So, it's going to be 110 in Phoenix today (but it's a dry heat), and I'm inside just reading threads and trying to learn stuff. Most lifters (without limiters) have a travel of .200, and the normal suggestion is to pre-load the lifters to half of its travel, which is .100. Many suggest pre-loading more, such as .140 for example to reduce valvetrain noise. I can understand it might make an initial difference at start up, but when the hydraulic lifters are pumped up, it should even out. So, mechanically, how does pre-loading lifters deeper make the valvetrain quieter?

 

There’s more pressure on the lifter and pushrods so less vibration lash noise.

 

All hydraulic lifters have a specific bleed rate, in another words spring pressure is usually stronger than the hydraulic fluid in the lifter body which will allow oil to be pumped up to the rockers.. if a lifter pumps up all the way and does not bleed down when lifting the valve open there is a good chance that valve may come in contact with a piston.. Over revving a motor could float the valve allowing the lifter to pump up and cause contact with a piston... Now all cylinders grow when they get up to temp. I don't know how much they grow but they do. So as the temp goes up the preload goes down. But there are other things that can cause lifter noise or ticking, one being a week valve springs.. or even worn rockers where the pushrod mates.. but mostly a .140" preload it's used when high lift aggressive ramp cams are used. It definitely will help to quiet things down..

 

lmao! I absolutely hate that dry heat expression.....

 

Hotrod is all over it, use to know the amount of thermal growth on a Harley but can't remember it like a lot of things anymore.

 

Hot Rod Nailed it... I strive to set up adjustables, in the center... if bleed down is a problem, resulting in noise, even if only one lifter is bleeding down too fast, add more compression...
Edit; I think you will find that most adjustable pushrod users are Ex-Shovelhead guys... ya get accustomed..
I prefer non Adjustables as I have had failures at the Threaded portion.. but, Some of my equipment gets "borderline abused"
Custom length Pushrods are out there... non adjustable..

 

hi racepress, I'm also trying understand lifter preload.... If I take my top end off for a rebuild, pistons, ev27 cam etc but don't mill the heads, and I decide to re-use the stock pushrods (low mileage).... How do I go about setting the preload to 140?
Thanks for any advice.

 

You don't, stock pushrods = non adjustable.

 

If your not going to machine any surfaces, and If the engine is stock, it should have about .100" preload.
Then going from stock head gaskets to .030" Cometics will gain about .015", if your pistons are in the hole enough to use Cometic .010" base gaskets, you gain another .005" or .010", so your at or near .125"., which should be OK.

 

Thanks Schex, yes Cometic .030 HG and base gasket and pistons zero decked.

So if there is no adjustment to the pushrod, what I need to adjust or set to proper tolerances when I'm putting the heads back together? Just follow the manual as per reassembly?

also, I guess the downside of not having adjustables is that if I get a lot of valvetrain noise with the ev27 I can't really adjust preload and quieten it down....
Thanks