In a message dated 96-10-02 10:38:16 EDT, gcram@wdni.com (Cram, Geoff)
writes:
<< I've often wondered what the deal was with crank surface buildups. How do
they avoid air pockets, do the journals wear as well as the original
material, can nitriding be done, how much does it cost? >>
Two methods available, welding or flame coating.
For flame coating the part is first heated in a kiln to fairly high
temperature (like nearly red hot), then rotated in a fixture while metal dust
is sprayed onto the surface within an acetylene flame. I think this process
is rather expensive, like a few hundred dollars if memory serves, but others
may know the price. One advantage is that with the proper choice of metal
powder it can produce a very hard surface, very scuff resistant. My crank
grinder guy doesn't like it though, says it's hard to grind and sometimes
flakes off in the process if not properly applied.
The method being used this time around on my crankshaft is surface welding.
The part is chucked in a rotating fixture, welding wire is fed through a
small tube and automatically indexed along the surface as the part turns.
The process is really automatic MIG welding. With each successive rotation
of the part the weld beads overlap a bit. I don't think there are any weld
voids when it's done, but I'll certainly let you know when I see the finished
product. Once the thing is welded and ground it's pretty much like the
original part, flame hardening or nitriding can stilll be done same as usual.
It may be possible to use a harder metal alloy for the welding wire to
produce a hard surface, but I'd have to check on that.
The shop is charging $25 per journal for the welding (4 this time) and $10
per journal for grinding (7 places) for a total of $170. The main journals
have to be ground to the next size smaller because of the possibility of
slight warpage from the heat of the welding process. For those of you who
are real particular about things, balancing of the crankshaft may be in order
afterwards, but for normal use it won't be far enough out to worry about
balancing it.
A few years ago I tossed out a crankshaft that had one bad rod journal. If I
had known at the time that it was this easy I could have had it repaired for
the $25.
Live and learn,
Barney Gaylord -- 1958 MGA
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