It would be nice to see the original Ford FEA, MSST and DET analysis for our
cams. I had the theory that because of the asymmetry of the pulley the chain
tugs the sprocket along the shaft in a direction the splines can not
resist.
Another theory is because the cams have a very uneven turning load they take
a hammering which causes the hard brittle splines to fracture and loosen.
The exact mechanism may be a combination of the two. Busted up splines allow
the sprocket to travel and slip. Uneven turning effort causes a hammering cycle
loading and unload each spline with every valve opening. Welding is fine for now
as a patch. What has become clear to me is a final resolution should involve a
fresh design - not a patch of the existing product from Ford/Yamaha.
The story Don and I got was unlike the V6 SHO the V8 was in the prototype
stage when the call came to rush it to production. If true it would explain
why something as important as cam design was released to production without
through design process.
Too bad this page is # 3 of the thread, I wanted to grab it before it gets
passed over.
| Author |
Topic:
To weld or not to weld? Here is the answer...... |
DougLee25
SHO Member
Member # 787
|
posted
December 10, 2002 08:22 PM
Not that
anyone really cares, but here's my two cents... I have put this
situation into some finite element software. For those who don't
know what finite element analysis (FEA) is, it's a means to
analyze where stress concentrations are. This is denoted by color
changing areas on the graphical output. A red area means high
stress concentrations are at that point, and failure is definitely
within the realm of possibility. Although both means of fixing the
gear to the shaft are viable, I see two things in the graphs. With
the pin option, a high stress concentration area occurs right
where the hole would be drilled. Stress risers occur when there
are holes in material, and thus the explanation of the red areas.
Looking at the welded output, no stress risers occur here. This is
because no metal has been removed, and thus why the red area is
not shown anymore. The heat affected zone (HAZ) will occur near
the weld, and actually hot work the metal. Thinking logically
about these two options... pinning removes metal, whereas welding
adds metal. I believe the welded option, when done properly, is
the best way to fix this problem. My opinion is backed up by the
FEA analysis. You make the decision.
Doug
--------------------
Paint And Body Work Completed, SHO Lettering Colored In Florescent
Green, AC Finally Fixed, Rod Shifter, Coneless, Full 60k Done By
Me, New Clutch, New Motor Mounts, Slicers, Full Black Leather
Interior From '91 SHO, New Headliner, A Few Stereo Mods
Posts: 268
| From: Hatboro | Registered: Aug 2001 |
IP: Logged |
|
mholhut
SHO Member
Member # 110
|
posted
December 11, 2002 02:37 AM
Doug,
That has to be the most comprehensive support for proper cam weld
solutions. When all you have is speculation, you have to rely on
pure data!
--------------------
Mike Holhut
2K Lincoln LS8 Sport, Black
Former '96 SHO, Ebony Satin
Posts: 544
| From: MA | Registered: Jan 2001 | IP: Logged |
|
DougLee25
SHO Member
Member # 787
|
posted
December 11, 2002 08:03 AM
Too bad
you've been the only one who listens... No one else on this forum
does...
--------------------
Paint And Body Work Completed, SHO Lettering Colored In Florescent
Green, AC Finally Fixed, Rod Shifter, Coneless, Full 60k Done By
Me, New Clutch, New Motor Mounts, Slicers, Full Black Leather
Interior From '91 SHO, New Headliner, A Few Stereo Mods
Posts: 268
| From: Hatboro | Registered: Aug 2001 |
IP: Logged |
|
rjensen
SHO Junior
Member
Member # 3483
|
posted
December 11, 2002 03:17 PM
a couple of
things,
I listened, so, you can never say "no-one else on this forum
listens" again. Also, real data is cool, so where is it? Got
any way to post the scans? If so, can you reconcile the metallurgy
of the cam/sprocket with the extent of stress and make projections
as to time to failure, if any? If so, how would you take into
account metallurgy changes in the immediate area of the weld,
which I would expect to be dependant upon method, filler, shielding
gas, residual oil, phase of the moon...
Also, in the event your data shows a failure mode within the
realistic operational conditions, I would imagine two conditions,
one with a spun or near spun sprocket, and another with a normally
seated sprocket capable of taking up much, most all (?) of the tort ional
(oops, maybe sheer on the pin/weld) stress.
My WAG is that in any event, with the long term metal fatigue
scenario as a possible exception, that the chain would jump or
break before a solid pin or good weld.
rj
Posts: 8
| From: San Diego | Registered: Nov 2002 |
IP: Logged |
|
DougLee25
SHO Member
Member # 787
|
posted
December 11, 2002 04:40 PM
quote:
Originally
posted by rjensen:
a couple of things,
Can you reconcile the metallurgy of the cam/sprocket with the
extent of stress and make projections as to time to failure, if
any? If so, how would you take into account metallurgy changes
in the immediate area of the weld, which I would expect to be
dependant upon method, filler, shielding gas, residual oil,
phase of the moon...
