So I got some valve covers and cut them up. Have them installed so I can adjust the valves.
So the first one I started loosening started clacking but then quieted down by the time I got to switch the wrench direction. Loosened again, clacked ..same thing. It quieted down.....,tried again, same thing. I just shut it down because I'm not sure if this is normal.?
This is with taking the socket off every time. Truck at full operating temp.... There's really good oil flow so I'm worried it's quieting down from that and I'm not listening right?
Obviously don't want to remove the rocker nut..
Any advice??
Thanks!
NOTE: Answer to your question at bottom. What you described makes sense to me,
just have to define some mechanical relationships so that we can discuss why this is happening.
****
Hmmm. I think I know what's going on, but this is one of those things that
will be a bit hard to describe with the written word, so bear with me. Note: This
is also a little bit tricky to pick up the first time or two that you try it, but if you
persevere then this is a very, very powerful diagnostic for sorting out exactly what's
going on with a pushrod engine with individually adjustable hydraulic lifters.
Before I go any further, you may uncover valuable adjustment/misadjustment data
that can be used later on for misfire troubleshooting/resolution. So I need you to
have a pen and paper handy to write down how much you had to back off each individual
rocker arm before it started clacking...and stayed clacking. More in a minute. (!)
****
Converting degrees of fastener rotation = thousandths of an inch upward or downward adjustment.
1) In order to be able to reason through the lifter preload adjustment, we need to translate
horizontal wrench movement into vertical adjustment. In order to do this,
we need to find out exactly how many threads the rocker arm studs and locknuts
have been machined for per inch.
EDIT: In reply #44 below Schurkey correctly pointed out that I was using the rocker arm
ball as the fulcrum in my example, but in reality just as soon as the rocker arm touches
the valve tip then *that* is the fulcrum, and I must now include the 1.5:1 rocker arm ratio to
calculate my vertical adjustment. Tip of the hat to Schurkey - I got it close, he got it right. :0)
Looking up the specs, the SBC rocker arm studs are 3/8" fine thread. Or 3/8" x 24 threads/inch.
Mr. Calculator tells me that 1" divided by 24 = .0416666" per thread. In order to make the rest
of this conversation easier (and also easier to document in the engine bay) let's just call it ~.
040" .060"
("Sixty Thousanths") per full turn, and ~.
010" .015" per quarter turn.
2) Now let's discuss what we are trying to do via careful listening. The way I understand it,
we have 3 distinct areas of adjustment for the SBC rocker arms. From too loose to too tight,
this is how it will sound:
* Too loose =
constant clacking. There is excess play in the entire moving assembly from
cam lobe > lifter > pushrod > rocker arm > valve tip. From constant clacking, we should be
able to transition into just quiet. No excess play in the system, but at the same time no
net preload into the hydraulic lifter.
* Preload window. Using the OEM lifter, the total preload window for the inner adjustment
mechanism (from just quiet at the top to fully bottomed out) is 2 full turns. (Or ~.
080" .120")
The factory setting is documented to be 1 full turn, which of course is ~.
040" .060" in. This is
so that as normal wear occurs (either slightly shorter as the valve seats recess upward or longer
as the cam lobe wears downward) the hydraulic lifter can compensate for these changing
measurements and keep things quiet during the normal service life...or at least through the warranty
period. (!)
* Too tight = lifter bottomed out, and rough running. NOTE: Way too tight is a solid miss due
to the associated valve being held open/off the seat. Hung open intake can lead to backfire out of the
throttle. Hung open exhaust can lead to backfire out the tailpipe. Both hung open = ?
NOTE: There is a *lot* of discussion about how much hydraulic lifter preload should be run. And
the reason for this is that experienced mechanics following the FSM have set aftermarket lifters
to the "1 turn preload" cold setting, and then had starting or misfire issues afterwards, which
could only be cleared up with a 'running preload' resetting of the valves?
As discussed elsewhere, aftermarket lifters were machined so that they only had a total of ~3/4
turn from the top (just quiet) to the internals being bottomed out.
So now, based on hard-won experience, you will hear the following recommendations:
(All from zero play {cold} or just quiet {running})
* 1/4 turn (~.
010" .015" preload) ; works for everything
* 1/2 turn (~.
020" .030" preload) ; works for everything
* 3/4 turn (~.
030" .045" preload) ; OEM lifters
* 1 turn (~.
040" .060" preload) ; OEM lifters per FSM
Personally, I use the 1/4" preload. Why? Back in the day, if I got a little too enthusiastic with
the go pedal (and no rev limiter) then not if but when I floated the valves and the lifters
took up the extra momentary clearance, then I only allowed them to 'pump up'
an extra ~.
010" .015", which meant that they recovered quicker than if I had them set to the
full ~.
040" .060" from the full turn of preload.)
The second reason is why I do it today. If I build a motor, set everything running to a quarter
turn, and then a year later one lifter starts clacking, then this tells me that there is now a ~.
010" .015"
worth of wear I need to investigate? (Or hopefully I just find a loose locknut that needs replacement.)
****
Finally, let's answer your question.
From your description, it sounds like you are loosening the adjusting nut until the lifter starts
clacking. Sounds like you are at the zero-lash point, right? But what's happening is that it
because of the tight clearances, the hydraulic internals take a few seconds to readust to the
new effective length of the entire assembly, and then it goes quiet again. This is expected
behavior, especially if the lifter got set pretty deep into it's preload window.
The solution? Loosen until just clacking Wait a few seconds? Went quiet again? Loosen
a bit more. Wait. Repeat until you loosen the lifter, and it stays clacking steadily. NOW when
you tighten this valve until it is just quiet, you will reach the 'zero lash/zero preload' point.
At this point you have now regained control over the true adjustment of this valve.
Helpful hints while doing this:
* Have pen & paper. Write down exactly what it took to adjust each valve to the zero position.
* Work 1/4 turn (90° swing) at a time. This allows you to quantify all this in .
010" .015" increments
if you wish, or want to talk to a machinist, camshaft support hotline, etc.
Example:
#1 exhaust: (3) 1/4 turns (~.045") ; no change in engine
#1 intake: (2) 1/4 turns (~.030") ; no change in engine
#3 intake: (6) 1/4 turns (~.090") ; engine smoothed out after adj. (!)
#3 exhaust: (2) turns (~.030") ; no change in engine
(and so on through the remaining 12 valve settings...)
****
The whole reason for going through this exercise is simply to find the
magic 'zero lash/zero preload' spot for all 16 lifters. Then if you set
the lash for 1/4 to 1/2 turn additional (I do this after finding the
'just quiet' spot sequentially on all 16 lifters, shutting down the
engine, and then setting the desired preload for all.)
If life is good, once you fire up the engine after all 16 have been
preloaded, it should be perfectly quiet. (No bent pushrods, no
carboned up sticky valve stems in guides, etc)
And if you set the preload to 1/4 turn, then as long we don't lose
more than .015" of lifter base/cam lobe to wear, then the valves
will stay quiet for a good, long, time.
Hope this made sense. Good on you for pursuing this. Once you
get all the way through this adjustment I'd really like to see what
you uncovered with your SBC "running preload" (old mechanics 'hot lash')
adjustment.
Quiet valvetrain / smooth running engine vibes in your general direction. :0)
Cheers --
