Valve Lash Adjustment
With the recent addition of our Little Bird Forum, it is only fitting we have one for their Y-Block engines.
All Y-blocks use solid lifters (and so do the early FE's), which need periodic adjustment. Valve lash adjustment is usually done as part of the tune-up procedure.
There are many proceedures for doing a lash adjustment, some employ special tools, feeler gauges, etc. Mechanics have done these for over fifty years. I won't pretend my method is 'better than yours', but please read it over for terrific insight that makes a very precision adjustment possible without buying any special tools.
In a perfect world, rocker arms are smooth and straight, but after many miles the mating surface to the valve becomes dimpled. This is normal as it 'cups' the valve stem. A feeler gauge cannot get inside the 'cup' for an accurate measurement.
Look at the side of your rocker arm for casting numbers and determine which ratio you have.
1.54:1 rockers are marked: ECG 6564-B2 or –B1.
Rockers without suffixes will be 1.43 ratio (so are #5751066).
The tappet adjust screw has 20 threads per inch. One turn represents .050” of linear travel. Multiply 1 turn times existing rocker ratio.
HIGH RATIO ROCKER ARMS (1.54:1) <--most Thunderbirds
Example, .050”(one turn) X 1.54(rocker arm ratio) = .077”.
Again, one full turn of the adjustment screw used in a 1.54 ratio rocker will represent .077” of tappet clearance.
Now, divide one turn of tappet clearance i.e, .077” by 60 (as in the 60 minuets of a clock dial). This number is .001283” = 1 minute of clock face rotation. So, 15 minutes of rotation (which is 90*) will = .0192” Very close to .019” which is the specification for valve tappet clearance on 292 and 312 engines.
*(Again, 15 minutes clock rotation = 90 degrees rotation; a scale easily understood and a super-close estimate to .019".)
Let's use it; with the lifter all the down obtain some tappet clearance then carefully rotate the adjust screw clockwise to obtain .000" valve lash. Just touching but not depressing the valve. (Roll the pushrod to feel zero pressure.)
Now rotate the adjust screw counterclockwise 90 degrees. The resulting clearance should be super-close to .019” regardless of rocker arm face wear.
If you have lower ratio rocker arms, you can still use this procedure.
LOW RATIO ROCKER ARMS (1.43:1) <--most Ford Cars
Adjusting 1.43:1 ratio rockers:
.050"(1 turn) x 1.43(arm ratio) = .0715" / 60(min) = .0011916 x 16(min) = .0190656"
Rotate the adjust screw 16 min. of rotation ccw. To obtain .01906” clearance. Again, this is super-accurate.
I hope this procedure helps everyone understand what's really going on and how to help tune your Y-Block. - Dave Dare
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