You learn something new every day,

Ive set valve lash a million times and probably have done it differently each time. Ive never really paid much attention to it. I usually run the motor and loosen the rocker nut till it taps, tighten it till it stops tapping and then add a full turn on a warm motor ( its not dead cold but i usually dont set it when its real hot)

pretty unscientific eh?

I decided to read a section I hadnt read in Dave Vizards "max horsepower small block chevy's on a budget" on lifters and he has an interesting way to set lash that he claims can be worth around 20 hp over the stock method (which is like how I do it but with just a quarter turn) on a warmed over 350.
I couldnt help but think how it might squeeze a few ponies out of a few of the Lo3's on the board. Basically he sets the lash as tight as it can go without keeping the valve off the seat.

the way he does this is he puts a feeler gauge between the valve and rocker (.010 for a cold motor, .006 for a hot motor) attaches a vacuum gauge, starts the engine, idles it between 1000 and 1200. He then tightens the rocker in question until the engine just begins to hang the valve open. You will be able to tell this because the engine will start to idle worse, i.e. lower vacuum, lower rpm. He then backs off just to the point where it no longer is hanging the valve, stops the engine, removes the feeler gauge and moves onto the next valve. The gauge acts as extra clearance beyond the "just enough" point.

basically this takes up the slack in the lifter to where it will go static at higher rpm so it acts like a solid giving you better performance since lift isnt absorbed by the lifter poppet because of oil aeration and such.

Youd probably want to get those little plastic clips they sell to cover the oil holes on the rockers when you do this since 1000 rpm with the valve cover off can be messy with those open.

I also wonder if it would do anything with the pathetically tiny stock cam since I dont imagine it accelerates the lifter that hard but hey it couldnt hurt to try on it considering how conservatively its set from the factory, it might be helpful especially for you LT1 cam guys with 1.6 rockers and aftermarket springs

let me live vicariously through you! try it

 

if you upgrade the cam to a bigger do you have to reset all the valve lashes anyway??

 

I didn't know you could replace a cam withOUT resetting the valve lash.
Good info. Not sure if it's worth anywhere near 20hp on an Lo3 but setting up valve lash for max performance should be everybody's goal. I've always done the till ticking and a full turn.

 

I was told once to go till ticking and then back off 1/4 turn. Tried this and it felt like more power comparied to 3/4 turn back off, so I stuck with it.

 

Actually Ive always set valve lash that way, it's the way my dad taught me to do it.

 

Damn Im the odd man out, I go till it stops chattering then 3/4ths turn Ill try that when I do my rockers.

 

I did mine hot and adjusted a 1/4 turn after tick stop.

5 months later of daily driving hasn't done me any harm.

 

Rocker lash on hydraulics always depends upon the lifter design. Can get into real trouble short lashing stock lifters. High-rev's only require 1/8-1/4 turn past zero.

Get a good set of Isky hydraulics and they will easily go to 7,500 RPM, properly lashed.

As for feeler gauges, do the math on TPI and there is no difference.

RBob.

 

thats what i have done before. does it matter what type of lifters you have?

 

same here

 

btw I hope i didnt imply that i thought 20 hp was possible out of your typical Lo3 from something like this. Warmed over 350 for him was 280 cam, 10.5:1 cr. and nor did he imply that the stock way was bad, he said it was very reliable but not the best for max performance.

just wanted to see if someone would test it out

 

On my 305 I went to ZERO lash and the motor ran great up to 125k. I didnt feel any more power but it ran quiet.