bwill03z

What would be the max lifter preload to run on LS7 lifters to be considered safe? The reason I’ asking is because I am currently running 7.400 pushrods with my tsp 228r cam on stock 243 heads and the sewing machine noise is awful. I had a shop measure and I want to say it was a preload of around .085-.090 but I’m not positive. If this is true then would going to a 7.425 be a bad idea? I plan on buying my own adjustable PR tool and checking but I don’t know if mine currently are too long or too short. I believe a higher preload would equal less noise but I didn’t want to be on the red area of excessive wear. Could lowering the preload from what I currently have produce less noise?! If anyone wants a video let me know and I will send one, this is driving me nuts. I have the Straub trunnion upgrade and while it made have quietened overall engine bay motor noise a bit it did not help the sewing machine sound. Just by the sound of my motor holding the rpm’s steady around 2k something has to be off

mykream

Ideally you want to measure preload with a solid lifter (a modded hydraulic lifter works for this). LS7 lifters have a very wide spread pre load range.. Anywhere from .020" to .120" of preload acceptable. Most like to keep them in the .070" range.

DetroitPlac

This is just my experience, and yours may vary...

I'm running a BTR stage 2 cam with LS7 lifters and 243's ported and milled just slightly. I started with 7.4" pushrods and the valvetrain was rather loud. I was measuring pre-load in the same range you are ~.090.

Since pushrods are "cheap" and relatively easy to swap, I ordered a set of 7.375 pushrods from BTR to bring the pre-load down a bit as an experiment. It was almost immediately quieter and has stayed that way for a few years now. Once the oil heats up it gets a bit louder, but not much. It's still noticeable though, my tuner said that's just how cammed LS1s sound.

bwill03z

I’ve heard a few other cammed c5’s and none are nearly as loud as mine. You wouldn’t happen to have a video of yours do you? I considered going down a size also and running a lower preload but assumed that would prob create more noise. With the base circle on this cam being smaller than stock I don’t see how I could possibly need a shorter pushrod... I expect noise and I’m ok with that, but I can’t help but think mine could be much quieter.. just sounds like the valvetrain is too loose. I’ve never tried measuring before but I’m going to give it a shot

DetroitPlac

I tried taking a video once, but I only have a phone to record with and it didn't pick up the noise well. Can barely hear it inside the car, but outside with the window down next to another car or a wall, it's noticeable.

From what I understand, noise has more to do with the lobe profiles (ramp rates) than anything else...my GUESS is that the lifters like a little extra cushion when dealing with higher ramp rates...at least that's how I explain the results I experienced to myself. I bought the new pushrods for $100 from BTR and sold my 7.4's after for $70...so the experiment really only cost me $30.

Have you taken the valve covers off to check to make sure you don't have any loose rockers? I'd start there...check the rockers to make sure they're all tight. A lose rocker can happen and will cause quite a racket.

mykream

I would be curious to know where they checked pushrod length at.

bwill03z

yes, all are good and tight

cylinder 1

mykream

Sorry I didn't specify (technically length should be checked on all valves.) what I meant... I meant did they check it just at TDC? Or did they check it correctly?

bwill03z

TDC I believe... isn’t that how you check?

mykream

No, you use EOIC (Exhaust Opening, Intake Closing)

Basically, when the exhaust is opening, the intake lifter will be on the base circle. When the intake is closing, the exhaust will be on its base circle.

bwill03z

Oh yea I’m sorry I believe that is how they did it.

vettenuts

I would also consider a larger OD pushrod since you may be changing. It will help with high RPM stability.

93Polo

Vettenuts created a few very good topics on here and LS1tech on measuring pushrods and pushrod diameter. 11/32" pushrods are more common now, if you can clear them go 3/8". 243s would have to clearanced for 3/8

DetroitPlac

Excellent point...I wish I had read those threads BEFORE I purchased my pushrods. 11/32" have gotten much more common these days, and would be worth the purchase if changing length. I'm still at 5/16"...which will be fine for my personal use (99% street car).

bwill03z

I believe the pushrods that came with the package are 5/16

DetroitPlac

Probably. That's what most packages come with.

bwill03z

Here is another quick video after I had the new trunnion kit put in, made no difference. To me it just sounds like there is slop in the valvetrain. So can going up or down a size in pushrods really make that big of a difference in noise? Going from the current 7.400 to either 7.375 or 7.425 could potentially clean up the sewing machine sound? Also I have noticed that it is a bit louder on the drivers side than the pass. I have checked and all rockers are tight.. Btw I am buying a pushrod checker today and going to try and get some measurements myself.

DetroitPlac

Starting with measurements is the right place to start. Once you know what your ACTUAL pre-load is, you can decide what makes the most sense. Too high or too low could create bad valve train noise. Completely guessing won't do any good.

helga203

When I changed mine from stock to Ls7 mine quiet it down with 7.4. Seem like it's a hit or miss with these lifters. My cam is close to your. I'm on stock rockes

bwill03z

Alright so let’s say I measure and I am right at the ideal preload with the 7.400 pr’s, what then?! Where would all that noise be coming from? If it’s simply just loud and not causing any premature wear I guess I will just get over it but surely it could potentially be quieter