Valve lash adjustment newbie question

[byrdman]

Hi Everybody,

I recently rebuilt my 1997 LT1 383 motor with the following: All Comp Cams parts in the valve train, K07-466-8 cam (XFI), 850-16 lifters, 1418-16 rockers (Magnum roller tip), 26918-16 springs.

I am using the engine off method (instructions from CC) for setting the valve lash. The documentation that came with the rockers says to add 1/2 turn after finding zero lash.

I can find the zero lash point when turning the push rod with my finger and tightening the adjusting nut, but when I turn the adjusting nut an addtional 1/2 turn the pushrod binds up to the point that I can't even turn it with my fingers. Is this normal?

If have never set valve lash on a motor before, the mechanic who rebuilt the motor set it initially. I have read a whole bunch of good information about the different methods of adjustment, but I haven't seen any mention of how the push rod will feel after the additional pre-load adjustment.

The reason I'm adjusting the valve lash is because the idle has been rough since the fist time I ran the motor after it was rebuilt.

Thanks for any information,

Mark

[DJ_Kovacs]

as you turn the pushrod while tightening the adjusting nut, you will feel a point where there is resistance on the puhrod, this is "zero lash", STOP, then add your pre-load, which is half a turn in your case, and leave it. the reason it feels tight is because the plunger in the lifter is forcing the push rod back up, but after a few minutes, it bleeds down, making the pushrod feel loose again, but DONT add more preload unless you do it all over again by loosening right off again. repeat for the remaining, making sure you go in firing order, and you are good to go.

Perhaps the "mechanic" tightened it down way too much, causing the valve to stay open, making it run like a**. If this doesnt solve your rough idle, you have something else wrong

[steveo]

once you have set the valve, if you wait a few minutes, you should be able to spin the pushrod easily again, with barely any resistance (lifter will soak it up and the pushrod will become fairly slack again)

if that doesn't happen you've probably taken it too far, maybe even bottomed it out

it's really tricky!

a much better way to find zero lash i've found (after screwing it up 20+ times) is:

- tighten them down like hell, even 1.5 turns, so the rod gets pushed fairly far into the lifter and the lifter drains most of its oil, then back them WAY off, like almost to the end of the stud, so there's a ton of room in there. you might even just remove the rockers at this point and set them aside.

- go have a few beers (like 20 beers maybe.. give it an hour if you want to be safe, they might take a while) and come back later, the rods will be fully extended, in fact if your lifters are healthy you can probably put a friggn ruler across them they will be so even

- don't touch the pushrods at all! they're fully extended and are right where they should be. Tighten the rocker nut until the thing just barely touches the end of the pushrod. there's zero. NOW set your preload.

this method only works on lifters that aren't screwed. they have springs that will push them to full extension when there's no load on the pushrod. if there's clogged passages or the spring has collapsed at all, the lifter may still work, but you won't be able to trust it to come all the way back up.

[DJ_Kovacs]

I dont know if i would trust myself to walk after 20 beers, let alone set valves.:lol: not that theres anything wrong with that, but thats alot of steps to adjust valves, and every book, gm, or otherwise recommend adjusting valves the way outlined below, and its pretty fool proof if you take your time. I think in this case, since he seems to be new at setting valve lash, the less steps involved, the better, until he gets his feet wet a little more:thumbsup: Here is a great writeup from shoebox's website, should make it clear as day http://shbox.com/1/4th_gen_tech2.html#adjust_valves

[billla]

I'm reading that you're using the "companion cylinder" method - this is the same approach I use and it works well.

I think you're doing fine; yes, you should not be able to rotate the pushrods with 1/2 turn of preload on them. DJ's description is perfect.

I'd suspect a vacuum leak or a programming problem more than valve adjustment as cause for a poor idle - but it never hurts to check.

Steveo...dude...I'm lost on that approach :)

[CKJ]

Be sure to either put some assembly lube or oil on the pushrod tips. This way you get 100% accurate resistance readings for zero lash.

[byrdman]

Thanks for all the outstanding replies!!!

Now I have a MUCH better idea on what to expect when making the valve lash adjustments!! That's what I will be doing this weekend and I will report back how things went. But I think I should hold off on the beers until after the job is done!:lol:

Thanks again,

Mark

:LS1LT1flag:

[byrdman]

Hi Everybody,

Finished up the valve lash adjustment, everything went very well!!:D Before the adjustment I think some of the rockers were too tight and some were too loose. Now when I run the motor it seems to rev quicker and overall sounds more quiet. Idle still seems to have a misfire though.

To find the zero lash I used a combination of vertical movement and spinning the push rod with my fingers. Overall, it seems as though the adjustments are good becuase of how the engine runs now.:thumbsup:

Thanks again for all your help!!!

Mark

[DJ_Kovacs]

Good to hear!
As far as your misfire, if its all fresh, maybe its just the cam "loping" the way it should. Take it out and have some fun!