DeTomaso Mailing List: July 2001, Message #79

DorCm@aol.com wrote:
 
> How can I tell if I have the fast bleed hydraulic lifters?  They were in the
> motor when I got it and never thought to check them out. What are the pros
> and cons to theses also.
  Hi, the pros is that you can run a much wilder cam and still get
relatively good
RPM bottom end performance and vacuum to run the brakes.  The fast bleed
down characteristics of these lifters 
allows them to subdue the rapid lift of the lobes at low RPM and then
more faithfully follow the high performance contours at higher RPM where
the bleed down time lessens. The best of both worlds?
The cons is that they are noisier (sounding much like solid lifters at
idle), and are more expensive, due to the limited sales volume and
increased manufacturing efforts.

  can you actually push on these to get them to collapse further with
the push rod.
Yes. I used a fixture that resembled a drill press (no motor power, of
course). Place an old pushrod in the chuck and place a lifter in a metal
can - filled with a light oil- under the rod. Time how much it takes to
collapse the plunger to the bottom.
  What makes them work (at least the ones I was involved - Cranes, I
believe- with as part of manufacturing
engineering/QC for a very large lifter manufacturer back in the 1970s)
is a greater internal plunger to lifter body clearance- we're talking
ranges in the few millionths of an inch here-  allowing the pressurized
oil to escape quicker, hence the name. I actually built an experimental
set for the Cleveland, but did not have the time to finish testing them.

  What are the insides like?  No check valve, weaker spring?
Actually, the same parts are inside, only the clearance from plunger to
body bore is greater than a stock lifter. We would increase the bleed
down time drastically.
  If memory serves, the permissible working range from the narrowest
lifter body ID to the widest was only 250 millionths of an inch, split
into some 30 different ranges, as measured with an air gage and other
specialized tooling.

  The only "home garage" test that I can think of is to submerge the
lifter in a light oil, pump all of the air out, and then time while push
down on the plunger until it bottoms out. Compare to a stock lifter's
bleed down time .... if I recall correctly, depending on the viscosity
of the media oil and other variables, 30 seconds for the stock lifter
verses 6 second for the fast lifter.  Hey, this was 25 years ago.
  If you have the classic solid lifter sound when the car is running
which goes away at higher RPM, and the suspect lifters all bleed down
very quickly as per this test, chances are that you have them.
  P.S.: Be sure to return the lifter to the same hole in the gallery
that it came out of ... it's now mated to a lobe of the cam, and
switching it is a problem in the making.
   Good luck, YMMV, Al.
> 
> Dorsey
> 
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