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Old 02-17-2010, 10:05 AM   #1 (permalink)
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Location: PA
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Hydraulic pushrod adjustment

Harley Davidson's hydraulic tappets max actuation range is .190-.200". (From zero lash to bottoming out) Factory adjustments usually ask for .100-.125" range. I've found they operate the best and the most quiet at .140-.150" range (cold set, not including cylinder growth at operating temps).

More with aftermarket cams then stock cams. Stock cams I set the pushrods at .125" or so.

Regardless, you need to know what thread pitch your pushrod threads are to adjust them properly.

TPI = threads per inch.

To find this, simply use a thread gauge, or count the threads in a one (1) inch section.

Keep in mind there's 6 wrench flats (flat sides of a nut) per 360* (full) turn of the pushrod adjusting nut.

1 complete 360* turn of a pushrod = 6 flats.

The most common thread groups are:

32tpi = 3.2 turns to .100" (.03125" per turn/.00520 per flat)

30tpi = 3.0 turns to .100" (.03333" per turn/.00555 per flat)

28tpi = 2.8 turns to .100" (.03571" per turn/.00595 per flat)

24tpi= 2.4 turns to .100" (.04165" per turn/.00694 per flat)

I run 24 tpi SE pushrods, set at 3.6 turns = .1499 tappet depth.

So, depending on your Brand/TPI, you would adjust the pushrod that many number of turns and be in the middle of the tappet depth range.

Brand list: (There are more. This is what I have.)

Revolution Performance Chromoly – 32 tpi
Jims Pro-Lite – 24 tpi
Slim Jims – 32 tpi
Andrews – 28 tpi
Andrews – 32 tpi
Crane New Time Savers – 28 tpi
Crane Old Time Savers – 24 tpi
Crane – 32 tpi
H-D – 32 tpi
S&S – 32 tpi
Screaming Eagle – 32 tpi
Screaming Eagle- 24 tpi
Rivera Taper Lite – 40 tpi
Rev Tech – 36 tpi

Adjusting a tappet requires a cold engine, due to cylinder growth at operating temps, changing the tappet operation depth. (slight decrease as the cylinder grows taller.)

Depending upon the Brand/TPI pushrod being used, the procedure is to get the lifter for the valve being adjusted on the base circle of the cam. The "Base Circle" of the cam is the lowers point the tappet rides on, indicating the valve is completely closed at that time.

The pushrod is then adjusted to the point of 0 lash.

"Zero Lash" is the point where there is no up/down play and but pushrod can still be turned easily using your oil covered thumb and index finger.

From that point, the pushrod is adjusted (extended) the required number of turns or wrench flats to set the plunger in the approximate center of the tappet's travel.

(.200" max = .100" center: See chart above for tpi and turns to .100")

After adjusting a tappet, it's critical to allow that tappet to sit for 15-20 minutes to bleed down and allow oil to escape from the hydraulic unit. Before turning the engine over to adjust another valve, you have to be able to spin the pushrod of the last adjusted valve with your fingers (now bled down) or you'll bend a pushrod or worse yet, bend a valve.
“When the going gets weird, the weird turn professional....” ~ Hunter S. Thompson~

R.I.P. Rubberdown. 1971-2012
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