job into a week long job.
If someone is running a off the shelf cam on pretty much standard heads I am sure there are those out there that would not mind sharing what they learned about pushrod length. There's no limt to the number of threads we can have about a similar topic. How I see it anyway.

 

One engine to the next, same cam being swapped, can be a SIGNIFICANT change in pushrod length required! While getting input from someone else on the forum with the same combo might give some folks a "warn and fuzzy" feeling of confidence, you must consider who is responsible for the shipping charges back and forth and delays of swapping out pushrods for the correct length.

 

ok.. Exactly how do you measure? I'm actually used to solid rockers in Honda's and pretty good at lash. This hydraulic sloppy **** has me all confused. (Kinda backwards right?) how the hell do you measure a length that collapses when you push on it? And who's to say if it's not already fully collapsed? My specific example. MS4 cam. Fully Ported LS6 heads, LS7 lifter.. (NEW, never seen oil pressure) I have the Comp cams length checker #2 part #7702-1. Please don't just tell us (newbs) to measure..(Predator......) Tell me how to measure and under what conditions.

I get the (mark the end of valve, see where it rubs) thing. ok.. what happens after i start the car and the pressure rises and now the lifter is running in an expanded position. I miss solid. everything is so concrete.

 

By not pushing on it. You're looking for zero lash, it requires a gentle touch when turning the rocker bolt.


The lifters have a spring under the plunger, so if it's collapsed it's broken/damaged/defective.

 

Quick answers.. great. Thank You.

But isn't there a squishy zone in between spring bottomed out (not actually broken and collapsed) and fully expanded that needs to be addressed? Oil pressure / no oil pressure differences in height?


I did read something in Tony Mamo's (AFR) Darth Vader build thread. Here's a quote..

"try to focus on airflow and efficiency and hit ALL the small details (perfect ring gap, cylinder wall sizing and finish, bearing clearance, focusing on windage loss reduction, degreed cam, lifter preload, pushrod selection, etc."


Could you explain Lifter Preload?

- obviously its preloaded. (I'm google-ing that for me as you read this) And I'm sure there's more than one theory? How, how much "preload", why etc.

It just seems there's so much more to consider in this than just "measure" whats there. I feel like the "measure it" statement is asking me to find out what a bearing clearance is when the bearing is made out of foam. ( for lack of a better example)


whew.. yep.. just As i thought.. no one agrees. lol. Here's the best advice I have found so far on the pre-load length. (base length barely touching + "0.0XX")

From Cunningham Motorsports, "...I shoot for .080"-.095". remember you guys have to take into account that when an all aluminum motor fully warms up the preload may reduce .007-.011", because of expansion of the aluminum due to heat......... just some food for thought guys"

Which Sounds like quite solid advice. So my question is.. What is GM's Spec (tolerance) on the LS7 Lifter preload, and at what temp? Warmed up or cold. (google-ing now) And i still don't have an answer to what is the exact way to measure a brand new lifters "Zero" lash length. (Just barely touching with no load- as close to anyway) is soaking them in oil overnight enough? Should they have oil pressure before measuring? (fully expanded) etc.. And I'll probably find that it depends on each batch of lifters and crazy no way to measure stuff like that.

Quite a bit later... I'm convinced no one knows. lol But.. I have a better understanding, just no closer to a solid yes or no. It seems since I will be running high rpm most of the time, 4-7K RPM (road race) I need to watch out for the lifter to "pump up" which affords me less preload "room." Otherwise it will pump up past the preload point and become like a solid lifter causing everything to bend or break. I'm coming to the conclusion that I should preload as little as possible. (still preloading enough to keep everything touching at low rpms of course) This is my newb conclusion. And realizing that LS7 (none of the others) lifter preload needs to take things into consideration like expected RPM, oil viscosity (bet you didn't think of that one...) And expected oil pressures - relative to rpm of course.

Here is a quote from a quote on another Forum. I liked the information, yet incomplete in ways. It is more complete than most.. \ Almost makes me wonder what a fully collapsed LS7 lifter length is (and is that number consistent between all LS7 lifters...) and just work with that number.

This is from from Katech on lifter preload:

1) The only way to properly check (and know where you are in the travel) is
to use a special checking lifter or completely compress a stock lifter.
a) Checking lifter consists of a lifter that has been disassembled
to install shims that lock the plunger at the top of travel in the lifter body.
If using this method you would add length to the checking pushrod to put the
final pushrods into the middle of travel of the plunger.
b) Using a stock lifter, you must make certain that you have pumped
all the oil out of the lifter. To do this leave it at valve full open (highest
spring load) for a while with an indicator on the pushrod side of the
rocker. Watch to see when the indicator stops moving (when the plunger is
fully compressed in the lifter body). Once you have compressed the lifter
rotate the engine to close the valve, extend your checking pushrod to full
length. Using this method you will subtract length from your checking
pushrod to put the final pushrods into the middle of travel of the plunger.

2) Typical plunger travel on Gen 3/4 lifters is 0.150 - 0.200 depending on
the manufacturer, year, etc. We recommend 0.075-0.100" from the bottom of travel (using method 'b' described above) or 0.075 from the top of travel (using method 'a' described above). That will generally put you close to the middle of travel. While there are many different strategies for where to put the plunger, for street use we strongly suggest that near the middle of travel is the safest for durability.

3) The more precise method of checking is 'a' because you are not guessing
that you got all the oil out.

I think I'm done confusing myself and others. I'm going to sleep on this. night.