Anyone school me on at least the eye ball method or by hand to get the rockers where they need to be even when noise is gone should I back each one off until I hear chatter then tighten it ever so slightly until it’s gone ?
Hello A97obs,
Here is a 48 second video that shows you the essence of how to go about a precise hydraulic
lifter preload adjustment on a idling SBC. Note: The video must be watched on YouTube, so
here's the link. EDIT: This is new YouTube behavior? Not allowing certain videos to play
on other sites?
Anyway, to proceed just click on the "
Watch on YouTube" phrase below:
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FWIW, there seems to be little debate on how to set the
lash on a SBC with solid lifters.
Find the cam specs, determine if they are for cold or hot adjustment, and follow the cam
manufacturer's recommendations.
But there seems to be a lively debate about the best method to set the proper preload
for a SBC running hydraulic lifters. (Flat tappet or roller hydraulic) I know of at least 3:
1) Method outlined in the Factory Service Manual. Of course it's legit, but to pull it off
the mechanic must be 100% on their crankshaft positioning and possess a good 'feel' for
achieving the zero-lash (zero clearance) initial setting so that the desired preload can
be cranked in from there.
1a) Similar to #1, but you set the preload by getting to TDC (compression) on #1,
setting both valves for that cylinder alone, and then turning the crank 90°, and
setting the valves for the next cylinder in the firing order, repeating until all cylinders
are done. This is the way that The Elders taught me a million years ago.
2) There's a second method involving turning the crank to TDC, removing the excess play
from all 16 rocker arm/lifter assemblies. Then turn the crank 90°, check all 16 lifters again,
and remove the excess clearance from any where clearance is now uncovered. (ie: whichever
lifters are now dwelling on the cam's base circle. Turn the crank 90° & check them all again.
Eventually you will end up catching all 16 lifters on the base circle, and all 16 will be zero lashed.
Once all 16 are slop-free, you *then* crank in the desired preload on top of that. Done.
This looks to be a real-world simplification of method #1 in that you don't have to keep
track of cylinder numbering, firing order, intake vs exhaust valve, and finally is TDC #1 on
the compression stroke vs the exhaust stroke. (!) It's pretty cool conceptually, especially
late on Sunday night after a full on weekend thrash...and you have to drive it to work on
Monday. (I plan on trying this for myself on my next build.)
3) Both methods #1 & #2 have the undeniable benefit that you get to set the lash while the
engine is off. Matter of fact I always start off getting the preload as close as I can during
initial engine assembly...but I'm at the point now where I will subsequently perform a final
'running adjustment' to really dial it all in.
My technique is pretty much exactly the same as the 48 second video, with the exception that
while the engine is running I will loosen them until they clatter, tighten them back up until they
just go quiet,
and then I leave it be and move right to the next one in line. (This way the engine
doesn't run rough or want to die, causing me to blip the throttle, overcompensate, & slinging
hot oil everywhere.) And yes, this observation is from hard won personal experience. :0)
Once all the lash is set, then I simply shut the engine off and *NOW* I add my desired amount
of preload to all 8 assemblies on that bank. (1/4 turn, 1/2 turn, etc) After sitting for a minute
or two all the extra height from the trapped oil in the internal chambers will have bled down, so
when you start it back up it still runs perfectly smooth. It's like a magic trick for your buddies.
Purists will advocate strongly for method #1. And how can you argue with the FSM? Another
forum member has recently advocated for method #2. It makes sense, and is intriguing. Method
#3 is actually not that messy as long as you have an old set of tin valve covers where you cut
the tops off and use a set of deflector clips to keep the oil from shooting on the shop walls.
An optimization would be to use a hole saw and make 8 holes for socket access. By doing this
the shooter holes are covered, and also the far end by the valve stem tip where the oil accumulates
(after lubricating the pivot ball) gets flung. Your choice.
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The bottom line is use whatever method that allows YOU to get the same exact preload established
for all 16 of your hydraulic lifters. If you are having difficulty getting this important adjustment
perfected for your engine (not too loose or not too tight) don't feel bad, for this is an area that a
lot of people new to SBC wrenching have trouble getting this right.
Too tight and it's rough running and eventually leading to one or more burned valves. (Valves can't
get rid of their heat into the water jacket unless they are given the opportunity to fully couple with
the valve seat.)
Too loose and the engine sounds horrible. Off bad enough and you run the risk of having 1 or more
pushrods getting unceremoniously kicked out of the oscillating circuit.
Hope the above answered your questions. This is a skill worthy of mastering, and then finding a
young motorhead of the next generation to pass it along to. I am so glad that one of the elders
did just that for a young & impressionable Road Trip way back when paisley vinyl roofs were a thing. :0)
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By the way, good find on the flipped rocker arm nut & sharing the photo with us. (!) Also, it's not
unheard of for the engine to crank over a bit slower after getting all the valves set correctly, for the
starter may now be working against higher compression than when the valves were set too tight and
some of the cranking pressure fighting the starter was being bled off. (!)
You are making good progress. Keep up the good work. And continue to let us know what you discover.
Cheers --