I never
furthered my analysis to conduct life predictions to time of
failure. I'm sure I could bust out the books, but a TIG weld with
the proper filler rod and amperage setting will provide sufficient
penetration to extend the life of the combo further than it is
presently. Phase of the moon isn't gonna effect shit, sorry!
quote:
Also, in the event your data shows a failure mode within the
realistic operational conditions, I would imagine two
conditions, one with a spun or near spun sprocket, and another
with a normally seated sprocket capable of taking up much, most
all (?) of the tort ional (oops, maybe sheer on the pin/weld)
stress.
The actual
weld really isn't taking up the torsional stress associated with
the cam and sprocket. The weld is to secure the sprocket from
shearing off the knurls on the camshaft. The reason why this
happens is due to the hardness of the shaft and gear combo. One is
harder than the other, and thus why they strip. If there were of
equal hardness, or a weld was put there to begin with, the
sprocket would have no means of rocking back and forth, eventually
shearing off the knurls.
It just seems to me that Ford didn't design according to the MSST
(maximum shear stress theory) or DET (distortion energy theory)
when the combo was first introduced. When designing any piece that
experiences shear stresses, these are two guide lines that must be
adhered to. The stresses experienced by the shaft must fall well
outside the failure envelope, and thus why it has been failing in
service.
Doug
--------------------
Paint And Body Work Completed, SHO Lettering Colored In Florescent
Green, AC Finally Fixed, Rod Shifter, Coneless, Full 60k Done By
Me, New Clutch, New Motor Mounts, Slicers, Full Black Leather
Interior From '91 SHO, New Headliner, A Few Stereo Mods
Posts: 268
| From: Hatboro | Registered: Aug 2001 |
IP: Logged |
|
SHODWN
SHO Member
Member # 865
|
posted
December 13, 2002 09:02 AM
Doug, don't
feel bad. its not you nobody listens to logic here. they just see
pics and say " Wow I don't want that to happen"
But im reversing the effect soon enough after we get done testing
a pinned cam. it will be a while though bigger fish to fry right
now.
--------------------
http://www.shoforum.com/images/st_moneyshot.jpg
http://mediaservice.photoisland.com/auction/Aug/20028313854650333923507.jpg
Kirk J Doucette
Stormtrooper
97 White V8
M&M Flow Induction Hood
MAC Kwik Cool
Flowmasters
By-Pass Pipe
No Resonator
TCI-823800 Trans Cooler
Carbotechs Front and Rear
26mm Swaybar
2nd Generation K&N Cone Filter
Full 3" Cold Air induction installed below front bumper
Kumho 235/45/17
Black SVT 17" wheels
Cobra Twin Piston PBR Calipers
13" Porterfeild Cryo treated directional rotors
Black outs
Modified Tail Lights
8" Mtx SUB (in rear deck)
Ported,Polished, and Powder Coated intake
3 pod pilla gauges
ASP Crank UDP
SHO SHOP PS UDP
Simpson Harnesses
Plus more but this is too long already
SHODWN Vanity Plate
15.1@91mph 2.1 60ft
216hp/239ft tq
For sale as of 5/20/02
Posts: 1286
| From: Spencer,Ma usa | Registered: Sep 2001 |
IP: Logged |
|
ZexySho
SHO Junior
Member
Member # 2108
|
posted
December 13, 2002 08:00 PM
IMHO trying
to estimate expected service life of a cam weld repair would yield
questionable results at best. The FEA analysis is cool and makes
perfect sense however. Manual welding is more of an art than a
science. If done properly on a non-spun cam it is quite reasonable
to expect the weld repair to outlast the rest of the engine. A
more important aspect to consider however that could immediately
shorten the life of these repairs is delayed hydrogen cracking. If
the weld area is not degreased well before laying down the filler,
the atomic hydrogen (from hydrocarbons in petroleum based oils)
will be absorbed into the hot liquid weld metal. Once the weld is
solidified individual hydrogen atoms start to combine to form
hydrogen molecules. At this stage the weld is far less capable of
accepting this hydrogen without cracking. These cracks do not form
right away and can take days to develop, well after the engine is
closed up and running. An ounce of prevention is the ticket here.
Wendell
97 T-red (welded for 20k now)
91 Black 5-spd
Posts: 4
| From: Dayton, Ohio | Registered: Apr 2002 |
IP: Logged |
|
